Supraspinatus-to-Glenoid Contact Occurs During Standardized Overhead Reaching Motion

Background: Rotator cuff tears may result from repeated mechanical deformation of the cuff tendons, and internal impingement of the supraspinatus tendon against the glenoid is one such proposed mechanism of deformation. Purpose: To (1) describe the changing proximity of the supraspinatus tendon to the glenoid during a simulated overhead reaching task and (2) determine the relationship between scapular morphology and this proximity. Additionally, the patterns of supraspinatus-to-glenoid proximity were compared with previously described patterns of supraspinatus-to-coracoacromial arch proximity. Study Design: Descriptive laboratory study. Methods: Shoulder models were created from magnetic resonance images of 20 participants. Standardized kinematics were imposed on the models to simulate functional reaching, and the minimum distances between the supraspinatus tendon and the glenoid and the supraspinatus footprint and the glenoid were calculated every 5° between 0° and 150° of humerothoracic elevation. The angle at which contact between the supraspinatus and the glenoid occurred was documented. Additionally, the relationship between glenoid morphology (version and inclination) and the contact angle was evaluated. Descriptive statistics were calculated for the minimum distances, and glenoid morphology was assessed using Pearson correlation coefficients and simple linear regressions. Results: The minimum distances between the tendon and the glenoid and between the footprint and the glenoid decreased as elevation increased. Contact between the tendon and the glenoid occurred in all participant models at a mean elevation of 123° ± 10°. Contact between the footprint and the glenoid occurred in 13 of 20 models at a mean of 139° ± 10°. Less glenoid retroversion was associated with lower tendon-to-glenoid contact angles ( r = –0.76; R 2 = 0.58; P < .01). Conclusion: This study found that the supraspinatus tendon progressively approximated the glenoid during simulated overhead reaching. Additionally, all participant models eventually made contact with the glenoid by 150° of humerothoracic elevation, although anatomic factors influenced the precise angle at which contact occurred. Clinical Relevance: Contact between the supraspinatus and the glenoid may occur frequently within the range of elevation required for overhead activities. Therefore, internal impingement may be a prevalent mechanism for rotator cuff deformation that could contribute to cuff pathology.

Is Workload Associated with Internal Impingement in Professional Baseball Players? An Analysis of Days of Rest, Innings Pitched and Batters Faced (221)

Objectives: Determine if workload; as measured by number of days rest between outings, innings pitched, batters faced, and being a starting pitcher; associates with risk for internal impingement in professional baseball pitchers. Methods: All professional baseball pitchers who were diagnosed with internal impingement between 2011-2017 were identified using the major league baseball (MLB) Health and Injury Tracking System (HITS). A separate player usage dataset was used to determine workload. We then compared workload variables between pitcher-games 2, 6, 12, and >12 weeks prior to documented internal impingement and pitcher games from a control group who were never diagnosed with internal impingement. In a paired analysis, we compared the acute workload (2, 6, 12 weeks) prior to injury and the injured pitcher’s workload >12 weeks prior to injury. Results: There were 624 pitchers who suffered from internal impingement in professional baseball. Across all time points, players with more innings pitched per game, more batters faced per game, and fewer days rest in between games were associated with a subsequent internal impingement compared to controls. Pitchers who threw four or more innings per game had a 1.3-fold increase in percent of players with subsequent internal impingement compared to pitchers who threw only one inning per game. Significantly more starting pitchers were diagnosed with internal impingement over multiple time points compared to controls. Conclusions: Greater pitcher workload was associated with increased risk for internal impingement in professional baseball players. Throwing four or more innings per game increase a pitcher’s risk for internal impingement 1.3-fold compared to pitchers who threw one inning per game. Starting pitchers are more likely to sustain a LD/TM tear than control pitchers.

The Area of Impingement in the Throwing Versus Nonthrowing Shoulder of Collegiate Baseball Players: An MRI Study of the Simulated Late-Cocking Phase of Throwing

Background: During shoulder abduction and external rotation, internal impingement can occur when compressive forces between the greater tuberosity and the posterior glenoid rim pinch the undersurface of the rotator cuff. Previous studies on internal impingement have focused on qualitative results such as pathological findings; however, few studies have quantified the area of impingement (AOI) of the rotator cuff muscles between the greater tuberosity and the posterior glenoid rim. Purpose: To compare the AOI between the throwing and nonthrowing shoulders of baseball players. Study Design: Controlled laboratory study. Methods: A total of 14 asymptomatic male collegiate baseball players participated in this study. The AOI in both the throwing and the nonthrowing shoulders was calculated using magnetic resonance imaging (MRI) scans. The MRI measurements were collected with the shoulder at 90° of abduction and at 90° and 100° of external rotation. The area, width, and depth of impingement as well as cystic changes in the greater tuberosity and degeneration in the posterior labrum were compared between the throwing and nonthrowing shoulders. Results: The AOI was significantly greater in the throwing shoulders than in the nonthrowing shoulders (90° of external rotation: 32.4 vs 19.1 mm2, respectively; 100° of external rotation, 28.0 vs 15.6 mm2, respectively; P < .001 for both). Compared with the nonthrowing shoulders, there were more positive findings in the throwing shoulders regarding greater tuberosity cystic changes (0 vs 7, respectively; P = .006) and posterior labral degeneration (3 vs 13, respectively; P < .001). Conclusion: The AOI and the number of lesions in the greater tuberosity and posterior labrum were greater in throwing shoulders than in nonthrowing shoulders. Therefore, damage to the insertion of the rotator cuff muscles may affect internal impingement. Clinical Relevance: Lesions in the greater tuberosity and posterior labrum in throwing shoulders may increase the AOI by expanding the joint gap behind the glenohumeral joint. Impingement of the greater tuberosity and the posterior glenoid rim may lead to rotator cuff tears.

A partial articular-sided supraspinatus tear caused by the biceps tendon: a novel etiology of internal impingement

Our patient is a 19-year-old female who presented with left shoulder pain. Diagnostic arthroscopy revealed an articular-sided supraspinatus tear. When the shoulder was taken out of traction and placed in 90 degrees of abduction and external rotation, we visualized the biceps tendon directly impinging the undersurface of the supraspinatus tendon.

A New Method of Contact Stress Measurement for Analyzing Internal Impingement Syndrome of the Shoulder: Potentials and Preliminary Evaluation

Shoulder impingement syndrome causes critical disorders such as rotator cuff tear or superior labrum anterior to posterior (SLAP) lesion in both the general public and in athletes whose sports involve throwing. Nevertheless, the biomechanics of the syndrome still have not been clarified. Contact stress measurement in vivo during shoulder motion is essential to identifying the biomechanics of the syndrome. There have been no reports to date regarding internal impingement syndrome among the syndrome studied by using the finite element method (FEM). The proposed method simulates the internal impingement syndrome according to shoulder motion using the FEM. The method solves the critical process zone error at the supraspinatus tendon insertion according to impingement of the 3D biomechanical model by relaxing the boundary condition for representation of shoulder motion. The simulation results confirmed that the proposed method allowed for the analysis of internal impingement syndrome by measuring contact stress (23.13 MPa) during shoulder motion. The performance of the proposed method was examined through the differential displacement (maximum 3.28 mm) in shoulder motion by boundary condition relaxation. The result of the simulation was consistent with the clinical findings.