Glenohumeral bone loss and anterior instability
The management of bone loss associated with anterior shoulder instability remains a challenge. (1) Contemporary goals for treatment include stable reduction, prevention of redislocation, restoration of motion and strength, and an early return to functional activities. Current reconstructive procedures address restoration of the functional integrity of the anterior capsulolabral complex as well as bone defects of the humeral head or glenoid that contribute to instability.
Functional Anatomy Static Stabilizers (Table 1)
The shallow ball-and-socket glenohumeral articulation is deepened by increased glenoid articular cartilage thickness at its periphery (2) and the glenoid labrum. (3) Variations combinations of proximal humeral retrotorsion and glenoid version exist within the normal range; combined with synchronous scapulothoracic and glenohumeral motion, they allow for articular contact throughout the entire range of normal shoulder motion. (3) Abnormalities of the normal articular anatomy, such as humeral head or glenoid bone loss or labral disruption, may therefore contribute to shoulder instability.
The glenohumeral ligaments are collagenous band-like structures that reinforce the thin capsular tissue. During glenohumeral motion, the glenohumeral ligaments promote stability by reciprocal tensioning and may also provide proprioceptive proprioceptive feedback to modulate rotator cuff contraction. (4-6) In the relaxed, dependent arm, an intact shoulder capsule is essential for the maintenance of negative glenohumeral intra-articular pressure, and hence articular opposition. Capsuloligamentous disruption may occur as an acute event, such as with a labral detachment (Bankart lesion), at the time of anterior shoulder dislocation or with repetitive injury and plastic deformation of the ligaments. (7)
Dynamic Stabilizers (Table 1)
The long head of the biceps brachii is an important dynamic stabilizer to superior and anterior translation of the humeral head. Disruption of the biceps origin is often observed in association with shoulder instability. (8,9)
The rotator cuff (supraspinatus, infraspinatus, teres minor, subscapularis muscles) surrounds the glenohumeral articulation and its capsule. It contributes to dynamic stability by concavity-compression (in which rotator cuff contraction confers a centering effect on the humeral head within the glenoid concavity) and by the steering effect (in which coordinated contraction of the rotator cuff tends to "steer" the humeral head into the glenoid with shoulder motion). (10,11) Injury to the rotator cuff may occur as a result of acute trauma or chronic repetitive wear.
Bone Loss and Anterior Shoulder Instability
Hill-Sachs lesions most commonly occur in the patient with recurrent shoulder dislocation but may also occur with an initial dislocation. Anterior shoulder dislocations are much more common than posterior dislocations. (12,13) During an anterior dislocation, the posterolateral aspect of the humeral head contacts the anteroinferior rim of the glenoid, often resulting in a classic Hill-Sach defect. (13,14) This defect has been observed in up to 80% of patients with initial anterior dislocation and in 100% of patients with recurrent anterior instability. (14,15)
An engaging Hill-Sachs lesion occurs when the long axis of the impression defect is parallel to the anteroinferior glenoid, allowing the glenoid rim to "fall into" the defect. An engaging Hill-Sachs lesion imposes a restriction to full, stable glenohumeral motion. (16) A nonengaging...