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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
Classifying Bone Loss and Recognizing Its Effects
Burkhart and De Beer13 helped define the role and significance of bone loss in the setting of shoulder instability. They defined significant bone loss as an engaging Hill-Sachs lesion of the humerus in an abducted and externally rotated position or an “inverted pear” lesion of the glenoid. Overall analysis revealed recurrence in 4% of cases without significant bone loss and 65% of cases with significant bone loss. In a subanalysis of contact-sport athletes in the setting of bone loss, the failure rate increased to 89%, from 6.5%. Aiding in the quantitative assessment of glenoid bone loss, Itoi and colleagues17 showed that 21% glenoid bone loss resulted in instability that would not be corrected by a soft-tissue procedure alone. Bone loss of 20% to 25% has since been considered a “critical amount,” above which an arthroscopic Bankart has been questioned. More recently, several authors have shown that even less bone loss can have a significant effect on outcomes. Shaha and colleagues18 established that a subcritical level of bone loss (13.5%) on the anteroinferior glenoid resulted in clinical failure (as determined with the Western Ontario Shoulder Instability Index) even in cases in which frank recurrence or subluxation was avoided. It is thought that, in recurrent instability, glenoid bone loss incident rate is as high as 90%, and the corresponding percentage of patients with Hill-Sachs lesions is almost 100%.19,20 Thus, it is increasingly understood that bone loss is a bipolar issue and that both sides must be considered in order to properly address shoulder instability in this setting. In 2007, Yamamoto and colleagues21 introduced the glenoid track, a method for predicting whether a Hill-Sachs lesion will engage. Di Giacomo and colleagues22 refined the track concept to quantitatively determine which lesions will engage in the setting of both glenoid and humeral bone loss. Metzger and colleagues,23 confirming the track concept arthroscopically, found that manipulation with anesthesia and arthroscopic visualization was well predicted by preoperative track measurements, and thus these measurements can be a good guide for surgical management (Figures 1A, 1B). 
Strategies for Addressing Bone Loss in Anterior Shoulder Instability
Several approaches for managing bone loss in shoulder instability have been described—the most common being coracoid transfer (Latarjet procedure). Waterman and colleagues25 recently studied the effects of coracoid transfer, distal tibial allograft, and iliac crest augmentation on anterior shoulder instability in US military patients treated between 2006 and 2012. Of 64 patients who underwent a bone block procedure, 16 (25%) had a complication during short-term follow-up. Complications included neurologic injury, pain, infection, hardware failure, and recurrent instability. 
Conclusion
Traumatic anterior shoulder instability is a common pathology that continues to significantly challenge the readiness of the US military. Military surgeon-researchers have a long history of investigating approaches to the treatment of this pathology—applying good science to a large controlled population, using a single medical record, and demonstrating a commitment to return service members to the ready defense of the nation.
Am J Orthop. 2017;46(4):184-189. Copyright Frontline Medical Communications Inc. 2017. All rights reserved.
1. Owens BD, Dawson L, Burks R, Cameron KL. Incidence of shoulder dislocation in the United States military: demographic considerations from a high-risk population. J Bone Joint Surg Am. 2009;91(4):791-796.
2. Owens BD, Duffey ML, Nelson BJ, DeBerardino TM, Taylor DC, Mountcastle SB. The incidence and characteristics of shoulder instability at the United States Military Academy. Am J Sports Med. 2007;35(7):1168-1173.
3. Owens BD, Nelson BJ, Duffey ML, et al. Pathoanatomy of first-time, traumatic, anterior glenohumeral subluxation events. J Bone Joint Surg Am. 2010;92(7):1605-1611.
4. DeBerardino TM, Arciero RA, Taylor DC, Uhorchak JM. Prospective evaluation of arthroscopic stabilization of acute, initial anterior shoulder dislocations in young athletes. Two- to five-year follow-up. Am J Sports Med. 2001;29(5):586-592.
5. Aronen JG, Regan K. Decreasing the incidence of recurrence of first time anterior shoulder dislocations with rehabilitation. Am J Sports Med. 1984;12(4):283-291.
6. Wheeler JH, Ryan JB, Arciero RA, Molinari RN. Arthroscopic versus nonoperative treatment of acute shoulder dislocations in young athletes. Arthroscopy. 1989;5(3):213-217.
7. Bottoni CR, Wilckens JH, DeBerardino TM, et al. A prospective, randomized evaluation of arthroscopic stabilization versus nonoperative treatment in patients with acute, traumatic, first-time shoulder dislocations. Am J Sports Med. 2002;30(4):576-580.
8. Dickens JF, Owens BD, Cameron KL, et al. Return to play and recurrent instability after in-season anterior shoulder instability: a prospective multicenter study. Am J Sports Med. 2014;42(12):2842-2850.
9. Owens BD, DeBerardino TM, Nelson BJ, et al. Long-term follow-up of acute arthroscopic Bankart repair for initial anterior shoulder dislocations in young athletes. Am J Sports Med. 2009;37(4):669-673.
10. DeBerardino TM, Arciero RA, Taylor DC. Arthroscopic stabilization of acute initial anterior shoulder dislocation: the West Point experience. J South Orthop Assoc. 1996;5(4):263-271.
11. Bottoni CR, Smith EL, Berkowitz MJ, Towle RB, Moore JH. Arthroscopic versus open shoulder stabilization for recurrent anterior instability: a prospective randomized clinical trial. Am J Sports Med. 2006;34(11):1730-1737.
12. Owens BD, Cameron KL, Peck KY, et al. Arthroscopic versus open stabilization for anterior shoulder subluxations. Orthop J Sports Med. 2015;3(1):2325967115571084.
13. Burkhart SS, De Beer JF. Traumatic glenohumeral bone defects and their relationship to failure of arthroscopic Bankart repairs: significance of the inverted-pear glenoid and the humeral engaging Hill-Sachs lesion. Arthroscopy. 2000;16(7):677-694.14. Shaha JS, Cook JB, Rowles DJ, Bottoni CR, Shaha SH, Tokish JM. Clinical validation of the glenoid track concept in anterior glenohumeral instability. J Bone Joint Surg Am. 2016;98(22):1918-1923.
15. Mologne TS, Provencher MT, Menzel KA, Vachon TA, Dewing CB. Arthroscopic stabilization in patients with an inverted pear glenoid: results in patients with bone loss of the anterior glenoid. Am J Sports Med. 2007;35(8):1276-1283.
16. Markenstein JE, Jaspars KC, van der Hulst VP, Willems WJ. The quantification of glenoid bone loss in anterior shoulder instability; MR-arthro compared to 3D-CT. Skeletal Radiol. 2014;43(4):475-483.
17. Itoi E, Lee SB, Berglund LJ, Berge LL, An KN. The effect of a glenoid defect on anteroinferior stability of the shoulder after Bankart repair: a cadaveric study. J Bone Joint Surg Am. 2000;82(1):35-46.
18. Shaha JS, Cook JB, Song DJ, et al. Redefining “critical” bone loss in shoulder instability: functional outcomes worsen with “subcritical” bone loss. Am J Sports Med. 2015;43(7):1719-1725.
19. Piasecki DP, Verma NN, Romeo AA, Levine WN, Bach BR Jr, Provencher MT. Glenoid bone deficiency in recurrent anterior shoulder instability: diagnosis and management. J Am Acad Orthop Surg. 2009;17(8):482-493.
20. Provencher MT, Frank RM, Leclere LE, et al. The Hill-Sachs lesion: diagnosis, classification, and management. J Am Acad Orthop Surg. 2012;20(4):242-252.
21. Yamamoto N, Itoi E, Abe H, et al. Contact between the glenoid and the humeral head in abduction, external rotation, and horizontal extension: a new concept of glenoid track. J Shoulder Elbow Surg. 2007;16(5):649-656.
22. Di Giacomo G, Itoi E, Burkhart SS. Evolving concept of bipolar bone loss and the Hill-Sachs lesion: from “engaging/non-engaging” lesion to “on-track/off-track” lesion. Arthroscopy. 2014;30(1):90-98.
23. Metzger PD, Barlow B, Leonardelli D, Peace W, Solomon DJ, Provencher MT. Clinical application of the “glenoid track” concept for defining humeral head engagement in anterior shoulder instability: a preliminary report. Orthop J Sports Med. 2013;1(2):2325967113496213.
24. Arciero RA, Parrino A, Bernhardson AS, et al. The effect of a combined glenoid and Hill-Sachs defect on glenohumeral stability: a biomechanical cadaveric study using 3-dimensional modeling of 142 patients. Am J Sports Med. 2015;43(6):1422-1429.
25. Waterman BR, Chandler PJ, Teague E, Provencher MT, Tokish JM, Pallis MP. Short-term outcomes of glenoid bone block augmentation for complex anterior shoulder instability in a high-risk population. Arthroscopy. 2016;32(9):1784-1790.
26. Schroder DT, Provencher MT, Mologne TS, Muldoon MP, Cox JS. The modified Bristow procedure for anterior shoulder instability: 26-year outcomes in Naval Academy midshipmen. Am J Sports Med. 2006;34(5):778-786.
27. Provencher MT, Frank RM, Golijanin P, et al. Distal tibia allograft glenoid reconstruction in recurrent anterior shoulder instability: clinical and radiographic outcomes. Arthroscopy. 2017;33(5):891-897.
28. Tokish JM, Fitzpatrick K, Cook JB, Mallon WJ. Arthroscopic distal clavicular autograft for treating shoulder instability with glenoid bone loss. Arthrosc Tech. 2014;3(4):e475-e481.
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
Classifying Bone Loss and Recognizing Its Effects
Burkhart and De Beer13 helped define the role and significance of bone loss in the setting of shoulder instability. They defined significant bone loss as an engaging Hill-Sachs lesion of the humerus in an abducted and externally rotated position or an “inverted pear” lesion of the glenoid. Overall analysis revealed recurrence in 4% of cases without significant bone loss and 65% of cases with significant bone loss. In a subanalysis of contact-sport athletes in the setting of bone loss, the failure rate increased to 89%, from 6.5%. Aiding in the quantitative assessment of glenoid bone loss, Itoi and colleagues17 showed that 21% glenoid bone loss resulted in instability that would not be corrected by a soft-tissue procedure alone. Bone loss of 20% to 25% has since been considered a “critical amount,” above which an arthroscopic Bankart has been questioned. More recently, several authors have shown that even less bone loss can have a significant effect on outcomes. Shaha and colleagues18 established that a subcritical level of bone loss (13.5%) on the anteroinferior glenoid resulted in clinical failure (as determined with the Western Ontario Shoulder Instability Index) even in cases in which frank recurrence or subluxation was avoided. It is thought that, in recurrent instability, glenoid bone loss incident rate is as high as 90%, and the corresponding percentage of patients with Hill-Sachs lesions is almost 100%.19,20 Thus, it is increasingly understood that bone loss is a bipolar issue and that both sides must be considered in order to properly address shoulder instability in this setting. In 2007, Yamamoto and colleagues21 introduced the glenoid track, a method for predicting whether a Hill-Sachs lesion will engage. Di Giacomo and colleagues22 refined the track concept to quantitatively determine which lesions will engage in the setting of both glenoid and humeral bone loss. Metzger and colleagues,23 confirming the track concept arthroscopically, found that manipulation with anesthesia and arthroscopic visualization was well predicted by preoperative track measurements, and thus these measurements can be a good guide for surgical management (Figures 1A, 1B).
Strategies for Addressing Bone Loss in Anterior Shoulder Instability
Several approaches for managing bone loss in shoulder instability have been described—the most common being coracoid transfer (Latarjet procedure). Waterman and colleagues25 recently studied the effects of coracoid transfer, distal tibial allograft, and iliac crest augmentation on anterior shoulder instability in US military patients treated between 2006 and 2012. Of 64 patients who underwent a bone block procedure, 16 (25%) had a complication during short-term follow-up. Complications included neurologic injury, pain, infection, hardware failure, and recurrent instability.
Conclusion
Traumatic anterior shoulder instability is a common pathology that continues to significantly challenge the readiness of the US military. Military surgeon-researchers have a long history of investigating approaches to the treatment of this pathology—applying good science to a large controlled population, using a single medical record, and demonstrating a commitment to return service members to the ready defense of the nation.
Am J Orthop. 2017;46(4):184-189. Copyright Frontline Medical Communications Inc. 2017. All rights reserved.
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
Classifying Bone Loss and Recognizing Its Effects
Burkhart and De Beer13 helped define the role and significance of bone loss in the setting of shoulder instability. They defined significant bone loss as an engaging Hill-Sachs lesion of the humerus in an abducted and externally rotated position or an “inverted pear” lesion of the glenoid. Overall analysis revealed recurrence in 4% of cases without significant bone loss and 65% of cases with significant bone loss. In a subanalysis of contact-sport athletes in the setting of bone loss, the failure rate increased to 89%, from 6.5%. Aiding in the quantitative assessment of glenoid bone loss, Itoi and colleagues17 showed that 21% glenoid bone loss resulted in instability that would not be corrected by a soft-tissue procedure alone. Bone loss of 20% to 25% has since been considered a “critical amount,” above which an arthroscopic Bankart has been questioned. More recently, several authors have shown that even less bone loss can have a significant effect on outcomes. Shaha and colleagues18 established that a subcritical level of bone loss (13.5%) on the anteroinferior glenoid resulted in clinical failure (as determined with the Western Ontario Shoulder Instability Index) even in cases in which frank recurrence or subluxation was avoided. It is thought that, in recurrent instability, glenoid bone loss incident rate is as high as 90%, and the corresponding percentage of patients with Hill-Sachs lesions is almost 100%.19,20 Thus, it is increasingly understood that bone loss is a bipolar issue and that both sides must be considered in order to properly address shoulder instability in this setting. In 2007, Yamamoto and colleagues21 introduced the glenoid track, a method for predicting whether a Hill-Sachs lesion will engage. Di Giacomo and colleagues22 refined the track concept to quantitatively determine which lesions will engage in the setting of both glenoid and humeral bone loss. Metzger and colleagues,23 confirming the track concept arthroscopically, found that manipulation with anesthesia and arthroscopic visualization was well predicted by preoperative track measurements, and thus these measurements can be a good guide for surgical management (Figures 1A, 1B).
Strategies for Addressing Bone Loss in Anterior Shoulder Instability
Several approaches for managing bone loss in shoulder instability have been described—the most common being coracoid transfer (Latarjet procedure). Waterman and colleagues25 recently studied the effects of coracoid transfer, distal tibial allograft, and iliac crest augmentation on anterior shoulder instability in US military patients treated between 2006 and 2012. Of 64 patients who underwent a bone block procedure, 16 (25%) had a complication during short-term follow-up. Complications included neurologic injury, pain, infection, hardware failure, and recurrent instability.
Conclusion
Traumatic anterior shoulder instability is a common pathology that continues to significantly challenge the readiness of the US military. Military surgeon-researchers have a long history of investigating approaches to the treatment of this pathology—applying good science to a large controlled population, using a single medical record, and demonstrating a commitment to return service members to the ready defense of the nation.
Am J Orthop. 2017;46(4):184-189. Copyright Frontline Medical Communications Inc. 2017. All rights reserved.
1. Owens BD, Dawson L, Burks R, Cameron KL. Incidence of shoulder dislocation in the United States military: demographic considerations from a high-risk population. J Bone Joint Surg Am. 2009;91(4):791-796.
2. Owens BD, Duffey ML, Nelson BJ, DeBerardino TM, Taylor DC, Mountcastle SB. The incidence and characteristics of shoulder instability at the United States Military Academy. Am J Sports Med. 2007;35(7):1168-1173.
3. Owens BD, Nelson BJ, Duffey ML, et al. Pathoanatomy of first-time, traumatic, anterior glenohumeral subluxation events. J Bone Joint Surg Am. 2010;92(7):1605-1611.
4. DeBerardino TM, Arciero RA, Taylor DC, Uhorchak JM. Prospective evaluation of arthroscopic stabilization of acute, initial anterior shoulder dislocations in young athletes. Two- to five-year follow-up. Am J Sports Med. 2001;29(5):586-592.
5. Aronen JG, Regan K. Decreasing the incidence of recurrence of first time anterior shoulder dislocations with rehabilitation. Am J Sports Med. 1984;12(4):283-291.
6. Wheeler JH, Ryan JB, Arciero RA, Molinari RN. Arthroscopic versus nonoperative treatment of acute shoulder dislocations in young athletes. Arthroscopy. 1989;5(3):213-217.
7. Bottoni CR, Wilckens JH, DeBerardino TM, et al. A prospective, randomized evaluation of arthroscopic stabilization versus nonoperative treatment in patients with acute, traumatic, first-time shoulder dislocations. Am J Sports Med. 2002;30(4):576-580.
8. Dickens JF, Owens BD, Cameron KL, et al. Return to play and recurrent instability after in-season anterior shoulder instability: a prospective multicenter study. Am J Sports Med. 2014;42(12):2842-2850.
9. Owens BD, DeBerardino TM, Nelson BJ, et al. Long-term follow-up of acute arthroscopic Bankart repair for initial anterior shoulder dislocations in young athletes. Am J Sports Med. 2009;37(4):669-673.
10. DeBerardino TM, Arciero RA, Taylor DC. Arthroscopic stabilization of acute initial anterior shoulder dislocation: the West Point experience. J South Orthop Assoc. 1996;5(4):263-271.
11. Bottoni CR, Smith EL, Berkowitz MJ, Towle RB, Moore JH. Arthroscopic versus open shoulder stabilization for recurrent anterior instability: a prospective randomized clinical trial. Am J Sports Med. 2006;34(11):1730-1737.
12. Owens BD, Cameron KL, Peck KY, et al. Arthroscopic versus open stabilization for anterior shoulder subluxations. Orthop J Sports Med. 2015;3(1):2325967115571084.
13. Burkhart SS, De Beer JF. Traumatic glenohumeral bone defects and their relationship to failure of arthroscopic Bankart repairs: significance of the inverted-pear glenoid and the humeral engaging Hill-Sachs lesion. Arthroscopy. 2000;16(7):677-694.14. Shaha JS, Cook JB, Rowles DJ, Bottoni CR, Shaha SH, Tokish JM. Clinical validation of the glenoid track concept in anterior glenohumeral instability. J Bone Joint Surg Am. 2016;98(22):1918-1923.
15. Mologne TS, Provencher MT, Menzel KA, Vachon TA, Dewing CB. Arthroscopic stabilization in patients with an inverted pear glenoid: results in patients with bone loss of the anterior glenoid. Am J Sports Med. 2007;35(8):1276-1283.
16. Markenstein JE, Jaspars KC, van der Hulst VP, Willems WJ. The quantification of glenoid bone loss in anterior shoulder instability; MR-arthro compared to 3D-CT. Skeletal Radiol. 2014;43(4):475-483.
17. Itoi E, Lee SB, Berglund LJ, Berge LL, An KN. The effect of a glenoid defect on anteroinferior stability of the shoulder after Bankart repair: a cadaveric study. J Bone Joint Surg Am. 2000;82(1):35-46.
18. Shaha JS, Cook JB, Song DJ, et al. Redefining “critical” bone loss in shoulder instability: functional outcomes worsen with “subcritical” bone loss. Am J Sports Med. 2015;43(7):1719-1725.
19. Piasecki DP, Verma NN, Romeo AA, Levine WN, Bach BR Jr, Provencher MT. Glenoid bone deficiency in recurrent anterior shoulder instability: diagnosis and management. J Am Acad Orthop Surg. 2009;17(8):482-493.
20. Provencher MT, Frank RM, Leclere LE, et al. The Hill-Sachs lesion: diagnosis, classification, and management. J Am Acad Orthop Surg. 2012;20(4):242-252.
21. Yamamoto N, Itoi E, Abe H, et al. Contact between the glenoid and the humeral head in abduction, external rotation, and horizontal extension: a new concept of glenoid track. J Shoulder Elbow Surg. 2007;16(5):649-656.
22. Di Giacomo G, Itoi E, Burkhart SS. Evolving concept of bipolar bone loss and the Hill-Sachs lesion: from “engaging/non-engaging” lesion to “on-track/off-track” lesion. Arthroscopy. 2014;30(1):90-98.
23. Metzger PD, Barlow B, Leonardelli D, Peace W, Solomon DJ, Provencher MT. Clinical application of the “glenoid track” concept for defining humeral head engagement in anterior shoulder instability: a preliminary report. Orthop J Sports Med. 2013;1(2):2325967113496213.
24. Arciero RA, Parrino A, Bernhardson AS, et al. The effect of a combined glenoid and Hill-Sachs defect on glenohumeral stability: a biomechanical cadaveric study using 3-dimensional modeling of 142 patients. Am J Sports Med. 2015;43(6):1422-1429.
25. Waterman BR, Chandler PJ, Teague E, Provencher MT, Tokish JM, Pallis MP. Short-term outcomes of glenoid bone block augmentation for complex anterior shoulder instability in a high-risk population. Arthroscopy. 2016;32(9):1784-1790.
26. Schroder DT, Provencher MT, Mologne TS, Muldoon MP, Cox JS. The modified Bristow procedure for anterior shoulder instability: 26-year outcomes in Naval Academy midshipmen. Am J Sports Med. 2006;34(5):778-786.
27. Provencher MT, Frank RM, Golijanin P, et al. Distal tibia allograft glenoid reconstruction in recurrent anterior shoulder instability: clinical and radiographic outcomes. Arthroscopy. 2017;33(5):891-897.
28. Tokish JM, Fitzpatrick K, Cook JB, Mallon WJ. Arthroscopic distal clavicular autograft for treating shoulder instability with glenoid bone loss. Arthrosc Tech. 2014;3(4):e475-e481.
1. Owens BD, Dawson L, Burks R, Cameron KL. Incidence of shoulder dislocation in the United States military: demographic considerations from a high-risk population. J Bone Joint Surg Am. 2009;91(4):791-796.
2. Owens BD, Duffey ML, Nelson BJ, DeBerardino TM, Taylor DC, Mountcastle SB. The incidence and characteristics of shoulder instability at the United States Military Academy. Am J Sports Med. 2007;35(7):1168-1173.
3. Owens BD, Nelson BJ, Duffey ML, et al. Pathoanatomy of first-time, traumatic, anterior glenohumeral subluxation events. J Bone Joint Surg Am. 2010;92(7):1605-1611.
4. DeBerardino TM, Arciero RA, Taylor DC, Uhorchak JM. Prospective evaluation of arthroscopic stabilization of acute, initial anterior shoulder dislocations in young athletes. Two- to five-year follow-up. Am J Sports Med. 2001;29(5):586-592.
5. Aronen JG, Regan K. Decreasing the incidence of recurrence of first time anterior shoulder dislocations with rehabilitation. Am J Sports Med. 1984;12(4):283-291.
6. Wheeler JH, Ryan JB, Arciero RA, Molinari RN. Arthroscopic versus nonoperative treatment of acute shoulder dislocations in young athletes. Arthroscopy. 1989;5(3):213-217.
7. Bottoni CR, Wilckens JH, DeBerardino TM, et al. A prospective, randomized evaluation of arthroscopic stabilization versus nonoperative treatment in patients with acute, traumatic, first-time shoulder dislocations. Am J Sports Med. 2002;30(4):576-580.
8. Dickens JF, Owens BD, Cameron KL, et al. Return to play and recurrent instability after in-season anterior shoulder instability: a prospective multicenter study. Am J Sports Med. 2014;42(12):2842-2850.
9. Owens BD, DeBerardino TM, Nelson BJ, et al. Long-term follow-up of acute arthroscopic Bankart repair for initial anterior shoulder dislocations in young athletes. Am J Sports Med. 2009;37(4):669-673.
10. DeBerardino TM, Arciero RA, Taylor DC. Arthroscopic stabilization of acute initial anterior shoulder dislocation: the West Point experience. J South Orthop Assoc. 1996;5(4):263-271.
11. Bottoni CR, Smith EL, Berkowitz MJ, Towle RB, Moore JH. Arthroscopic versus open shoulder stabilization for recurrent anterior instability: a prospective randomized clinical trial. Am J Sports Med. 2006;34(11):1730-1737.
12. Owens BD, Cameron KL, Peck KY, et al. Arthroscopic versus open stabilization for anterior shoulder subluxations. Orthop J Sports Med. 2015;3(1):2325967115571084.
13. Burkhart SS, De Beer JF. Traumatic glenohumeral bone defects and their relationship to failure of arthroscopic Bankart repairs: significance of the inverted-pear glenoid and the humeral engaging Hill-Sachs lesion. Arthroscopy. 2000;16(7):677-694.14. Shaha JS, Cook JB, Rowles DJ, Bottoni CR, Shaha SH, Tokish JM. Clinical validation of the glenoid track concept in anterior glenohumeral instability. J Bone Joint Surg Am. 2016;98(22):1918-1923.
15. Mologne TS, Provencher MT, Menzel KA, Vachon TA, Dewing CB. Arthroscopic stabilization in patients with an inverted pear glenoid: results in patients with bone loss of the anterior glenoid. Am J Sports Med. 2007;35(8):1276-1283.
16. Markenstein JE, Jaspars KC, van der Hulst VP, Willems WJ. The quantification of glenoid bone loss in anterior shoulder instability; MR-arthro compared to 3D-CT. Skeletal Radiol. 2014;43(4):475-483.
17. Itoi E, Lee SB, Berglund LJ, Berge LL, An KN. The effect of a glenoid defect on anteroinferior stability of the shoulder after Bankart repair: a cadaveric study. J Bone Joint Surg Am. 2000;82(1):35-46.
18. Shaha JS, Cook JB, Song DJ, et al. Redefining “critical” bone loss in shoulder instability: functional outcomes worsen with “subcritical” bone loss. Am J Sports Med. 2015;43(7):1719-1725.
19. Piasecki DP, Verma NN, Romeo AA, Levine WN, Bach BR Jr, Provencher MT. Glenoid bone deficiency in recurrent anterior shoulder instability: diagnosis and management. J Am Acad Orthop Surg. 2009;17(8):482-493.
20. Provencher MT, Frank RM, Leclere LE, et al. The Hill-Sachs lesion: diagnosis, classification, and management. J Am Acad Orthop Surg. 2012;20(4):242-252.
21. Yamamoto N, Itoi E, Abe H, et al. Contact between the glenoid and the humeral head in abduction, external rotation, and horizontal extension: a new concept of glenoid track. J Shoulder Elbow Surg. 2007;16(5):649-656.
22. Di Giacomo G, Itoi E, Burkhart SS. Evolving concept of bipolar bone loss and the Hill-Sachs lesion: from “engaging/non-engaging” lesion to “on-track/off-track” lesion. Arthroscopy. 2014;30(1):90-98.
23. Metzger PD, Barlow B, Leonardelli D, Peace W, Solomon DJ, Provencher MT. Clinical application of the “glenoid track” concept for defining humeral head engagement in anterior shoulder instability: a preliminary report. Orthop J Sports Med. 2013;1(2):2325967113496213.
24. Arciero RA, Parrino A, Bernhardson AS, et al. The effect of a combined glenoid and Hill-Sachs defect on glenohumeral stability: a biomechanical cadaveric study using 3-dimensional modeling of 142 patients. Am J Sports Med. 2015;43(6):1422-1429.
25. Waterman BR, Chandler PJ, Teague E, Provencher MT, Tokish JM, Pallis MP. Short-term outcomes of glenoid bone block augmentation for complex anterior shoulder instability in a high-risk population. Arthroscopy. 2016;32(9):1784-1790.
26. Schroder DT, Provencher MT, Mologne TS, Muldoon MP, Cox JS. The modified Bristow procedure for anterior shoulder instability: 26-year outcomes in Naval Academy midshipmen. Am J Sports Med. 2006;34(5):778-786.
27. Provencher MT, Frank RM, Golijanin P, et al. Distal tibia allograft glenoid reconstruction in recurrent anterior shoulder instability: clinical and radiographic outcomes. Arthroscopy. 2017;33(5):891-897.
28. Tokish JM, Fitzpatrick K, Cook JB, Mallon WJ. Arthroscopic distal clavicular autograft for treating shoulder instability with glenoid bone loss. Arthrosc Tech. 2014;3(4):e475-e481.
