Application of Unilateral Biportal Endoscopy in Lumbar Double Crush Syndrome: A Retrospective Study and Literature-Based Classification

Application of Unilateral Biportal Endoscopy in Lumbar Double Crush Syndrome: A Retrospective Study and Literature-Based Classification | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Application of Unilateral Biportal Endoscopy in Lumbar Double Crush Syndrome: A Retrospective Study and Literature-Based Classification Wenlong Wang, Xingchen Yao, Yi Ding, Chuanchao Du, Jincai Yang, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9127627/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 14 You are reading this latest preprint version Abstract Objective Double Crush Syndrome (DCS) represents a relatively uncommon peripheral neuropathy caused by compression of the same nerve at two distinct sites. A single lumbar nerve root traverses a long pathway within the spinal structure, making it susceptible to compression at multiple sites. This dual-site entrapment results in dysfunction of a single nerve root and may be easily overlooked in clinical practice, often leading to suboptimal therapeutic outcomes. Considering the limited number of reported cases involving double-site compression of lumbar nerve roots, the present study aimed to report our institutional experience in managing such cases. All patients were treated using a unilateral biportal endoscopic (UBE) technique to achieve decompression at both compression sites. Furthermore, a comprehensive literature review on DCS was conducted, and a novel classification system was proposed based on the patterns of pathology described in previous reports. Methods A total of 16 patients diagnosed with DCS were retrospectively analyzed. Demographic data, clinical symptom characteristics, pre- and postoperative imagings, intraoperative details, functional outcome scores, patient satisfaction, and postoperative complications were collected and reviewed. These data were used to evaluate the efficacy and safety of UBE in the treatment of lumbar DCS. In addition, all English-language publications on DCS published after the year 2000 were systematically reviewed. The included studies were categorized according to the anatomical locations and pathological types of compression to establish a new classification system for DCS. Results Among the 16 patients, 12 had double crush of the L5 nerve root and 4 had double crush of the L4 nerve root. All patients underwent single-stage dual-site decompression using the UBE technique. Postoperative clinical symptom scores improved significantly, and no recurrence of symptoms was observed at 1-year follow-up. The mean endoscopic operation time was 118.4 ± 13.5 minutes, the mean postoperative bed rest duration was 1.8 ± 0.9 days, and the mean postoperative hospital stay was 4.7 ± 1.5 days. The patients’ mean postoperative visual analog scale (VAS) for low back pain and leg pain, as well as their Oswestry Disability Index (ODI), showed a significant decrease compared with preoperative values, with no significant changes observed after the 1-month follow-up. Postoperative imagings confirmed complete decompression in all cases, and no severe complications occurred. Based on the literature review, the newly proposed classification system divided DCS into two major categories comprising five subtypes. Conclusion This study reported the clinical outcomes of UBE in the treatment of type IIc DCS and reviewed the latest literature on DCS. The use of UBE for DCS has not been previously reported. Our findings demonstrated that single-stage, double-site decompression using the UBE technique achieved favorable clinical outcomes in patients with type IIc DCS. Given the considerable pathological diversity of DCS, classification and discussion based on the newly proposed system are essential for improving clinical understanding and management of this condition. Double crush syndrome Unilateral biportal endoscopy Classification system Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Introduction The definition and standard diagnostic test of Double Crush Syndrome (DCS) remain imprecise [ 1 ]. In general, most authors describe DCS as a condition in which a single peripheral nerve is compressed at two or more distinct sites along its pathway [ 2 ]. Clinically, DCS presents with symptoms similar to those of a single-site peripheral neuropathy, which contributes to its relatively low reported incidence and frequent underdiagnosis. However, due to the cumulative effect of these compressed insults, the resulting neural damage may be more severe than that caused by a single lesion [ 3 ]. Therefore, accurate recognition of DCS and effective decompression at all involved sites are of critical importance [ 4 ]. Peripheral nerves have long and complex anatomical pathways with wide distributions, leading to diverse pathological mechanisms of entrapment. Consequently, the reported presentations and definitions of DCS vary considerably among published studies. The reported incidences range from 6.7% to as high as 73% [ 2 ]. Moreover, there are substantial discrepancies in the reported incidence of DCS across the literatures. Thus, systematic review and classification of the published studies are essential to facilitate clearer understanding and more meaningful discussion within specific subtypes of DCS. Recently, most published studies involve double crush occurring at vertebral structures and peripheral corridors of the same nerve, for example, cervical radiculopathy combined with carpal tunnel syndrome (CTS) [ 4 , 5 , 6 , 7 , 8 ], or lumbar radiculopathy combined with common peroneal nerve entrapment [ 9 , 10 , 11 ]. A single lumbar nerve root traverses a long pathway within the spinal structure, making it susceptible to compression at multiple sites. However, reports specifically focusing on double crush of a single lumbar nerve root caused by an intraspinal canal lesion and a lateral lesion are exceedingly rare [ 12 , 13 , 14 ]. This subtype of lumbar DCS represents a unique but clinically significant entity. In the present study, we report a series of such cases treated using unilateral biportal endoscopy (UBE) for decompression at both lumbar compression sites, achieving satisfactory clinical outcomes. To our knowledge, this represents the first report describing the application of the UBE technique for this specific type of DCS, as well as the largest case series to date. Material and Methods A retrospective review was conducted of all patients who underwent lumbar UBE surgery in our department between 2020 and 2024. Among them, 16 patients diagnosed with lumbar DCS (7 males and 9 females) were included in this study. The study protocol was approved by the Institutional Ethics Committee of our hospital (approval number: 2019-K-183). All patients agreed to participate in the study and signed informed consent forms. Inclusion and Exclusion Criteria The inclusion criteria were as follows: a) Presence of typical clinical manifestations of single lumbar nerve root compression with poor response to conservative treatment; b) Radiological confirmation of double-site compression involving the same nerve root; c) Patients who underwent single-stage decompression using the UBE technique at our institution; d) The postoperative follow-up period reached 12 months. The exclusion criteria were as follows: a) Decompression involving different nerve roots; b) Radiological evidence of multi-root compression; c) Decompression procedures not performed under the UBE technique; d) Presence of severe systemic diseases or other spinal disorders that could interfere with the assessment; e) Incomplete clinical data or failure to complete a minimum follow-up of 12 months. Data Collection and Evaluation Preoperative demographic data, clinical characteristics, and imaging findings were collected. The responsible nerve root and the two sites of compression were identified based on radiological evaluation. Radiological assessment included plain radiographs, magnetic resonance imaging (MRI), myelography, and computed tomography (CT), which were analyzed in correlation with the patients’ neurological symptoms. Operative parameters, including endoscopic operative time, time to postoperative ambulation, length of hospital stay, and intraoperative or postoperative complications, were recorded. Postoperative imaging studies were performed to confirm decompression. Patient satisfaction was assessed at discharge, and clinical follow-up evaluations were conducted at 1, 3, 6, and 12 months postoperatively. Pain intensity of the lower back and affected lower limb was evaluated using the visual analog scale (VAS), and functional outcomes were assessed using the Oswestry Disability Index (ODI) before surgery, immediately after surgery, and during follow-up visits. Statistical analysis Numeric variables are expressed as mean (± SD) and discrete outcomes as number of cases (%). The effectiveness of the surgery was assessed by comparing the preoperative and postoperative clinical data. Continuous outcomes were compared by paired Student t test, Welch t test or Mann-Whitney U test according to data distribution. The alpha risk was set to 5% and two-tailed tests were used. Statistical analysis was performed with SPSS software (version 27.0; IBM Corp, Armonk, NY, USA). Surgical Procedures Position, Anesthesia, and Skin Incision The patient was placed in the prone position on a radiolucent Jackson spinal table and put under general anesthesia. The surgeon stood on the lesion side. Under anteroposterior fluoroscopic projection, two sets of skin incision lines were drawn, corresponding to the two operative segments: one pair for the intraspinal canal lesion (Endoscopic Portal 1 and Working Portal 1), and another pair for the lateral lesion (Endoscopic Portal 2 and Working Portal 2). The cross point (green point) of the lower endplate line and the medial margin of the pedicle line was marked. Endoscopic Portal 1 and Working Portal 1 were made 1.5 cm cranial and caudal to the cross point. Endoscopic Portal 2 and Working Portal 2 were made along a line located 2 cm lateral to the lateral margin of the pedicle line (green dashed line), using the “P + 2” incision approach. These two incisions were approximately 3 cm apart and, under lateral fluoroscopic projection, symmetrically converged toward the paraspinal lesion (Fig. 1 ). Paramedian Approach Decompression for Intraspinal Lesions Transverse skin incisions measuring 1 cm in length were executed aligned with Endoscopy Portal 1 and Working Portal 1. To facilitate soft tissue dissection and secure operative space, serial dilators were utilized. Subsequently, an arthroscope was introduced via the endoscopy portal, partnered with implementing a saline irrigation system. Soft tissue cauterization and hemorrhage control were achieved by deploying a radiofrequency probe. The foundational bony structure viewed under endoscopy corresponded to the intersection of the lower margin of the spinous process and the lower margin of the lamina. This pivotal point served as the docking site. Ipsilateral partial laminotomy of the upper and lower laminae was performed using a high-speed burr until full exposure of the ligamentum flavum (LF) from the proximal end to the distal end was achieved. The ipsilateral inferior articular process (IAP) was partially removed using Kerrison rongeurs and osteotomes to disclose the medial articular surface of the superior articular process (SAP) in deep portion. Then, the SAP was partially removed. The ipsilateral LF was completely removed to expose the dural sac and right traversing nerve root. The dural sac and traversing nerve root were then retracted medially with a nerve retractor to expose the ventral structure of the nerve root. The intervertebral disc was inspected, and if a disc herniation was present, discectomy was performed followed by radiofrequency ablation of the annulus fibrosus. Finally, adequate decompression was confirmed by ensuring that the traversing nerve root was relaxed and free of compression (Fig. 2 a). Paraspinal Approach Decompression for Lateral Lesion Similarly, two 1-cm incisions were made along Portal 2 and Working Portal 2, and the soft tissues were dissected using the radiofrequency probe until reaching the lateral margin of the pars interarticularis. A high-speed burr was used to remove a small portion of the bone at the lateral edge, exposing the deeper LF. After resecting the tip of the SAP with a chisel, part of the LF was removed to expose the deep exiting nerve root. Decompression was carried out along the exiting nerve root, and any additional paraspinal compressive lesions were removed until the exiting root was fully decompressed (Fig. 2 b). Final Checking Point Decompressed nerve root is confirmed by the nerve root length and slackness. Negative pressure drainage was inserted in the decompression area, and then the incisions were closed. Results A total of 16 patients with lumbar DCS were included, consisting of 7 men and 9 women. The average age at the time of surgery was 71.9 ± 7.3 years (range, 60–88 years), the mean body mass index (BMI) was 25.6 ± 2.9 kg/m² (range, 20.0-30.8 kg/m²), and the mean duration of symptoms was 10.7 ± 6.4 months (range, 2–24 months). Twelve patients presented with L5 DCS, and four patients had L4 DCS. Among the patients with L5 nerve root DCS, seven cases resulted from unilateral L4-5 lateral recess stenosis (LRS) combined with L5-S1 foraminal stenosis (FS); one case involved L4-5 posterolateral lumbar disc herniation (LDH) combined with L5-S1 FS; one case involved L4-5 LRS combined with L5-S1 far-out syndrome (FOS); and three cases involved L4-5 LRS combined with L5-S1 extraforaminal lumbar disc herniation (ELDH). Among the patients with L4 nerve root DCS, two cases resulted from unilateral L3-4 LRS combined with L4-5 ELDH; one case involved L3-4 posterolateral LDH combined with L4-5 FS; and one case resulted from unilateral L3-4 LRS combined with L4-5 FS. The demographic data and clinical characteristics of patients with the various pathological types of DCS were presented in Table 1 . Table 1 Baseline Demographic Characteristics of Patients With Various Types of DCS Compressed Nerve Root Pathological Type Number of Cases (n, %) Age and Gender Duration of Symptoms (months) L5 Nerve Root L4-5 LRS with L5-S1 FS 7 (44%) 68, Male 18 66, Female 9 81, Female 8 68, Female 9 88, Female 12 77, Male 24 75, Female 11 L4-5 LRS with L5-S1 ELDH 3 (19%) 72, Male 2 79, Male 5 68, Male 3 L4-5 LDH with L5-S1 FS 1 (6%) 64, Female 3 L4-5 LRS with L5-S1 FOS 1 (6%) 74, Female 22 L4 Nerve Root L3-4 LRS with L4-5 ELDH 2 (13%) 60, Female 14 76, Male 4 L3-4 LDH with L4-5 FS 1 (6%) 71, Male 13 L3-4 LRS with L4-5 FS 1 (6%) 64, Female 10 LRS: lateral recess stenosis; FS: foraminal stenosis; ELDH: extraforaminal lumbar disc herniation; LDH: lumbar disc herniation; FOS: far-out syndrome The mean endoscopic operative time for all patients was 118.4 ± 13.5 minutes. Postoperative ambulation was achieved on average at 1.8 ± 0.9 days, and the mean postoperative hospital stay was 4.7 ± 1.5 days. The mean preoperative VAS score for low back pain was 2.8 ± 1.1. Postoperatively, the VAS scores for low back pain were 2.9 ± 1.0 on the first day, 2.3 ± 0.8 at 1 month, 1.9 ± 0.7 at 3 months, 1.4 ± 0.6 at 6 months, and 1.5 ± 0.8 at 1 year. The mean preoperative VAS score for the affected limb was 6.0 ± 1.2. Postoperatively, the VAS scores for the affected limb were 2.2 ± 0.9 on the first day, 1.1 ± 0.6 at 1 month, 0.8 ± 0.5 at 3 months, 0.8 ± 0.7 at 6 months, and 0.9 ± 0.7 at 1 year. The mean preoperative Oswestry Disability Index (ODI) was 75.9 ± 4.7%. Postoperatively, 35.5 ± 5.7% at 1-month follow-up, 27.9 ± 4.5% at 3 months, 20.6 ± 5.2% at 6 months, and 19.2 ± 6.3% at 1 year. Changes in postoperative clinical outcomes are shown in Fig. 3 . Overview of DCS Double crush syndrome (DCS) refers to a condition in which a single peripheral nerve is subjected to compression at multiple sites. A typical example is the coexistence of radicular cervical spondylosis and a peripheral entrapment neuropathy. This cumulative compressive effect results in more severe neural injury and symptoms than compression occurring at a single site. DCS was first described by Upton and McComas in 1973 [ 15 ], and subsequent literature has reported a relatively high prevalence of concurrent carpal tunnel syndrome or cubital tunnel syndrome among patients with cervical radiculopathy. Because no definitive anatomical or electrodiagnostic criteria exist to confirm the presence of DCS, reported incidence rates range broadly from 6.7% to 73%, making objective identification of dual-site nerve injury particularly challenging. One proposed pathophysiologic mechanism is that proximal axonal compression impairs axoplasmic transport, resulting in neural dysfunction and increasing the susceptibility of the same nerve to distal injury. However, Ökmen et al. questioned the existence of DCS after finding no significant differences in peripheral nerve morphology, assessed via ultrasonography, between the symptomatic and asymptomatic limbs of patients with cervical radiculopathy. Classification of DCS Based on Published Literatures A literature search identified 43 publications on DCS published after the year 2000. Based on the anatomical distribution of symptoms, the author classified DCS into upper-extremity (Type I) and lower-extremity (Type II) categories. (1) Type I: Upper-Extremity DCS Most reports on DCS involve the upper extremities. According to the underlying pathology, upper-extremity DCS can be divided into two subtypes: Type Ia Cervical radiculopathy combined with peripheral nerve entrapment. Among all dual-site compressive neuropathies, cervical radiculopathy combined with CTS is the most widely reported [ 2 , 4 ]. Cervical radiculopathy with cubital tunnel syndrome has also been frequently described [ 16 , 17 ], whereas combinations involving other peripheral entrapment neuropathies, such as suprascapular nerve entrapment, are less common and often limited to case reports [ 18 ]. For this category of DCS, most authors agree that decompression at both sites yields superior clinical outcomes compared with single-site decompression. Type Ib Double-site peripheral nerve entrapment in the upper extremity. This subtype is also commonly described, though mostly as a case report. The pathological patterns are more diverse, including double entrapment of the ulnar nerve at the elbow and the wrist [ 19 ], CTS combined with pronator syndrome [ 20 , 21 ], and concurrence of cubital tunnel syndrome and the lower trunk of the brachial plexus compression [ 22 ], among others. (2) Type II: Lower-Extremity DCS Reports of DCS involving the lower extremities are substantially less common. Based on pathological patterns, lower-extremity DCS can be categorized into three subtypes: Type IIa Lumbar radiculopathy combined with peripheral nerve entrapment. This subtype has primarily been reported in cases of L5 nerve root radiculopathy accompanied by common peroneal nerve entrapment [ 10 , 11 ]. Type IIb Double-level peripheral nerve entrapment in the lower extremity. Only two case reports have described this subtype, both involving traumatic injuries that resulted in dual-site peripheral nerve compression, suggesting that this pattern is relatively rare [ 23 , 24 ]. Type IIc Dual-site compression of a single lumbar spinal nerve root. This subtype involves compression of the same nerve root at two separate locations around the spinal structure due to various pathological causes. Although even less frequently reported, the dual-level nerve-root compression has clinical implications similar to classic DCS [ 14 , 15 ]. If one of the compressive sites is overlooked, surgical treatment may fail to provide complete symptom relief. In addition to the difficulty of establishing a definitive diagnosis, clinical management of DCS presents another major challenge [ 13 ]. Discussion Given the large number of cervical and lumbosacral spinal nerves and their long anatomical pathway, including multiple osteomuscular anatomical corridors, multilevel compression can occur at various sites, making reports of DCS relatively common. However, the diversity of these pathological compression patterns often leads to considerable variability in clinical presentation. Therefore, DCS cases reported in the literature should be classified according to differences in anatomical location and underlying pathology, which would facilitate more standardized discussion and improve academic communication. In the present study, we primarily performed decompression for Type IIc DCS. The characteristics of these cases differ substantially from those of upper-extremity DCS, lumbar radiculopathy combined with peripheral nerve entrapment, or dual-site entrapment of lower-extremity peripheral nerves. Correspondingly, the therapeutic strategies also differ significantly. A precise classification of DCS helps improve our understanding of its pathological features and provides a more systematic basis for clinical communication and treatment planning. For Type Ia DCS, there is ongoing debate regarding which lesion, cervical radiculopathy or peripheral entrapment, plays the dominant pathological role and which should be addressed first. Holloway and Stoy et al argue that cervical radiculopathy is the primary pathology in Type Ia DCS and that cervical decompression alone can achieve satisfactory outcomes [ 25 , 7 ]. In contrast, the findings of Hansen et al [ 5 ] suggest the opposite-that isolated peripheral nerve decompression is sufficient to produce good clinical results. Other studies, including Ochoa-Cacique [ 4 ] and Gullborg et al [ 16 ], advocate decompressing both sites to achieve optimal therapeutic outcomes. Furthermore, Wessel et al [ 26 ] and Galarza et al [ 17 ] reported that some patients who underwent cervical decompression required subsequent peripheral nerve release due to persistent symptoms. Both authors emphasized that nerve damage in DCS tends to be more severe, and postoperative outcomes are generally inferior compared with single-site radiculopathy. In addition, Byvaltsev et al [ 27 ] concluded that simultaneous two-site decompression provides greater benefit than staged procedures. For Type Ib DCS, the number of published studies and reported cases remains limited. However, Kong et al [ 28 ] noted that this pattern of dual-level peripheral entrapment may not be uncommon. Several authors have described more severe symptoms in these patients [ 22 , 29 , 30 ] and have advocated for decompression at both sites to achieve meaningful improvement [ 19 , 22 , 31 , 32 , 33 ]. Conversely, some studies have suggested that single-site decompression may still yield satisfactory outcomes in select cases [ 20 , 21 ]. Type IIa DCS is the most commonly reported form of lower-extremity DCS, typically involving L5 radiculopathy combined with common peroneal nerve entrapment [ 10 , 11 , 12 ]. Zheng et al [ 34 ] also reported that approximately 4.8% of patients with lumbar nerve-root compression had concomitant tarsal tunnel syndrome, with no significant difference in the distribution of affected nerve roots (L4, L5, or S1). Many authors emphasize that peripheral entrapment should not be overlooked in patients with lumbar radiculopathy because the distal lesion may play a more significant role [ 10 , 11 ]. Persistent symptoms may remain after lumbar decompression alone [ 12 ], and in some cases, isolated peripheral decompression may even obviate the need for lumbar surgery [ 10 ]. Type IIb DCS is the rarest among all categories and is easily overlooked. Borgia et al [ 23 ] described a patient whose symptoms persisted after tarsal tunnel release, and the subsequent evaluation identified an additional proximal nerve injury. Giannoudis et al [ 24 ] reported a series of acetabular fractures complicated by sciatic nerve damage, among which nine patients had concurrent common peroneal nerve injury. All presented with foot drop, and none recovered over 4.3 years of follow-up, highlighting the severity of nerve injury associated with dual-level peripheral compression. Type IIc DCS represents the pathological subtype included in our study. This form has been only sparsely documented in the literature, mostly in case reports [ 13 , 14 , 15 , 35 ]. In this subtype, all compression sites are located within or around the spinal canal, and lumbar imaging typically allows clear identification of the compressed sites and pathological features. Most authors recommend single-stage decompression of all pathological sites [ 15 , 35 ]. Kanamoto et al [ 13 ] reported five patients whose symptoms persisted after L4-5 laminectomy. Using DTI to quantitatively assess nerve-root compression, they found decreased FA values and increased ADC values, radiographic indicators that can help detect dual-site nerve root compression preoperatively and potentially prevent decompression failure. The lumbar spinal nerve roots travel a relatively long course within and around the spinal canal, making them particularly susceptible to compression from degenerative and other pathological factors. Iwasaki et al [ 14 ] reported a case in which the L5 nerve root was simultaneously compressed at the L4-5 lateral recess and by a far-out syndrome (FOS). Wu et al [ 35 ] described cases involving multi-level compression of the nerve root within the lateral recess, foramen, and extraforaminal region. Using a contralateral uniportal endoscopic technique with oblique decompression extending to the extraforaminal zone, they were able to achieve full-length nerve root decompression in this special subtype of DCS, demonstrating a relatively minimally invasive option for select DCS patterns. This IIc-type DCS is not limited to degenerative disease. Nishimura et al [ 15 ] have also reported multiple compression sites caused by epidermoid tumor and sacral Tarlov Cyst. Overall, however, reported cases of dual-site compression of a lumbar nerve root around the spine remain relatively rare. The present study provides a clinical retrospective analysis specifically targeting IIc-type DCS and encompasses a range of pathological combinations, including lateral recess stenosis with concurrent FS, as well as LSS with extraforaminal lesions such as ELDH and FOS, pathologies that have not been previously reported together in the literature. The UBE technique was first introduced by Antoni et al [ 36 ] in Argentina and has evolved over the years to cover nearly all types of lumbar degenerative conditions. Owing to its wide visualization field and greater operative flexibility, UBE has become an essential component of spinal endoscopy technique, particularly when addressing complex pathological factors [ 37 ]. IIc-type DCS represents a unique and complex subtype of lumbar degenerative disease. The use of UBE for decompression leverages its advantages by enabling thorough elimination of dual-site pathological compression. Notably, no significant complications occurred in any of the patients included in this study. Existing literatures consistently support the principle that, in IIc-type DCS, dual-site decompression should be performed whenever possible to avoid residual symptoms. In this study, all patients underwent single-stage UBE surgery that successfully addressed all compression sites along a single nerve root, resulting in satisfactory clinical outcomes at 1-year follow-up. This represents the first published application of UBE for DCS and the largest reported cohort of patients with IIc-type DCS to date. Limitations This study is retrospective in nature. Because of the rarity and specificity of this subtype disease, it was not possible to include a large sample size. In addition, the follow-up period was relatively short; therefore, long-term outcomes remain unclear. Prospective, controlled studies with larger cohorts are needed to further validate and supplement our findings. Conclusion In this study, we report the first clinical series to evaluate UBE for the management of Type IIc lumbar DCS. Single-stage dual-site decompression using UBE provided reliable symptom relief, significant improvement in pain and disability scores, and satisfactory radiological outcomes without major complications. These findings suggest that UBE is a safe and effective minimally invasive option for patients with dual-level compression of a single lumbar nerve root. Given the rarity and pathological diversity of this condition, the classification framework proposed in this study may facilitate clearer diagnostic recognition and more standardized clinical decision-making. Further prospective studies with larger cohorts and long-term follow-up are needed to validate these results and to refine the optimal management strategy for this unique subtype of DCS. Declarations Author contributions WW contributed to study design, manuscript drafting, and illustration preparation. XY and YD were responsible for case inclusion and exclusion. CD collected and organized the clinical data. JY, LG, and YH performed the surgeries and conducted patient follow-up. All authors reviewed final version of the manuscript. Funding The study did not receive any financial support. Data availability No datasets were generated or analyzed during the current study. Ethics approval and consent to participate The study was conducted in accordance with the Declaration of Helsinki and approved by the Ethics Committee of Beijing Chaoyang Hospital, Capital Medical University (approval number: 2019-K-183). Written informed consent was obtained from all participants or their legal guardians. Clinical trial number Not applicable Competing interests The authors declare no competing interests. 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J Am Podiatr Med Assoc. 2012;102(4):330–3. 10.7547/1020330 . Giannoudis PV, Costa AAD, Raman R, et al. Double-crush syndrome after acetabular fractures. A sign of poor prognosis[J]. J Bone Joint Surg Br. 2005;87(3):401–7. 10.1302/0301-620x.87b3.15253 . Holloway M, Cady-McCrea C, Carroll T et al. (2025) Order of surgical intervention in double-crush syndrome[J]. Eur Spine J, Online ahead of print. 10.1007/s00586-025-09291-0 Wessel LE, Fufa DT, Canham RB, et al. Outcomes following Peripheral Nerve Decompression with and without Associated Double Crush Syndrome: A Case Control Study[J]. Plast Reconstr Surg. 2017;139(1):119–27. 10.1097/PRS.0000000000002863 . Byvaltsev VA, Kalinin AA, Polkin RA, et al. Simultaneous Versus Staged Surgery for Double Crush Syndrome of Cervical Radiculopathy and Peripheral Nerve Compression at the Wrist: A Retrospective Single-Center Study[J]. Spine (Phila Pa 1976). 2024;49(19):E307–14. 10.1097/BRS.0000000000004950 . Kong G, Brutus JP, Vo TT, et al. The prevalence of double- and multiple crush syndromes in patients surgically treated for peripheral nerve compression in the upper limb[J]. Hand Surg Rehabil. 2023;42(6):475–81. 10.1016/j.hansur.2023.09.002 . Ren HJ, Ye X, Li PY, et al. Outcomes of ulnar nerve decompression for double crush syndrome[J]. Br J Neurosurg. 2024;38(2):468–71. 10.1080/02688697.2021.1889463 . Smith TM, Sawyer SF, Sizer PS, et al. The double crush syndrome: a common occurrence in cyclists with ulnar nerve neuropathy-a case-control study[J]. Clin J Sport Med. 2008;18(1):55–61. 10.1097/JSM.0b013e31815c1d7a . Huang YG, Chang SM. Double crush syndrome due to plating of humeral shaft fracture[J]. Indian J Orthop. 2014;48(2):223–5. 10.4103/0019-5413.128774 . Azócar C, Corvalán G, Orellana P, et al. Intraoperative immediate strength recovery following lacertus fibrosus release in patients with proximal median nerve compression at the elbow[J]. Int Orthop. 2023;47(11):2781–6. 10.1007/s00264-023-05888-6 . Gong G, Wang L, Zhang J, et al. Ulnar nerve double crush by entrapment of a peri-cubital tunnel ganglion cyst and cubital tunnel: a case report[J]. BMC Musculoskelet Disord. 2025;26(1):270. 10.1186/s12891-025-08526-x . Zheng C, Zhu Y, Jiang J, et al. The prevalence of tarsal tunnel syndrome in patients with lumbosacral radiculopathy[J]. Eur Spine J. 2016;25(3):895–905. 10.1007/s00586-015-4246-x . Wu PH, Kim HS, Jang IT. How I do it? Uniportal full endoscopic contralateral approach for lumbar foraminal stenosis with double crush syndrome[J]. Acta Neurochir (Wien). 2020;162(2):305–10. 10.1007/s00701-019-04157-z . Antoni DJ, Claro ML, Poehling GG, et al. Translaminar lumbar epidural endoscopy: anatomy, technique, and indications[J]. Arthroscopy. 1996;12(3):330–4. 10.1016/s0749-8063(96)90069-9 . Park MK, Son SK, Park WW, et al. Unilateral Biportal Endoscopy for Decompression of Extraforaminal Stenosis at the Lumbosacral Junction: Surgical Techniques and Clinical Outcomes[J]. Neurospine. 2021;18(4):871–9. 10.14245/ns.2142146.073 . Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Revision requested 27 Apr, 2026 Reviews received at journal 22 Apr, 2026 Reviews received at journal 22 Apr, 2026 Reviews received at journal 17 Apr, 2026 Reviews received at journal 16 Apr, 2026 Reviewers agreed at journal 10 Apr, 2026 Reviewers agreed at journal 09 Apr, 2026 Reviewers agreed at journal 09 Apr, 2026 Reviewers agreed at journal 07 Apr, 2026 Reviewers invited by journal 05 Apr, 2026 Editor invited by journal 31 Mar, 2026 Editor assigned by journal 30 Mar, 2026 Submission checks completed at journal 30 Mar, 2026 First submitted to journal 15 Mar, 2026 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-9127627","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":619862855,"identity":"80990158-bed4-4aaf-85d7-4392e18f9a9d","order_by":0,"name":"Wenlong Wang","email":"","orcid":"","institution":"Beijing Chao-Yang Hospital","correspondingAuthor":false,"prefix":"","firstName":"Wenlong","middleName":"","lastName":"Wang","suffix":""},{"id":619862856,"identity":"8d1cce47-97db-4f28-8ff8-7fcae751e0ea","order_by":1,"name":"Xingchen Yao","email":"","orcid":"","institution":"Beijing Chao-Yang Hospital","correspondingAuthor":false,"prefix":"","firstName":"Xingchen","middleName":"","lastName":"Yao","suffix":""},{"id":619862857,"identity":"906536c9-91ec-4da9-8d21-33a55ee9fe90","order_by":2,"name":"Yi Ding","email":"","orcid":"","institution":"Beijing Chao-Yang Hospital","correspondingAuthor":false,"prefix":"","firstName":"Yi","middleName":"","lastName":"Ding","suffix":""},{"id":619862858,"identity":"cc626be7-aa4d-4287-aeea-9be9fbb7b5b6","order_by":3,"name":"Chuanchao Du","email":"","orcid":"","institution":"Beijing Chao-Yang Hospital","correspondingAuthor":false,"prefix":"","firstName":"Chuanchao","middleName":"","lastName":"Du","suffix":""},{"id":619862859,"identity":"75a3f4be-6906-4f31-98fd-394e1591a81d","order_by":4,"name":"Jincai Yang","email":"","orcid":"","institution":"Beijing Chao-Yang Hospital","correspondingAuthor":false,"prefix":"","firstName":"Jincai","middleName":"","lastName":"Yang","suffix":""},{"id":619862860,"identity":"0c9b7af6-cdc2-4149-85e1-5b2113152b08","order_by":5,"name":"Li Guan","email":"","orcid":"","institution":"Beijing Chao-Yang Hospital","correspondingAuthor":false,"prefix":"","firstName":"Li","middleName":"","lastName":"Guan","suffix":""},{"id":619862861,"identity":"e1625a17-24a3-436d-b02f-3e12703b890a","order_by":6,"name":"Yong Hai","email":"","orcid":"","institution":"Beijing Chao-Yang Hospital","correspondingAuthor":false,"prefix":"","firstName":"Yong","middleName":"","lastName":"Hai","suffix":""},{"id":619862862,"identity":"5098d400-05e4-43d3-89df-cbce8f089bc3","order_by":7,"name":"Aixing Pan","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAyElEQVRIiWNgGAWjYBACPijNwyb/+MCBDz+I0MIGJhMY5PgZ0hIPzuwhQYuxZEOO8WEONmK0sJ89+OHjD4bEDQfOfDjMwMMgzy92gIAWnrxkyRkJQC0HezccLrBgMJw5O4GQw3LMmHlAWg7zbjg8g4chweA2IS38b8yY/4C0HON5cJiHjRgtEkBbwN7v4WEgVssboOo0YCBLsBkAA1mCsF/4+XMMP/ywAUalBPPjD0CWPL80AS1Q8B/GkCBK+SgYBaNgFIwCAgAAoOU/N7aMNeUAAAAASUVORK5CYII=","orcid":"","institution":"Beijing Chao-Yang Hospital","correspondingAuthor":true,"prefix":"","firstName":"Aixing","middleName":"","lastName":"Pan","suffix":""}],"badges":[],"createdAt":"2026-03-15 09:38:50","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9127627/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9127627/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":106726889,"identity":"6718745c-9c35-499c-8d7e-ca4fc60e4a6d","added_by":"auto","created_at":"2026-04-12 18:37:31","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":10820369,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ea \u003c/strong\u003eA schematic illustration of a common form of Double Crush Syndrome (DCS) involving a single lumbar nerve root.\u003cstrong\u003e b \u003c/strong\u003eEndoscopy Portal 1 and Working Portal 1 are used to decompress intraspinal lesions. They are positioned 1.5 cm cranial and caudal to the green point, which is defined as the intersection between the medial pedicle line and the superior margin of the intervertebral space. Endoscopy Portal 2 and Working Portal 2 are designed for the management of paraspinal lesions. They are located 2 cm lateral to the lateral pedicle line, allowing direct convergence toward the paraspinal pathological site.\u003c/p\u003e","description":"","filename":"Fig1.png","url":"https://assets-eu.researchsquare.com/files/rs-9127627/v1/8223a8064406d01a1ab9098f.png"},{"id":106725061,"identity":"69be30ce-03b2-4e20-a47a-c6ac0ee24c7b","added_by":"auto","created_at":"2026-04-12 18:31:14","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":5288834,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ea \u003c/strong\u003eEntering the spinal canal through the interlaminar space, partial resection of the ligamentum flavum and facet joint was performed, followed by thorough decompression of the traversing nerve root. \u003cstrong\u003eb\u003c/strong\u003e Through the paraspinal approach, decompression of the lateral lesion was performed by resecting part of the lateral margin of the pars interarticularis and the tip of the superior articular process, thereby exposing the exiting nerve root. Exploration was then extended laterally until the exiting root was fully decompressed.\u003c/p\u003e","description":"","filename":"Fig2.png","url":"https://assets-eu.researchsquare.com/files/rs-9127627/v1/4197edc5bb44a5da0ab56606.png"},{"id":106545478,"identity":"43f0ceaa-429b-4e02-9002-7fbbb09ad2a8","added_by":"auto","created_at":"2026-04-09 16:45:57","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":1071086,"visible":true,"origin":"","legend":"\u003cp\u003eChanges in patients’ VAS for low back pain and lower extremity pain, and ODI over time\u003c/p\u003e","description":"","filename":"Fig3.png","url":"https://assets-eu.researchsquare.com/files/rs-9127627/v1/83919a0f08bac47c6a318a43.png"},{"id":106545482,"identity":"c6c6750c-e5de-4e50-a748-2b00c6fab82a","added_by":"auto","created_at":"2026-04-09 16:45:57","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":16498300,"visible":true,"origin":"","legend":"\u003cp\u003eA 66-year-old female patient with left L4-5 lateral recess stenosis combined with left L5-S1 foraminal stenosis. \u003cstrong\u003ea\u003c/strong\u003eMRI demonstrating left L4-5 lateral recess stenosis with compression of the left L5 nerve root. \u003cstrong\u003eb\u003c/strong\u003e MRI showing left L5-S1 foraminal stenosis with compression of the left L5 nerve root. \u003cstrong\u003ec\u003c/strong\u003e CT revealing osseous stenosis of the left L5-S1 foramen. \u003cstrong\u003ed\u003c/strong\u003e CT demonstrating left L4-5 lateral recess stenosis. \u003cstrong\u003ee\u003c/strong\u003e Endoscopic view showing the decompressed left L4-5 lateral recess and traversing L5 nerve root. \u003cstrong\u003ef\u003c/strong\u003e \u0026nbsp;Endoscopic view showing the decompressed L5-S1 foramen and exiting L5 nerve root. \u003cstrong\u003eg\u003c/strong\u003e CT showing the decompressed left L4-5 lateral recess. \u003cstrong\u003eh\u003c/strong\u003e CT showing the decompressed left L5-S1 foramen.\u003c/p\u003e","description":"","filename":"Fig4.png","url":"https://assets-eu.researchsquare.com/files/rs-9127627/v1/8b1fba409c9c56acb3cfa456.png"},{"id":106545479,"identity":"7167b084-eee4-42cd-a8a3-ebae87ad9039","added_by":"auto","created_at":"2026-04-09 16:45:57","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":19120490,"visible":true,"origin":"","legend":"\u003cp\u003eA 64-year-old female patient with left L4-5 posterolateral lumbar disc herniation combined with left L5-S1 foraminal stenosis. \u003cstrong\u003ea\u003c/strong\u003e MRI demonstrating left L4-5 left posterolateral lumbar disc herniation with compression of the left L5 nerve root. \u003cstrong\u003eb\u003c/strong\u003e MRI showing left L5-S1 foraminal stenosis with compression of the left L5 nerve root. \u003cstrong\u003ec\u003c/strong\u003e CT revealing osseous stenosis of the left L5-S1 foramen. \u003cstrong\u003ed\u003c/strong\u003eCT demonstrating left L4-5 disc herniation. \u003cstrong\u003ee\u003c/strong\u003e Endoscopic view showing the decompressed traversing L5 nerve root after left L4-5 discectomy. \u003cstrong\u003ef\u003c/strong\u003e \u0026nbsp;Endoscopic view showing the decompressed L5-S1 foramen and exiting L5 nerve root. \u003cstrong\u003eg\u003c/strong\u003e CT showing the decompressed left L4-5 discectomy. \u003cstrong\u003eh\u003c/strong\u003e CT showing the decompressed left L5-S1 foramen.\u003c/p\u003e","description":"","filename":"Fig5.png","url":"https://assets-eu.researchsquare.com/files/rs-9127627/v1/3afd3c2342fde6abe458a555.png"},{"id":106726024,"identity":"8a233f97-10bb-4c9c-917f-22b91166d8e4","added_by":"auto","created_at":"2026-04-12 18:34:58","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":1741972,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic illustration of two categories and five subtypes of Double Crush Syndrome (DCS).\u003c/p\u003e","description":"","filename":"Fig6.png","url":"https://assets-eu.researchsquare.com/files/rs-9127627/v1/199f1f4ad5daaba5cf63a203.png"},{"id":106728194,"identity":"2bc4e286-d43c-42bb-b5ad-8d6ad1bc14af","added_by":"auto","created_at":"2026-04-12 18:42:07","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":51383911,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9127627/v1/8c578f97-c625-4c02-a955-4dc8f9e08248.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Application of Unilateral Biportal Endoscopy in Lumbar Double Crush Syndrome: A Retrospective Study and Literature-Based Classification","fulltext":[{"header":"Introduction","content":"\u003cp\u003eThe definition and standard diagnostic test of Double Crush Syndrome (DCS) remain imprecise [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. In general, most authors describe DCS as a condition in which a single peripheral nerve is compressed at two or more distinct sites along its pathway [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. Clinically, DCS presents with symptoms similar to those of a single-site peripheral neuropathy, which contributes to its relatively low reported incidence and frequent underdiagnosis. However, due to the cumulative effect of these compressed insults, the resulting neural damage may be more severe than that caused by a single lesion [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Therefore, accurate recognition of DCS and effective decompression at all involved sites are of critical importance [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e].\u003c/p\u003e \u003cp\u003ePeripheral nerves have long and complex anatomical pathways with wide distributions, leading to diverse pathological mechanisms of entrapment. Consequently, the reported presentations and definitions of DCS vary considerably among published studies. The reported incidences range from 6.7% to as high as 73% [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. Moreover, there are substantial discrepancies in the reported incidence of DCS across the literatures. Thus, systematic review and classification of the published studies are essential to facilitate clearer understanding and more meaningful discussion within specific subtypes of DCS.\u003c/p\u003e \u003cp\u003eRecently, most published studies involve double crush occurring at vertebral structures and peripheral corridors of the same nerve, for example, cervical radiculopathy combined with carpal tunnel syndrome (CTS) [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e], or lumbar radiculopathy combined with common peroneal nerve entrapment [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. A single lumbar nerve root traverses a long pathway within the spinal structure, making it susceptible to compression at multiple sites. However, reports specifically focusing on double crush of a single lumbar nerve root caused by an intraspinal canal lesion and a lateral lesion are exceedingly rare [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. This subtype of lumbar DCS represents a unique but clinically significant entity. In the present study, we report a series of such cases treated using unilateral biportal endoscopy (UBE) for decompression at both lumbar compression sites, achieving satisfactory clinical outcomes. To our knowledge, this represents the first report describing the application of the UBE technique for this specific type of DCS, as well as the largest case series to date.\u003c/p\u003e"},{"header":"Material and Methods","content":"\u003cp\u003eA retrospective review was conducted of all patients who underwent lumbar UBE surgery in our department between 2020 and 2024. Among them, 16 patients diagnosed with lumbar DCS (7 males and 9 females) were included in this study. The study protocol was approved by the Institutional Ethics Committee of our hospital (approval number: 2019-K-183). All patients agreed to participate in the study and signed informed consent forms.\u003c/p\u003e \u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eInclusion and Exclusion Criteria\u003c/h2\u003e \u003cp\u003eThe inclusion criteria were as follows: a) Presence of typical clinical manifestations of single lumbar nerve root compression with poor response to conservative treatment; b) Radiological confirmation of double-site compression involving the same nerve root; c) Patients who underwent single-stage decompression using the UBE technique at our institution; d) The postoperative follow-up period reached 12 months.\u003c/p\u003e \u003cp\u003eThe exclusion criteria were as follows: a) Decompression involving different nerve roots; b) Radiological evidence of multi-root compression; c) Decompression procedures not performed under the UBE technique; d) Presence of severe systemic diseases or other spinal disorders that could interfere with the assessment; e) Incomplete clinical data or failure to complete a minimum follow-up of 12 months.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eData Collection and Evaluation\u003c/h3\u003e\n\u003cp\u003ePreoperative demographic data, clinical characteristics, and imaging findings were collected. The responsible nerve root and the two sites of compression were identified based on radiological evaluation. Radiological assessment included plain radiographs, magnetic resonance imaging (MRI), myelography, and computed tomography (CT), which were analyzed in correlation with the patients\u0026rsquo; neurological symptoms.\u003c/p\u003e \u003cp\u003eOperative parameters, including endoscopic operative time, time to postoperative ambulation, length of hospital stay, and intraoperative or postoperative complications, were recorded. Postoperative imaging studies were performed to confirm decompression. Patient satisfaction was assessed at discharge, and clinical follow-up evaluations were conducted at 1, 3, 6, and 12 months postoperatively.\u003c/p\u003e \u003cp\u003ePain intensity of the lower back and affected lower limb was evaluated using the visual analog scale (VAS), and functional outcomes were assessed using the Oswestry Disability Index (ODI) before surgery, immediately after surgery, and during follow-up visits.\u003c/p\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003eStatistical analysis\u003c/h2\u003e \u003cp\u003eNumeric variables are expressed as mean (\u0026plusmn;\u0026thinsp;SD) and discrete outcomes as number of cases (%). The effectiveness of the surgery was assessed by comparing the preoperative and postoperative clinical data. Continuous outcomes were compared by paired Student \u003cem\u003et\u003c/em\u003e test, Welch t test or Mann-Whitney U test according to data distribution. The alpha risk was set to 5% and two-tailed tests were used. Statistical analysis was performed with SPSS software (version 27.0; IBM Corp, Armonk, NY, USA).\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eSurgical Procedures\u003c/h3\u003e\n\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003ePosition, Anesthesia, and Skin Incision\u003c/h2\u003e \u003cp\u003eThe patient was placed in the prone position on a radiolucent Jackson spinal table and put under general anesthesia. The surgeon stood on the lesion side. Under anteroposterior fluoroscopic projection, two sets of skin incision lines were drawn, corresponding to the two operative segments: one pair for the intraspinal canal lesion (Endoscopic Portal 1 and Working Portal 1), and another pair for the lateral lesion (Endoscopic Portal 2 and Working Portal 2). The cross point (green point) of the lower endplate line and the medial margin of the pedicle line was marked. Endoscopic Portal 1 and Working Portal 1 were made 1.5 cm cranial and caudal to the cross point. Endoscopic Portal 2 and Working Portal 2 were made along a line located 2 cm lateral to the lateral margin of the pedicle line (green dashed line), using the \u0026ldquo;P\u0026thinsp;+\u0026thinsp;2\u0026rdquo; incision approach. These two incisions were approximately 3 cm apart and, under lateral fluoroscopic projection, symmetrically converged toward the paraspinal lesion (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eParamedian Approach Decompression for Intraspinal Lesions\u003c/h2\u003e \u003cp\u003eTransverse skin incisions measuring 1 cm in length were executed aligned with Endoscopy Portal 1 and Working Portal 1. To facilitate soft tissue dissection and secure operative space, serial dilators were utilized. Subsequently, an arthroscope was introduced via the endoscopy portal, partnered with implementing a saline irrigation system. Soft tissue cauterization and hemorrhage control were achieved by deploying a radiofrequency probe. The foundational bony structure viewed under endoscopy corresponded to the intersection of the lower margin of the spinous process and the lower margin of the lamina. This pivotal point served as the docking site. Ipsilateral partial laminotomy of the upper and lower laminae was performed using a high-speed burr until full exposure of the ligamentum flavum (LF) from the proximal end to the distal end was achieved. The ipsilateral inferior articular process (IAP) was partially removed using Kerrison rongeurs and osteotomes to disclose the medial articular surface of the superior articular process (SAP) in deep portion. Then, the SAP was partially removed. The ipsilateral LF was completely removed to expose the dural sac and right traversing nerve root. The dural sac and traversing nerve root were then retracted medially with a nerve retractor to expose the ventral structure of the nerve root. The intervertebral disc was inspected, and if a disc herniation was present, discectomy was performed followed by radiofrequency ablation of the annulus fibrosus. Finally, adequate decompression was confirmed by ensuring that the traversing nerve root was relaxed and free of compression (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea).\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eParaspinal Approach Decompression for Lateral Lesion\u003c/h3\u003e\n\u003cp\u003eSimilarly, two 1-cm incisions were made along Portal 2 and Working Portal 2, and the soft tissues were dissected using the radiofrequency probe until reaching the lateral margin of the pars interarticularis. A high-speed burr was used to remove a small portion of the bone at the lateral edge, exposing the deeper LF. After resecting the tip of the SAP with a chisel, part of the LF was removed to expose the deep exiting nerve root. Decompression was carried out along the exiting nerve root, and any additional paraspinal compressive lesions were removed until the exiting root was fully decompressed (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e\n\u003ch3\u003eFinal Checking Point\u003c/h3\u003e\n\u003cp\u003eDecompressed nerve root is confirmed by the nerve root length and slackness. Negative pressure drainage was inserted in the decompression area, and then the incisions were closed.\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003eA total of 16 patients with lumbar DCS were included, consisting of 7 men and 9 women. The average age at the time of surgery was 71.9\u0026thinsp;\u0026plusmn;\u0026thinsp;7.3 years (range, 60\u0026ndash;88 years), the mean body mass index (BMI) was 25.6\u0026thinsp;\u0026plusmn;\u0026thinsp;2.9 kg/m\u0026sup2; (range, 20.0-30.8 kg/m\u0026sup2;), and the mean duration of symptoms was 10.7\u0026thinsp;\u0026plusmn;\u0026thinsp;6.4 months (range, 2\u0026ndash;24 months). Twelve patients presented with L5 DCS, and four patients had L4 DCS.\u003c/p\u003e \u003cp\u003eAmong the patients with L5 nerve root DCS, seven cases resulted from unilateral L4-5 lateral recess stenosis (LRS) combined with L5-S1 foraminal stenosis (FS); one case involved L4-5 posterolateral lumbar disc herniation (LDH) combined with L5-S1 FS; one case involved L4-5 LRS combined with L5-S1 far-out syndrome (FOS); and three cases involved L4-5 LRS combined with L5-S1 extraforaminal lumbar disc herniation (ELDH).\u003c/p\u003e \u003cp\u003eAmong the patients with L4 nerve root DCS, two cases resulted from unilateral L3-4 LRS combined with L4-5 ELDH; one case involved L3-4 posterolateral LDH combined with L4-5 FS; and one case resulted from unilateral L3-4 LRS combined with L4-5 FS. The demographic data and clinical characteristics of patients with the various pathological types of DCS were presented in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eBaseline Demographic Characteristics of Patients With Various Types of DCS\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCompressed Nerve Root\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePathological Type\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eNumber of Cases (n, %)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eAge and Gender\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eDuration of Symptoms (months)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"11\" rowspan=\"12\"\u003e \u003cp\u003eL5\u003c/p\u003e \u003cp\u003eNerve Root\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\" morerows=\"6\" rowspan=\"7\"\u003e \u003cp\u003eL4-5 LRS with L5-S1 FS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\" morerows=\"6\" rowspan=\"7\"\u003e \u003cp\u003e7\u003c/p\u003e \u003cp\u003e(44%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e68, Male\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e18\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e66, Female\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e9\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e81, Female\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e68, Female\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e9\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e88, Female\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e12\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e77, Male\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e24\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e75, Female\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e11\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003eL4-5 LRS with L5-S1 ELDH\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003e3\u003c/p\u003e \u003cp\u003e(19%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e72, Male\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e79, Male\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e68, Male\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eL4-5 LDH with L5-S1 FS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1\u003c/p\u003e \u003cp\u003e(6%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e64, Female\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eL4-5 LRS with L5-S1 FOS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1\u003c/p\u003e \u003cp\u003e(6%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e74, Female\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e22\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"3\" rowspan=\"4\"\u003e \u003cp\u003eL4\u003c/p\u003e \u003cp\u003eNerve Root\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eL3-4 LRS with L4-5 ELDH\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e2\u003c/p\u003e \u003cp\u003e(13%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e60, Female\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e14\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e76, Male\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eL3-4 LDH with L4-5 FS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1\u003c/p\u003e \u003cp\u003e(6%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e71, Male\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e13\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eL3-4 LRS with L4-5 FS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1\u003c/p\u003e \u003cp\u003e(6%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e64, Female\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"5\"\u003eLRS: lateral recess stenosis; FS: foraminal stenosis; ELDH: extraforaminal lumbar disc herniation; LDH: lumbar disc herniation; FOS: far-out syndrome\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe mean endoscopic operative time for all patients was 118.4\u0026thinsp;\u0026plusmn;\u0026thinsp;13.5 minutes. Postoperative ambulation was achieved on average at 1.8\u0026thinsp;\u0026plusmn;\u0026thinsp;0.9 days, and the mean postoperative hospital stay was 4.7\u0026thinsp;\u0026plusmn;\u0026thinsp;1.5 days. The mean preoperative VAS score for low back pain was 2.8\u0026thinsp;\u0026plusmn;\u0026thinsp;1.1. Postoperatively, the VAS scores for low back pain were 2.9\u0026thinsp;\u0026plusmn;\u0026thinsp;1.0 on the first day, 2.3\u0026thinsp;\u0026plusmn;\u0026thinsp;0.8 at 1 month, 1.9\u0026thinsp;\u0026plusmn;\u0026thinsp;0.7 at 3 months, 1.4\u0026thinsp;\u0026plusmn;\u0026thinsp;0.6 at 6 months, and 1.5\u0026thinsp;\u0026plusmn;\u0026thinsp;0.8 at 1 year. The mean preoperative VAS score for the affected limb was 6.0\u0026thinsp;\u0026plusmn;\u0026thinsp;1.2. Postoperatively, the VAS scores for the affected limb were 2.2\u0026thinsp;\u0026plusmn;\u0026thinsp;0.9 on the first day, 1.1\u0026thinsp;\u0026plusmn;\u0026thinsp;0.6 at 1 month, 0.8\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5 at 3 months, 0.8\u0026thinsp;\u0026plusmn;\u0026thinsp;0.7 at 6 months, and 0.9\u0026thinsp;\u0026plusmn;\u0026thinsp;0.7 at 1 year. The mean preoperative Oswestry Disability Index (ODI) was 75.9\u0026thinsp;\u0026plusmn;\u0026thinsp;4.7%. Postoperatively, 35.5\u0026thinsp;\u0026plusmn;\u0026thinsp;5.7% at 1-month follow-up, 27.9\u0026thinsp;\u0026plusmn;\u0026thinsp;4.5% at 3 months, 20.6\u0026thinsp;\u0026plusmn;\u0026thinsp;5.2% at 6 months, and 19.2\u0026thinsp;\u0026plusmn;\u0026thinsp;6.3% at 1 year. Changes in postoperative clinical outcomes are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003eOverview of DCS\u003c/h2\u003e \u003cp\u003eDouble crush syndrome (DCS) refers to a condition in which a single peripheral nerve is subjected to compression at multiple sites. A typical example is the coexistence of radicular cervical spondylosis and a peripheral entrapment neuropathy. This cumulative compressive effect results in more severe neural injury and symptoms than compression occurring at a single site. DCS was first described by Upton and McComas in 1973 [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e], and subsequent literature has reported a relatively high prevalence of concurrent carpal tunnel syndrome or cubital tunnel syndrome among patients with cervical radiculopathy.\u003c/p\u003e \u003cp\u003eBecause no definitive anatomical or electrodiagnostic criteria exist to confirm the presence of DCS, reported incidence rates range broadly from 6.7% to 73%, making objective identification of dual-site nerve injury particularly challenging. One proposed pathophysiologic mechanism is that proximal axonal compression impairs axoplasmic transport, resulting in neural dysfunction and increasing the susceptibility of the same nerve to distal injury. However, \u0026Ouml;kmen et al. questioned the existence of DCS after finding no significant differences in peripheral nerve morphology, assessed via ultrasonography, between the symptomatic and asymptomatic limbs of patients with cervical radiculopathy.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003eClassification of DCS Based on Published Literatures\u003c/h2\u003e \u003cp\u003eA literature search identified 43 publications on DCS published after the year 2000. Based on the anatomical distribution of symptoms, the author classified DCS into upper-extremity (Type I) and lower-extremity (Type II) categories.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003e(1) Type I: Upper-Extremity DCS\u003c/h2\u003e \u003cp\u003eMost reports on DCS involve the upper extremities. According to the underlying pathology, upper-extremity DCS can be divided into two subtypes:\u003c/p\u003e \u003cp\u003e \u003cstrong\u003eType Ia\u003c/strong\u003e \u003cp\u003eCervical radiculopathy combined with peripheral nerve entrapment. Among all dual-site compressive neuropathies, cervical radiculopathy combined with CTS is the most widely reported [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. Cervical radiculopathy with cubital tunnel syndrome has also been frequently described [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e], whereas combinations involving other peripheral entrapment neuropathies, such as suprascapular nerve entrapment, are less common and often limited to case reports [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. For this category of DCS, most authors agree that decompression at both sites yields superior clinical outcomes compared with single-site decompression.\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003eType Ib\u003c/strong\u003e \u003cp\u003eDouble-site peripheral nerve entrapment in the upper extremity.\u003c/p\u003e \u003c/p\u003e \u003cp\u003eThis subtype is also commonly described, though mostly as a case report. The pathological patterns are more diverse, including double entrapment of the ulnar nerve at the elbow and the wrist [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e], CTS combined with pronator syndrome [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e], and concurrence of cubital tunnel syndrome and the lower trunk of the brachial plexus compression [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e], among others.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003e(2) Type II: Lower-Extremity DCS\u003c/h2\u003e \u003cp\u003eReports of DCS involving the lower extremities are substantially less common. Based on pathological patterns, lower-extremity DCS can be categorized into three subtypes:\u003c/p\u003e \u003cp\u003e \u003cstrong\u003eType IIa\u003c/strong\u003e \u003cp\u003eLumbar radiculopathy combined with peripheral nerve entrapment. This subtype has primarily been reported in cases of L5 nerve root radiculopathy accompanied by common peroneal nerve entrapment [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e].\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003eType IIb\u003c/strong\u003e \u003cp\u003eDouble-level peripheral nerve entrapment in the lower extremity.\u003c/p\u003e \u003c/p\u003e \u003cp\u003eOnly two case reports have described this subtype, both involving traumatic injuries that resulted in dual-site peripheral nerve compression, suggesting that this pattern is relatively rare [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003cstrong\u003eType IIc\u003c/strong\u003e \u003cp\u003eDual-site compression of a single lumbar spinal nerve root. This subtype involves compression of the same nerve root at two separate locations around the spinal structure due to various pathological causes. Although even less frequently reported, the dual-level nerve-root compression has clinical implications similar to classic DCS [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. If one of the compressive sites is overlooked, surgical treatment may fail to provide complete symptom relief. In addition to the difficulty of establishing a definitive diagnosis, clinical management of DCS presents another major challenge [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e].\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"Discussion","content":"\u003cp\u003eGiven the large number of cervical and lumbosacral spinal nerves and their long anatomical pathway, including multiple osteomuscular anatomical corridors, multilevel compression can occur at various sites, making reports of DCS relatively common. However, the diversity of these pathological compression patterns often leads to considerable variability in clinical presentation. Therefore, DCS cases reported in the literature should be classified according to differences in anatomical location and underlying pathology, which would facilitate more standardized discussion and improve academic communication.\u003c/p\u003e \u003cp\u003eIn the present study, we primarily performed decompression for Type IIc DCS. The characteristics of these cases differ substantially from those of upper-extremity DCS, lumbar radiculopathy combined with peripheral nerve entrapment, or dual-site entrapment of lower-extremity peripheral nerves. Correspondingly, the therapeutic strategies also differ significantly. A precise classification of DCS helps improve our understanding of its pathological features and provides a more systematic basis for clinical communication and treatment planning.\u003c/p\u003e \u003cp\u003eFor Type Ia DCS, there is ongoing debate regarding which lesion, cervical radiculopathy or peripheral entrapment, plays the dominant pathological role and which should be addressed first. Holloway and Stoy et al argue that cervical radiculopathy is the primary pathology in Type Ia DCS and that cervical decompression alone can achieve satisfactory outcomes [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. In contrast, the findings of Hansen et al [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e] suggest the opposite-that isolated peripheral nerve decompression is sufficient to produce good clinical results. Other studies, including Ochoa-Cacique [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e] and Gullborg et al [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e], advocate decompressing both sites to achieve optimal therapeutic outcomes. Furthermore, Wessel et al [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e] and Galarza et al [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e] reported that some patients who underwent cervical decompression required subsequent peripheral nerve release due to persistent symptoms. Both authors emphasized that nerve damage in DCS tends to be more severe, and postoperative outcomes are generally inferior compared with single-site radiculopathy. In addition, Byvaltsev et al [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e] concluded that simultaneous two-site decompression provides greater benefit than staged procedures.\u003c/p\u003e \u003cp\u003eFor Type Ib DCS, the number of published studies and reported cases remains limited. However, Kong et al [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e] noted that this pattern of dual-level peripheral entrapment may not be uncommon. Several authors have described more severe symptoms in these patients [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e] and have advocated for decompression at both sites to achieve meaningful improvement [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e, \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e, \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]. Conversely, some studies have suggested that single-site decompression may still yield satisfactory outcomes in select cases [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eType IIa DCS is the most commonly reported form of lower-extremity DCS, typically involving L5 radiculopathy combined with common peroneal nerve entrapment [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. Zheng et al [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e] also reported that approximately 4.8% of patients with lumbar nerve-root compression had concomitant tarsal tunnel syndrome, with no significant difference in the distribution of affected nerve roots (L4, L5, or S1). Many authors emphasize that peripheral entrapment should not be overlooked in patients with lumbar radiculopathy because the distal lesion may play a more significant role [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. Persistent symptoms may remain after lumbar decompression alone [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e], and in some cases, isolated peripheral decompression may even obviate the need for lumbar surgery [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eType IIb DCS is the rarest among all categories and is easily overlooked. Borgia et al [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e] described a patient whose symptoms persisted after tarsal tunnel release, and the subsequent evaluation identified an additional proximal nerve injury. Giannoudis et al [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e] reported a series of acetabular fractures complicated by sciatic nerve damage, among which nine patients had concurrent common peroneal nerve injury. All presented with foot drop, and none recovered over 4.3 years of follow-up, highlighting the severity of nerve injury associated with dual-level peripheral compression.\u003c/p\u003e \u003cp\u003eType IIc DCS represents the pathological subtype included in our study. This form has been only sparsely documented in the literature, mostly in case reports [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]. In this subtype, all compression sites are located within or around the spinal canal, and lumbar imaging typically allows clear identification of the compressed sites and pathological features. Most authors recommend single-stage decompression of all pathological sites [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]. Kanamoto et al [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e] reported five patients whose symptoms persisted after L4-5 laminectomy. Using DTI to quantitatively assess nerve-root compression, they found decreased FA values and increased ADC values, radiographic indicators that can help detect dual-site nerve root compression preoperatively and potentially prevent decompression failure.\u003c/p\u003e \u003cp\u003eThe lumbar spinal nerve roots travel a relatively long course within and around the spinal canal, making them particularly susceptible to compression from degenerative and other pathological factors. Iwasaki et al [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e] reported a case in which the L5 nerve root was simultaneously compressed at the L4-5 lateral recess and by a far-out syndrome (FOS). Wu et al [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e] described cases involving multi-level compression of the nerve root within the lateral recess, foramen, and extraforaminal region. Using a contralateral uniportal endoscopic technique with oblique decompression extending to the extraforaminal zone, they were able to achieve full-length nerve root decompression in this special subtype of DCS, demonstrating a relatively minimally invasive option for select DCS patterns. This IIc-type DCS is not limited to degenerative disease. Nishimura et al [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e] have also reported multiple compression sites caused by epidermoid tumor and sacral Tarlov Cyst. Overall, however, reported cases of dual-site compression of a lumbar nerve root around the spine remain relatively rare.\u003c/p\u003e \u003cp\u003eThe present study provides a clinical retrospective analysis specifically targeting IIc-type DCS and encompasses a range of pathological combinations, including lateral recess stenosis with concurrent FS, as well as LSS with extraforaminal lesions such as ELDH and FOS, pathologies that have not been previously reported together in the literature. The UBE technique was first introduced by Antoni et al [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e] in Argentina and has evolved over the years to cover nearly all types of lumbar degenerative conditions. Owing to its wide visualization field and greater operative flexibility, UBE has become an essential component of spinal endoscopy technique, particularly when addressing complex pathological factors [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIIc-type DCS represents a unique and complex subtype of lumbar degenerative disease. The use of UBE for decompression leverages its advantages by enabling thorough elimination of dual-site pathological compression. Notably, no significant complications occurred in any of the patients included in this study. Existing literatures consistently support the principle that, in IIc-type DCS, dual-site decompression should be performed whenever possible to avoid residual symptoms. In this study, all patients underwent single-stage UBE surgery that successfully addressed all compression sites along a single nerve root, resulting in satisfactory clinical outcomes at 1-year follow-up. This represents the first published application of UBE for DCS and the largest reported cohort of patients with IIc-type DCS to date.\u003c/p\u003e \u003cdiv id=\"Sec17\" class=\"Section2\"\u003e \u003ch2\u003eLimitations\u003c/h2\u003e \u003cp\u003eThis study is retrospective in nature. Because of the rarity and specificity of this subtype disease, it was not possible to include a large sample size. In addition, the follow-up period was relatively short; therefore, long-term outcomes remain unclear. Prospective, controlled studies with larger cohorts are needed to further validate and supplement our findings.\u003c/p\u003e \u003c/div\u003e"},{"header":"Conclusion","content":"\u003cp\u003eIn this study, we report the first clinical series to evaluate UBE for the management of Type IIc lumbar DCS. Single-stage dual-site decompression using UBE provided reliable symptom relief, significant improvement in pain and disability scores, and satisfactory radiological outcomes without major complications. These findings suggest that UBE is a safe and effective minimally invasive option for patients with dual-level compression of a single lumbar nerve root. Given the rarity and pathological diversity of this condition, the classification framework proposed in this study may facilitate clearer diagnostic recognition and more standardized clinical decision-making. Further prospective studies with larger cohorts and long-term follow-up are needed to validate these results and to refine the optimal management strategy for this unique subtype of DCS.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAuthor contributions \u003c/strong\u003eWW contributed to study design, manuscript drafting, and illustration preparation. XY and YD were responsible for case inclusion and exclusion. CD collected and organized the clinical data. JY, LG, and YH performed the surgeries and conducted patient follow-up. All authors reviewed final version of the manuscript.\u003c/p\u003e\n\n\u003cp\u003e\u003cstrong\u003eFunding \u003c/strong\u003eThe study did not receive any financial support.\u003c/p\u003e\n\n\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e No datasets were generated or analyzed during the current study.\u003c/p\u003e\n\n\n\u003cp\u003e\u003cstrong\u003eEthics approval and consent to participate \u003c/strong\u003eThe study was conducted in accordance with the Declaration of Helsinki and approved by the Ethics Committee of Beijing Chaoyang Hospital, Capital Medical University (approval number: 2019-K-183). Written informed consent was obtained from all participants or their legal guardians.\u003c/p\u003e\n\n\u003cp\u003e\u003cstrong\u003eClinical trial number\u003c/strong\u003e Not applicable\u003c/p\u003e\n\n\u003cp\u003e\u003cstrong\u003eCompeting interests \u003c/strong\u003eThe authors declare no competing interests.\u003c/p\u003e\n\n\u003cp\u003e\u003cstrong\u003eData availability \u003c/strong\u003eThe datasets used and analysed during the current study are available from the corresponding author on reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eGhali M, Ehlen QT, Kholodovsky E, et al. Double Crush Syndrome: A Review of the Literature[J]. 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Neurospine. 2021;18(4):871\u0026ndash;9. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.14245/ns.2142146.073\u003c/span\u003e\u003cspan address=\"10.14245/ns.2142146.073\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"bmc-surgery","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"bsur","sideBox":"Learn more about [BMC Surgery](http://bmcsurg.biomedcentral.com/)","snPcode":"","submissionUrl":"https://www.editorialmanager.com/bsur/default.aspx","title":"BMC Surgery","twitterHandle":"@BMC_series","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"em","reportingPortfolio":"BMC Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Double crush syndrome, Unilateral biportal endoscopy, Classification system","lastPublishedDoi":"10.21203/rs.3.rs-9127627/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9127627/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eObjective\u003c/h2\u003e \u003cp\u003eDouble Crush Syndrome (DCS) represents a relatively uncommon peripheral neuropathy caused by compression of the same nerve at two distinct sites. A single lumbar nerve root traverses a long pathway within the spinal structure, making it susceptible to compression at multiple sites. This dual-site entrapment results in dysfunction of a single nerve root and may be easily overlooked in clinical practice, often leading to suboptimal therapeutic outcomes. Considering the limited number of reported cases involving double-site compression of lumbar nerve roots, the present study aimed to report our institutional experience in managing such cases. All patients were treated using a unilateral biportal endoscopic (UBE) technique to achieve decompression at both compression sites. Furthermore, a comprehensive literature review on DCS was conducted, and a novel classification system was proposed based on the patterns of pathology described in previous reports.\u003c/p\u003e\u003ch2\u003eMethods\u003c/h2\u003e \u003cp\u003eA total of 16 patients diagnosed with DCS were retrospectively analyzed. Demographic data, clinical symptom characteristics, pre- and postoperative imagings, intraoperative details, functional outcome scores, patient satisfaction, and postoperative complications were collected and reviewed. These data were used to evaluate the efficacy and safety of UBE in the treatment of lumbar DCS. In addition, all English-language publications on DCS published after the year 2000 were systematically reviewed. The included studies were categorized according to the anatomical locations and pathological types of compression to establish a new classification system for DCS.\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e \u003cp\u003eAmong the 16 patients, 12 had double crush of the L5 nerve root and 4 had double crush of the L4 nerve root. All patients underwent single-stage dual-site decompression using the UBE technique. Postoperative clinical symptom scores improved significantly, and no recurrence of symptoms was observed at 1-year follow-up. The mean endoscopic operation time was 118.4\u0026thinsp;\u0026plusmn;\u0026thinsp;13.5 minutes, the mean postoperative bed rest duration was 1.8\u0026thinsp;\u0026plusmn;\u0026thinsp;0.9 days, and the mean postoperative hospital stay was 4.7\u0026thinsp;\u0026plusmn;\u0026thinsp;1.5 days. The patients\u0026rsquo; mean postoperative visual analog scale (VAS) for low back pain and leg pain, as well as their Oswestry Disability Index (ODI), showed a significant decrease compared with preoperative values, with no significant changes observed after the 1-month follow-up. Postoperative imagings confirmed complete decompression in all cases, and no severe complications occurred. Based on the literature review, the newly proposed classification system divided DCS into two major categories comprising five subtypes.\u003c/p\u003e\u003ch2\u003eConclusion\u003c/h2\u003e \u003cp\u003e This study reported the clinical outcomes of UBE in the treatment of type IIc DCS and reviewed the latest literature on DCS. The use of UBE for DCS has not been previously reported. Our findings demonstrated that single-stage, double-site decompression using the UBE technique achieved favorable clinical outcomes in patients with type IIc DCS. Given the considerable pathological diversity of DCS, classification and discussion based on the newly proposed system are essential for improving clinical understanding and management of this condition.\u003c/p\u003e","manuscriptTitle":"Application of Unilateral Biportal Endoscopy in Lumbar Double Crush Syndrome: A Retrospective Study and Literature-Based Classification","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-04-09 16:45:52","doi":"10.21203/rs.3.rs-9127627/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2026-04-27T10:21:50+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-04-22T19:28:41+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-04-22T11:26:26+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-04-17T07:51:39+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-04-17T02:05:11+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"204963911728306380328624257519254923510","date":"2026-04-11T01:27:23+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"285151307404906180464333653790211977917","date":"2026-04-09T08:28:59+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"193215313367433125671902987666677351985","date":"2026-04-09T05:31:37+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"186749743703564694389266308055738708405","date":"2026-04-08T00:41:56+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-04-05T20:36:28+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2026-03-31T11:28:20+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-03-30T10:00:48+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-03-30T10:00:17+00:00","index":"","fulltext":""},{"type":"submitted","content":"BMC Surgery","date":"2026-03-15T09:24:51+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"bmc-surgery","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"bsur","sideBox":"Learn more about [BMC Surgery](http://bmcsurg.biomedcentral.com/)","snPcode":"","submissionUrl":"https://www.editorialmanager.com/bsur/default.aspx","title":"BMC Surgery","twitterHandle":"@BMC_series","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"em","reportingPortfolio":"BMC Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"08a87376-9365-4651-ae64-ed51384c0de7","owner":[],"postedDate":"April 9th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-05-08T15:42:53+00:00","versionOfRecord":[],"versionCreatedAt":"2026-04-09 16:45:52","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9127627","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9127627","identity":"rs-9127627","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}