Tibiofemoral rotation after isolated MPFL reconstruction in recurrent patellar dislocation with elevated TT–TG distance

Tibiofemoral rotation after isolated MPFL reconstruction in recurrent patellar dislocation with elevated TT–TG distance | 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 Tibiofemoral rotation after isolated MPFL reconstruction in recurrent patellar dislocation with elevated TT–TG distance QingLyu Shi, RunZe Li, Hua Li, LiChao Zhang, YanLin Li, GuoLiang Wang This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7776795/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Background This study aimed to retrospectively present the radiologic outcomes in a cohort with recurrent patella dislocation (RPD) who have an elevated tibial tubercle–trochlear groove (TT-TG) distance (> 20 mm) following isolated medial patellofemoral ligament reconstruction (i-MPFL-R), and to exhibit the tibiofemoral rotation in RPD patients. Methods RPD patients with a TT-TG distance exceeding 20 mm and tibial tubercle-posterior cruciate ligament (TT-PCL) distance within 24 mm who underwent i-MPFL-R between 2018 and 2022 in our department were included. Clinical outcomes and remeasurement of TT-TG distance and other radiological measurements were analysed postoperatively. Data from the contralateral knee of each patient were analysed for contral. Results A total of 51 knees with a median follow-up time of 36 months were included. TT-TG distance has significantly decreased after i-MPFL-R in those patients (pre 24.30[22.25,25.85]mm vs post 20.20[18.25,22.65]mm,P < 0.001) compared with contralateral knee (pre 21.95 ± 3.20mm, 95%CI: 21.04–22.85 vs post 20.30[19.15,23.45]mm, P = 0.471). No significant changes were observed in the TT-PCL distance. Additionally, there was a synchronous decrease in tibiofemoral rotation (TFR) and patellar tilt angle (PTA) after i-MPFL-R in these patients (pre 9.83 ± 3.57°, 95%CI: 8.83–10.84 vs post 6.96 ± 3.13°, 95%CI: 6.08–7.84, P < 0.001) and (pre 28.51[24.26,33.76]° vs post 12.13[6.53,18.48]°, P < 0.001), compared with contralateral knee (pre 8.51 ± 3.37°, 95%CI: 7.57–9.46 vs post 8.46 ± 3.52°, 95%CI: 7.47–9.45, P = 0.889) and (pre 23.01 ± 7.57°, 95%CI: 20.88–25.13 vs post 26.60[15.70,30.65]°, P = 0.848), respectively. Conclusion The elevated TT–TG distance caused by excessive tibiofemoral rotation decreased following i-MPFL-R, which may be attributed to the tibiofemoral rotation effect during patellar reduction. The tibiofemoral rotation makes TT-TG, TFR, and PTA collectively form a triad of radiological measurements to be considered in patellar instability. Tibiofemoral rotation Recurrent patellar dislocation Pathological TT–TG distance Isolated MPFL reconstruction Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 1. Background Tibiofemoral rotation (TFR) is an important aspect of knee joint movement and is sometimes referred to as the screw-home mechanism in some literature[ 1 ]. It is crucial for the knee joint to perform complex movement patterns. This rotational movement directly affects the load distribution in the knee joint and significantly influences knee health[ 2 ]. In recent years, imaging techniques such as magnetic resonance imaging (MRI), biplanar X-ray imaging systems, and finite element analysis have continuously advanced, allowing researchers to observe and quantify tibiofemoral rotation in greater detail[ 3 ]. In routine knee joint imaging, besides directly measuring TFR angle, the tibial tubercle-trochlear groove (TT-TG) distance is most closely related to TFR[ 4 – 6 ]. The TT-TG distance has been first described by Goutallier in 1978 for evaluating the tibial tubercle lateralisation (TTL) in patients with recurrent patellar dislocation (RPD)[ 7 ]. Dejour et al first proposed a pathological threshold of 20 mm by comparing the control group to the patients with patellar instability[ 8 ]. Subsequent research revealed TT–TG distance is affected not only by actual TTL but also by TFR[ 4 – 6 ]. Biomechanical studies have shown that the medial patellofemoral ligament (MPFL) isometry is notably compromised when the TT-TG distance exceeds 20 mm[ 9 ]. Consequently, medial patellofemoral ligament reconstruction with tibial tuberosity osteotomy (MPFLR + TTO) may offer advantages in such cases[ 10 ]. However, a limited body of clinical research indicates that even in the presence of a TT-TG distance exceeding 20 mm, MPFLR + TTO does not appear to provide additional benefits compared to isolated MPFL reconstruction (i-MPFL-R)[ 11 – 15 ]. Therefore, some alternative methods to evaluate TTL have been proposed, and the application of these methods in determining TTO has been explored. Among them, the tibial tubercle-posterior cruciate ligament (TT-PCL) distance, described by Seitlinger et al, with a cutoff value of 24 mm, has been studied extensively because it is less affected by TFR[ 16 ]. Even so, well-defined and widely agreed upon surgical indications for TTO remain to be seen[ 17 , 18 ]. The TFR phenomenon, particularly its impact on imaging measurements, may contribute to these inconsistencies in diagnostic interpretations that affect treatment decisions. The purpose of this study was to evaluate the radiologic outcome after i-MPFL-R for RPD patients with TT–TG distance exceeding 20 mm and TT-PCL distance within 24mm. The influence of altered tibiofemoral kinematics on postoperative radiographic findings remains unexplored[ 19 ]. 2. Methods 2.1.Patients This cohort study involved a retrospective analysis of data. From 2018 to 2022, RPD patients with a TT-TG distance exceeding 20 mm and TT-PCL distance within 24 mm, who continued to experience dislocation symptoms despite undergoing a standard physiotherapy program, were included in the study. These patients underwent i-MPFL-R in the author's department. A minimum follow-up period of 24 months was required for this study. The radiological and clinical data were gathered for all patients meeting the inclusion criteria. The exclusion criteria comprised the following conditions: (1) Revision case. (2) Loss to clinical follow-up. (3) Absence of either pre- or post-operative radiological data. (4) Concomitant other knee ligaments’ injuries. (5) Presence of severe trochlear dysplasia (types C and D, classified according to the Dejour classification system). (6) In cases of patella alta (CDI > 1.2) or patella baja (CDI < 0.6) based on Caton–Deschamps Index (CDI). (7) Presence by comorbidities such as inflammatory or neurological disorders. 2.2.Radiologic measurement While the ankle joint positioned neutrally, knee joints with flexion of 0° were scanned by a 64-row CT scanner (United Imaging uCT760). All measurements were conducted by two experienced examiners in a blinded and randomized manner. Six indicators were measured: (I) CDI (Fig. 1 A)[ 20 ]. (II) Trochlear dysplasia (TD) classified according to the Dejour classification system[ 21 ]. (III) TT–TG distance (Fig. 1 B) assessed according to the technique described by Schoettle et al's technique[ 22 ]. (IV) TT–PCL distance (Fig. 1 C) assessed according to the technique described by Seitlinger et al's method[ 16 ]. (V) TFR (Fig. 1 D), where a positive angle indicates external rotation of the proximal tibia relative to the distal femur[ 23 ]. (VI) Patellar tilt angle (PTA, Fig. 1 E), referenced to the dorsal femoral condyle line to mitigate the impact of trochlear dysplasia[ 8 , 24 ]. Given the symmetry observed between paired knees in patients with RPD across various factors such as presentation timing and symptom severity[ 25 ], the radiological indicators of the contralateral side were also measured and included in the analysis as controls. 2.3.Clinical examination The clinical data, comprising the occurrence of postoperative patellar subluxation or dislocation, Kujala score, and Lysholm score, were assessed by experienced surgeons at a minimum follow-up duration of 24 months. 2.4.Surgical technique All patients underwent anatomical double-bundle MPFL reconstruction using half of the autograft peroneus longus tendon to minimize the impact of semitendinous muscle cutting on tibial rotation. The graft, with a thickness ranging from 2.5 to 3 mm and a length of 15–20 cm, was employed. The femoral tunnel was positioned under intraoperative fluoroscopy using the method described by Schottle et al[ 26 ]. Two double-loaded suture anchors were placed into the proximal 1/3 and equator of the medial patellar rim. The graft was initially secured on the patellar side, and the free ends of the graft were subsequently passed through the femoral tunnel. To prevent excessive tension on the reconstructed MPFL, continuous knee flexion and extension movements were performed. Patellar tracking was confirmed through arthroscopic examination. The femoral end was ultimately secured using a bioabsorbable interference screw while maintaining the knee at a flexion angle of 20 to 30 degrees. 2.5.Postoperative rehabilitation A rehabilitation exercise protocol should be established integrating both open and closed chain exercises. Open chain training could commence immediately without immobilization, while closed chain training necessitated immobilization for a period of 6–8 weeks[ 27 ]. Regular outpatient dynamic evaluations were recommended, with monthly assessments during the initial three months, to assess rehabilitation progress and make necessary adjustments to the exercise plan. 2.6.Statistical analysis All statistical analyses were conducted using IBM SPSS 27.0 (IBM Corp.Armonk, NY, USA). The reliability of the radiological measurements was assessed using the intra- and inter-class correlation coefficients (ICC). Normality tests were performed using the Kolmogorov-Smirnov test. Results for normally distributed data were presented as mean ± standard deviation with 95% confidence intervals (CIs), whereas skewed distributions were depicted using medians along with 25th and 75th percentiles. The Wilcoxon test (paired samples) was applied for analysis when the distribution of differences between preoperative and postoperative values is skewed, whereas the paired-sample t-test was utilized for normally distributed differences. A significance level of < 0.05 was considered statistically significant. 3D modeling were conducted using Mimics 21.0 software. 3. Results A cohort of 51 knees from 51 patients, with a median follow-up time of 36 months (range 24–48 months), is enrolled in the study. Figure 2 illustrates the patient selection process. Table 1 exhibits the basic demographic data, including age, sex, BMI, CDI, and the incidence of trochlear dysplasia. Table 1 Basic information for all patients 51 knees in 51 Patients with RPD Age ,y 21.96 ± 8.62 (13 ~ 47) Sex(female/male),n 31/20 BMI,Kg/m 2 20.70 ± 2.39 Affected side,(Left/Right) 25/26 Trochlea dysplasia,n(%) A37(72.6%) / B14(27.4%) Caton–Deschamps Index 1.10 ± 0.075 Number of dislocations,n 3.5 (2 ~ 6) 3.1. Radiologic Result The TT-TG distance exhibited a significant reduction following i-MPFL-R in this cohort (pre 24.30 [22.25,25.85] mm vs post 20.20 [18.25,22.65] mm, P < 0.001) compared to contralateral knee (pre 21.95 ± 3.20 mm, 95%CI: 21.04–22.85 vs post 20.30 [19.15,23.45] mm, P = 0.471). There were no significant changes observed in the TT-PCL distance on either side. Additionally, both the TFR and PTA in the cohort showed a synchronous decrease following i-MPFL-R (pre 9.83 ± 3.57°, 95%CI: 8.83–10.84 vs post 6.96 ± 3.13°, 95%CI: 6.08–7.84, P < 0.001) and (pre 28.51 [24.26,33.76]° vs post 12.13 [6.53,18.48]°, P < 0.001), in comparison to contralateral knee (pre 8.51 ± 3.37°, 95%CI: 7.57–9.46 vs post 8.46 ± 3.52°, 95%CI: 7.47–9.45, P = 0.889) and (pre 23.01 ± 7.57°, 95%CI: 20.88–25.13 vs post 26.60 [15.70,30.65]°, P = 0.848), respectively. The alterations in TT-TG, TT-PCL, TFR, and PTA pre- and post-operatively on both the affected and contralateral sides are illustrated in Fig. 3 (A1-D1), (A2-D2), respectively. Based on CT scan data from a patient within this cohort, Fig. 4 clearly illustrates the trajectories of patellar reduction following i-MPFL-R. Through the utilization of three-dimensional reconstruction and image integration techniques, Fig. 4 also portrays the positional relationship between the tibia and femur post patellar reduction. It is evident that irrespective of the chosen reference bone, the reduction of TFR may contribute to the observed decrease in TT-TG distance. 3.2.Clinical results and complications At the final follow-up assessment, all patients achieved a satisfactory Kujala score of 87.2 ± 8.9 and Lysholm score of 88.9 ± 11.0. There were no instances of redislocation or patellofemoral pain reported among the patients. Furthermore, no other major complications such as wound infection, delayed union, or nonunion were observed. Five cases of patient-reported stiffness within 2 months post-surgery were noted, all of which were successfully resolved through extended rehabilitation. 4. Discussion The function of the MPFL has not been investigated as comprehensively as other knee ligaments[ 28 ]. Kinematic data from cadaver study suggested that in MPFL-deficient knees, the patella exhibits a lateral shift at full extension[ 29 – 31 ], while MPFL reconstruction reduces this lateral tracking[ 32 , 33 ]. On the other hand, the increased TFR angle is associated with patellar maltracking in patients with RPD[ 34 ]. Through radiologic follow-up of this cohort with RPD, this study proposes that the patellar reduction process may involve a complex biomechanical mechanism, including the restitution of TFR and the consequent reduction in TT-TG distance. Furthermore, the alteration in tibiofemoral rotation may reflect the impact of MPFL on its femoral attachment. Our surgical team has long observed the TFR after i-MPFL-R in RPD patients. However, accurately describing this phenomenon requires strict statistical analysis, which in turn depends on selecting a suitable patient group. Through long-term exploration, we have found that the TT-TG distance is dynamic and can serve as an amplifier, magnifying TFR to a statistically significant level. Therefore, we selected a group of patients as research subjects who met the following criteria: First, they have pathological TT-TG distance. And second, they have normal TT-PCL distance to limit excessive TTL. We monitored postoperative imaging in this specific patient group to demonstrate the TFR after i-MPFL-R. The significance of our study is not to change current treatment options, but to raise surgeons’ awareness of TFR in the assessment of the knee joint. There are many methods for the imaging assessment of patellar instability. Why do we choose PTA to form a triad of imaging measurement indicators along with TT-TG and TFR? Our considerations are as follows. The dislocation and subsequent reduction of the patella involve changes in the relative positions of the femur, tibia, and patella. Neither TT-TG nor TFR measurements include the positional information of the patella. Therefore, when analysing tibiofemoral rotation in RPD patients, a parameter providing positional information of the patella—namely, patellar deviation—is needed, which can be evaluated through various methods, including patellar tilt angle[ 8 , 24 ],lateral patellofemoral angle[ 35 ],lateral patellar displacement[ 35 ]. Among them, PTA uses the dorsal femoral condyle line as a reference to measure the deviation angle of the patella. Similarly, both TT-TG and TFR use this line as the reference, so their three share the same reference system. The analysis in this study also indicated that PTA, TT-TG, and TFR demonstrated the same trend of change during patellar reduction. To exhibit the tibiofemoral rotation, this cohort also showed some unique characteristics. Among all the risk factors of patellar dislocation, correcting the PTA is considered particularly challenging[ 36 ]. Although i-MPFL-R effectively stabilized the patella, it did not lead to an improvement in PTA in the examined population[ 37 ]. However, in this cohort, i-MPFL-R resulted in a significant decrease in PTA. To explore the reason, we conducted a subgroup analysis and showed that 37 out of the 51 patients had experienced an acute dislocation within 7 days prior to surgery. The notable reduction in TT-TG, TFR, and PTA predominantly originated from this subgroup. Acute patellar dislocation can cause intra-articular hemorrhage and swelling, potentially worsening patellar displacement and exerting an amplified impact on the TFR and TT-TG, as illustrated in Fig. 5 . Therefore, it is necessary to consider this effect when conducting radiological measurements during the acute phase of patellar dislocation. In the literature review, the inter- and intra-observer reliability (as measured by ICC) of TT-TG ranged from 0.807 to 0.98 and 0.553 to 0.99, respectively. For TT-PCL, the inter- and intra-observer reliability ranged from 0.553 to 0.99 and 0.88 to 0.981, respectively[ 38 ]. This study also reported the inter- and intra-observer reliability of TT-TG, TT-PCL, TFR, and PTA, assessed through CT scans with repeated measurements pre- and post-surgery (Fig. 2 ). Notably, the contralateral side, which did not undergo surgical intervention, highlights the reliability of repeated measurements at distinct time points. The variation in quadriceps muscle contraction[ 24 ], slight differences in scanning angles, and variations in the selection of reference points in trochlea dysplasia[ 36 ] may contribute to discrepancies in measurement results. Aggregating a series of measurements may provide more robust insights than relying on a single parameter. This study's results are limited by the small sample size; therefore, they should be interpreted as exploratory and potentially subject to variation in larger study populations. In line with discussions in other studies, there is a lack of consistency in the cut-off values for TT-TG and TT-PCL[ 39 – 41 ]. While this study did not delve into the selection of cut-off values, it underscored the TFR during patellar reduction and its subsequent impact on the TT-TG distance. 5. Conclusions The elevated TT–TG distance caused by excessive tibiofemoral rotation decreased following i-MPFL-R, which may be attributed to the tibiofemoral rotation effect during patellar reduction. The tibiofemoral rotation makes TT-TG, TFR, and PTA collectively form a triad of radiological measurements to be considered in patellar instability. Abbreviations recurrent patella dislocation (RPD) tibial tubercle–trochlear groove(TT-TG) tibial tubercle-posterior cruciate ligament(TT-PCL) tibiofemoral rotation(TFR) patellar tilt angle(PTA) isolated medial patellofemoral ligament reconstruction (i-MPFL-R) medial patellofemoral ligament (MPFL) medial patellofemoral ligament reconstruction with tibial tuberosity osteotomy (MPFLR + TTO) tibial tubercle lateralisation(TTL) trochlea dysplasia(TD) Caton–Deschamps Index(CDI) Declarations Ethics approval and consent to participate All procedures performed in studies involving human participants were in accordance with the ethical standards of the national research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards. The study was approved by the Bioethics Committee of the first affiliated hospital of Kunming Medical University(No.2022L224).And informed consent was provided by all the patients. Consent for publication Not applicable Availability of data and materials The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request. Competing interests The authors declare that they have no competing interests Funding The research leading to these results received funding from [Technological innovation talents of Yunnan Province] under Grant Agreement No[202105AD160018]. Authors' contributions [QingLyu Shi] and [GuoLiang Wang] designed the study. [QingLyu Shi] and [GuoLiang Wang] performed the surgical operation. [Hua Li] and [LiChao Zhang] Collected and measured image data for each patient. [RunZe Li] conducted the statistical analysis. [GuoLiang Wang] and [YanLin Li] evaluated the postoperative function of each patient. [QingLyu Shi] and [RunZe Li] wrote the main manuscript text. [RunZe Li] prepared figures 1-3,[QingLyu Shi] prepared figures 4-5. All authors reviewed the manuscript. 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Tibial tubercle to trochlear groove distance versus tibial tubercle to posterior cruciate ligament distance for predicting patellar instability: a systematic review. Knee surgery, sports traumatology, arthroscopy. official J ESSKA. 2023;31(8):3243–58. Zhang LTM, Wu S, Xu T, Zhang K, Xie X,Fu W. Tibial Tubercle-Trochlear Groove Distance Has Better Diagnostic Reliability Than Tubercle-Posterior Cruciate Ligament Distance For Predicting Patellar Instability: A Systematic Review. Orthop Surg. 2023;15(9):2225–34. Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted 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. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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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-7776795","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":530698687,"identity":"135b522d-a8ac-462d-b12e-3e3f08abb290","order_by":0,"name":"QingLyu Shi","email":"","orcid":"","institution":"the First Affiliated Hospital of Kunming Medical University","correspondingAuthor":false,"prefix":"","firstName":"QingLyu","middleName":"","lastName":"Shi","suffix":""},{"id":530698688,"identity":"f9d39b01-f104-4c19-9a29-7c5e7a5f79af","order_by":1,"name":"RunZe Li","email":"","orcid":"","institution":"the First Affiliated Hospital of Kunming Medical University","correspondingAuthor":false,"prefix":"","firstName":"RunZe","middleName":"","lastName":"Li","suffix":""},{"id":530698689,"identity":"8a14a607-6ea0-44a1-9da5-fa1a051187e2","order_by":2,"name":"Hua Li","email":"","orcid":"","institution":"the First Affiliated Hospital of Kunming Medical University","correspondingAuthor":false,"prefix":"","firstName":"Hua","middleName":"","lastName":"Li","suffix":""},{"id":530698690,"identity":"f40dffb9-58cf-49dd-a059-7bc8d7f11077","order_by":3,"name":"LiChao Zhang","email":"","orcid":"","institution":"the First Affiliated Hospital of Kunming Medical University","correspondingAuthor":false,"prefix":"","firstName":"LiChao","middleName":"","lastName":"Zhang","suffix":""},{"id":530698691,"identity":"ca9debba-86b9-4992-b9b5-3378dfb7d213","order_by":4,"name":"YanLin Li","email":"","orcid":"","institution":"the First Affiliated Hospital of Kunming Medical University","correspondingAuthor":false,"prefix":"","firstName":"YanLin","middleName":"","lastName":"Li","suffix":""},{"id":530698692,"identity":"c6b18a9f-cf3c-4e4d-b280-abc22bc30df5","order_by":5,"name":"GuoLiang Wang","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAzUlEQVRIiWNgGAWjYBACfmbG5gcJBhLMjO2NjQ8/EKNFsr35mMGHAgt25p7DzcYSxGgxOHMsQXLGhwp+9hnpbQI8RLnsRo6BMY+BhDTvzIdtDBIMdnK6DQR0MM7IMXgM1GIsOTux7UEBQ7Kx2QECWpglILYkG85ObDeQYDiQuI2QFjagFmmglvr9Nw+2SfAQo4WHB+R9UCDPYCRSiwQ7KJBBWnoSgYFsQIRf7A+DovJPHTAqjz98+KHCTo6gFjRgQJryUTAKRsEoGAU4AABeZ0G19lqEXQAAAABJRU5ErkJggg==","orcid":"","institution":"the First Affiliated Hospital of Kunming Medical University","correspondingAuthor":true,"prefix":"","firstName":"GuoLiang","middleName":"","lastName":"Wang","suffix":""}],"badges":[],"createdAt":"2025-10-04 01:53:10","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7776795/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7776795/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":93776014,"identity":"6f2e4d0d-40a2-4f84-9e92-e3100c653384","added_by":"auto","created_at":"2025-10-17 12:34:23","extension":"docx","order_by":0,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":8750283,"visible":true,"origin":"","legend":"","description":"","filename":"Manuscript.docx","url":"https://assets-eu.researchsquare.com/files/rs-7776795/v1/8dcdc218f151a98d394dbe8d.docx"},{"id":93780069,"identity":"fce2b57f-d76e-45e1-88a5-85beaf08b71d","added_by":"auto","created_at":"2025-10-17 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12:34:23","extension":"xml","order_by":13,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":95505,"visible":true,"origin":"","legend":"","description":"","filename":"02563bb6a79549b890a6ef00973e8a531structuring.xml","url":"https://assets-eu.researchsquare.com/files/rs-7776795/v1/42f19eae2e781d9afa3319d5.xml"},{"id":93776021,"identity":"c11b5677-e30b-449d-9c8c-432bd445c195","added_by":"auto","created_at":"2025-10-17 12:34:23","extension":"html","order_by":14,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":104212,"visible":true,"origin":"","legend":"","description":"","filename":"earlyproof.html","url":"https://assets-eu.researchsquare.com/files/rs-7776795/v1/143c1d1d5f535cb993153aef.html"},{"id":93776010,"identity":"d27a851f-3ab3-421d-a9b8-82c959bd48ea","added_by":"auto","created_at":"2025-10-17 12:34:23","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":530978,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSchematic diagram shows the methods of measuring the (A)CDI, (B)TT-TG,(C)TT-PCL,(D)TFR, (E)PTA. \u003c/strong\u003e(A) The knee joint was reconstructed in the sagittal direction according to the direction of patellar tilting. The length of patellar (a) and patella to tibia (b) were measured. Caton-Deschamps Index was the ratio of b to a. (B) Overlay the slice showing the proximal trochlear groove of the femur with the slice showing the tibial tuberosity. The TT–TG (c) was defined as the distance between the deepest point of the trochlear groove (b) and the the tip of tibial tubercle (a), parallel to the dorsal femoral condylar line (dFCL). (C) Overlay the slice showing the prominent tibial insertion of the posterior cruciate ligament (PCL) with the slice showing the tibial tuberosity. The TT-PCL (c) distance was defined as the distance between the tip of the tibial tubercle (a) and the medial border of the PCL (b), parallel to the dorsal tibial condylar line (dTCL). (D) Overlay the slice showing the proximal trochlear groove of the femur with the slice showing the prominent tibial insertion of the PCL. The TFR was defined as the angle between the dFCL and the dTCL. (E) Select the slice with maximum patellar width. PTA was defined as the angle between the long axis of the patella (a) and dFCL.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-7776795/v1/41fbcefcf9208013327cb527.png"},{"id":93777654,"identity":"76fb945f-ada8-4e9b-95b7-72bf90db1db5","added_by":"auto","created_at":"2025-10-17 12:42:23","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":134676,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eFlow chart of patient selection\u003c/strong\u003e. i-MPFL-R isolated medial patellofemoral ligament reconstruction, FU follow-up, TT-TG tibial tubercle-trochlear groove, TT-PCL tibial tubercle-posterior cruciate ligament, TFR tibiofemoral rotation, PTA Patellar tilt angle.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-7776795/v1/8c820b065a8989c4890f0f8b.png"},{"id":93776012,"identity":"88dab369-2d62-4d8f-a167-7dbe14202280","added_by":"auto","created_at":"2025-10-17 12:34:23","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":177471,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eBox plots display pre- and post- operative changes of (A1)TT-TG, (B1)TT-PCL, (C1)TFR and (D1)PTA measurements on the affected side and the (A2)TT-TG, (B2)TT-PCL, (C2)TFR and (D2)PTA measurements on the contralateral side. \u003c/strong\u003eNormal distribution was depicted as mean±standard deviation with 95% confidence intervals (CIs), whereas skewed distributions were depicted as medians with 25th and 75th percentile. 'Pt' indicates that the p value is derived from the paired-samples T-test. 'Pw' indicates that the p value is derived from the paired-samples Wilcoxon test. '*' is for significance values. ICC:intra- or inter- class correlation coefficient.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-7776795/v1/60896d188e3912c7baa741c9.png"},{"id":93777651,"identity":"a75f1474-abd1-4d17-a29a-1c73fa0406c6","added_by":"auto","created_at":"2025-10-17 12:42:23","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":608898,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eThe three-dimensional reconstruction from the pre- and post-operative CT scan images of one patient in this cohorts.\u003c/strong\u003e (A1),(A2) Pre- and (B1),(B2) post- operative images were integrated by the technology of image processing to show the reduction trajectories of the patella. The rotation of the tibia and patella can be observed in the same direction when using the femur as a reference (C1), whereas the rotation of the femur and patella can be observed in the opposite direction when using the tibia as a reference (C2).\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-7776795/v1/f54a1537692591629ab5c103.png"},{"id":93778920,"identity":"91766e6a-0e1b-4b2a-8c74-cbb87fde1e8b","added_by":"auto","created_at":"2025-10-17 12:50:23","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":600178,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eA series of MRI scans conducted on the cohort of this study exhibited different PTA values\u003c/strong\u003e: (A)PTA=7°, (B)PTA=16°, (C)PTA=26°, (D)PTA=29°. From scenario (A) to (D), the progressive exacerbation of knee swelling suggests a potentially more severe patellar dislocation injury, which results in an increase in PTA.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-7776795/v1/5576bbcd594f4bf8df51a15a.png"},{"id":96708280,"identity":"e4ec871c-8eaf-43d6-b1b4-aa206b9013aa","added_by":"auto","created_at":"2025-11-25 10:00:04","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3011797,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7776795/v1/7a3ac538-705a-4da3-bb20-61199d4635d4.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Tibiofemoral rotation after isolated MPFL reconstruction in recurrent patellar dislocation with elevated TT–TG distance","fulltext":[{"header":"1. Background","content":"\u003cp\u003e\u003cul\u003e\u003cli\u003e\u003cp\u003eTibiofemoral rotation (TFR) is an important aspect of knee joint movement and is sometimes referred to as the screw-home mechanism in some literature[\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. It is crucial for the knee joint to perform complex movement patterns. This rotational movement directly affects the load distribution in the knee joint and significantly influences knee health[\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. In recent years, imaging techniques such as magnetic resonance imaging (MRI), biplanar X-ray imaging systems, and finite element analysis have continuously advanced, allowing researchers to observe and quantify tibiofemoral rotation in greater detail[\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e].\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003eIn routine knee joint imaging, besides directly measuring TFR angle, the tibial tubercle-trochlear groove (TT-TG) distance is most closely related to TFR[\u003cspan additionalcitationids=\"CR5\" citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. The TT-TG distance has been first described by Goutallier in 1978 for evaluating the tibial tubercle lateralisation (TTL) in patients with recurrent patellar dislocation (RPD)[\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. Dejour et al first proposed a pathological threshold of 20 mm by comparing the control group to the patients with patellar instability[\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Subsequent research revealed TT\u0026ndash;TG distance is affected not only by actual TTL but also by TFR[\u003cspan additionalcitationids=\"CR5\" citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e].\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003eBiomechanical studies have shown that the medial patellofemoral ligament (MPFL) isometry is notably compromised when the TT-TG distance exceeds 20 mm[\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. Consequently, medial patellofemoral ligament reconstruction with tibial tuberosity osteotomy (MPFLR\u0026thinsp;+\u0026thinsp;TTO) may offer advantages in such cases[\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. However, a limited body of clinical research indicates that even in the presence of a TT-TG distance exceeding 20 mm, MPFLR\u0026thinsp;+\u0026thinsp;TTO does not appear to provide additional benefits compared to isolated MPFL reconstruction (i-MPFL-R)[\u003cspan additionalcitationids=\"CR12 CR13 CR14\" citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. Therefore, some alternative methods to evaluate TTL have been proposed, and the application of these methods in determining TTO has been explored. Among them, the tibial tubercle-posterior cruciate ligament (TT-PCL) distance, described by Seitlinger et al, with a cutoff value of 24 mm, has been studied extensively because it is less affected by TFR[\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. Even so, well-defined and widely agreed upon surgical indications for TTO remain to be seen[\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. The TFR phenomenon, particularly its impact on imaging measurements, may contribute to these inconsistencies in diagnostic interpretations that affect treatment decisions.\u003c/p\u003e\u003c/li\u003e\u003c/ul\u003e\u003c/p\u003e\u003cp\u003eThe purpose of this study was to evaluate the radiologic outcome after i-MPFL-R for RPD patients with TT\u0026ndash;TG distance exceeding 20 mm and TT-PCL distance within 24mm. The influence of altered tibiofemoral kinematics on postoperative radiographic findings remains unexplored[\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e].\u003c/p\u003e"},{"header":"2. Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003e2.1.Patients\u003c/h2\u003e\u003cp\u003eThis cohort study involved a retrospective analysis of data. From 2018 to 2022, RPD patients with a TT-TG distance exceeding 20 mm and TT-PCL distance within 24 mm, who continued to experience dislocation symptoms despite undergoing a standard physiotherapy program, were included in the study. These patients underwent i-MPFL-R in the author's department. A minimum follow-up period of 24 months was required for this study. The radiological and clinical data were gathered for all patients meeting the inclusion criteria. The exclusion criteria comprised the following conditions: (1) Revision case. (2) Loss to clinical follow-up. (3) Absence of either pre- or post-operative radiological data. (4) Concomitant other knee ligaments\u0026rsquo; injuries. (5) Presence of severe trochlear dysplasia (types C and D, classified according to the Dejour classification system). (6) In cases of patella alta (CDI\u0026thinsp;\u0026gt;\u0026thinsp;1.2) or patella baja (CDI\u0026thinsp;\u0026lt;\u0026thinsp;0.6) based on Caton\u0026ndash;Deschamps Index (CDI). (7) Presence by comorbidities such as inflammatory or neurological disorders.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\u003ch2\u003e2.2.Radiologic measurement\u003c/h2\u003e\u003cp\u003eWhile the ankle joint positioned neutrally, knee joints with flexion of 0\u0026deg; were scanned by a 64-row CT scanner (United Imaging uCT760). All measurements were conducted by two experienced examiners in a blinded and randomized manner. Six indicators were measured: (I) CDI (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eA)[\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. (II) Trochlear dysplasia (TD) classified according to the Dejour classification system[\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. (III) TT\u0026ndash;TG distance (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eB) assessed according to the technique described by Schoettle et al's technique[\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. (IV) TT\u0026ndash;PCL distance (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eC) assessed according to the technique described by Seitlinger et al's method[\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. (V) TFR (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eD), where a positive angle indicates external rotation of the proximal tibia relative to the distal femur[\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. (VI) Patellar tilt angle (PTA, Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eE), referenced to the dorsal femoral condyle line to mitigate the impact of trochlear dysplasia[\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. Given the symmetry observed between paired knees in patients with RPD across various factors such as presentation timing and symptom severity[\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e], the radiological indicators of the contralateral side were also measured and included in the analysis as controls.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\u003ch2\u003e2.3.Clinical examination\u003c/h2\u003e\u003cp\u003eThe clinical data, comprising the occurrence of postoperative patellar subluxation or dislocation, Kujala score, and Lysholm score, were assessed by experienced surgeons at a minimum follow-up duration of 24 months.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\u003ch2\u003e2.4.Surgical technique\u003c/h2\u003e\u003cp\u003eAll patients underwent anatomical double-bundle MPFL reconstruction using half of the autograft peroneus longus tendon to minimize the impact of semitendinous muscle cutting on tibial rotation. The graft, with a thickness ranging from 2.5 to 3 mm and a length of 15\u0026ndash;20 cm, was employed. The femoral tunnel was positioned under intraoperative fluoroscopy using the method described by Schottle et al[\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. Two double-loaded suture anchors were placed into the proximal 1/3 and equator of the medial patellar rim. The graft was initially secured on the patellar side, and the free ends of the graft were subsequently passed through the femoral tunnel. To prevent excessive tension on the reconstructed MPFL, continuous knee flexion and extension movements were performed. Patellar tracking was confirmed through arthroscopic examination. The femoral end was ultimately secured using a bioabsorbable interference screw while maintaining the knee at a flexion angle of 20 to 30 degrees.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e\u003ch2\u003e2.5.Postoperative rehabilitation\u003c/h2\u003e\u003cp\u003eA rehabilitation exercise protocol should be established integrating both open and closed chain exercises. Open chain training could commence immediately without immobilization, while closed chain training necessitated immobilization for a period of 6\u0026ndash;8 weeks[\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. Regular outpatient dynamic evaluations were recommended, with monthly assessments during the initial three months, to assess rehabilitation progress and make necessary adjustments to the exercise plan.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\u003ch2\u003e2.6.Statistical analysis\u003c/h2\u003e\u003cp\u003eAll statistical analyses were conducted using IBM SPSS 27.0 (IBM Corp.Armonk, NY, USA). The reliability of the radiological measurements was assessed using the intra- and inter-class correlation coefficients (ICC). Normality tests were performed using the Kolmogorov-Smirnov test. Results for normally distributed data were presented as mean\u0026thinsp;\u0026plusmn;\u0026thinsp;standard deviation with 95% confidence intervals (CIs), whereas skewed distributions were depicted using medians along with 25th and 75th percentiles. The Wilcoxon test (paired samples) was applied for analysis when the distribution of differences between preoperative and postoperative values is skewed, whereas the paired-sample t-test was utilized for normally distributed differences. A significance level of \u0026lt;\u0026thinsp;0.05 was considered statistically significant. 3D modeling were conducted using Mimics 21.0 software.\u003c/p\u003e\u003c/div\u003e"},{"header":"3. Results","content":"\u003cp\u003eA cohort of 51 knees from 51 patients, with a median follow-up time of 36 months (range 24\u0026ndash;48 months), is enrolled in the study. Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e illustrates the patient selection process. Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e exhibits the basic demographic data, including age, sex, BMI, CDI, and the incidence of trochlear dysplasia.\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\u003eBasic information for all patients\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"2\"\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\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e\u003cp\u003e51 knees in 51 Patients with RPD\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eAge ,y\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e21.96\u0026thinsp;\u0026plusmn;\u0026thinsp;8.62 (13\u0026thinsp;~\u0026thinsp;47)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSex(female/male),n\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e31/20\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eBMI,Kg/m\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e20.70\u0026thinsp;\u0026plusmn;\u0026thinsp;2.39\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eAffected side,(Left/Right)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e25/26\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eTrochlea dysplasia,n(%)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eA37(72.6%) / B14(27.4%)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCaton\u0026ndash;Deschamps Index\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e1.10\u0026thinsp;\u0026plusmn;\u0026thinsp;0.075\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eNumber of dislocations,n\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e3.5 (2\u0026thinsp;~\u0026thinsp;6)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e\u003ch2\u003e3.1. Radiologic Result\u003c/h2\u003e\u003cp\u003eThe TT-TG distance exhibited a significant reduction following i-MPFL-R in this cohort (pre 24.30 [22.25,25.85] mm vs post 20.20 [18.25,22.65] mm, P\u0026thinsp;\u0026lt;\u0026thinsp;0.001) compared to contralateral knee (pre 21.95\u0026thinsp;\u0026plusmn;\u0026thinsp;3.20 mm, 95%CI: 21.04\u0026ndash;22.85 vs post 20.30 [19.15,23.45] mm, P\u0026thinsp;=\u0026thinsp;0.471). There were no significant changes observed in the TT-PCL distance on either side. Additionally, both the TFR and PTA in the cohort showed a synchronous decrease following i-MPFL-R (pre 9.83\u0026thinsp;\u0026plusmn;\u0026thinsp;3.57\u0026deg;, 95%CI: 8.83\u0026ndash;10.84 vs post 6.96\u0026thinsp;\u0026plusmn;\u0026thinsp;3.13\u0026deg;, 95%CI: 6.08\u0026ndash;7.84, P\u0026thinsp;\u0026lt;\u0026thinsp;0.001) and (pre 28.51 [24.26,33.76]\u0026deg; vs post 12.13 [6.53,18.48]\u0026deg;, P\u0026thinsp;\u0026lt;\u0026thinsp;0.001), in comparison to contralateral knee (pre 8.51\u0026thinsp;\u0026plusmn;\u0026thinsp;3.37\u0026deg;, 95%CI: 7.57\u0026ndash;9.46 vs post 8.46\u0026thinsp;\u0026plusmn;\u0026thinsp;3.52\u0026deg;, 95%CI: 7.47\u0026ndash;9.45, P\u0026thinsp;=\u0026thinsp;0.889) and (pre 23.01\u0026thinsp;\u0026plusmn;\u0026thinsp;7.57\u0026deg;, 95%CI: 20.88\u0026ndash;25.13 vs post 26.60 [15.70,30.65]\u0026deg;, P\u0026thinsp;=\u0026thinsp;0.848), respectively. The alterations in TT-TG, TT-PCL, TFR, and PTA pre- and post-operatively on both the affected and contralateral sides are illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e (A1-D1), (A2-D2), respectively.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eBased on CT scan data from a patient within this cohort, Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e clearly illustrates the trajectories of patellar reduction following i-MPFL-R. Through the utilization of three-dimensional reconstruction and image integration techniques, Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e also portrays the positional relationship between the tibia and femur post patellar reduction. It is evident that irrespective of the chosen reference bone, the reduction of TFR may contribute to the observed decrease in TT-TG distance.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\u003ch2\u003e3.2.Clinical results and complications\u003c/h2\u003e\u003cp\u003eAt the final follow-up assessment, all patients achieved a satisfactory Kujala score of 87.2\u0026thinsp;\u0026plusmn;\u0026thinsp;8.9 and Lysholm score of 88.9\u0026thinsp;\u0026plusmn;\u0026thinsp;11.0. There were no instances of redislocation or patellofemoral pain reported among the patients. Furthermore, no other major complications such as wound infection, delayed union, or nonunion were observed. Five cases of patient-reported stiffness within 2 months post-surgery were noted, all of which were successfully resolved through extended rehabilitation.\u003c/p\u003e\u003c/div\u003e"},{"header":"4. Discussion","content":"\u003cp\u003eThe function of the MPFL has not been investigated as comprehensively as other knee ligaments[\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. Kinematic data from cadaver study suggested that in MPFL-deficient knees, the patella exhibits a lateral shift at full extension[\u003cspan additionalcitationids=\"CR30\" citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e], while MPFL reconstruction reduces this lateral tracking[\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e, \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]. On the other hand, the increased TFR angle is associated with patellar maltracking in patients with RPD[\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]. Through radiologic follow-up of this cohort with RPD, this study proposes that the patellar reduction process may involve a complex biomechanical mechanism, including the restitution of TFR and the consequent reduction in TT-TG distance. Furthermore, the alteration in tibiofemoral rotation may reflect the impact of MPFL on its femoral attachment.\u003c/p\u003e\u003cp\u003eOur surgical team has long observed the TFR after i-MPFL-R in RPD patients. However, accurately describing this phenomenon requires strict statistical analysis, which in turn depends on selecting a suitable patient group. Through long-term exploration, we have found that the TT-TG distance is dynamic and can serve as an amplifier, magnifying TFR to a statistically significant level. Therefore, we selected a group of patients as research subjects who met the following criteria: First, they have pathological TT-TG distance. And second, they have normal TT-PCL distance to limit excessive TTL. We monitored postoperative imaging in this specific patient group to demonstrate the TFR after i-MPFL-R. The significance of our study is not to change current treatment options, but to raise surgeons\u0026rsquo; awareness of TFR in the assessment of the knee joint.\u003c/p\u003e\u003cp\u003eThere are many methods for the imaging assessment of patellar instability. Why do we choose PTA to form a triad of imaging measurement indicators along with TT-TG and TFR? Our considerations are as follows. The dislocation and subsequent reduction of the patella involve changes in the relative positions of the femur, tibia, and patella. Neither TT-TG nor TFR measurements include the positional information of the patella. Therefore, when analysing tibiofemoral rotation in RPD patients, a parameter providing positional information of the patella\u0026mdash;namely, patellar deviation\u0026mdash;is needed, which can be evaluated through various methods, including patellar tilt angle[\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e],lateral patellofemoral angle[\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e],lateral patellar displacement[\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]. Among them, PTA uses the dorsal femoral condyle line as a reference to measure the deviation angle of the patella. Similarly, both TT-TG and TFR use this line as the reference, so their three share the same reference system. The analysis in this study also indicated that PTA, TT-TG, and TFR demonstrated the same trend of change during patellar reduction.\u003c/p\u003e\u003cp\u003eTo exhibit the tibiofemoral rotation, this cohort also showed some unique characteristics. Among all the risk factors of patellar dislocation, correcting the PTA is considered particularly challenging[\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]. Although i-MPFL-R effectively stabilized the patella, it did not lead to an improvement in PTA in the examined population[\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e]. However, in this cohort, i-MPFL-R resulted in a significant decrease in PTA. To explore the reason, we conducted a subgroup analysis and showed that 37 out of the 51 patients had experienced an acute dislocation within 7 days prior to surgery. The notable reduction in TT-TG, TFR, and PTA predominantly originated from this subgroup. Acute patellar dislocation can cause intra-articular hemorrhage and swelling, potentially worsening patellar displacement and exerting an amplified impact on the TFR and TT-TG, as illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e. Therefore, it is necessary to consider this effect when conducting radiological measurements during the acute phase of patellar dislocation.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eIn the literature review, the inter- and intra-observer reliability (as measured by ICC) of TT-TG ranged from 0.807 to 0.98 and 0.553 to 0.99, respectively. For TT-PCL, the inter- and intra-observer reliability ranged from 0.553 to 0.99 and 0.88 to 0.981, respectively[\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e]. This study also reported the inter- and intra-observer reliability of TT-TG, TT-PCL, TFR, and PTA, assessed through CT scans with repeated measurements pre- and post-surgery (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Notably, the contralateral side, which did not undergo surgical intervention, highlights the reliability of repeated measurements at distinct time points. The variation in quadriceps muscle contraction[\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e], slight differences in scanning angles, and variations in the selection of reference points in trochlea dysplasia[\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e] may contribute to discrepancies in measurement results. Aggregating a series of measurements may provide more robust insights than relying on a single parameter.\u003c/p\u003e\u003cp\u003eThis study's results are limited by the small sample size; therefore, they should be interpreted as exploratory and potentially subject to variation in larger study populations. In line with discussions in other studies, there is a lack of consistency in the cut-off values for TT-TG and TT-PCL[\u003cspan additionalcitationids=\"CR40\" citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e]. While this study did not delve into the selection of cut-off values, it underscored the TFR during patellar reduction and its subsequent impact on the TT-TG distance.\u003c/p\u003e"},{"header":"5. Conclusions","content":"\u003cp\u003eThe elevated TT\u0026ndash;TG distance caused by excessive tibiofemoral rotation decreased following i-MPFL-R, which may be attributed to the tibiofemoral rotation effect during patellar reduction. The tibiofemoral rotation makes TT-TG, TFR, and PTA collectively form a triad of radiological measurements to be considered in patellar instability.\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cp\u003erecurrent patella dislocation (RPD)\u003c/p\u003e\u003cp\u003etibial tubercle\u0026ndash;trochlear groove(TT-TG)\u003c/p\u003e\u003cp\u003etibial tubercle-posterior cruciate ligament(TT-PCL)\u003c/p\u003e\u003cp\u003etibiofemoral rotation(TFR)\u003c/p\u003e\u003cp\u003epatellar tilt angle(PTA)\u003c/p\u003e\u003cp\u003eisolated medial patellofemoral ligament reconstruction (i-MPFL-R)\u003c/p\u003e\u003cp\u003emedial patellofemoral ligament (MPFL)\u003c/p\u003e\u003cp\u003emedial patellofemoral ligament reconstruction with tibial tuberosity osteotomy (MPFLR\u0026thinsp;+\u0026thinsp;TTO)\u003c/p\u003e\u003cp\u003etibial tubercle lateralisation(TTL)\u003c/p\u003e\u003cp\u003etrochlea dysplasia(TD)\u003c/p\u003e\u003cp\u003eCaton\u0026ndash;Deschamps Index(CDI)\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003eEthics approval and consent to participate\u003c/p\u003e\n\u003cp\u003eAll procedures performed in studies involving human participants were in accordance with the ethical standards of the national research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards. The study was approved by the Bioethics Committee of the first affiliated hospital of Kunming Medical University(No.2022L224).And informed consent was provided by all the patients.\u003c/p\u003e\n\u003cp\u003eConsent for publication\u003c/p\u003e\n\u003cp\u003eNot applicable\u003c/p\u003e\n\u003cp\u003eAvailability of data and materials\u003c/p\u003e\n\u003cp\u003eThe datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.\u003c/p\u003e\n\u003cp\u003eCompeting interests\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no competing interests\u003c/p\u003e\n\u003cp\u003eFunding\u003c/p\u003e\n\u003cp\u003eThe research leading to these results received funding from [Technological innovation talents of Yunnan Province] under Grant Agreement No[202105AD160018].\u003c/p\u003e\n\u003cp\u003eAuthors\u0026apos; contributions\u003c/p\u003e\n\u003cp\u003e[QingLyu Shi] and [GuoLiang Wang] designed the study. [QingLyu Shi] and [GuoLiang Wang] performed the surgical operation. [Hua Li] and [LiChao Zhang] Collected and measured \u0026nbsp;image data for each patient. [RunZe Li] conducted the statistical analysis. [GuoLiang Wang] and [YanLin Li] evaluated the postoperative function of each patient. [QingLyu Shi] and [RunZe Li] wrote the main manuscript text. [RunZe Li] \u0026nbsp; prepared figures 1-3,[QingLyu Shi] prepared figures 4-5.\u003c/p\u003e\n\u003cp\u003eAll authors reviewed the manuscript.\u003c/p\u003e\n\u003cp\u003eAcknowledgements\u003c/p\u003e\n\u003cp\u003eWe would like to express our gratitude to Yi Zhao from the Kunming Youth Mental Health Center for his invaluable assistance in the design of the illustration.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eZhang LK, Wang XM, Niu YZ, Liu HX, Wang F. Relationship between Patellar Tracking and the Screw-home Mechanism of Tibiofemoral Joint. 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Knee surgery, sports traumatology, arthroscopy. official J ESSKA. 2023;31(8):3243\u0026ndash;58.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eZhang LTM, Wu S, Xu T, Zhang K, Xie X,Fu W. Tibial Tubercle-Trochlear Groove Distance Has Better Diagnostic Reliability Than Tubercle-Posterior Cruciate Ligament Distance For Predicting Patellar Instability: A Systematic Review. Orthop Surg. 2023;15(9):2225\u0026ndash;34.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"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":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Tibiofemoral rotation, Recurrent patellar dislocation, Pathological TT–TG distance, Isolated MPFL reconstruction","lastPublishedDoi":"10.21203/rs.3.rs-7776795/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7776795/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eBackground\u003c/h2\u003e\u003cp\u003eThis study aimed to retrospectively present the radiologic outcomes in a cohort with recurrent patella dislocation (RPD) who have an elevated tibial tubercle\u0026ndash;trochlear groove (TT-TG) distance (\u0026gt;\u0026thinsp;20 mm) following isolated medial patellofemoral ligament reconstruction (i-MPFL-R), and to exhibit the tibiofemoral rotation in RPD patients.\u003c/p\u003e\u003ch2\u003eMethods\u003c/h2\u003e\u003cp\u003eRPD patients with a TT-TG distance exceeding 20 mm and tibial tubercle-posterior cruciate ligament (TT-PCL) distance within 24 mm who underwent i-MPFL-R between 2018 and 2022 in our department were included. Clinical outcomes and remeasurement of TT-TG distance and other radiological measurements were analysed postoperatively. Data from the contralateral knee of each patient were analysed for contral.\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e\u003cp\u003eA total of 51 knees with a median follow-up time of 36 months were included. TT-TG distance has significantly decreased after i-MPFL-R in those patients (pre 24.30[22.25,25.85]mm vs post 20.20[18.25,22.65]mm,P\u0026thinsp;\u0026lt;\u0026thinsp;0.001) compared with contralateral knee (pre 21.95\u0026thinsp;\u0026plusmn;\u0026thinsp;3.20mm, 95%CI: 21.04\u0026ndash;22.85 vs post 20.30[19.15,23.45]mm, P\u0026thinsp;=\u0026thinsp;0.471). No significant changes were observed in the TT-PCL distance. Additionally, there was a synchronous decrease in tibiofemoral rotation (TFR) and patellar tilt angle (PTA) after i-MPFL-R in these patients (pre 9.83\u0026thinsp;\u0026plusmn;\u0026thinsp;3.57\u0026deg;, 95%CI: 8.83\u0026ndash;10.84 vs post 6.96\u0026thinsp;\u0026plusmn;\u0026thinsp;3.13\u0026deg;, 95%CI: 6.08\u0026ndash;7.84, P\u0026thinsp;\u0026lt;\u0026thinsp;0.001) and (pre 28.51[24.26,33.76]\u0026deg; vs post 12.13[6.53,18.48]\u0026deg;, P\u0026thinsp;\u0026lt;\u0026thinsp;0.001), compared with contralateral knee (pre 8.51\u0026thinsp;\u0026plusmn;\u0026thinsp;3.37\u0026deg;, 95%CI: 7.57\u0026ndash;9.46 vs post 8.46\u0026thinsp;\u0026plusmn;\u0026thinsp;3.52\u0026deg;, 95%CI: 7.47\u0026ndash;9.45, P\u0026thinsp;=\u0026thinsp;0.889) and (pre 23.01\u0026thinsp;\u0026plusmn;\u0026thinsp;7.57\u0026deg;, 95%CI: 20.88\u0026ndash;25.13 vs post 26.60[15.70,30.65]\u0026deg;, P\u0026thinsp;=\u0026thinsp;0.848), respectively.\u003c/p\u003e\u003ch2\u003eConclusion\u003c/h2\u003e\u003cp\u003eThe elevated TT\u0026ndash;TG distance caused by excessive tibiofemoral rotation decreased following i-MPFL-R, which may be attributed to the tibiofemoral rotation effect during patellar reduction. The tibiofemoral rotation makes TT-TG, TFR, and PTA collectively form a triad of radiological measurements to be considered in patellar instability.\u003c/p\u003e","manuscriptTitle":"Tibiofemoral rotation after isolated MPFL reconstruction in recurrent patellar dislocation with elevated TT–TG distance","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-10-17 12:34:18","doi":"10.21203/rs.3.rs-7776795/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"189a4355-f8f7-4463-bba1-642ce764fedb","owner":[],"postedDate":"October 17th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-11-22T12:08:59+00:00","versionOfRecord":[],"versionCreatedAt":"2025-10-17 12:34:18","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7776795","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7776795","identity":"rs-7776795","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}