The Pectoralis Minor Reverting the Scapula to its Quadrupedal State of Protraction Causes Chronic Shoulder Pain in Humans

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Iyengar, James Friedman This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8888856/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 The human shoulder is distinguished by unparalleled motion but also chronic pain. This includes syndromes such as subacromial pain (SAPS), scapular dyskinesis (SD), occupational shoulder disorder (OSD), & thoracic outlet (TOS). Proposed pathophysiology and conventional treatments for these remain unsatisfactory. The upper trunk of the brachial plexus controls the muscles which mediate scapulothoracic glide, except for the ventral pectoralis minor (PM) which is controlled by the lower trunk that controls the hand. This neurologic asymmetry can produce persistent protraction of the scapula. Protraction is the default position in quadrupeds, but in bipeds deforms the scapula’s many connections, generating headaches/neck stiffness, upper back tightness, shoulder weakness, and hand numbness. We hypothesize the root cause of chronic shoulder pain is the PM pulling the scapula into protraction and report the outcomes of PM tenotomy with infraclavicular brachial plexus neurolysis (PM + ICN) for patients with the above disorders. Methods Patients with a referring diagnosis of SAPS, SD, TOS, and/or OSD, who exhibited scapular protraction with medial coracoid tenderness on exam, were treated with PM + ICN. Scapular dyskinesis was classified as none (no protraction), dynamic (protraction while reaching overhead but none at rest), static (protraction at rest). Neuropathy was diagnosed via the scratch-collapse test. Patients underwent PM + ICN, with secondary neurolysis at 3 months for residual pain or weakness. Outcomes included self-reported pain, shoulder abduction range-of-motion (ROM), and need for secondary neurolysis. Results N = 283 patients were included: 240 SAPS, 13 SD, 151 TOS, 47 OSD. Average age was 51. At one-year, scapular dyskinesis normalized from 99% static to 94% none, average pain decreased from 7.4 to 2.1, and average shoulder abduction range-of-motion increased from 97 to 171 degrees. (All p < 0.01). 18% required secondary neurolysis, most commonly of the ulnar (11%), radial (10%), and axillary (9%) nerves. Conclusions The human shoulder girdle delivers unparalleled motion but suffers from chronic pain because the scapula is prone to revert to its ancestral quadrupedal state of protraction, due to the PM’s unique lower trunk innervation. Certain patients suffering from chronic shoulder pain refractory to other treatments may benefit substantially from PM + ICN with infrequent secondary neurolysis. pectoralis minor scapular dyskinesis subacromial impingement thoracic outlet chronic pain Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Introduction The first hallmark of the human shoulder is its incredible motion, the most of any joint in the mammal kingdom.( 1 , 2 ) This attribute developed alongside bipedal gait( 3 , 4 ) and hand prehension( 5 ), enabling humans to throw with velocity and precision.( 5 ) Throwing conferred a distinct predation advantage while hunting( 6 ) which accelerated further social and cognitive development, constituting a pivotal step in our evolution as a species.( 2 ) The theme of the shoulder has been described as the “perfect compromise between motion and stability.”( 7 ) These dual aims mandate highly-complex and uniquely-specialized anatomy( 1 , 8 , 9 ): seventeen muscles innervated by eleven nerves acting across four articulations stabilized by four groups of ligaments.( 10 ) Perhaps the most mysterious element of this machinery is the scapula, the dynamic link between the axial skeleton and upper limb.( 11 ) The second hallmark of the human shoulder is chronic pain and dysfunction, with a lifetime prevalence nearly 70%.( 12 ) Typically, the pain centers at the shoulder but can extend up the neck, around the upper back, and down to the hand( 13 ), and can manifest as headaches, tightness, stiffness, weakness, numbness, and/or coolness.( 14 ) Shoulder pain syndromes include subacromial pain or impingement (SAPS), thoracic outlet (TOS), scapular dyskinesis (SD), and occupational shoulder disorder (OSD, also called work-related musculoskeletal disorder involving the shoulder). Despite best efforts, these remain intractable and mysterious.( 13 , 15 – 18 ) Diagnosis is challenging( 19 – 21 ), treatments exhibit questionable efficacy( 22 – 25 ), and pathophysiology tends to be convoluted and rely on numerous vague causes.( 26 – 29 ) Thus, the central mystery of the human shoulder is why is the remarkable motion coupled with vulnerability to chronic pain? Previously, we described the Human Disharmony Loop (HDL), a clinical model of dysfunction.( 26 , 30 , 31 ) The scapula glides along the thorax and performs two critical functions to enable overhead reach: ( 1 ) optimizing length-tension relationships for the deltoid and rotator cuff and ( 2 ) maintaining articular congruity to prevent impingement. This scapulothoracic motion is coordinated by the peri-scapular stabilizers which can be categorized into three groups relative to the thorax: dorsal (trapezius, rhomboids, levator scapulae), lateral (serratus anterior), and ventral (pectoralis minor or PM). (Fig. 1 ) Of these, the ventral PM is unique in that it is innervated by the lower C8-T1 roots which also control the hand.( 26 ) This asymmetry, potentially a sequelae of evolution, renders the scapula prone to protraction.( 26 , 31 ) Protraction narrows the subacromial and costoclavicular spaces, stretches the upper trapezius and rhomboids, irritates the occipital nerves, and tensions the brachial plexus. The pathoanatomy generates four clusters of symptoms: headaches and neck stiffness, upper back tightness, shoulder weakness, and hand numbness/tingling.( 31 ) (Fig. 2 ) Surgical treatment consists of PM tenotomy with infraclavicular neurolysis (PM + ICN). In our previous reports, PM + ICN uniformly improved pain and function in patients with SAPS, TOS, OSD, and SD( 26 , 30 – 32 ), suggesting these diverse mysterious entities may actually be manifestations of a common underlying phenomenon. The HDL theoretically incorporates these syndromes (Fig. 2 ) and explains their symptoms via clear pathways. (Fig. 3 ) The HDL may also answer why the shoulder’s remarkable motion is coupled with susceptibility to pain, since it descended from the quadrupedal forelimb. Hence, we hypothesize that chronic shoulder pain results from the PM disturbing scapular mechanics, and patients suffering from these syndromes will benefit from PM + ICN. Materials and Methods This is a combined retrospective and prospective case series of consecutive patients treated at two centers. All were evaluated by a fellowship-trained board-certified hand, sports, or shoulder surgeon. Inclusion criteria included a diagnosis of SAPS, SD, TOS, and/or OSD made by the referring provider, and meeting HDL diagnostic criteria.( 31 ) Exclusion criteria included: follow-up < 1 year, age < 13. All patients trialed at least 3 months of physical therapy before surgery. Patients were seen at 2, 6, 12, and 52 weeks postoperatively. Scapular dyskinesis on exam was classified as none (no protraction), dynamic (protraction while reaching overhead but none at rest), static (protraction at rest). Neuropathy was diagnosed via the scratch-collapse test (SCT).( 33 ) Patients underwent PM + ICN, followed by physical therapy emphasizing trapezius and rhomboid strengthening to retract the scapula.( 30 ) At 3 months, patients with provocative neuropathic lesions on exam and lingering pain were offered secondary neurolysis. Outcomes included visual analogue scale pain scores out of 10, shoulder abduction range-of-motion (ROM), clinical neuropathy, and need for secondary neurolysis. Student’s t -test and Chi-squared analyses compared continuous and categorical variables of interest, respectively. All analysis was performed using STATA v14.0. Institutional Review Board (IRB) approval was obtained. Informed consent was waived by the ethics committee as all data was anonymous and the study posed minimal risk to patients. This study adheres to the STROBE guidelines. Results N = 283 patients were included. Average age was 51 years. 67% were female, average BMI was 30. Laterality of presentation was 59% right, 41% left. Patients had a history of 85% SAPS, 18% TOS, 17% OSD, 5% SD. Surgical history included 28% subacromial decompression with adjunct procedures, 10% reverse total shoulder arthroplasty, 2% 1st rib resection and scalenectomy, 17% cervical spine fusion, 28% distal neurolysis. (Table 1 ) Following PM + ICN, average pain decreased from 7.4 to 2.1 and average shoulder abduction increased from 97 degrees to 171 degrees. Scapular dyskinesis normalized from 99% static protraction to 94% none. Clinical neuropathy decreased as follows: thoracic outlet 56◊2%, suprascapular notch 59◊1%, quadrilateral space 83◊15%, radial tunnel 70◊20%, cubital tunnel 22◊20%, carpal tunnel 43◊16%. (All p < 0.01). (Fig. 4 ) Overall, 18% of patients required secondary neurolysis, most commonly of the ulnar (11%), radial (10%), and axillary (9%) nerves. (Table 2 ) Median follow-up was 21 months. Table 1 Patient Characteristics Variable N = 283 Age 1 51 (49, 53) Sex Male 93 (33%) Female 190 (67%) BMI 1 30 ( 29 , 31 ) Shoulder Syndrome Subacromial impingement (SAPS) Scapular dyskinesis (SD) Thoracic outlet (TOS) Occupational shoulder disorder (OSD) 240 (85%) 13 (5%) 51 (18%) 47 (17%) Surgical History Subacromial decompression + adjunct procedures 2 79 (28%) Reverse total shoulder arthroplasty 27 (10%) 1st rib resection + scalenectomy 5 (2%) Cervical spine fusion 48 (17%) Distal neurolysis (carpal, cubital) 80 (28%) Hand Dominance Right 247 (87%) Left 36 (13%) Laterality Right 166 (59%) Left 117 (41%) Median Follow-up (months) 21 1. Average (95% CI) 2. Adjunct procedures include rotator cuff repair, distal clavicle excision, biceps tenodesis, bursectomy, and/or labral repair Table 2 Clinical Outcomes Outcome Preoperative Postoperative P-Value Pain 1 7.4 (7.2, 7.6) 2.1 (1.8, 2.3) < 0.01 Shoulder Abduction ROM 1 97 (93, 101) 171 (168, 174) < 0.01 Scapular Dyskinesis Stage 2 None Dynamic Static 0 (0%) 4 (1%) 279 (99%) 267 (94%) 13 (5%) 3 (1%) < 0.01 Neuropathic Lesions 3 Thoracic outlet 159 (56%) 6 (2%) Suprascapular notch 166 (59%) 4 (1%) Quadrilateral space 236 (83%) 43 (15%) < 0.01 Radial tunnel 197 (70%) 56 (20%) Cubital tunnel 62 (22%) 57 (20%) Carpal tunnel 122 (43%) 46 (16%) Secondary Neurolysis 4 52 (18%) Thoracic outlet Suprascapular 4 (1%) 2 (1%) Quadrilateral space N/A 26 (9%) N/A Radial 29 (10%) Cubital 33 (11%) Carpal 18 (6%) 1. Average (95% CI) 2. Scapular dyskinesis was classified based on physical exam as none (no protraction), dynamic (protraction with overhead reach), static (protraction at rest) 3. Neuropathic lesions were diagnosed via a positive scratch-collapse test at each location 4. Patients were offered secondary neurolysis at 3 months for clinical deficits and provocative lesions on exam Caption: The trapezius and serratus anterior rotate the scapula (left), while the PM protracts the scapula or hunches the shoulder (right). A single anatomic source produces chronic pain symptoms of the upper limb girdle (top) and generates the pathoanatomy behind SAPS, TOS, OSD and SD (bottom) Caption: The HDL anatomically incorporates SD, OSD, SAPS, TOS, connects them via clear pathways, and explains all symptoms including neuropathy. Caption: PM tenotomy normalizes the mechanics of the scapula by eliminating the protracting force, substantially reducing pain and increasing ROM. In quadrupeds, the scapula predominantly alternates between protraction while standing or sprinting (left) to retraction while crouching (right). Top: Axial view comparing the baseline position of the scapula in Rhesus monkeys versus humans. In our ancestors, the scapula sits laterally against the thorax in a protracted state and is held in this optimal position during locomotion by the pectoralis minor. Bottom: Protraction is ideal in quadrupeds but pathological in humans. Discussion In this study, disconnecting the PM from the scapula dramatically reduced pain and increased function when applied to chronic pain of the shoulder. (Fig. 4 ) Our findings imply that SAPS, TOS, SD, and OSD are manifestations of warped scapular mechanics. The PM may constitute their common anatomic source and optimal surgical target. (Fig. 2 ) Three lines of evidence demonstrate the current understanding behind chronic shoulder pain is incorrect. First, a plethora of vague causes must be invoked: acromion morphology variations, rotator cuff degradation, tensile forces, etc. for SAPS( 34 ); cervical rib and scalene variations, anomalous fibrofascial bands, repetitive trauma, postural changes, altered girdle mechanics, muscle spam, etc. for TOS( 28 , 35 ); repetitive tasks, poor posture, cumulative trauma for OSD( 36 ); and clavicle/scapula fractures, AC/glenohumeral joint pathology, rotator cuff injury, post-traumatic muscle injury, soft tissue tightness, etc. for SD.( 37 ) But these remain vague and unexplained; more likely, these are associations.( 26 ) (Notably, regardless of cause, “the salient clinical manifestation of the dyskinetic scapula is protraction”, suggesting a common source.( 38 )) Second, these syndromes feature symptoms outside their proposed pathophysiology, including radiating neuropathy in SAPS( 19 ), occipital headaches in TOS( 39 ), and neck pain in SD.( 40 ) Third, and most importantly, current treatments which target the proposed culprits – i.e., altering acromion morphology, decompressing the thoracic outlet, optimizing ergonomics against poor posture – uniformly fail to demonstrate efficacy.( 22 – 24 ) The HDL offers a unifying framework centered on the scapula, the great coordinator of function. Due to its unique lower trunk innervation, the PM can pull the scapula in its direction of protraction. Protraction, the three-dimensional combination of lateral translation with anterior tilt and internal rotation( 41 ), is the motion of hunching the shoulder. (Fig. 5 ) Our findings suggest the principal protractor of the scapula is the PM and the principal cause behind most SD is the PM. Protraction deforms all the scapula’s connections( 41 ) and produces the subacromial impingement of SAPS( 30 ), costoclavicular narrowing of TOS( 32 ), and occipital neuritis and myofascial stretch of OSD.( 42 ) Current treatments are targeting pathoanatomic sequelae, hence their inefficacy. The key to deciphering the shoulder’s mysteries is to answer why the command center of the brain that controls the hand also controls the PM. Evolution provides the answer. For quadrupeds, coordination between the forepaw and ventral chain is crucial for locomotion. The human shoulder girdle evolved from the quadrupedal forelimb but differs in key anatomy and morphology. In quadrupeds, the glenohumeral joint exhibits less motion but far more stability( 3 ), while the scapula is long and narrow with a horizontal spine.( 43 ) The scapula rests laterally against the thorax( 3 , 43 ) and principally moves between protraction while standing and sprinting to retraction while crouching.( 44 ) (Fig. 5 ) The ventral chain maintains the scapula protracted against the thorax during the high velocities of sprinting, and must coordinate with the forepaw for optimal locomotion. Thus, the lower trunk controls both. In contrast, the human glenohumeral joint provides far more motion( 3 ), with a scapula that sits dorsally against the thorax( 45 ) and is shorter and taller with an oblique spine.( 43 ) The scapula’s principal motion is rotation, mediated by the trapezius and serratus anterior, raising the glenoid as a mobile platform for the humeral head while reaching overhead.( 43 , 44 ) In short, each girdle evolved for different goals: quadrupeds to sprint for catching prey, humans to throw stones for hunting. However, even humans start as quadrupeds. Our PM retains its lower trunk innervation, and our scapular machinery has a defect: the PM can overpower the other muscles, swing the scapula into protraction, and pathologize its many connections, producing chronic pain. This common anatomic source generates the protraction of SD, headaches and neck and upper back tightness of OSD, shoulder weakness of SAPS, and hand numbness in TOS. Of all possible directions, humans tend to hunch our shoulders (or protract our scapulas) because this is the default optimum in our ancestors. (Fig. 6 ) This study suffers from key limitations. As a case series limited to two sites, our results must be replicated before widespread adoption. The lack of control group means unknown confounders and/or placebo effect could explain the findings, although this is unlikely given the large degree of improvement seen in intractable disorders. Neuropathy was diagnosed via the SCT which suffers drawbacks( 46 ), but no gold standard exists.( 47 ) Ultimately, the HDL model is based on physical exam findings and anatomic principles in a theoretical framework, but not objective testing such as MRIs or EMGs, introducing subjectivity. However, history and physical constitute the cornerstones of medicine( 48 , 49 ), and testing has failed to elucidate the true nature of chronic shoulder pain despite exhaustive efforts.( 19 , 22 ) Our principal outcomes of pain and ROM are subjective, although we contend these metrics are most meaningful for patients. We do not employ standardized patient-reported outcomes (PROs), but these are simply numerical aggregates of subjective responses, can be harder for patients to interpret, and may convey differences that are statistically significant but not clinically meaningful.( 50 , 51 ) Future research should compare PM + ICN to standard of care for treatment of SAPS, TOS, OSD, and SD in larger, randomized trials, to definitively prove our assertions. Notably, 18% of patients required subsequent neurolysis, highlighting the complexity of chronic shoulder pain. We maintain the optimal treatment for patients meeting HDL criteria is PM + ICN followed by close surveillance with secondary neurolysis for residual symptoms if needed. This study should be interpreted considering these limitations. Conclusion The human shoulder offers unparalleled motion but suffers from chronic pain because it evolved from the quadrupedal forelimb. Our scapula retains a propensity to protract, optimal for our ancestors but pathological to us. The PM constitutes the anatomic source and ideal surgical target to treat certain patients suffering from chronic shoulder pain. Declarations Ethics approval and consent to participate: Institutional Review Board (IRB) approval was obtained from both institutions: St Joseph’s Medical Center Research and Quality Committee and St. Luke’s Institutional Review Board. Informed consent was waived by the ethics committees as all data was anonymous and the study posed minimal risk to patients. Consent for publication: Not applicable. Funding: No funding was received for this study. Author Contribution KS and JF conceived of the study idea and methodology. KS wrote the original draft. KS and JF and JI collected the data. JF and JI revised the study. All authors read and approved the final manuscript. Acknowledgements: Not applicable. Clinical trial number: Not applicable. Data Availability All data can be accessed at [https://doi.org/10.6084/m9.figshare.30951170](https:/doi.org/10.6084/m9.figshare.30951170) References Kuhn JE. Throwing, the Shoulder, and Human Evolution. Am J Orthop (Belle Mead NJ). 2016;45(3):110–4. Roach NT, Venkadesan M, Rainbow MJ, Lieberman DE. Elastic energy storage in the shoulder and the evolution of high-speed throwing in Homo. Nature. 2013;498(7455):483–6. Arias-Martorell J. The morphology and evolutionary history of the glenohumeral joint of hominoids: A review. Ecol Evol. 2019;9(1):703–22. Preuschoft H. 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Iyengar","email":"","orcid":"","institution":"Sutter Health","correspondingAuthor":false,"prefix":"","firstName":"Jaicharan","middleName":"J.","lastName":"Iyengar","suffix":""},{"id":634326398,"identity":"d049b0b0-4646-44db-9104-3bec224fa8d8","order_by":2,"name":"James Friedman","email":"","orcid":"","institution":"Sutter Health","correspondingAuthor":false,"prefix":"","firstName":"James","middleName":"","lastName":"Friedman","suffix":""}],"badges":[],"createdAt":"2026-02-16 00:23:19","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8888856/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8888856/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":108807601,"identity":"cea89094-e1c5-452a-84ed-3a3dd569d4e0","added_by":"auto","created_at":"2026-05-08 15:30:56","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":623779,"visible":true,"origin":"","legend":"\u003cp\u003ePeri-Scapular Stabilizers That Control Scapulothoracic Glide\u003c/p\u003e\n\u003cp\u003eCaption: The trapezius and serratus anterior rotate the scapula (left), while the PM protracts the scapula or hunches the shoulder (right).\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-8888856/v1/ee952941ac04e7591e55e7b2.png"},{"id":108724749,"identity":"f228e295-0b34-40f9-b32d-6daa7eb5e7f1","added_by":"auto","created_at":"2026-05-07 16:52:19","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":579473,"visible":true,"origin":"","legend":"\u003cp\u003eHuman Disharmony Loop Symptoms and Pathoanatomy\u003c/p\u003e\n\u003cp\u003eA single anatomic source produces chronic pain symptoms of the upper limb girdle (top) and generates the pathoanatomy behind SAPS, TOS, OSD and SD (bottom)\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-8888856/v1/a682832fc0212cce3aa1ee77.png"},{"id":108805798,"identity":"d0e082cf-c436-4d4f-a6b1-f510bf269b01","added_by":"auto","created_at":"2026-05-08 15:26:55","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":368354,"visible":true,"origin":"","legend":"\u003cp\u003eHuman Disharmony Loop Unification of Shoulder Syndromes\u003c/p\u003e\n\u003cp\u003eCaption: The HDL anatomically incorporates SD, OSD, SAPS, TOS, connects them via clear pathways, and explains all symptoms including neuropathy.\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-8888856/v1/8eec9f92c481c1fa97e50298.png"},{"id":108724752,"identity":"d6181367-f0f9-49a1-a384-fdd60fc8f135","added_by":"auto","created_at":"2026-05-07 16:52:19","extension":"jpeg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":140656,"visible":true,"origin":"","legend":"\u003cp\u003eClinical Improvements Following Normalization of Scapular Kinematics\u003c/p\u003e\n\u003cp\u003eCaption: PM tenotomy normalizes the mechanics of the scapula by eliminating the protracting force, substantially reducing pain and increasing ROM.\u003c/p\u003e","description":"","filename":"floatimage4.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-8888856/v1/702dedb2fa3d78682580916d.jpeg"},{"id":108724754,"identity":"cb48342c-86c5-4ac4-9a03-94d29464d291","added_by":"auto","created_at":"2026-05-07 16:52:19","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":630907,"visible":true,"origin":"","legend":"\u003cp\u003eScapula Motion in Quadrupeds\u003c/p\u003e\n\u003cp\u003eIn quadrupeds, the scapula predominantly alternates between protraction while standing or sprinting (left) to retraction while crouching (right).\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-8888856/v1/f9057a00dc714ee6f5797cf8.png"},{"id":108724753,"identity":"1ea1787a-ec06-4d1a-8305-2fc4bc66dff5","added_by":"auto","created_at":"2026-05-07 16:52:19","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":360105,"visible":true,"origin":"","legend":"\u003cp\u003eResting Scapula Position in Quadrupeds versus Humans\u003c/p\u003e\n\u003cp\u003eTop: Axial view comparing the baseline position of the scapula in Rhesus monkeys versus humans. In our ancestors, the scapula sits laterally against the thorax in a protracted state and is held in this optimal position during locomotion by the pectoralis minor.\u003c/p\u003e\n\u003cp\u003eBottom: Protraction is ideal in quadrupeds but pathological in humans.\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-8888856/v1/25dc4fefdac78cd79f205a10.png"},{"id":108810360,"identity":"6fbc0634-5ac0-430f-a3d4-a892cb6cee9f","added_by":"auto","created_at":"2026-05-08 15:58:32","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2991476,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8888856/v1/ccc1fd97-45bc-4df9-b42f-c6a8da103457.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"The Pectoralis Minor Reverting the Scapula to its Quadrupedal State of Protraction Causes Chronic Shoulder Pain in Humans","fulltext":[{"header":"Introduction","content":"\u003cp\u003eThe first hallmark of the human shoulder is its incredible motion, the most of any joint in the mammal kingdom.(\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e) This attribute developed alongside bipedal gait(\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e) and hand prehension(\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e), enabling humans to throw with velocity and precision.(\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e) Throwing conferred a distinct predation advantage while hunting(\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e) which accelerated further social and cognitive development, constituting a pivotal step in our evolution as a species.(\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e) The theme of the shoulder has been described as the \u0026ldquo;perfect compromise between motion and stability.\u0026rdquo;(\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e) These dual aims mandate highly-complex and uniquely-specialized anatomy(\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e): seventeen muscles innervated by eleven nerves acting across four articulations stabilized by four groups of ligaments.(\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e) Perhaps the most mysterious element of this machinery is the scapula, the dynamic link between the axial skeleton and upper limb.(\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e)\u003c/p\u003e \u003cp\u003eThe second hallmark of the human shoulder is chronic pain and dysfunction, with a lifetime prevalence nearly 70%.(\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e) Typically, the pain centers at the shoulder but can extend up the neck, around the upper back, and down to the hand(\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e), and can manifest as headaches, tightness, stiffness, weakness, numbness, and/or coolness.(\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e) Shoulder pain syndromes include subacromial pain or impingement (SAPS), thoracic outlet (TOS), scapular dyskinesis (SD), and occupational shoulder disorder (OSD, also called work-related musculoskeletal disorder involving the shoulder). Despite best efforts, these remain intractable and mysterious.(\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan additionalcitationids=\"CR16 CR17\" citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e) Diagnosis is challenging(\u003cspan additionalcitationids=\"CR20\" citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e), treatments exhibit questionable efficacy(\u003cspan additionalcitationids=\"CR23 CR24\" citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e), and pathophysiology tends to be convoluted and rely on numerous vague causes.(\u003cspan additionalcitationids=\"CR27 CR28\" citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e)\u003c/p\u003e \u003cp\u003eThus, the central mystery of the human shoulder is why is the remarkable motion coupled with vulnerability to chronic pain?\u003c/p\u003e \u003cp\u003ePreviously, we described the Human Disharmony Loop (HDL), a clinical model of dysfunction.(\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e, \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e) The scapula glides along the thorax and performs two critical functions to enable overhead reach: (\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e) optimizing length-tension relationships for the deltoid and rotator cuff and (\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e) maintaining articular congruity to prevent impingement. This scapulothoracic motion is coordinated by the peri-scapular stabilizers which can be categorized into three groups relative to the thorax: dorsal (trapezius, rhomboids, levator scapulae), lateral (serratus anterior), and ventral (pectoralis minor or PM). (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) Of these, the ventral PM is unique in that it is innervated by the lower C8-T1 roots which also control the hand.(\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e) This asymmetry, potentially a sequelae of evolution, renders the scapula prone to protraction.(\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e, \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e) Protraction narrows the subacromial and costoclavicular spaces, stretches the upper trapezius and rhomboids, irritates the occipital nerves, and tensions the brachial plexus. The pathoanatomy generates four clusters of symptoms: headaches and neck stiffness, upper back tightness, shoulder weakness, and hand numbness/tingling.(\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e) (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e) Surgical treatment consists of PM tenotomy with infraclavicular neurolysis (PM\u0026thinsp;+\u0026thinsp;ICN).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn our previous reports, PM\u0026thinsp;+\u0026thinsp;ICN uniformly improved pain and function in patients with SAPS, TOS, OSD, and SD(\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e, \u003cspan additionalcitationids=\"CR31\" citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e), suggesting these diverse mysterious entities may actually be manifestations of a common underlying phenomenon. The HDL theoretically incorporates these syndromes (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e) and explains their symptoms via clear pathways. (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e) The HDL may also answer why the shoulder\u0026rsquo;s remarkable motion is coupled with susceptibility to pain, since it descended from the quadrupedal forelimb. Hence, we hypothesize that chronic shoulder pain results from the PM disturbing scapular mechanics, and patients suffering from these syndromes will benefit from PM\u0026thinsp;+\u0026thinsp;ICN.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"Materials and Methods","content":"\u003cp\u003eThis is a combined retrospective and prospective case series of consecutive patients treated at two centers. All were evaluated by a fellowship-trained board-certified hand, sports, or shoulder surgeon. Inclusion criteria included a diagnosis of SAPS, SD, TOS, and/or OSD made by the referring provider, and meeting HDL diagnostic criteria.(\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e) Exclusion criteria included: follow-up \u0026lt;\u0026thinsp;1 year, age\u0026thinsp;\u0026lt;\u0026thinsp;13. All patients trialed at least 3 months of physical therapy before surgery. Patients were seen at 2, 6, 12, and 52 weeks postoperatively. Scapular dyskinesis on exam was classified as none (no protraction), dynamic (protraction while reaching overhead but none at rest), static (protraction at rest). Neuropathy was diagnosed via the scratch-collapse test (SCT).(\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e) Patients underwent PM\u0026thinsp;+\u0026thinsp;ICN, followed by physical therapy emphasizing trapezius and rhomboid strengthening to retract the scapula.(\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e) At 3 months, patients with provocative neuropathic lesions on exam and lingering pain were offered secondary neurolysis. Outcomes included visual analogue scale pain scores out of 10, shoulder abduction range-of-motion (ROM), clinical neuropathy, and need for secondary neurolysis. Student\u0026rsquo;s \u003cem\u003et\u003c/em\u003e-test and Chi-squared analyses compared continuous and categorical variables of interest, respectively. All analysis was performed using STATA v14.0. Institutional Review Board (IRB) approval was obtained. Informed consent was waived by the ethics committee as all data was anonymous and the study posed minimal risk to patients. This study adheres to the STROBE guidelines.\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003e \u003cem\u003eN\u003c/em\u003e\u0026thinsp;=\u0026thinsp;283 patients were included. Average age was 51 years. 67% were female, average BMI was 30. Laterality of presentation was 59% right, 41% left. Patients had a history of 85% SAPS, 18% TOS, 17% OSD, 5% SD. Surgical history included 28% subacromial decompression with adjunct procedures, 10% reverse total shoulder arthroplasty, 2% 1st rib resection and scalenectomy, 17% cervical spine fusion, 28% distal neurolysis. (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) Following PM\u0026thinsp;+\u0026thinsp;ICN, average pain decreased from 7.4 to 2.1 and average shoulder abduction increased from 97 degrees to 171 degrees. Scapular dyskinesis normalized from 99% static protraction to 94% none. Clinical neuropathy decreased as follows: thoracic outlet 56\u0026loz;2%, suprascapular notch 59\u0026loz;1%, quadrilateral space 83\u0026loz;15%, radial tunnel 70\u0026loz;20%, cubital tunnel 22\u0026loz;20%, carpal tunnel 43\u0026loz;16%. (All \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.01). (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e) Overall, 18% of patients required secondary neurolysis, most commonly of the ulnar (11%), radial (10%), and axillary (9%) nerves. (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e) Median follow-up was 21 months.\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\u003ePatient Characteristics\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\" colname=\"c1\"\u003e \u003cp\u003eVariable\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003eN\u003c/em\u003e\u0026thinsp;=\u0026thinsp;283\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAge\u003csup\u003e1\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e51 (49, 53)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSex\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMale 93 (33%)\u003c/p\u003e \u003cp\u003eFemale 190 (67%)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBMI\u003csup\u003e1\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e30 (\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e, \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eShoulder Syndrome\u003c/p\u003e \u003cp\u003eSubacromial impingement (SAPS)\u003c/p\u003e \u003cp\u003eScapular dyskinesis (SD)\u003c/p\u003e \u003cp\u003eThoracic outlet (TOS)\u003c/p\u003e \u003cp\u003eOccupational shoulder disorder (OSD)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e240 (85%)\u003c/p\u003e \u003cp\u003e13 (5%)\u003c/p\u003e \u003cp\u003e51 (18%)\u003c/p\u003e \u003cp\u003e47 (17%)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSurgical History\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSubacromial decompression +\u003c/p\u003e \u003cp\u003eadjunct procedures\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e79 (28%)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eReverse total shoulder arthroplasty\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e27 (10%)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1st rib resection\u0026thinsp;+\u0026thinsp;scalenectomy\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e5 (2%)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCervical spine fusion\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e48 (17%)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eDistal neurolysis (carpal, cubital)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e80 (28%)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHand Dominance\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eRight 247 (87%)\u003c/p\u003e \u003cp\u003eLeft 36 (13%)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLaterality\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eRight 166 (59%)\u003c/p\u003e \u003cp\u003eLeft 117 (41%)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMedian Follow-up (months)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e21\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"2\"\u003e1. Average (95% CI)\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"2\"\u003e2. Adjunct procedures include rotator cuff repair, distal clavicle excision, biceps tenodesis, bursectomy, and/or labral repair\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eClinical Outcomes\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\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=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eOutcome\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePreoperative\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003ePostoperative\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eP-Value\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePain\u003csup\u003e1\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e7.4 (7.2, 7.6)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2.1 (1.8, 2.3)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.01\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eShoulder Abduction ROM\u003csup\u003e1\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e97 (93, 101)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e171 (168, 174)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.01\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eScapular Dyskinesis Stage\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eNone\u003c/p\u003e \u003cp\u003eDynamic\u003c/p\u003e \u003cp\u003eStatic\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0 (0%)\u003c/p\u003e \u003cp\u003e4 (1%)\u003c/p\u003e \u003cp\u003e279 (99%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e267 (94%)\u003c/p\u003e \u003cp\u003e13 (5%)\u003c/p\u003e \u003cp\u003e3 (1%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.01\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNeuropathic Lesions\u003csup\u003e3\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eThoracic outlet\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e159 (56%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e6 (2%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSuprascapular notch\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e166 (59%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e4 (1%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eQuadrilateral space\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e236 (83%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e43 (15%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.01\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRadial tunnel\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e197 (70%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e56 (20%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCubital tunnel\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e62 (22%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e57 (20%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCarpal tunnel\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e122 (43%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e46 (16%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSecondary Neurolysis\u003csup\u003e4\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e52 (18%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eThoracic outlet\u003c/p\u003e \u003cp\u003eSuprascapular\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e4 (1%)\u003c/p\u003e \u003cp\u003e2 (1%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eQuadrilateral space\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eN/A\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e26 (9%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eN/A\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRadial\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e29 (10%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCubital\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e33 (11%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCarpal\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e18 (6%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"4\"\u003e1. Average (95% CI)\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"4\"\u003e2. Scapular dyskinesis was classified based on physical exam as none (no protraction), dynamic (protraction with overhead reach), static (protraction at rest)\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"4\"\u003e3. Neuropathic lesions were diagnosed via a positive scratch-collapse test at each location\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"4\"\u003e4. Patients were offered secondary neurolysis at 3 months for clinical deficits and provocative lesions on exam\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"4\"\u003eCaption: The trapezius and serratus anterior rotate the scapula (left), while the PM protracts the scapula or hunches the shoulder (right).\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"4\"\u003eA single anatomic source produces chronic pain symptoms of the upper limb girdle (top) and generates the pathoanatomy behind SAPS, TOS, OSD and SD (bottom)\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"4\"\u003eCaption: The HDL anatomically incorporates SD, OSD, SAPS, TOS, connects them via clear pathways, and explains all symptoms including neuropathy.\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"4\"\u003eCaption: PM tenotomy normalizes the mechanics of the scapula by eliminating the protracting force, substantially reducing pain and increasing ROM.\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"4\"\u003eIn quadrupeds, the scapula predominantly alternates between protraction while standing or sprinting (left) to retraction while crouching (right).\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"4\"\u003eTop: Axial view comparing the baseline position of the scapula in Rhesus monkeys versus humans. In our ancestors, the scapula sits laterally against the thorax in a protracted state and is held in this optimal position during locomotion by the pectoralis minor.\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"4\"\u003eBottom: Protraction is ideal in quadrupeds but pathological in humans.\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eIn this study, disconnecting the PM from the scapula dramatically reduced pain and increased function when applied to chronic pain of the shoulder. (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e) Our findings imply that SAPS, TOS, SD, and OSD are manifestations of warped scapular mechanics. The PM may constitute their common anatomic source and optimal surgical target. (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e)\u003c/p\u003e \u003cp\u003eThree lines of evidence demonstrate the current understanding behind chronic shoulder pain is incorrect. First, a plethora of vague causes must be invoked: acromion morphology variations, rotator cuff degradation, tensile forces, etc. for SAPS(\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e); cervical rib and scalene variations, anomalous fibrofascial bands, repetitive trauma, postural changes, altered girdle mechanics, muscle spam, etc. for TOS(\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e); repetitive tasks, poor posture, cumulative trauma for OSD(\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e); and clavicle/scapula fractures, AC/glenohumeral joint pathology, rotator cuff injury, post-traumatic muscle injury, soft tissue tightness, etc. for SD.(\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e) But these remain vague and unexplained; more likely, these are associations.(\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e) (Notably, regardless of cause, \u0026ldquo;the salient clinical manifestation of the dyskinetic scapula is protraction\u0026rdquo;, suggesting a common source.(\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e)) Second, these syndromes feature symptoms outside their proposed pathophysiology, including radiating neuropathy in SAPS(\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e), occipital headaches in TOS(\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e), and neck pain in SD.(\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e) Third, and most importantly, current treatments which target the proposed culprits \u0026ndash; i.e., altering acromion morphology, decompressing the thoracic outlet, optimizing ergonomics against poor posture \u0026ndash; uniformly fail to demonstrate efficacy.(\u003cspan additionalcitationids=\"CR23\" citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e)\u003c/p\u003e \u003cp\u003eThe HDL offers a unifying framework centered on the scapula, the great coordinator of function. Due to its unique lower trunk innervation, the PM can pull the scapula in its direction of protraction. Protraction, the three-dimensional combination of lateral translation with anterior tilt and internal rotation(\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e), is the motion of hunching the shoulder. (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e) Our findings suggest the principal protractor of the scapula is the PM and the principal cause behind most SD is the PM. Protraction deforms all the scapula\u0026rsquo;s connections(\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e) and produces the subacromial impingement of SAPS(\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e), costoclavicular narrowing of TOS(\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e), and occipital neuritis and myofascial stretch of OSD.(\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e) Current treatments are targeting pathoanatomic sequelae, hence their inefficacy.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe key to deciphering the shoulder\u0026rsquo;s mysteries is to answer why the command center of the brain that controls the hand also controls the PM. Evolution provides the answer. For quadrupeds, coordination between the forepaw and ventral chain is crucial for locomotion. The human shoulder girdle evolved from the quadrupedal forelimb but differs in key anatomy and morphology. In quadrupeds, the glenohumeral joint exhibits less motion but far more stability(\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e), while the scapula is long and narrow with a horizontal spine.(\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e) The scapula rests laterally against the thorax(\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e) and principally moves between protraction while standing and sprinting to retraction while crouching.(\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e) (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e) The ventral chain maintains the scapula protracted against the thorax during the high velocities of sprinting, and must coordinate with the forepaw for optimal locomotion. Thus, the lower trunk controls both. In contrast, the human glenohumeral joint provides far more motion(\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e), with a scapula that sits dorsally against the thorax(\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e) and is shorter and taller with an oblique spine.(\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e) The scapula\u0026rsquo;s principal motion is rotation, mediated by the trapezius and serratus anterior, raising the glenoid as a mobile platform for the humeral head while reaching overhead.(\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e, \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e) In short, each girdle evolved for different goals: quadrupeds to sprint for catching prey, humans to throw stones for hunting.\u003c/p\u003e \u003cp\u003eHowever, even humans start as quadrupeds. Our PM retains its lower trunk innervation, and our scapular machinery has a defect: the PM can overpower the other muscles, swing the scapula into protraction, and pathologize its many connections, producing chronic pain. This common anatomic source generates the protraction of SD, headaches and neck and upper back tightness of OSD, shoulder weakness of SAPS, and hand numbness in TOS. Of all possible directions, humans tend to hunch our shoulders (or protract our scapulas) because this is the default optimum in our ancestors. (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e)\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThis study suffers from key limitations. As a case series limited to two sites, our results must be replicated before widespread adoption. The lack of control group means unknown confounders and/or placebo effect could explain the findings, although this is unlikely given the large degree of improvement seen in intractable disorders. Neuropathy was diagnosed via the SCT which suffers drawbacks(\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e), but no gold standard exists.(\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e) Ultimately, the HDL model is based on physical exam findings and anatomic principles in a theoretical framework, but not objective testing such as MRIs or EMGs, introducing subjectivity. However, history and physical constitute the cornerstones of medicine(\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e, \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e), and testing has failed to elucidate the true nature of chronic shoulder pain despite exhaustive efforts.(\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e) Our principal outcomes of pain and ROM are subjective, although we contend these metrics are most meaningful for patients. We do not employ standardized patient-reported outcomes (PROs), but these are simply numerical aggregates of subjective responses, can be harder for patients to interpret, and may convey differences that are statistically significant but not clinically meaningful.(\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e, \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e) Future research should compare PM\u0026thinsp;+\u0026thinsp;ICN to standard of care for treatment of SAPS, TOS, OSD, and SD in larger, randomized trials, to definitively prove our assertions. Notably, 18% of patients required subsequent neurolysis, highlighting the complexity of chronic shoulder pain. We maintain the optimal treatment for patients meeting HDL criteria is PM\u0026thinsp;+\u0026thinsp;ICN followed by close surveillance with secondary neurolysis for residual symptoms if needed. This study should be interpreted considering these limitations.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eThe human shoulder offers unparalleled motion but suffers from chronic pain because it evolved from the quadrupedal forelimb. Our scapula retains a propensity to protract, optimal for our ancestors but pathological to us. The PM constitutes the anatomic source and ideal surgical target to treat certain patients suffering from chronic shoulder pain.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e \u003cstrong\u003eEthics approval and consent to participate:\u003c/strong\u003e \u003cp\u003e Institutional Review Board (IRB) approval was obtained from both institutions: St Joseph\u0026rsquo;s Medical Center Research and Quality Committee and St. Luke\u0026rsquo;s Institutional Review Board. Informed consent was waived by the ethics committees as all data was anonymous and the study posed minimal risk to patients.\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003eConsent for publication:\u003c/strong\u003e \u003cp\u003eNot applicable.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eFunding:\u003c/h2\u003e \u003cp\u003eNo funding was received for this study.\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eKS and JF conceived of the study idea and methodology. KS wrote the original draft. KS and JF and JI collected the data. JF and JI revised the study. All authors read and approved the final manuscript.\u003c/p\u003e\u003ch2\u003eAcknowledgements:\u003c/h2\u003e \u003cp\u003eNot applicable.\u003c/p\u003e \u003cp\u003eClinical trial number: Not applicable.\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eAll data can be accessed at [https://doi.org/10.6084/m9.figshare.30951170](https:/doi.org/10.6084/m9.figshare.30951170)\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eKuhn JE. Throwing, the Shoulder, and Human Evolution. Am J Orthop (Belle Mead NJ). 2016;45(3):110\u0026ndash;4.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRoach NT, Venkadesan M, Rainbow MJ, Lieberman DE. Elastic energy storage in the shoulder and the evolution of high-speed throwing in Homo. Nature. 2013;498(7455):483\u0026ndash;6.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eArias-Martorell J. 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Shoulder Elb. 2015;7(4):289\u0026ndash;97.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDonnelly JM, Simons DG, Travell. Simons \u0026amp; Simons' myofascial pain and dysfunction: the trigger point manual. Third edition. ed. Philadelphia: Wolters Kluwer Health; 2019. xxvii, 935 pages p.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLarson S. Functional morphology of the shoulder in primates. Postcranial Adaptation Nonhum Primates. 1993:45\u0026ndash;69.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYoung NM. Function, ontogeny and canalization of shape variance in the primate scapula. J Anat. 2006;209(5):623\u0026ndash;36.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePreuschoft H, Hohn B, Scherf H, Schmidt M, Krause C, Witzel U. Functional Analysis of the Primate Shoulder. Int J Primatol. 2010;31(2):301\u0026ndash;20.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eJain NS, Zukotynski B, Barr ML, Cortez A, Benhaim P. The Scratch-Collapse Test: A Systematic Review and Statistical Analysis. Hand (N Y). 2024;19(7):1054\u0026ndash;61.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGabriel DC, Demetri L, Zhang D. The Role of Confirmatory Testing in Carpal Tunnel Syndrome: Electrodiagnostic Study, Ultrasound and CTS-6. J Hand Surg Asian Pac Vol. 2025;30(1):3\u0026ndash;9.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMuhrer JC. The importance of the history and physical in diagnosis. Nurse Pract. 2014;39(4):30\u0026ndash;5. quiz 6.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNatt B, Szerlip HM. The lost art of the history and physical. Am J Med Sci. 2014;348(5):423\u0026ndash;5.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCampbell R, Ju A, King MT, Rutherford C. Perceived benefits and limitations of using patient-reported outcome measures in clinical practice with individual patients: a systematic review of qualitative studies. Qual Life Res. 2022;31(6):1597\u0026ndash;620.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZini MLL, Banfi G. A Narrative Literature Review of Bias in Collecting Patient Reported Outcomes Measures (PROMs). Int J Environ Res Public Health. 2021;18:23.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"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":"pectoralis minor, scapular dyskinesis, subacromial impingement, thoracic outlet, chronic pain","lastPublishedDoi":"10.21203/rs.3.rs-8888856/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8888856/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eBackground\u003c/h2\u003e \u003cp\u003eThe human shoulder is distinguished by unparalleled motion but also chronic pain. This includes syndromes such as subacromial pain (SAPS), scapular dyskinesis (SD), occupational shoulder disorder (OSD), \u0026amp; thoracic outlet (TOS). Proposed pathophysiology and conventional treatments for these remain unsatisfactory. The upper trunk of the brachial plexus controls the muscles which mediate scapulothoracic glide, except for the ventral pectoralis minor (PM) which is controlled by the lower trunk that controls the hand. This neurologic asymmetry can produce persistent protraction of the scapula. Protraction is the default position in quadrupeds, but in bipeds deforms the scapula\u0026rsquo;s many connections, generating headaches/neck stiffness, upper back tightness, shoulder weakness, and hand numbness. We hypothesize the root cause of chronic shoulder pain is the PM pulling the scapula into protraction and report the outcomes of PM tenotomy with infraclavicular brachial plexus neurolysis (PM\u0026thinsp;+\u0026thinsp;ICN) for patients with the above disorders.\u003c/p\u003e\u003ch2\u003eMethods\u003c/h2\u003e \u003cp\u003ePatients with a referring diagnosis of SAPS, SD, TOS, and/or OSD, who exhibited scapular protraction with medial coracoid tenderness on exam, were treated with PM\u0026thinsp;+\u0026thinsp;ICN. Scapular dyskinesis was classified as none (no protraction), dynamic (protraction while reaching overhead but none at rest), static (protraction at rest). Neuropathy was diagnosed via the scratch-collapse test. Patients underwent PM\u0026thinsp;+\u0026thinsp;ICN, with secondary neurolysis at 3 months for residual pain or weakness. Outcomes included self-reported pain, shoulder abduction range-of-motion (ROM), and need for secondary neurolysis.\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e \u003cp\u003e \u003cem\u003eN\u003c/em\u003e\u0026thinsp;=\u0026thinsp;283 patients were included: 240 SAPS, 13 SD, 151 TOS, 47 OSD. Average age was 51. At one-year, scapular dyskinesis normalized from 99% static to 94% none, average pain decreased from 7.4 to 2.1, and average shoulder abduction range-of-motion increased from 97 to 171 degrees. (All \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.01). 18% required secondary neurolysis, most commonly of the ulnar (11%), radial (10%), and axillary (9%) nerves.\u003c/p\u003e\u003ch2\u003eConclusions\u003c/h2\u003e \u003cp\u003eThe human shoulder girdle delivers unparalleled motion but suffers from chronic pain because the scapula is prone to revert to its ancestral quadrupedal state of protraction, due to the PM\u0026rsquo;s unique lower trunk innervation. Certain patients suffering from chronic shoulder pain refractory to other treatments may benefit substantially from PM\u0026thinsp;+\u0026thinsp;ICN with infrequent secondary neurolysis.\u003c/p\u003e","manuscriptTitle":"The Pectoralis Minor Reverting the Scapula to its Quadrupedal State of Protraction Causes Chronic Shoulder Pain in Humans","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-05-07 16:52:02","doi":"10.21203/rs.3.rs-8888856/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":"6212a9bb-520c-454f-9af9-6b4c827c3627","owner":[],"postedDate":"May 7th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2026-05-07T16:52:02+00:00","versionOfRecord":[],"versionCreatedAt":"2026-05-07 16:52:02","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8888856","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8888856","identity":"rs-8888856","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}