Biomechanics of Overhead Throwing
Overhead throwing involves well-coordinated movements, often at the upper limits of physiologic restraint. Pitching in baseball is one of the most well-researched overhead activities, and has been described as six discrete phases: wind up, stride, cocking, acceleration, deceleration, and follow through (1–7). The goal of overhead throwing is to smoothly transition from one phase to the next while maintaining the maximum amount of kinetic energy until ball release (1). Shoulder pathology can occur at various stages of throwing; however, the cocking and acceleration phases are most commonly implicated, due to excessive abduction and external rotation of the glenohumeral joint (8). Repeatedly positioning the shoulder in this way causes attenuation of the anterior capsular structures and may lead to contraction of the posterior capsular structures and rotator cuff with time (9).
Pathophysiology of Shoulder Instability
Shoulder instability encompasses a spectrum of disease ranging from subluxation to frank dislocation (10,11). While a large number of instability events occur following trauma, repetitive attenuation of the capsuloligamentous structures about the shoulder also can lead to instability. Overhead athletes are more likely to experience subluxation type events due to repetitive microtrauma (12–14). During subluxation, the humeral head translates beyond normal physiological limits, but maintains contact with the glenoid, often resulting in translation to, but not beyond the glenoid rim (11,14). While subluxation is often overlooked, it can be problematic, especially in overhead athletes (15). In 2007, Owens et al. (15) reported that subluxation may comprise up to 85% of instability events. Additionally, in this series of patients, all of whom were U.S. military cadets, 41% of instability events were noncontact in nature, most commonly due to missed punches in boxing (15). Shoulder subluxation and dislocation can be associated with several injuries, which are considered to be pathognomonic for instability. During an anterior shoulder dislocation, injury typically occurs to the anterior inferior labroligamentous, which also is known as a Bankart lesion (12,16,17).
History and Physical Examination
Attention should be paid to the duration and location of the pain as well as at what point during overhead motion the pain occurs. Examiners should be aware of physical exam findings consistent with instability, labral tears, and biceps pathology when evaluating this patient population. Examination should begin with inspection and palpation of both shoulders, as well as a thorough assessment of range of motion in flexion, extension, abduction, and internal rotation. It is not uncommon for overhead athletes to suffer from glenohumeral internal rotation deficit (GIRD) of greater than 25 degrees compared to the nonthrowing shoulder, leading to posterior shoulder pain (9). If possible, examination should be performed with the patient supine to stabilize the scapula during shoulder range of motion (18). Noonan et al. measured humeral torsion and shoulder range of motion in professional pitchers with GIRD and found them to have decreased humeral head retrotorsion, as well as decreased internal rotation and total arc range of motion compared to unaffected counterparts (9). External rotation was equivalent in pitchers with and without GIRD (9). A systematic review of 2195 shoulders found that adaptive changes in shoulder range of motion may be suggestive of injury risk, with less total shoulder motion, and external rotation gain being associated with injury, albeit these differences did not reach significance (19). Camp et al. (20) also investigated the significance of adaptive changes due to GIRD on shoulder and elbow injuries in professional baseball players. Their study did not find an association between GIRD and shoulder injury; however, they did report an increase in elbow injuries in pitchers with less shoulder external rotation and flexion (20). Ultimately, there remains debate on the influence of GIRD on shoulder injury; however, it is important to identify and consider as a cause of instability, especially in throwers.
Following inspection, palpation, and range of motion, provocative testing should be performed. The sulcus sign and the load-shift test are commonly used to evaluate for anterior and posterior shoulder instability (18). The hyperabduction test (i.e., Gagey test), assesses the competency of the inferior glenohumeral ligament, and can be used to evaluate for inferior shoulder instability (21). The Kim test and jerk test load the posterior labrum and should be used to evaluate for posterior labral pathology. Kim et al. (21) demonstrated that the Kim test had a sensitivity of 80% and a specificity of 94%, with a sensitivity of 97% when the Kim and jerk tests were combined. Additionally, the authors commented that the Kim test was better at identifying posterior-inferior labral injuries (from 5 o’clock to 7 o’clock positions), while the jerk test was more accurate for direct posterior labral pathology (from 7 o’clock to 10 o’clock positions in the right shoulder, or 2 o’clock to 5 o’clock positions in the left shoulder) (21). Patients with suspected hyperlaxity or connective tissue disorders should be evaluated for the Beighton criteria (22,23).
Superior labral anterior to posterior (SLAP) and biceps pathology can be examined via numerous provocative maneuvers including O’Brien’s active compression, Speed’s test, crank test, resisted supine external rotation test, and major sheer test (18,24,25). Meserve et al. (26) performed a meta-analysis examining the efficacy of various tests in diagnosing superior labral pathology, which was confirmed either by MRI or intraoperative findings. The authors recommended using the active compression test first, followed by the crank test, and Speed’s test when superior labral pathology was suspected (26). Cook et al. (24) evaluated the diagnostic accuracy of five tests: anterior compression (O’Brien’s), bicep load II test, dynamic labral sheer test (O’Driscoll), Speed’s test, and labral tension test as standalone and combined tests in patients with confirmed superior labral pathology on arthroscopy. The authors found that the bicep load II test was the only test that showed accuracy in diagnosing isolated SLAP injury. No test in isolation or combination of tests resulted in a significant positive or negative predictive value (27). Correct diagnosis of this complex pathology requires a combination of clinical suspicion, physical examination, and advanced imaging modalities.
Imaging studies may be helpful in confirming or making the diagnosis of shoulder instability, particularly in patients who report subluxation as opposed to dislocation. Owens et al. (11) proposed subclassifying subluxation as either a transient luxation, or benign subluxation. Patients with transient luxation have MRI findings similar to patients with a history of dislocation, including a Bankart lesion, as well as Hill-Sachs lesion, or even a subtle bone bruise on the posterior superior aspect of the humeral head (14). All patients with shoulder subluxation or dislocation should undergo radiographic evaluation including true AP (Grashey), scapular Y, and axillary lateral radiographs. The Bernageau view allows for an en fosse view of the glenoid and can be used to evaluate for anterior inferior bone loss (24). Computed tomography (CT) also can be useful in the evaluation of bone loss patterns, both on the glenoid and humeral head (so called bi-polar bone loss) (28). Typically magnetic resonance imaging (MRI), specifically MR arthrography (MRA), is considered the gold standard for evaluation of the capsulolabral injuries that result from dislocation or subluxation events (18,29). MRA allows for controlled distension of the shoulder capsule and can more clearly define the anatomy of the labrum. The sensitivity of MRI for SLAP tears has been reported to be as high as 90% (18,30). Owens et al. (14) evaluated the usefulness of MRI following acute traumatic subluxation events and found that MRI correctly identified a Bankart lesion in 26 of 27 shoulders, and Hill Sachs lesions in 25 of 27 patients. In the same patient cohort, plain radiographs identified only two Hill Sachs lesions (14). Ultimately, a combination of diagnostic tests and clinical suspicion are required to make the correct diagnosis. Depending on the patient’s sport, signs and symptoms with regards to the presentation of instability may vary.
The repetitive nature of pitching in baseball puts players at risk for shoulder instability due to microtrauma and microinstability (31) (Table). Reinold et al. (32) found a 5-degree increase in external rotation among professional baseball pitchers at the end of the season compared with the beginning of the season. This progressive loss of internal rotation and increase in external rotation can theoretically cause attenuation of the anterior capsular tissues and lead to microinstability (9). Injuries to the labrum, both anterior-inferior (Bankart lesion), and superior (SLAP lesion), are common among baseball players, especially pitchers. Specifically, SLAP tears may be related to GIRD (33). Burkhart et al. reported on a series of 124 baseball pitchers with type II SLAP lesions (detachment of biceps anchor) and reported that the mean GIRD was 53 degrees in the overall patient cohort, with mean GIRD of 33 degrees in those with type II SLAP lesions (31).
Less common shoulder injuries also have been described in baseball players. A case series of five professional baseball players found that an isolated tear of the mid substance of the anterior shoulder capsule can contribute to microinstability (12). All players in this study ultimately required surgical intervention after a failure of nonoperative treatment and returned to play at a mean of 13.3 months (12). Another case series identified four professional baseball pitchers with humeral avulsions of the inferior glenohumeral ligament (HAGL), three of whom ultimately required surgery (17). Nakagawa et al. performed a retrospective analysis of 51 baseball players of varying levels of competition with painful shoulders due to repetitive throwing who underwent arthroscopic surgery between 1995 and 1999 at a single Japanese institution. Twenty-four players were pitchers with the rest being position players. The authors sought to better characterize risk factors for the development of a painful Bennett lesion (i.e., mineralization of the IGHL). Of the 51 patients, 24 had a bony spur (Bennett group) and 27 did not (control group). Within the Bennett group, 13 patients had a painful lesion, while 11 were asymptomatic. Posterior joint laxity, no deficit of internal rotation, and an avulsed posterior-inferior glenoid fragment on computed tomography scan were determined to be the characteristic clinical features in shoulders with a painful Bennett lesion (34). These studies demonstrate the various, and sometimes-atypical ways in which shoulder instability can present in baseball players. Physicians should be aware of this, especially in those athletes who fail nonoperative management, and yet have a “normal” MRI.
The overhand tennis serve puts tennis players at risk of developing shoulder instability in a mechanism similar to that of overhead throwers (35). For this reason, tennis players also are susceptible to GIRD and SLAP tears, which may alter shoulder kinematics or lead to subtle instability (35). Lädermann et al. (36) sought to examine glenohumeral instability and impingement patterns during tennis movements by determining the type and frequency of impingement as well as the amount of shoulder subluxation. Ten former asymptomatic professional tennis players were recruited and evaluated for internal and external impingement as well as glenohumeral instability using optical motion capture (OMC) kinematics testing, MRI, and clinical exam. All players had a competent rotator cuff clinically, while MRI revealed cuff lesions in six of the subjects (encompassing three interstitial tears of the supraspinatus and eight partial articular supraspinatus tendon avulsions [PASTA] lesions). Labral tears were evident in five of the athletes (two posterior, two inferior, and two posterosuperior lesions). There was no evidence of Bennett or Bankart lesions. OMC testing revealed anterosuperior impingement in two athletes during their forehand. Four athletes were found to have anterior and lateral subacromial impingement and seven were found to have posterosuperior impingement during the late cocking phase of serving (36). The authors recommended utilizing a more compact serve motion to minimize impingement that can occur along with instability.
Volleyball produces different kinematics than throwing; however, this sport also involves repetitive overhead activity, which can stress the glenohumeral joint beyond its physiologic limits. However, because the movements required for serving, spiking, and setting in volleyball are slightly different than overhead throwing, athletes will manifest their instability in a different form, typically as multidirectional instability (MDI) (35). It can be difficult to predict what patients are at risk for further injury, or progression to frank dislocation. Therefore, patients should be closely monitored with regards to their symptoms and performance, and be removed from play if symptoms persist. Kinetic forces about the shoulder are the greatest during spiking, and those athletes who frequently perform this activity both in games and practice should be monitored for signs of overuse (37). Over time, the repetitive motion associated with the volleyball serve can lead to chronic attenuation of the capsular tissue, resulting in apprehension during overhead activity with the arm in forward elevation and abduction or even activities of daily living. Patients with redundant capsular tissue may be candidates for a capsular shift, remplissage, or both. Jones et al. reported on the outcomes of 20 overhead athletes (six baseball, four swimming, three softball, three volleyball, three tennis, and one water polo) who underwent arthroscopic capsular plication (12 with suture, eight with suture anchors) for debilitating shoulder pain secondary to symptoms of anterior instability without evidence of frank dislocation (38). At a mean follow-up of 3.6 years, 18 (90%) patients returned to play, with 17 (85%) at their preinjury level of play. The two patients who failed to return to play had concomitant rotator cuff injury and continued pain postoperatively (38).
While HAGL lesions have been described in baseball athletes, this injury also may be seen in competitive volleyball players, as the extreme abduction and external rotation obtained during a volleyball serve can approach that experienced during a baseball pitch. However, the presurgical diagnosis of HAGL lesion as a cause for anterior shoulder instability can be difficult. Taljanovic et al. (39) examined a series of four female collegiate volleyball players with chronic activity-related pain and inferior capsular laxity and/or instability in their dominant shoulders. The authors were specifically interested in the presence of HAGL lesions as evidenced by MR arthrogram and arthroscopy. All four patients were found to have HAGL lesions. Three also were found to have articular sided partial-thickness rotator cuff tears and three were found to have labral tears, which were repaired with suture anchors (one SLAP, one midline posterior labral avulsion tear, and one chronic appearing anterior inferior avulsion tear). The authors emphasized that repetitive microtrauma from overhead hitting in volleyball can lead to inferior capsular laxity and subsequent HAGL lesions (39). Physicians should keep this injury in mind when evaluating volleyball players.
Similar to volleyball, swimmers also are subject to MDI and generalized ligamentous laxity (40). “Swimmer’s shoulder” is a term used to encompass a wide array of pathology (subacromial impingement, biceps or rotator cuff tendonitis, or just generalized shoulder pain), which effects this patient population (41). Tate et al. investigated risk factors for shoulder pain and disability, although not necessarily instability, across the career of swimmers by examining 236 swimmers ages 8–77 (41). The pain profile and symptomology varied with age and exposure. Patients younger than 12 years primarily had pain, whereas older patients more commonly complained of disability and inability to use their shoulders; with high school athletes being the most symptomatic (41). The factors found to contribute most to shoulder pain were greater swimming exposure, history of traumatic injury (common in swimmers who also played water polo), and those who experienced feelings of subjective instability (41). This study underlies the importance of educating swimmers about the risk factors for developing long-term disability in general, so that issues such as recurrent instability, which has been shown to contribute to shoulder pain later in life, may be addressed sooner rather than later.
Sein et al. (41) hypothesized that training volume in swimming correlated with injury rates. The authors surveyed 80 elite swimmers ages 13 to 25 years via questionnaire and correlated their physical examination findings with MRI examination. Overall, 91% reported some type of shoulder pain, while 84% had positive impingement signs on examination, and 69% had supraspinatus tendinopathy on MRI (41). The authors found that increased tendon thickness on MRI positively correlated with tendinopathy, while shoulder laxity measurements correlated with impingement findings on physical examination. The weekly number of hours and mileage per week correlated with tendinopathy, with those swimming >15 h·wk−1 being twice as likely to have tendinopathy (41). While overhead sports, such as baseball, have implemented pitch counts and limited number of innings pitched to decrease injury rates, no such limitation exists in swimming; potentially predisposing these athletes to instability and further injury.
Throwing the javelin mimics the biomechanics of throwing seen in baseball pitchers, thus predisposing these athletes to similar pathology in the late cocking and early acceleration phases of throwing. Herrington (42) found that javelin throwers present with greater external rotation in their throwing arm than nonthrowing arm, similar to GIRD in baseball pitchers, potentially leading to impingement and other posterior shoulder pathology. Maintenance of muscular balance of the rotator cuff and glenohumeral joint is crucial given the explosive nature of javelin throwing (42). Kim et al. (43) investigated the effect of 8 wk of targeted therapy aimed at rotator cuff strengthening and range of motion analysis in elite javelin throwers and found that all 10 athletes had improved rotator cuff strength, core stability, flexibility, and throw distance following therapy.
Shoulder instability in American football players is typically reported in offensive linemen, who experience traumatic loading of their glenohumeral joint, often leading to subluxation and dislocation (44). Quarterbacks also are at risk for shoulder instability, due to shoulder mechanics similar to those experienced in other overhead-throwing athletes (45). Because traumatic dislocations are less common in quarterbacks, it may be more difficult to suspect and diagnose symptoms of instability in these athletes. Kelly et al. (46) reviewed 1534 quarterback injuries in the NFL from 1980 to 2001 and found that the shoulder was the second most injured part of the body (15.2% of injuries). Among shoulder injuries, trauma (82.3%) was the most common cause, with overuse injuries accounting for 14% of injuries. Anterior instability was more common following traumatic injury, with a reported rate of 8% of shoulder injuries. Overuse, however, only accounted for 0.4% of shoulder injuries (46). Posterior instability also accounted for 0.4% of throwing injuries (46). This study demonstrates that quarterbacks may suffer from subtle, performance-affecting shoulder instability, even in the absence of a traumatic mechanism. Furthermore, repetitive throwing may further exacerbate instability resulting from trauma.
Depending on the athlete’s mechanism of injury, symptoms, and desire to finish the season, initial treatment consisting of nonoperative therapy may be considered, especially in MDI and patients with subluxation. In the case of MDI, careful assessment for general ligamentous laxity is important, and in the absence of a traumatic event, patients with MDI should typically undergo a course of nonoperative management with physical therapy focusing on scapular stabilization and strengthening of the rotator cuff (35). Athletes with micro instability warrant special consideration. Recent trends in management of this issue are aimed at both prevention and when possible nonoperative treatment, often times via similar rehabilitation techniques (32). The primary objective is maintenance of full range of motion of the glenohumeral joint, particularly during the throwing motion. Overhead athletes typically have abnormally high shoulder range of motion, ranging from 29 to 137 degrees of external rotation (ER), 54 to 61 degrees of internal rotation (IR), and 183 to 198 degrees of total ER/IR motion (32). Strengthening, particularly of the shoulder external rotators, lower trapezius, and scapular stabilizers also are crucial (32). Reinold and Gill (32) describe a 4-phase rehabilitation process consisting of: 1) acute phase (diminish pain, improve posterior motion, reestablish shoulder stability, 2) intermediate phase (progress strength, improve ER/IR balance, core strengthening), 3) advanced strengthening phase (aggressive strengthening, neuromuscular control), and 4) return to activity phase. Overall duration of treatment is dependent on the athlete and the severity of injury.
Nonoperative therapy also can potentially be considered in first time dislocators. Initial therapy should be aimed at resolving any scapular maltracking, or range of motion deficits, especially in athletes with GIRD (32). Fedoriw et al. (33) demonstrated the effectiveness of nonoperative treatment in high performance throwers. A review of 119 pitchers who had SLAP tears and GIRD treated nonoperatively with physical therapy demonstrated that all players were able to return to an acceptable level of play without surgical intervention (33). Athletes who experience first-time dislocation in season will often desire to return to play following nonoperative management (47). The literature has shown that frequently an athlete may return to play following approximately 3 wk of rehabilitation; however, it is crucial to counsel these athletes regarding the risk of recurrence (47). Recurrence can be especially high in younger athletes. Gigis et al. (48) compared treatment of first time dislocaters aged 15 to 18 years that underwent conservative versus arthroscopic management. Among the 27 patients managed conservatively, 19 (70.3%) experienced recurrent dislocation (48). It is important to note that this study included patients with traumatic dislocation and their individual sport was not specified. While bracing may help limit the risk of repeat instability events, it can be severely limiting, especially in the case of throwers (49).
If nonoperative management does not provide symptomatic relief and return to the same level of play, operative treatment should be performed to address the underlying pathology (e.g., Bankart repair plus treatment of associated injuries, i.e., bone loss, Hill-Sachs lesion, posterior labral tear, HAGL, etc). In the aforementioned study, arthroscopic Bankart repair in patients aged 15 to 18 years lowered the recurrence rate from 70.3% to 13.1% (48). While technical considerations vary among surgeons, it is worth considering that these high performance overhead athletes will likely stress their repairs more than the average patient. Stein et al. (50) evaluated sport specific activity scores in different types of athletes: noncontact, contact, overhead, and martial arts. The study found that while all athletes returned to sport at 32 months postoperatively, overhead athletes and martial artists required prolonged rehabilitation to reach sport specific proficiency, demonstrating the importance of determining functional demand of the patient when counseling them regarding their outcome.
Bankart repair often consists of an arthroscopic single row of suture anchors placed along the anterior glenoid rim to restore the capsulolabral bumper and enhance glenohumeral stability (10). In athletes or patients with a higher risk of recurrence due to activity level, open repair may be considered (51,52). Nassiri et al. (53) performed a systematic review examining rates of return to play after arthroscopic versus open Bankart repair in overhead athletes (baseball, tennis, volleyball, and freestyle swimming). Athletes were classified as grade 1, full return to play; grade 2, diminished return to play; and grade 3, failure to return to play. Return to play was similar between arthroscopic (72% grade 1, 24.2% grade 2, and 7.2% grade 3) and open repair (68.7% grade 1, 34.5% grade 2, and 8.3% grade 3) (54). While rates of return were relatively similar, recurrence rates differed between the two groups with 11.4% in the arthroscopic group experiencing recurrent dislocation or subluxation, compared with 2.8% in the open repair group (54). Fabricant et al. (51) recommend double row arthroscopic Bankart repair for patients with a high-risk of recurrence, such as overhead athletes. While several studies have demonstrated that double row repair may better restore capsulolabral anatomy and contact surface area, no clinical studies have shown it to be superior to single row Bankart repair (55,56). Based on current literature, the authors recommend the following algorithm for the management of instability in overhead athletes (Fig.) (44,51,57,58).
There is literature to support return to a high level of play in baseball pitchers who undergo surgical treatment for symptoms of overhead instability and pathology including SLAP tear, GIRD, and rotator cuff disease; however, outcomes are mixed (12,32,33,59,60). Van Kleunen et al. (60) reported on high level throwers (baseball players) who underwent surgical treatment for an infraspinatus tear, SLAP tear, and GIRD and found that while all 17 of their patients attempted a return to play, only six returned to their preinjury level, while five performed at a lower level or changed position, and six were not able to return to play. Park et al. (59) reviewed the outcomes of 24 elite overhead athletes (16 baseball players, three javelin throwers, three volleyball players, and two badminton players) who underwent arthroscopic SLAP repair and found that 12 of 24 returned to play. Of note, return to play in baseball players was 38% compared with 75% in the other athletes (59). The authors did not comment on whether athletes returned to their prior level of play or not. This information can be used to help counsel high performance overhead athletes. It is crucial to determine the degree of instability, as well as concomitant pathology, and the effect of shoulder instability on performance. Athletes, coaches, and athletic trainers should understand that surgical repair may not lead to return to play at an equivalent level, especially in baseball players.
Sport-Specific Return to Play Criteria
Return to play is a major marker of successful treatment for all athletes who sustain injuries. Because of the physiologic demands placed on a surgical repair for shoulder instability in overhead athletes, special precautions should be taken. In 2014, Ialenti et al. performed a systematic review on return to play at preinjury level following surgery for shoulder instability in athletes. Specific procedures included open and arthroscopic Bankart repair and Latarjet (61). The authors evaluated 16 papers which commented on the return to play of any sport, including 1036 athletes, and reported a return to equivalent level of play of 71% for arthroscopic Bankart, 73% for Latarjet, and 66% for open Bankart (61). Outcome measures were similar among all groups. The study did not, however, comment on postoperative precautions, length of time to return to play, or rates of return to play for specific sports (61). Also, in 2014, Stone et al. performed a systematic review of return to play following open Bankart repair in both contact and noncontact sports (61). Twenty-nine papers with mean 51-month follow up met inclusion criteria and found that on average, unrestricted return to play was achieved at 23.2 wk (59). A majority of athletes in the studies reviewed were able to return to noncontact sports at 1 to 16 wk (61).
DeFroda et al. (61) reviewed the physical rehabilitation protocols of thirty academic orthopedic institutions following arthroscopic Bankart repair. On average, patients were recommended to be immobilized in a sling for 4.8 wk, with full passive range of motion expected at a mean of 9.2 wk, and full active range of motion recommended by 12.2 wk (61). The reviewed protocols recommended return to play and competition at 32.4 wk, and 39.3 wk respectively; which is much later than in the review by Stone et al. (62,63) These studies demonstrate that ultimately, rehabilitation and time to return to play is highly variable and likely depends on surgeon-specific preferences, as well as the type of athletic activity.
Overhead athletes may manifest symptoms of instability in a very different manner than collision athletes. It is important to perform a thorough physical examination, to determine when in the overhead motion pain occurs, and to understand the specific symptoms experienced by the athlete. Physical therapy and stretching are often beneficial, however in patients who fail conservative management, operative stabilization may be necessary. Additionally, evaluation for concomitant injuries such as humeral head or glenoid bone loss, HAGL lesions, or tendinopathy, and rotator cuff tears should be considered and addressed as necessary. Patients should be counseled that while return to play following surgery is likely, they might need to consider changing position (pitchers). It also is important for overhead athletes to understand that they may not be able to return to their preoperative level of play depending on the injury and the specific requirements for their sport and position.
The authors declare no conflict of interest and do not have any financial disclosures.
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