Traumatic Anterior Shoulder Instability: The US Military Experience

Take-Home Points

• Arthroscopic stabilization performed early results in better outcomes in patients with Bankart lesions.
• A subcritical level of bone loss of 13.5% has been shown to have a significant effect on outcomes, in addition to the established “critical amount”.
• Bone loss is a bipolar issue. Both sides must be considered in order to properly address shoulder instability.
• Off-track measurement has been shown to be even more positively predictive of outcomes than glenoid bone loss assessment.

• There are several bone loss management options including, the most common coracoid transfer, as well as distal tibial allograft and distal clavicular autograft.

Given its relatively young age, high activity level, and centralized medical care system, the US military population is ideal for studying traumatic anterior shoulder instability. There is a long history of military surgeons who have made significant contributions that have advanced our understanding of this pathology and its treatment and results. In this article, we describe the scope, treatment, and results of this pathology in the US military population.

Incidence and Pathology

At the United States Military Academy (USMA), Owens and colleagues¹ studied the incidence of shoulder instability, including dislocation and subluxation, and found anterior instability events were far more common than in civilian populations. The incidence of shoulder instability was 0.08 per 1000 person-years in the general US population vs 1.69 per 1000 person-years in US military personnel. The factors associated with increased risk of shoulder instability injury in the military population were male sex, white race, junior enlisted rank, and age under 30 years. Owens and colleagues² noted that subluxation accounted for almost 85% of the total anterior instability events. Owens and colleagues³ found the pathology in subluxation events was similar to that in full dislocations, with a soft-tissue anterior Bankart lesion and a Hill-Sachs lesion detected on magnetic resonance imaging in more than 90% of patients. In another study at the USMA, DeBerardino and colleagues⁴ noted that 97% of arthroscopically assessed shoulders in first-time dislocators involved complete detachment of the capsuloligamentous complex from the anterior glenoid rim and neck—a so-called Bankart lesion. Thus, in a military population, anterior instability resulting from subluxation or dislocation is a common finding that is often represented by a soft-tissue Bankart lesion and a Hill-Sachs defect.

Natural History of Traumatic Anterior Shoulder Instability in the Military

Several studies have evaluated the outcomes of nonoperative and operative treatment of shoulder instability. Although most have found better outcomes with operative intervention, Aronen and Regan⁵ reported good results (25% recurrence at nearly 3-year follow-up) with nonoperative treatment and adherence to a strict rehabilitation program. Most other comparative studies in this population have published contrary results. Wheeler and colleagues⁶ studied the natural history of anterior shoulder dislocations in a USMA cadet cohort and found recurrent instability after shoulder dislocation in 92% of cadets who had nonoperative treatment. Similarly, DeBerardino and colleagues⁴ found that, in the USMA, 90% of first-time traumatic anterior shoulder dislocations managed nonoperatively experienced recurrent instability. In a series of Army soldiers with shoulder instability, Bottoni and colleagues⁷ reported that 75% of nonoperatively managed patients had recurrent instability, and, of these, 67% progressed to surgical intervention. Nonoperative treatment for a first-time dislocation is still reasonable if a cadet or soldier needs to quickly return to functional duties. Athletes who develop shoulder instability during their playing season have been studied in a military population as well. In a multicenter study of service academy athletes with anterior instability, Dickens and colleagues⁸ found that, with conservative management and accelerated rehabilitation of in-season shoulder instability, 73% of athletes returned to sport by a mean of 5 days. However, the durability of this treatment should be questioned, as 64% later experienced recurrence.

Arthroscopic Stabilization of Acute Anterior Shoulder Dislocations

In an early series of cases of traumatic anterior shoulder instability in USMA cadets, Wheeler and colleagues⁶ found that, at 14 months, 78% of arthroscopically stabilized cases and 92% of nonoperatively treated cases were successful. Then, in the 1990s, DeBerardino and colleagues⁴ studied a series of young, active patients in the USMA and noted significantly better results with arthroscopic treatment, vs nonoperative treatment, at 2- to 5-year follow-up. Of the arthroscopically treated shoulders, 88% remained stable during the study and returned to preinjury activity levels, and 12% experienced recurrent instability (risk factors included 2+ sulcus sign, poor capsular labral tissue, and history of bilateral shoulder instability). In a long-term follow-up (mean, 11.7 years; range, 9.1-13.9 years) of the same cohort, Owens and colleagues⁹ found that 14% of patients available for follow-up had undergone revision stabilization surgery, and, of these, 21% reported experiencing subluxation events. The authors concluded that, in first-time dislocators in this active military population, acute arthroscopic Bankart repair resulted in excellent return to athletics and subjective function, and had acceptable recurrence and reoperation rates. Bottoni and colleagues,⁷ in a prospective, randomized evaluation of arthroscopic stabilization of acute, traumatic, first-time shoulder dislocations in the Army, noted an 89% success rate for arthroscopic treatment at an average follow-up of 36 months, with no recurrent instability. DeBerardino and colleagues¹⁰ compared West Point patients treated nonoperatively with those arthroscopically treated with staples, transglenoid sutures, or bioabsorbable anchors. Recurrence rates were 85% for nonoperative treatment, 22% for staples, 14% for transglenoid sutures, and 10% for bioabsorbable anchors.

Arthroscopic Versus Open Stabilization of Anterior Shoulder Instability

In a prospective, randomized clinical trial comparing open and arthroscopic shoulder stabilization for recurrent anterior instability in active-duty Army personnel, Bottoni and colleagues¹¹ found comparable clinical outcomes. Stabilization surgery failed clinically in only 3 cases, 2 open and 1 arthroscopic. The authors concluded that arthroscopic stabilization can be safely performed for recurrent shoulder instability and that arthroscopic outcomes are similar to open outcomes. In a series of anterior shoulder subluxations in young athletes with Bankart lesions, Owens and colleagues¹² found that open and arthroscopic stabilization performed early resulted in better outcomes, regardless of technique used. Recurrent subluxation occurred at a mean of 17 months in 3 of the 10 patients in the open group and 3 of the 9 patients in the arthroscopic group, for an overall recurrence rate of 31%. The authors concluded that, in this patient population with Bankart lesions caused by anterior subluxation events, surgery should be performed early.

Bone Lesions

Burkhart and De Beer¹³ first noted that bone loss has emerged as one of the most important considerations in the setting of shoulder instability in active patients. Other authors have found this to be true in military populations.^14,15

The diagnosis of bone loss may include historical findings, such as increased number and ease of dislocations, as well as dislocation in lower positions of abduction. Physical examination findings may include apprehension in the midrange of motion. Advanced imaging, such as magnetic resonance arthrography, has since been validated as equivalent to 3-dimensional computed tomography (3-D CT) in determining glenoid bone loss.¹⁶ In 2007, Mologne and colleagues¹⁵ studied the amount of glenoid bone loss and the presence of fragmented bone or attritional bone loss and its effect on outcomes. They evaluated 21 patients who had arthroscopic treatment for anterior instability with anteroinferior glenoid bone loss between 20% and 30%. Average follow-up was 34 months. All patients received 3 or 4 anterior anchors. No patient with a bone fragment incorporated into the repair experienced recurrence or subluxation, whereas 30% of patients with attritional bone loss had recurrent instability.¹⁵