Posterior shoulder instability occurs in approximately 10% to 17% of all glenohumeral instability events in young, active military cadets and has an incidence rate of 1.1 per 100,000 person years in the general population [9, 16, 17]. Approximately 4% of all shoulder injuries reported in National Collegiate Athletic Association (NCAA) football players are associated with posterior instability, occurring most often in offensive and defensive linemen [7, 10]. Furthermore, a recent study specifically examining NCAA football players undergoing MRI at the National Football League (NFL) combine reported that 22.5% of players showed evidence of isolated posterior labral tears, and an additional 22.5% of players displayed evidence of combined anterior and posterior labral tears .
To our knowledge, there are no studies examining posterior instability in high-risk cohorts, particularly in-season athletes. In the general population, nonoperative treatment of posterior labral tears often is successful, with surgical management reserved for individuals who do not respond to therapy . However, in high-risk, high-demand athletes, posterior labral tears may have detrimental effects on their career and ability to compete at a high level . Earlier surgical management of tears in NFL prospects before entering the combine was found to result in a greater amount of playing time during the athlete’s second year of professional football competition . But because the reported posterior shoulder instability injuries undergoing surgical treatment in NCAA football players is low, prognostic studies evaluating these in-season injuries are also lacking. Furthermore, because an increasing number of anterior instability events has been correlated with increasing levels of bone loss, increased attention to early glenohumeral stabilization has recently been advocated in this high-risk population .
Therefore, we asked the following questions: (1) What proportion of athletes returned to play during the season after posterior instability in collegiate football players? (2) How much time did athletes lose to injury, what proportion of athletes opted to undergo surgery, and what proportion of athletes experienced recurrent instability after a posterior instability episode during a collegiate football season?
Patients and Methods
Study Design and Setting
The methods of this study have been described by our group for anterior instability . After obtaining institutional review board approval, we conducted a prospective, observational study of NCAA Division 1 Football Bowl Subdivision (FBS) players at the three universities (The United States Military Academy, The United States Air Force Academy, and the United States Naval Academy), to determine the outcomes of in-season posterior glenohumeral instability in collision athletes. This cohort represents a homogenous patient population with comparable access to care, similar post-competition employment and all exist within a similar closed-health care system that minimizes confounding factors in follow-up and care. Athletes who sustained a shoulder instability event at the participating institutions during their competitive season were recruited to participate in this study. A total 250 athletes were followed in the study, and 0.04 posterior instability events per athlete-seasons occurred during the study period. Athletes who sustained posterior instability during the regular football season were included in the cohort. All athletes in the observed cohort attempted an initial course of nonoperative treatment during the season and attempted to return to play during the same season.
The primary outcome of interest was the ability to return to play during the same football season. Secondary outcomes of interest were the time lost from sport because of the posterior instability injury, what proportion of athletes opted to undergo surgery and what proportion of athletes experienced recurrent instability.
The study population included all in-season, competitive intercollegiate varsity football players at three NCAA Division I FBS football programs during the 2011 to 2012 academic year. The study eligibility criterion was a traumatic posterior instability event occurring during the athlete’s competitive intercollegiate season, as defined by the NCAA. All athletes desired to pursue initial nonoperative treatment so they could return to play during the current season. All athletes had a minimum of 1 year of eligibility remaining after experiencing in-season instability. All athletes attempted a course of nonoperative management.
Injury Definitions, Surveillance, and Follow-up
Medical care for athletes at the three study institutions was provided in a closed healthcare system, and all injured athletes were evaluated at the orthopaedic and sports medicine clinics at these institutions . Furthermore, all athletes included in this study had a baseline injury history that was available and obtained preseason that was used to determine a new or preexisting glenohumeral instability. Athletes were evaluated after self-reporting a shoulder injury during competition. After clinical evaluation by an orthopaedic surgeon at each institution, we determined that an athlete had posterior glenohumeral instability if they had a mechanism of injury and history of symptoms consistent with posterior glenohumeral instability with associated positive physical examination findings for posterior instability, including a positive jerk and/or Kim test. As previously defined, a dislocation was described as a traumatic injury resulting in manual reduction, and a subluxation was defined as transient instability event that did not result in manual reduction but that was associated with a positive jerk and/or Kim test result [4, 20]. A MRI arthrogram was performed after injuries with symptoms clinically consistent with posterior instability. Those injuries with history, mechanism, new physical examination findings and positive imaging findings consistent with a posterior shoulder instability event (dislocation or subluxation) were included in analysis.
Ten athletes were identified during the observed period who sustained a posterior instability event. All athletes sustained glenohumeral subluxation events, and no athletes sustained a dislocation event that required a manual reduction. All athletes attempted to return to play during the same season as their initial injury and were included in analysis.
The date of injury, baseline demographics, and injury details were documented at the time of injury. Athletes were followed throughout the football season, and the subsequent date of unrestricted return to football participation was documented. For athletes who returned to play, we conducted active surveillance to determine the incidence of any recurrent posterior instability during the remainder of the season in which they were injured. Recurrent posterior instability was diagnosed using the same criteria listed above. Athletes who received surgical stabilization completed a standard postoperative protocol consisting of 6 weeks of sling immobilization, followed by ROM exercises and strengthening exercises at 3 months. Clearance to return to full-duty and contact sports was granted no sooner than 6 months after surgery. Athletes treated operatively who were subsequently deemed eligible to return to play were followed during their next immediate competitive season to determine whether they were able to return to play, and if they returned to play, whether they experienced recurrent instability during the season. The closed healthcare systems at the study institutions allowed for excellent injury detection, follow-up, and surgical documentation .
Management and Return-to-Play Criteria
The return-to-play criteria used for this observational study are based on a previously published return-to-play protocol after in-season shoulder instability [5, 11, 18]. If the player was asymptomatic, performed all rehabilitative exercises, demonstrated symmetry and full strength, and was able to perform sport-specific exercises without pain or limitations, they were cleared for full participation. After return to play, all athletes were prospectively followed to assess the recurrence of instability. Successful return to play was defined as the ability to return to full sport activities and complete the season. Recurrent instability after return to play was not an absolute indication for immediate surgical stabilization. Final surgical management decisions were made by the athlete and the medical treatment team alone. All stabilization procedures were performed arthroscopically in either the beach chair or lateral decubitus position at the discretion of the operating surgeon.
Outcomes and Statistical Analysis
Our primary outcome of return to play was defined as return to full-contact participation (practice or game) in football without surgical intervention during the same season of the initial injury, regardless of additional instability sustained during the remainder of the season. Time lost from sport was calculated by the number of days between the injury date and the return to play date. Return to play after surgery was determined by active surveillance of patients undergoing surgical stabilization to determine whether they returned to full participation in subsequent football seasons. The number of recurrences was determined by the athlete’s report of subluxation or dislocation during activity. All athletes who returned to play after surgery were monitored for recurrent instability. Descriptive statistics were calculated using medians with ranges, and frequencies and proportions were used for categorical variables.
Return to Play
Of the 10 collegiate football players who experienced posterior instability in this study, seven returned to play during the season (Fig. 1). We observed no posterior dislocation events (Table 1). Seven of 10 athletes were linemen. The other three athletes consisted of a running back, a defensive tackle, and a wide receiver. Three of 10 patients had a history of nonoperatively treated, recurrent posterior shoulder instability, with the remaining seven reporting a first-time episode of primary traumatic posterior instability occurring during the season. Postinjury imaging demonstrated posterior labral tears in all patients, with associated anterior labral lesions in two patients and associated superior labral tears from anterior to posterior in two patients. Additionally, there were three posterior glenoid rim fractures and one posterior periosteal sleeve avulsion. The three posterior glenoid rim fractures had an average bone loss of 10% (range 4% to 18%) determined using the best fit circle method on the sagittal en face cut on MRI as previously described . One of three athletes with posterior glenoid rim fractures returned to in-season activity and did not undergo surgery, whereas the two athletes who had posterior osseous pathologic findings and underwent surgery did not return to competitive football the following year. Furthermore, of the five athletes with isolated posterior labral tears, only one was not able to return to football during the subsequent season. Of those athletes unable to return to sport, a decision for surgery was made an average of 78 days postinjury.
Table 1. -
In-season injury characteristics and return to sport after posterior instability in collegiate football players
|Athlete injury characteristics
||Proportion of athletes
||9 of 10
||3 of 10
||7 of 10
||1 (0 to 14)
|Number of subluxationsa
||4 (0 to 8)
|Proportion of recurrent in-season subluxations
||5 of 7
aData are shown as the median (range).
Time Lost to Injury, Surgical Intervention, and Recurrent Instability
The median (range) time lost because of injury for those athletes returning to sport was 1 (0 to 14) days, seven of 10 athletes underwent surgical stabilization following injury, and eight athletes described recurrent instability symptoms. Three athletes were able to return to play on the same day of their injury before imaging was completed. Of the seven athletes who returned to sport, all athletes were able to return before the next week of athletic competition.
Seven of 10 athletes underwent arthroscopic stabilization. Three opted for surgical management without returning to play during the same season, and four athletes returned to sport during the same season but underwent surgical management at the conclusion of the season. Only three athletes who were able to return to sport opted not to undergo surgical intervention. After surgery, four of seven athletes returned to football and none reported recurrent instability. The remaining three athletes chose not to return to football after surgery.
Of the 10 athletes diagnosed with posterior instability, eight had one or more episodes of recurrent instability. Of the seven athletes able to return to sport, five described recurrent instability events with a median (range) of four subluxation events (0 to 8 events) per athlete for the remainder of the season and two did not report recurrent instability events (one had an isolated labral tear and one had an osseous posterior glenoid fracture). Of the 10 athletes with posterior instability, only one was able to complete his season without reporting recurrent instability and without surgery at the conclusion of the season.
Previous work has evaluated an athletes’ ability to return to in-season sport after anterior shoulder instability and after surgical stabilization after posterior shoulder instability [4, 8]. However, previous studies have not determined an athlete’s ability to return to sport during the same season after posterior glenohumeral instability [3, 8, 10, 15]. Furthermore, no study that we know of has evaluated the injury, demographic, and athlete-specific variables allowing in-season return to football by comparing athletes who had recurrent instability with those without subsequent instability. Seven of 10 athletes in this series returned to sport during the same season, but only three athletes were able to fully return to sport without an arthroscopic stabilization procedure at the conclusion of the season. Furthermore, athletes who underwent surgical stabilization did not experience further recurrent instability.
This study is limited by the small cohort of athletes and the number of observed posterior instability events documented during the follow-up period. As noted in previous studies, posterior shoulder instability is uncommon [9, 16, 17]. Consequently, although this study reports the experience of three institutions, the total number of subjects included is small, which limits its ability to make definitive conclusions. Despite this size limitation, this study provides prognostic data for a population of athletes for whom no previous data have been published. As such, the data from this study can be used to help give surgeons and team physicians additional guidance on how to appropriately counsel their athletes. Following this, all athletes in this study who sustained a posterior instability event during the observed study period attempted to return to play. This desire for return to play without early surgical intervention is likely partially attributed to the athletes desire to return to sport regardless of physical injury and future disability. This observation may also be attributed to the medical staff’s bias at the time of post-injury counseling as previous literature has shown that most elite athletes are able to return to play after a glenohumeral instability event [1, 2, 9]. This study also did not distinguish between those athletes who sustained an instability event early in the season compared with later in the season, between starting position players versus backup athletes, or between the total number of competition opportunities remaining in the season. Even though these distinctions may be important, this study included all athletes who desired to return to play regardless of other factors to help determine if NCAA football athletes are able to return to sport successfully after a posterior instability injury as this is the most relevant question for injured athletes. Furthermore, the return-to-play rates found in this study are similar to other studies evaluating return to sport in collision athletes who sustained glenohumeral subluxation events . This study is also limited to a US Military Service Academy population, which somewhat limits its external validity compared with those athletes at other NCAA institutions due to the homogeneity of the population and the expected post-competition career requirements of military service. Nevertheless, the homogeneity of the population and its medical care allows some insight into the natural history of the injury process while minimizing confounding variables due to outside influences, and the population evaluated in this study likely is comparable to other NCAA Division 1 FBS players in terms of the level of expected athleticism, fitness, and training. Because of the rarity of this injury and the period studied, this study was designed to provide prognostic data only; we did not have a comparison group and we did not use validated patient-reported outcomes. Although these elements would be helpful to include in future studies, this study still provides additional information on the basic expectations of athletes and coaches in regard to the athletes’ ability to return to sport to complete the season, and whether they are likely to undergo surgery to treat their injury.
Return to Play
Seven of 10 athletes in this study returned to sport the same season after a posterior glenohumeral instability event. Although limited in size, the current study suggests that most high-level athletes return to football the same season after a posterior instability event without missing a large amount of competition. This is similar to previous studies evaluating collegiate contact athletes and NFL athletes that displayed a high rate of return to sport after a glenohumeral instability event [3, 15]. Although these findings may be partially a function of these athletes’ desires to compete regardless of physical injury, they do suggest that high-level athletes can be competitive despite an in-season shoulder instability event.
Time Lost to Injury, Surgical Intervention, and Recurrent Instability
Although athletes who returned to sport only missed a median of 1 day of sport after a posterior shoulder instability event, seven of 10 underwent surgical stabilization and eight of 10 experienced recurrent instability. Furthermore, only one athlete in this series was treated nonoperatively and reported no further instability episodes. The limited amount of time missed for the athletes sustaining a posterior instability event in this series was similar to the results of Okoroha et al. , who reported that NFL players who sustained subluxation events returned to sport the next week of competition, compared with athletes who missed 3 weeks of competition after a dislocation event. This distinction in subluxation versus dislocation is important to make as all athletes in the current study sustained a posterior subluxation event. Although exceptionally uncommon, the results of this study are likely limited to subluxations only, as the prognosis of a true posterior shoulder dislocation in collision athletes may likely be associated with a much lower return to play rate and need for early stabilization due to the degree of soft tissue injury at the time of dislocation.
Although four of seven athletes who underwent surgery completed their season, we found that most athletes eventually underwent surgery. Even though the timing surgery may likely have been dictated by a number of in-season and athlete-specific factors (such as, time of season, post-season competition, academic schedules), the decision to proceed with surgical intervention was likely influenced by the positive results seen in previous studies of NCAA collision athletes that have shown a high rate of return to high-level sport after surgical stabilization of glenohumeral anterior and posterior instability [1, 2, 19]. Interestingly, only four of seven athletes returned to sport in the current study, which may partially be attributed to their concomitant military occupational demands and future occupational requirements outside of their sport, as they must be fully medically cleared for all activities and military duties before graduation.
Eight of 10 athletes in the current study experienced recurrent instability symptoms. Furthermore, five of seven athletes who returned to sport experienced persistent instability symptoms a median of four additional times. This high frequency of recurrent instability is similar to that seen in those athletes with anterior shoulder instability . This high recurrence risk is concerning as increased levels of attritional glenoid bone loss has been found in conjunction with increasing numbers of glenohumeral instability events [5, 6]. As posterior glenoid bone loss greater than 20% has been shown to result in higher biomechanical failures, early stabilization may be reasonable in high-demand collision athletes . However, the intraarticular pathologic findings and bone loss associated with recurrent posterior instability are not as well-defined. Consequently, further studies specifically evaluating the effect of recurrent posterior instability on subsequent bone loss should be undertaken, especially considering the typically increased glenoid retroversion in these patients and the future limitations that untreated instability may have on the athlete’s career [16, 13].
This study found that although NCAA football athletes who sustain a posterior glenohumeral instability injury can return to sport during their season with few athletic days missed, they will likely sustain multiple recurrent instability events and undergo eventual surgery to treat this problem. The results of this study can help guide in-season management of posterior shoulder instability by allowing more appropriate postinjury counseling and decision making through the identification of those athletes who may require additional attention from medical staff during the season and possible modifications to training regimens to minimize long term disability. Further prospective studies involving a larger cohort over several seasons should be performed through collaborative studies across the NCAA that better assess function and injury risk factors before beginning collegiate athletics. This could better characterize the natural history and associated functional limitations that athletes may encounter during their collegiate careers.
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