Involvement of the Subscapular Bursa as a Cause of Throwing Pain

This study involved 110 baseball players who visited our hospital for consultation regarding their symptoms and who were followed up for at least 6 months. All were men with an average age of 27 years (range, 16–36 years). The dominant arm was affected in all players. The subjects comprised 52 high schooling, 11 collegiate, 9 professional, and 38 recreational level players. Their baseball playing positions were 50 pitchers, 9 catchers, 19 infielders, and 32 outfielders.


Introduction
Bursae exist in many parts of the body where a considerable degree of motion between parts of the anatomy occurs but where no cartilaginous joint is required [1].Particularly in areas of the shoulder joint where the muscles or tendons and bones cross each other, bursae between them play important roles in maintenance of joint function [2].Many previous studies have clarified both anatomically and clinically that the subacromial bursa helps the greater tuberosity of the humerus to smoothly glide under the coracoacromial arch [2][3][4][5][6].However, only a few studies have investigated the subscapular bursa [7,8] and the clinical importance of this bursa remains incompletely understood [9,10].Colas et al. [8] studied the course of the subscapularis muscle and the anatomy of the subscapular and subcoracoid bursae.Their cadaveric study indicated that the superior distal band of the subscapularis muscle coils along the coracoid process during external rotation in elevation and that

Evaluation and statistical analysis
The patients were examined to determine in which position their pain was provoked.The treatment was considered effective when pain was not provoked with arm rotation 1 or 2 weeks after arthrography.The patients were divided into three groups according to whether they could return to their premorbid playing level: Group A could play at their preinjury level 6 months after the treatment; in Group B, the treatment was effective, but pain was either not adequately reduced to return to their premorbid playing level or recurred in 6 months; and in Group C, the treatment was not effective and patients could not return to their playing level.Factors including skill level, playing position, symptom duration, and concomitant injury of the rotator cuff tendon were investigated with respect to their ability to affect the arthrography outcome.
Fisher's exact probability test was used to detect statistical differences between two groups regarding the results, and a statistically significant difference was considered to exist at p < 0.05.The chi-square test was used for analysis across four subgroups.

Results
Pain tended to be provoked with greater arm raising and extension (Table 1), and pain was provoked in all patients by external rotation at 135° of abduction (Figure 3).Pain with external rotation at 135° degrees of abduction decreased after arthrography in 92 players (84%).Thirty-three patients could continue at their playing level 6 months after treatment (Group A), while 59 patients either did not have adequate pain relief to return to their premorbid playing level or the pain recurred in 6 months (Group B).Eighteen patients (16%) were not relieved from pain and could not return to their playing level (Group C).

Skill level
We divided the subjects into four subgroups according to playing level.These four subgroups comprised 48 high schooling, 9 collegiate, 8 professional, and 27 recreational level players.Group A included 14 high school, 4 collegiate, 2 professional, and 13 recreational players; Group B, 34 high school, 5 collegiate, 6 professional, and 14 recreational players; and Group C, 4 high school, 2 collegiate, 1 professional, and 11 recreational players.Skill level did not affect the arthrography outcome (Table 2).

Symptom duration
Fifty-one patients were treated for less than 3 months after symptom onset, and their symptom duration was considered to be short.Fifteen patients with short-duration and 18 patients    with long-duration symptoms belonged to Group A, 33 with short-duration and 26 with long-duration symptoms belonged to Group B, and 3 with short-duration and 15 with long-duration symptoms belonged to Group C.There were more patients with short-duration symptoms in Groups A and B than in Group C (Fisher's exact probability test, P = 0.009) (Table 4).

Concomitant injury in rotator cuff tendon
Twenty-nine patients demonstrated pooling of dye in the rotator cuff, indicating injury to this structure.Nine patients with cuff tears and 24 without cuff tears belonged to Group A, 16 with cuff tears and 43 without cuff tears belonged to Group B, and 4 with cuff tears and 14 without cuff tears belonged to Group C. Tendon injury did not affect the result.In fact, a higher proportion of rotator cuff injury was noted in patients in Groups A and B, in whom the treatment proved effective (Table 5).
The subscapularis bursa lies between the subscapularis muscle and scapula under the coracoid process.The bursa helps the subscapularis muscle to coil around the coracoid process, especially during external rotation in elevation [8,22].
Irritation in this bursa may disturb throwing motion, and the arm is forced to rotate in such situations.In fact, pain tends to be provoked during external rotation with greater arm elevation and horizontal abduction in the clinical setting.The current study also showed that filling the joint and its bursa with liquid dye after arthrography reduced rotational pain in 84% of the players.
The arm position relative to the trunk during throwing is approximately 90° to 100° of abduction [23].In the present study, there was a discrepancy in comparison of the angle of abduction at which pain was provoked.We surmised that the reason for this discrepancy was that the arm was examined passively.During actual throwing activity, the scapulohumeral relationship approaches that with the arm passively elevated at 135° of abduction to generate rotational torque.
More patients in Groups A and B had short-duration symptoms (< 3 months) than in Group C, indicating that treatment efficacy is affected by symptom duration.If athletes with symptomatic shoulders continue playing baseball without treatment, their condition will worsen to more advanced stages until no treatment is effective.Friction of the subscapularis tendon might cause inflammation in the subscapular bursa.When inflammation is localized, it may resolve spontaneously.However, in more advanced stages, irritation in the bursa becomes extensive, and adhesion may develop, disturbing the gliding motion of the tendon.Restriction in the glenohumeral joint movement might affect coordination of the glenohumeral, scapulothoracic, and trunk movements, decreasing throwing performance or causing other injuries.Thus, we should educate athletes and their coaches to address throwing disability as quickly as possible.
Group B included patients whose symptoms recurred in less than 6 months despite the fact that distension arthrography temporarily relieved their pain.Some shoulder joint characteristics, including subtle instability, might predispose a player to developing symptom recurrence; however, the current study could not elucidate why their throwing pain recurred.Further shoulder examination for subtle instability or throwing motion analysis to investigate abnormal biomechanics is needed.If the cause of throwing pain is known, training for proper throwing motion could prevent recurrence.
To our knowledge, no author has ever pointed out the importance of the subscaplar bursa causing throwing pain.Hopefully, function of the subscapular bursa should be highlighted and more attention should be paid to its anatomy.We think physical therapies can alleviate further inflammation or damage with continued throwing by approaching scapular position or orientation.Myers et al. [24] demonstrated the scapula tipped posteriorly until maximum glenohumeral external rotation during throwing motion.Stretching the pectoralis minor muscle [25] might help this posterior tipping of the scapula and decrease glenohumeral contribution at maximum shoulder external rotation in throwing.This retrospective study had some limitations.We could not determine in which cases distension arthrography would be effective.Additionally, we could not determine how involvement of the subscapular bursa relates to previously reported pathological conditions such as internal impingement [16,19], glenohumeral internal rotation deficit [26], or SICK scapula syndrome [27].Further prospective studies with larger population are needed.

Figure 1 :
Figure 1: The antero-posterior x-ray image with the arm internally rotated shows the leakage of the dye into the ISP tendon (the white arrow), indicating its tendon injury.

Figure 2 :
Figure 2: a.The anterior-posterior x-ray image shows the dye bursting to the medial side below the coracoid process.b.The scapular Y view of the same patient shows the dye bursting anterior to the bone.The images indicated the dye distended to the subscapular bursa.

Figure 3 :
Figure 3: Pain was provoked with the arm externally rotated in 135 degrees of abduction.

Table 1 :
Percentage of players with provoked rotational pain at different positions.the scapular plane, b rotation in the coronal plane

Table 2
Skill level.

Table 3
Baseball playing position.