Mark Slabaugh, MD, FAAOS and Christopher Gaunder, MD
The treatment of athletes who have been diagnosed with posterior instability in season is difficult because there is little literature regarding the most optimal treatment algorithm and best outcomes for these athletes. Variables such as timing of the injury, sport and position played, patient motivation, and the natural history of the disease all play a role in helping determine the best treatment for athletes in season with posterior instability. Surgical treatment in season will remove the athlete from the playing field but has the advantage of reducing the risk of recurrence. Rehabilitation and/or bracing might facilitate returning to play within the same season but there is a risk of continued pain and/or instability. A team-based approach working with the team’s athletic trainer, physical therapist, and/or strength coach can help the team physician and athlete make an informed decision about how best to treat this pathology in season.
EPIDEMIOLOGY AND PATHOANATOMY
Although less common than anterior instability, posterior instability poses a challenge to the orthopedic surgeon when diagnosing and treating in-season athletes. Posterior glenohumeral instability has become an increasingly recognized problem and cause of significant shoulder pain and dysfunction. It represents around 10% to 20% of all shoulder instability events in athletes and can be seen at a much higher percentage in collegiate athletes and military populations secondary to their fitness requirements.1,2 Longitudinal cohort studies have demonstrated that male intercollegiate athletes are among the highest-risk patient population to sustain injuries that will ultimately lead to posterior shoulder instability needing surgical intervention.3 Male injury rates have been shown to be almost 9 times that of women in one longitudinal study looking at this specific injury.4 Whereas injury rates at a military academy for men have been shown to be 4.67 per 1000 person-years, in women it is only 2.04 per 1000 person-years.5 Sports with the highest incident rate of posterior instability are wrestling, football, gymnastics, and rugby in men, with basketball and rugby having the highest incident rate in women.5
Although the anatomic structures that make up the posterior aspect of the shoulder are well understood, there still remains questions as to whether it is the bony anatomy, soft-tissue laxity, or combination of both that could predispose to recurrent instability events. Glenoid retroversion has been questioned as a possible cause of posterior shoulder instability and is therefore an increasingly discussed topic because of its implications when it comes to addressing this problem surgically.5 It is thought that retroversion of the glenoid more than 10 degrees is a risk factor for posterior instability. Patients in one study were found to be 6 times more likely to have recurrent posterior instability with glenoid retroversion, and just 1-degree increased retroversion increases one’s risk of posterior instability 17%.6 It is currently unknown how much soft-tissue laxity contributes to isolated posterior pathology; however, it is well known that underlying elements of soft-tissue laxity can lead to injury of the posterior labrum.7,8 Static structures such as the glenoid labrum and posterior capsule have been shown to increase the depth of the glenoid, help with compression of the joint, contain the shoulder joint, and prevent shoulder subluxation posteriorly especially in adduction and internal rotation.9
PRESENTATION OF IN-SEASON POSTERIOR INSTABILITY
Unlike anterior instability in the athlete, the mechanism of injury can vary greatly depending on sport, position played, and level of competition. Frank traumatic dislocations, repetitive trauma, and ligamentous laxity make up the spectrum that these athletes can present with. Athletes who present with a frank dislocation in season are easily recognized because the injury is acute and the athlete will have an internally rotated and adducted shoulder with a history of a posterior directed force in a susceptible sport.10,11 Repetitive trauma with a posterior directed force is typically the culprit in sports such as weightlifting or football (interior linemen) and can lead to tearing of the labrum and capsule posteriorly. Ligamentous laxity is common in overhead athletes such as swimmers, volleyball players, and athletes who rely on increased range of motion of the shoulder to perform well in their sport leading to stretching out of the static stabilizers of the shoulder.
These varying causes of posterior instability can make the diagnosis extremely difficult for sports medicine physicians, especially in athletes who wish to remain on the field of play.12 It has been noted that the most common cause of posterior instability is recurrent subluxation, and typically athletes present with pain rather than complaints of instability.12,13 Therefore, sports medicine physicians should have a high clinical suspicion when athletes present with posterior shoulder pain during competition or during practice. This is especially true in athletes who have frequent adducted, internal rotation with posterior directed forces as part of their sport. Moreover, subtle worsening in athletic performance or decreased endurance strength over a period of time especially in overhead athletes should make the clinician suspicious of posterior instability in an athlete.14 Athletes can also present with mechanical symptoms when describing posterior instability. Subtle clicking and popping throughout a range of motion may be described as the humeral head shears over the posteriorly torn labrum. Although less common, an athlete may describe frank instability or may be able to voluntarily dislocate the shoulder posteriorly on examination.
Identifying at-risk athletes, who place posteriorly directed loads onto the shoulder, particularly swimmers, pitchers, weight lifters, and football players, will help physicians have a high index of suspicion for this entity. Additionally, attention should also be paid to athletes who as part of their sport are required to lift heavily, especially bench press or overhead lifting. Even batters with their lead shoulder are at risk of posterior shoulder instability.15,16 It is also well known that posterior shoulder instability is commonly found in conjunction with other shoulder conditions such as a superior labral tear, anterior labral tear, or capsular tears such as a reverse humeral avulsion of the glenoid ligaments. Therefore, because of the vague and varying presentation clinicians, should consider posterior instability in any athlete with the insidious onset of shoulder pain.
To confirm the diagnosis, a complete physical evaluation of the athlete must be performed. The examination on the sideline during competition should be the same as in the office. Often this is difficult because sports that have a higher prevalence of posterior instability are typically those for which removal of protective equipment is required. Therefore, a player with a suspected posterior instability event should be removed from competition and taken to the training room where a detailed examination can be performed. This includes taking the helmet, pads, and shirt off. Evaluation of the affected shoulder should be performed comparing to the nonaffected side. If a posterior dislocation is suspected when an athlete is holding the arm in an adducted internally rotated position, the physician should palpate the shoulder for any changes in shoulder contour or depressions. Range of motion in patients with a posterior dislocation is very painful and significantly limited, especially external rotation. In these patients a reduction maneuver is attempted as quickly as possible after the dislocation to facilitate the ease of the reduction. We prefer to have the athlete lie in the prone position with the arm slightly off the table. Traction on the shoulder is coupled with pressure on the posterior aspect of the shoulder with external rotation and adduction. A clunk will be felt as the humerus reduces into the glenoid.
Provocative exam maneuvers can be used to help delineate the subtleties of posterior glenohumeral instability. These tests help the provider identify painful sources that can lead to the posterior instability and eliminate other shoulder pathology. There are 4 routine tests that we use for the diagnosis of posterior instability, all of which are a variation of one another (Table 18-1).17–19 The diagnosis of posterior instability becomes much more sensitive when 2 or more of these exams are positive.17 These provocative tests during a game can be used to determine the extent of the injury and also help the physician to determine whether return to play is appropriate. Therefore, removing the patient from the game into the training room is key so a detailed examination can be performed. We have found that the push-pull test is especially helpful in determining return to play. If athletes have minimal pain with this test, they typically can be returned to play during the same competition. We typically like to simulate the forces they would experience in the game (ie, blocking) with the trainer in functional testing as well to determine whether they can safely be returned to play. If a patient can complete a voluntary jerk test, this is a more ominous indication of more significant pathology. If this maneuver is painful, then return to play is contraindicated.
When posterior instability is suspected, imaging studies are indicated. This is especially true in patients with a suspected posterior dislocation. In athletes with an acute unreduced dislocation, we typically do not order x-rays to confirm the diagnosis because the physical exam findings are pronounced. However, we do order radiographs directly after the reduction to confirm the reduction. A true anteroposterior (Grashey view), scapular-Y, and axillary views should be obtained in all patients. The axillary view is important to visualize a posterior dislocation, subluxation, or evidence of posterior glenoid bone loss or a posterior glenoid fracture. Magnetic resonance imaging (MRI) is also indicated in all athletes in season to evaluate the posterior soft tissue of the shoulder, including the labrum and posterior capsule. MR arthrogram is warranted in every patient with posterior instability unless there has been a recent traumatic dislocation where a traumatic effusion would be expected (Figure 18-2). We order an MRI in all patients with suspected posterior instability within a week of their instability event to ensure there are no contraindications to return to play (Table 18-2). In addition to posterior labral tears or posterior soft-tissue redundancy, several particular findings on MRI may be concerning for posterior instability. A reverse Hill-Sachs injury to the anterior humeral head secondary to subluxation or frank dislocation may be seen. There have also been descriptions of a posterior reverse humeral avulsion of the glenohumeral ligament.17,20 The MRI should also be scrutinized for any additional intra-articular findings because concomitant pathology is very frequent with posterior shoulder instability.
1. Jerk test: The patient sits upright with the arm forward elevated 90 degrees and internally rotated with an applied axial/posterior load to the humerus. Positive exam findings would include a clunk (dislocation) or pain often with another clunk (reduction) when the arm is brought back to abduction.
2. Kim test: The patient is seated with the arm in 90 degrees of abduction. While holding the patient’s elbow, the arm is elevated 45 degrees, simultaneously applying a downward posterior force on the arm. Positive exam findings would include pain or clunk.
3. Posterior load and shift test: The patient’s arm is placed in flexion, abduction and internal rotation with a posteriorly directed force. Positive exam findings would include pain or more translation than the contralateral side.
4. Push-pull test: Patient is lying supine with the shoulder in 90 degrees of abduction. The shoulder is posteriorly loaded. Positive findings would be pain or subluxation of the humeral head posteriorly or significant difference in the amount of translation when compared to the contralateral side (Figure 18-1).
- Loose body
- Chondral defect or GLAD lesion
- Bony reverse Bankart or bone loss greater than 10%
- Large reverse Hill-Sachs lesion
- Reverse HAGL lesion
- Labral tear greater than 270 degrees of circumference of glenoid
- Gross instability on clinical examination (grade 3)
- Recurrent symptoms (pain or instability event)
- Failure of nonoperative treatment
Abbreviations: GLAD, glenoid labral articular defect; HAGL, humeral avulsion of the glenohumeral ligament.
DETERMINATION OF TREATMENT FOR IN-SEASON ATHLETES WITH POSTERIOR INSTABILITY
The decision on how to best treat posterior instability in athletes in season is multifactorial and is best made with input from the entire medical team in conjunction with the athlete. Besides the team physician, the athletic trainer and the strength and conditioning coach will have keen insights and input and often know the athlete much better than the team physician. A team-based approach is key to the success of treating these athletes nonoperatively if this is the decision of the in-season athlete.
Special consideration is warranted for patients with acute posterior instability during competition. During a game when a patient comes onto the sideline with complaints and mechanism consistent with a posterior instability event, the examination findings are key to determining whether the athlete can return to play in the same game. Those patients with full range of motion with protective equipment removed and minimal pain with a push-pull maneuver can be safely returned to play that same game. These patients typically have decreased strength right after the instability event; however, their strength quickly returns to normal and is painless within minutes and therefore can be safely returned to the game. Thus, we keep the athletes in the training room for serial examinations to determine return-to-play ability. We have found that if athletes have not had any improvement in their strength or push-pull within 10 minutes, then they should be kept from same-day competition. Radiographs are obtained that day or the next both in patients who return to play and those who do not return.
In the office, when an athlete has a history and clinical examination combined with MRI findings of posterior instability and he or she is in season, the entire medical team confers to ensure that all parties are on the same page so that the athlete doesn’t receive conflicting information. The team physician can then counsel athletes and their family about the risks and the benefits of continuing to play with posterior instability or having surgery to treat their pathology. A typical discussion includes the risk and benefits of operative and nonoperative treatment of this injury so the athlete can make an informed decision that is best for himself or herself, the team, and their future aspirations. The athlete is counseled that the current thinking would indicate that there is a lower risk of redislocation, continued pain, and further injury to the labrum over the long-term with operative treatment.13,21–23 Our initial findings (unpublished data) have indicated that approximately 70% of patients can be returned to sport the same season but more than two-thirds elect surgery at the end of the season. The athlete is also counseled that it is unknown how much damage could take place if he or she is allowed to play through the season and then opts for surgery at the end of the season. With the current literature, it is unclear whether treating posterior instability nonoperatively in season could lead to further damage to the labrum over the course of one season. However, it has been well documented that patients with posterior instability (chronic and acute) can be successfully treated operatively with a labral reconstruction.13,22 Therefore, immediate risks with nonoperative treatment are not currently as well elucidated as with anterior instability.24–26
With this discussion, the athlete is counseled that there are some benefits to waiting over pursuing operative intervention in some cases. There have been certain studies that have shown that patients can return to sport with nonoperative treatment. Several authors have advocated that physical therapy is effective in treating posterior instability and thus surgery can be avoided in a certain subset of patients.14,27,28 In a study of 19 consecutive patients, therapy was able to allow all patients to return to their respective sport but no Tegner level was mentioned and thus it is unknown whether they returned to the same level of play or just returned to sport.27 In a nonrandomized trial comparing nonoperative rehabilitation with operative stabilization for posterior instability, one study found that both groups had significantly better outcomes at 1 year after diagnosis and treatment even though the operative group fared better than the rehabilitation group. However, in this study the patients who were treated nonoperatively were younger and had more clinical laxity, making the comparison of results between groups difficult.28 Additionally, there was no mention about return to sport in either group. Most authors recommend treating posterior instability nonoperatively for a period of 3 to 6 months to determine whether patients can become pain free and more functional with a physical therapy-based regimen.9,12
When consenting patients about their risk of recurrent symptoms, it is important to note that there is no study that has looked at posterior instability in athletes in season. There are a few studies that have indirectly looked at an athlete’s ability to return to sport with nonoperative treatment. In a study looking at the effect of posterior labral tears on the playing time in National Football League (NFL) athletes, the authors found that 78 of 221 athletes at the NFL Combine with posterior labral tears were treated nonoperatively. 29 However, it is unknown when these athletes sustained their injury and how long they had been playing with their posterior instability. Though, this study did note there was no difference in playing time between those treated nonoperatively and those treated surgically in their first season in the NFL, indicating there is a role for conservative treatment in the appropriately selected patients. One could surmise that athletes could be treated at least for one season without a compromise in playing time.
There are several factors to consider when contemplating treating athletes nonoperatively. The first consideration is the type of sport and the position that the athlete plays. Contact sports such as American football, in which athletes are exposed to significant posterior forces on the glenohumeral joint, make nonoperative treatment more difficult. Positions such as linemen, who are taught to keep their hands in close to their chest, are at much higher risk for failure of a course of nonoperative treatment because their blocking creates a posterior stress in the shoulder with relative internal rotation while trying to shed a blocker. In fact, the NFL study mentioned earlier has shown that the number of snaps linemen participate in during their second NFL season is significantly less both in offensive and defensive linemen with known posterior instability who were treated nonoperatively vs surgically.29 We consider athletes who compete in football, hockey, gymnastics, power lifting, and boxing to be more at risk for recurrent symptoms solely based on the sport they play.
The second consideration to understand when educating athletes is the imaging or MRI findings. Those patients with a small Kim lesion and no evidence of patulous capsule are treated much differently from those with a glenoid labral articular defect lesion and a loose body. In fact, there are several key findings on MRI that would make nonoperative treatment of the in-season athlete less desirable. We consider the following findings on imaging to be contraindications to nonoperative treatment in season: loose body, chondral defects/glenoid labral articular defect lesions, bony reverse Bankart, or bone loss greater than 10%, large engaging reverse Hill-Sachs, reverse humeral avulsion of the glenohumeral ligament lesion, and labral tears that are greater than 270 degrees of the circumference of the glenoid (see Table 18-2).
The last consideration for recommending nonoperative treatment is the severity of the injury. Athletes with posterior instability typically present with repetitive trauma and not one frank dislocation. It has been our experience that these patients with posterior instability typically present with pain and not frank instability, as other authors have found as well.30 We have found that the in-season rehabilitation is much quicker than for anterior instability. In a study of in-season bracing for anterior instability, the average time away from sport was approximately 10 days for anterior instability.31 In our experience athletes treated nonoperatively with posterior instability typically recover within a week. For those athletes who have a frank dislocation, we are much more conservative and they need more time to recover, typically 2 to 4 weeks.
The timing of the injury also plays a part in how we consent the athletes and their families. Those athletes who are injured at the beginning of the season or during the preseason are much more likely to return to competition than those who injure themselves during the last part of the season. Therefore, the time left during the season can help counsel athletes whether they will be able to return to play in season with posterior instability. Additionally, where an athlete is in terms of schooling can help determine the recommendation to continue playing vs immediate surgical intervention. Seniors in their last year of eligibility are much more apt to consider nonoperative treatment in season vs a freshman with several years of eligibility left.
With all these considerations in mind, we feel that most athletes can be treated nonoperatively and we offer the following treatment algorithm to all of our athletes who still have more than 2 weeks of competition left in their season. For those who are at the end of their season, we typically do not offer this because the likelihood of getting them back to meaningful competition is less likely. We feel the risk of a subsequent in-season instability event is low and therefore the risk of further chondral, labral, or bone damage is likewise low. However, we admit that this is based on level V data in our own experience at a Division I program. Therefore, we are currently conducting a prospective study to determine whether our hypothesis is correct. Our preliminary findings are that approximately two-thirds of athletes can be treated with in-season physical therapy and returned to sport safely (ie, no further instability episodes) until the end of the season when the status of their shoulder can be readdressed and surgery can be performed if necessary. Our treatment algorithm is shown in Figure 18-3.
For those athletes who desire to be treated nonoperatively and return to their sport in-season, a 4-phase therapy program is developed for the athlete with progression through the phases as soon as the athlete is able to complete each phase with no symptoms.32
The first phase, or acute phase, is begun right after the instability episode and focuses on reducing the inflammation from the traumatic subluxation or dislocation. The goals of this phase are to decrease pain, gain range of motion, and institute some simple strengthening exercises within the athlete’s tolerance. Initially, the therapist or trainer will initiate range-of-motion exercises with restrictions based on the athlete’s symptoms. If needed, passive range-of-motion exercises are instituted but the goal is to quickly move into active assisted or active range of motion for neuromuscular modulation to begin. As symptoms allow, isometric exercises are begun with focus on the internal and external rotators of the shoulder in addition to the deltoid. Initially, submaximal stimulation of these muscles is begun and then progressed as symptoms allow. Furthermore, modalities such as ice, laser therapy, and transcutaneous electrical nerve stimulation are used to facilitate pain control in this acute phase. We typically do not recommend any immobilization of the joint during this acute phase.