Static shoulder anatomy
Shoulder instability is defined as the abnormal motion of the humeral head in relation to the glenoid, that is accompanied by pain and discomfort. Normal stability is due to a balance of active musculature and static shoulder constraints. Static stabilizers include the labrum, glenohumeral (GH) ligaments, capsule and rotator interval, whereas dynamic constraints include the rotator cuff and scapular musculature. Considering these things, the authors undertook the present review to consolidate the current literature on shoulder anatomy and anatomical variation as it relates to instability.
The glenoid labrum is a fibrocartilaginous structure that doubles the depth and increases the surface area of the glenoid, as well as serves as an attachment point for the GH ligaments. The inferior portion of the labrum attaches firmly to the glenoid while the superior portion makes a loose mobile attachment. 1.5-6% individuals were also found to have a “Buford complex”, a variation where the superior labrum was absent and was replaced by a cord-like middle glenohumeral ligament (MGHL).
The superior glenohumeral ligament (SGHL) originates on the supraglenoid tubercle and inserts on the proximal tip of the lesser tuberosity. Comprised of two portions, direct and oblique, the ligament is responsible for anterior and inferior stabilization in adduction.
The MGHL originates on the labrum and inserts into the subscapularis tendon 2 cm medial to its insertion. Found in only 63-85% of instances the MGHL is taut in 45 degrees abduction, 10 degrees extension and external rotation.
The inferior glenohumeral ligament (IGHL) is a hammock-like structure that extends from the anteroinferior to posteroinferior portions of the glenoid. The anterior portion of the IGHL originates solely on the glenoid neck in 20% of cases and the glenoid neck and labrum in 80% of cases. The ligament attaches in a V-shape close to the cartilaginous rim of the humeral head. The posterior portion of the IGHL is less robust then the anterior portion and prevents dislocation during excessive flexion and internal rotation.
The rotator interval (RI) is a triangular space located in the anterosuperior portion of the glenohumeral space comprised of the coracohumeral ligament, SGHL and the joint capsule. Preliminary studies indicate that the RI has a significant impact on preventing anterior, posterior and inferior humeral head translation.
Knowledge of the anatomy and variation within the shoulder joint is essential for guiding the clinician in cases of instability and surgical revision.
> From: Itoigawa et al., Knee Surgs Sports Traumatol Arthrosc 24 (2016) 343-349(Epub ahead of print). All rights reserved to European Society of Sports Trauma. Click here for the Pubmed summary.