Anterior Glenohumeral Instability: Evaluation and Decision-Making

Introduction

Anterior instability represents over 70% of glenohumeral instability with a yearly incidence approaching 3% in high-risk populations. ^, Males sustain 70%–80% of instability episodes with subluxations being more common than frank dislocations. ^, About half (47%) of all dislocations occur in individuals between 15 and 29 years of age. A fall represents the most common cause (59%) of a dislocation with half (48%) occurring during sport or recreation.

Recurrent instability has short- and long-term consequences for the patient. In addition to immediate symptoms, recurrent instability results in an increased risk of glenoid and humeral bone loss as well as an increased risk of long-term arthropathy. Within anterior instability, there is growing evidence that surgical management yields better clinical results, but a thorough evaluation of the patient must be coupled with an understanding of individual goals to come to a shared decision for management of each patient.

Pathophysiology

A clear understanding of anatomy and, especially, the patient’s specific pathology are crucial to appropriate treatment of anterior instability. The limited bony stability of the glenohumeral joint allows significant motion which relies heavily on soft tissue stability. The dynamic stability provided by the concavity compression of the rotator cuff is the most important aspect, but critical stabilization is also provided by the passive effects of the capsuloligamentous complex, glenoid labrum, and the suction effect of negative intra-articular pressure. ^,

The pathology of anterior instability can vary based on a variety of factors. Anteroinferior labral tears (66%) and Hill-Sachs lesions (41%) represented the most common pathology seen on preoperative magnetic resonance images (MRIs) in patients who ultimately underwent surgery in the MOON (The Multicenter Orthopaedic Outcomes Network) cohort of 863 patients, though arthroscopic evaluation in a separate study found 97% of first-time dislocators suffered an anteroinferior labral tear. The typical Bankart lesion involves avulsion of the anteroinferior glenohumeral ligament-labral complex with or without bony avulsion.

The anteroinferior glenohumeral ligament represents the primary restraint to anterior translation of the humerus with the arm abducted and externally rotated, the common “apprehension” position ( Fig. 19.1 ). Humeral avulsion of the glenohumeral ligament (HAGL) is found in 9% of shoulders that require surgery for instability and can be found in the absence of other glenolabral pathology. Additionally, glenoid avulsion of the glenohumeral ligament (GAGL), where the ligament is disrupted from the glenoid separate from injury to the labrum, has also been reported as a cause of recurrent instability.

Bony pathology has a significant impact on the success of treatment for instability. As with Hill-Sachs lesions, glenoid bone loss affects about 40% of first-time dislocators. Recurrent dislocators are twice as likely to have glenoid bone loss and the number of dislocations had a moderate correlation ( r =.56) with the severity of glenoid bone loss in one computed tomography (CT) study of 218 patients.

Patient Evaluation

Careful evaluation of the patient should begin with a detailed history and should focus on causes of instability and risk factors for recurrence. The mechanism of dislocation and the amount of trauma required are important clues to differentiate volitional dislocators and patients with hyperlaxity/multidirectional instability—two typically nonoperative pathologies that are very distinct from traumatic glenohumeral dislocation. Additionally, previous treatment should be discussed and notes (and images, if available) should be obtained from any previous surgical procedures, if applicable. Ultimately, a clear understanding of the patient’s overall functional goals and other applicable details must be discussed to allow shared decision-making with regard to treatment. Of particular importance are details regarding sports participation including timing within season, position of play, and future plans for sports participation.

Physical Examination

A standard shoulder examination should be performed, evaluating overall range of motion and strength in addition to a neurovascular examination with a focus on the axillary nerve. Laxity should be evaluated via shoulder-specific tests such as the sulcus sign and Gagey hyperabduction sign while the Beighton Score can be used to document generalized joint laxity ( Table 19.1 ). ^, Persistent pain or weakness after an instability event should prompt careful evaluation for rotator cuff injury as well, a more common finding in contact athletes and patients over 40.

TABLE 19.1

Beighton Score

Adapted from Whitehead NA, Mohammed KD, Fulcher ML. Does the Beighton score correlate with specific measures of shoulder joint laxity? Orthop J Sports Med . 2018;6:232596711877063.

Joint Evaluation	Unilateral		Bilateral
At least 10 degrees of elbow hyperextension	1		2
Ability to oppose the thumb and forearm	1		2
At least 90 degrees of little finger hyperextension	1		2
At least 10 degrees of knee hyperextension	1		2
Ability to place palms flat on the floor with knees extended		1

Points are given for unilateral or bilateral findings and the composite score calculated.

Scores >4 are considered positive for generalized joint laxity.

Several tests have been described to specifically evaluate for anterior instability. Apprehension and relocation have specificity of 96% and 92% when apprehension (not pain) and relief were used as criteria for a positive test ( Fig. 19.2 ). A positive apprehension test has also been shown to identify patients at a higher risk of recurrence after an initial instability event. The test should be performed at varying levels of abduction as apprehension at lower levels of abduction may indicate higher degrees of bone loss.