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Shoulder Capsule / Rotator Interval Capsule

- Rotator Interval Capsule:
    - rotator interval is a triangular portion of shoulder capsule which lies between the supraspinatus and subscapularis tendons;
    - capsular anatomy: (Static Stabilizers / Capsule of the Shoulder)
          - interval capsule is reinforced by the superior glenohumeral and coracohumeral ligaments; 
          - references:
                  - Capsular ligaments of the shoulder. Anatomical and functional study of the anterior superior capsule
                  - Capsular restraints to anterior-posterior motion of the abducted shoulder: a biomechanical study. 
                  - The Vascular Anatomy of the Glenohumeral Capsule and Ligaments: An Anatomic Study.
                  - Static capsuloligamentous restraints to superior-inferior translation of the glenohumeral joint.
                  - The role of the rotator interval capsule in passive motion and stability of the shoulder.
          - 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;
                  - reference:
                       - Tensile properties of the superior glenohumeral and coracohumeral ligaments.
          - coacohumeral ligament:
                  - arises as an extraarticular ligament on the lateral surface of coracoid and inserts into the greater and lesser tuberosities, spanning 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.  
                       - Tensile properties of the superior glenohumeral and coracohumeral ligaments.
    - acts to limit flexion and external rotation;
    - tears of the rotator interval capsule:
          - may mimic rotator cuff tears;
          - impingment signs may be present along w/ biceps tendon tenderness;
          - may allow extravasation of dye into subacromial space, as well as the subscapularis fossa (w/ dye seen anterior to the subscapularis);
                 - leakage into the subscapularis fossa may require shoulder movement;
          - Harryman, et al, the authors report that sectioning of the rotator interval capsule allowed 50% posterior translation and 100% inferior translation;
    - management:
          - in cadaver experiments, imbrication of interval capsule helped to eliminate posterior and inferior instability;
          - if superior capsular structures are shortened w/o addressing the redundancy of the inferior capsule, may tend to push the humeral head inferiorly;
    - references: 
          - The role of the rotator interval capsule in passive motion and stability of the shoulder.  
          - The anatomy and histology of the rotator interval capsule of the shoulder. 

- Surgical Closure of the Rotator Interval:
        - Isolated closure of rotator interval defects for shoulder instability. 
        - Rotator interval lesion
        - Arthroscopic treatment of anterior-inferior glenohumeral instability. Two to five-year follow-up. 
        - Thermal versus suture treatment of symptomatic capsular laxity. 
        - Arthroscopic rotator interval repair in glenohumeral instability: description of an operative technique. 
        - The addition of rotator interval closure after arthroscopic repair of either anterior or posterior shoulder instability: effect on glenohumeral translation and range of motion. 
        - Arthroscopic rotator interval closure: effect of sutures on glenohumeral motion and anterior-posterior translation.
        - Arthroscopic rotator interval closure in shoulder instability repair: A retrospective study

        - effects on multidirectional instability: 
                 - Biomechanical analysis comparing a traditional superior-inferior arthroscopic rotator interval closure with a novel medial-lateral technique in a cadaveric multidirectional instability model.
                 - Effects of Capsular Plication and Rotator Interval Closure in Simulated Multidirectional Shoulder Instability
                 - The effects of thermal capsulorrhaphy and rotator interval closure on multidirectional laxity in the glenohumeral joint: a cadaveric biomechanical study. 

        - effects of rotator interval on posterior capsule:
                 - Letter to the Editor: The Use of Rotator Interval Closure in the Arthroscopic Treatment of Posterior Shoulder Instability

 Arthroscopic Rotator Interval Closure by Purse String Suture for Symptomatic Inferior Shoulder Instability