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Shoulder Capsule / Static Stabilizers of Shoulder

- Discussion:
    - w/ in joint capsule, variable ligs (superior, middle, & IGHL), are primary components of static restraint in glenohumeral joint.
    - glenoid version:
            - Biomechanical Evaluation of Glenoid Version and Dislocation Direction on the Influence of Anterior Shoulder Instability and
                      Development of Hill-Sachs Lesions

- Scapulohumeral Ligaments: (5 scapulohumeral ligaments):
    - rotator interval capsule:
           - superior glenohumeral ligaments:
                  - has two sites of origin: supraglenoid tubercle - just anterior to long head of biceps origin on superior labrum and the base
                            of coracoid;
                  - arthroscopically it may be hidden by the biceps tendon;
                  - inserts on proximal aspect of lesser tuberosity;
                  - at 0 deg abduction, superior & MGHL develops most strain, and together w/ the coracohumeral ligament stabilize the
                            shoulder in adduction;
                  - it helps to prevent posterior and inferior instability;
           - coacohumeral ligament:
                  - an extraarticular ligament on the lateral surface of coracoid and inserts into the greater and lesser tuberosities, spanning the
                            bicipital groove;
                  - sectioning of coracohumeral ligaments produces anteroinferior instability;
                  - represents folded thickening of glenohumeral capsule in area of rotator interval between subscapularis & supraspinatus;
                  - w/ body upright & arm in dependent position, coracohumeral & MGHL play important roles in resisting inf translation.
                  - references:
                        - The structure and function of the coracohumeral ligament: An anatomic and microscopic study.  
                        - An anatomic and histologic study of the coracohumeral ligament.
                        - Arthroscopic release of the rotator interval and coracohumeral ligament: an anatomic study in cadavers.
                        - Subscapularis, medial, and lateral head coracohumeral ligament insertion anatomy. Arthroscopic appearance and incidence of "hidden" rotator interval lesions.

    - middle glenohumeral ligaments:
           - arises from the anatomic neck and inserts into the mid-anterior labrum;
           - middle part of the ligament is seen just posterior to subscapularis;
           - may be poorly defined in upto 30% of patients;
           - when a Buford complex is present (physiologic antero-superior sublabral hole), the middle ligament may appear cord-like and
                  will often be frayed;
                  - attempts to close down this sub-labral hole w/ a absorable tack anchor may precipitate frozen shoulder;
           - middle glenohumeral ligament limits external rotation at 45 deg of abduction;
           - w/ body upright & arm in dependent position, coracohumeral & MGHL play important roles in resisting inf translation;
           - reference:
                  The Buford complex--the "cord-like" middle glenohumeral ligament and absent anterosuperior labrum complex: a normal anatomic capsulolabral variant.

           - midrange stability:
concavity compression: muscular compression of the humeral head into the glenoid fossa stabilizes the glenohumeral
                                     joint against shear forces.
                        - depends on the depth of the concavity and the magnitude of the compressive force. 
                        - references:
                               - Dynamic glenohumeral stability provided by the rotator cuff muscles in the mid-range and end-range of motion. A study in cadavera
                               - Mechanics of glenohumeral instability.
    - antero-inferior glenohumeral ligament

- Posterior Capsule:
    - antero-inferior glenohumeral ligament
    - posteriosuperior quad of capsule is devoid of ligamentous condensations;
    - posterior capsule and the teres minor restrain internal rotation;
    - posteroinferior capsule provides primary restraint to post dislocation;
    - post-sup capsule & sup GHL provides 2ndry restraint to post dislocation

Stabilizing mechanisms preventing anterior dislocation of the glenohumeral joint.

Capsular ligaments of the shoulder. Anatomical and functional study of the anterior superior capsule.

Year Book: Anterior Capsulolabral Reconstruction of the Shoulder in Athletes in Overhand Sports.

Capsular restraints to anterior-posterior motion of the abducted shoulder: A biomechanical study

The structure and function of the coracohumeral ligament: An anatomic and microscopic study

The Vascular Anatomy of the Glenohumeral Capsule and Ligaments: An Anatomic Study.

Comparison of Glenohumeral Mechanics Following a Capsular Shift and Anterior Tightening

Combined Posterior Bankart Lesion and Posterior Humeral Avulsion of the Glenohumeral Ligaments Associated With Recurrent Posterior Shoulder Instability. 

Experiments on the tensile strength of the anterior capsular structures of the shoulder joint in man

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