The primary research question is to determine whether patients who undergo a stabilization of the shoulder using a novel decision-making algorithm (ISIS Score) have improved disease-specific quality of life at 1 year post-operatively, as measured by the Western Ontario Instability Index (WOSI) compared with patients who undergo stabilization using a conventional decision-making algorithm. Secondary outcomes include the American Shoulder and Elbow Surgeon's (ASES) score, and difference in recurrence rates of dislocation between the two decision-making algorithms.

The bony architecture of the glenohumeral joint is often likened to that of a golf ball and tee. This geometry provides a functional benefit by allowing for a large arc of motion, but also confers an inherent instability that can result in traumatic anterior shoulder dislocation. By far the most common type of glenohumeral instability is anterior dislocation, accounting for over 90% of all shoulder dislocations. The glenohumeral joint relies on a complex network of static and dynamic structures that aid in stabilizing the joint. Compromise of these structures leads to dislocation and often, recurrent instability. Structures providing static stability to the glenohumeral joint include the congruency of the humeral head and glenoid, the glenoid labrum, glenohumeral ligaments surrounding the joint, and negative intra-articular pressure. Dynamic stabilizers are primarily muscular and include the rotator cuff, which provides a compressive stabilizing effect, the tendon of the long head of the biceps, and muscles that stabilize the scapula.

The current accepted "standard" protocol depends on the amount of glenoid bone loss. Typically, when there is little bone loss, the treatment of anterior recurrent instability involves Bankart arthroscopic stabilization. In the setting of significant glenoid bone loss (>25%), the Latarjet technique involving bone grafting of the glenoid defect is indicated in order to address the aforementioned higher risk of recurrence in this setting.

Balg and Boileau proposed a comprehensive score in 2007 including: age at surgery, degree of sport participation (pre-operative), type of sport (pre-operative), shoulder hyperlaxity, Hill-Sachs on AP radiograph and glenoid loss of contour on AP radiograph at the first consultation: the Instability Severity Index Score (ISIS). In contrast to the standard treatment protocol, the authors propose that an ISIS ≦3 points is an indication for arthroscopic Bankart repair, and a score of greater than 3 is an indication for a Latarjet procedure (open stabilization with coracoid bone graft).

This study would be the first to investigate the ISIS decision-making algorithm, an exciting and novel approach to the treatment of shoulder instability, and to compare it to the conventional treatment algorithm within the framework of a prospective, randomized controlled study. If the new ISIS decision-making algorithm proves to be effective at decreasing recurrence instability rates, improving function and quality of life, while maintaining low complication rates, it has the potential to lead to widespread practice change within the Orthopaedic community in North America and abroad.

Inclusion Criteria:

1. Recurrent anterior instability (dislocation or subluxation) with or without hyperlaxity, including a clinical history of traumatic anterior instability of the shoulder, with positive apprehension or relocation tests.
2. Provide consent

Exclusion Criteria:

1. Patients with a concomitant rotator cuff lesion or humeral avulsion of the anteroinferior glenohumeral ligament (HAGL)
2. An acute first-time dislocation
3. Previous shoulder surgery
4. Surgery for a painful, unstable shoulder without true dislocation or subluxation
5. Patients with active worker's compensation claims (due to the expectation of lower rates of success in this patient population)
6. Active joint or systemic infection
7. Patients with convulsive disorders, collagen diseases, previous shoulder surgeries, and any other conditions that might affect the mobility of the joint
8. Major medical illness (life expectancy less than 2 years or unacceptably high operative risk)
9. Unable to speak or read English/French
10. Inability to provide informed consent and comply with requirements of participation
11. Unwilling to be followed for 2 years