关节镜下盂肱关节前方松解对原发性冻结肩的早期疗效

目的观察应用关节镜进行关节囊前方松解术对原发性冻结肩的治疗效果。 方法2015年3月至2017年3月陕西省人民医院收治的60例原发性冻结肩患者,所有患者经术前MRI检查或术中探查确诊,排除由其余肩部疾病(骨折、肩峰撞击、肩袖损伤、钙化性肌腱炎)引起的继发性冻结肩,所有患者应用关节镜行盂肱关节前方松解术。采集术前及术后的疼痛视觉评分(VAS)、Constant评分、复旦大学肩关节功能评分系统(FUSS),应用单因素重复测量方差分析对结果进行统计学分析评估,对肩关节各方向的被动活动度应用配对t检验方法进行统计学分析。 结果所有患者术后均未出现腋神经损伤或肩关节不稳等并发症。与术前相比,术后12周时患者的VAS评分[(0.7±0.6)vs (8.1±0.7),F ＝38.01]、Constant评分[(93.9±3.0)vs (34.2±3.4),F ＝121.42]及FUSS评分[(93.8±1.3)vs (40.1±2.2),F ＝220.09]差异有统计学意义(均为P <0.01);同时,与术前相比,患肩被动外展[(152±13)° vs (74±9)°,t ＝37.678]、前屈[(156±12)° vs (60±10)°,t ＝46.469]、体侧外旋[(66±11)° vs (8±3)°,t ＝37.762]及内旋在术后12周时明显改善(均为P <0.01)。 结论应用关节镜对盂肱关节囊前方结构进行彻底松解,可有效改善原发性冻结肩患者肩关节功能。     

Determining the resting position of the glenohumeral joint: a cadaver study

STUDY DESIGN: Single-session repeated-measures design. OBJECTIVE: To define the resting position of the glenohumeral joint by investigating the magnitude of the anterior and posterior displacements of the humeral head and medial and lateral rotation ranges of motion (ROMs) of the glenohumeral joint at different abduction angles in cadaver specimens. BACKGROUND AND PURPOSE: The resting position of a joint is the position in the joint's ROM at which the joint capsule has its greatest laxity. It is frequently chosen as the position for assessing and treating joints with dysfunction. However, no study has been conducted to determine the resting position of the glenohumeral joint. METHODS: Seven freshly frozen cadaver shoulder specimens (age at time of death [mean +/- SD] was 66.9 +/- 2.5 years) were studied. Specimens were mounted on a system that uses computer-controlled hydraulics and motors to induce and monitor translation and rotation movements of the glenohumeral joint. The magnitudes of total displacement (DTotal) of the head of the humerus and total ROM (RTotal) of the glenohumeral joint were measured in the plane of the scapula at 0 degrees (neutral), 30 degrees, 40 degrees, 50 degrees, 60 degrees, and the end range of glenohumeral joint abduction. The resting position was determined as the midpoint of the shared range of the 95% to 99.9% confidence intervals of the predicted abduction position where the peaks of displacement and rotation occurred. RESULTS: The DTotal measurements (mean +/- SD) at 0 degrees, 30 degrees, 40 degrees, 50 degrees, 60 degrees, and the end range of glenohumeral joint abduction were 30.53 +/- 9.35, 44.87 +/- 7.34, 45.35 +/- 8.53, 43.99 +/- 10.02, 39.63 +/- 9.85, and 23.80 +/- 10.42 mm, respectively. The RTotal measurements (mean +/- SD) for the same positions were 67.15 degrees +/- 15.87 degrees, 95.64 degrees +/- 24.26 degrees, 98.88 degrees +/- 29.56 degrees, 97.08 degrees +/- 30.17 degrees, 90.91 degrees +/- 28.73 degrees, and 63.48 degrees +/- 25.93 degrees, respectively. The resting position was located at 39.33 degrees +/- 4.37 degrees of glenohumeral abduction (45.13% +/- 7.58% of the available abduction ROM). The resting position (Y) varied linearly with the maximum available abduction ROM (X) (Y = 0.607X - 13.120, R2 = 0.679, F = 10.61, P = 0.023). There was a main effect of joint position on both displacement (P<0.001) and rotation ROM (P<0.001). CONCLUSION: In the plane of the scapula, the resting position of the glenohumeral joint (angle measured between the scapula and humerus) occurred at 39 degrees of abduction (45% of the maximum available abduction ROM) and varied linearly with the amount of available abduction ROM. This finding suggests that in patients with glenohumeral joint hypomobility the resting position is located closer to neutral and that evaluation and treatment should be initiated accordingly at a smaller angle of abduction than the traditional resting position. Our data were derived from cadaver specimens, therefore, caution should be taken when generalizing the results of the present study to a patient population.     

Patients undergoing stabilization surgery for recurrent, traumatic anterior shoulder instability commonly have restricted passive external rotation

An important component in the surgical treatment of recurrent anterior shoulder dislocations is the Bankart repair. This is often supplemented with ligament plication for perceived laxity. The glenohumeral ligaments define translational laxity and restrict glenohumeral range of motion. The purpose of this study was to measure the external rotation (ER) range of motion of patients under anesthesia for glenohumeral stabilization surgery. A blinded observer measured bilateral shoulder ER in 15 patients by use of a standardized torque and goniometry. ER in the unstable shoulder with the arm abducted 90 degrees averaged 14 degrees less than that in the uninjured shoulder, and this was statistically significant. There was a significant loss of 11 degrees ER in the unstable shoulder with the arm at the side. The findings indicate that the glenohumeral joint in patients with a Bankart lesion is commonly rotationally stiff.     

Biomechanical tests for type II SLAP lesions of the shoulder joint before and after arthroscopic repair

Superior labral anterior-to-posterior (SLAP) lesions can cause shoulder pain partly by causing glenohumeral instability. The purpose of this study was to examine the effect of a simulated type II SLAP lesion and subsequent repair on glenohumeral translation of the vented shoulder. In eight cadaver joints, a robotic/UFS testing system was used to measure joint translation by applying an anterior, posterior, or inferior load of 50 N to each shoulder. The "apprehension tests" for anterior and posterior instability were simulated by applying an anterior load of 50 N with an external rotation torque of 3 Nm or a posterior load of 50 N with an internal rotation torque of 3 Nm. Each loading condition was applied at 30 degrees and 60 degrees of glenohumeral abduction with a constant joint compressive load (44 N) to the intact, simulated SLAP lesion, and repaired shoulder. Repair of the type II SLAP was then performed by placing a Suretac through the labrum both anterior and posterior to the biceps anchor and testing was repeated. ANOVA was used to compare translation of the intact joint, the joint after the type II SLAP lesion had been simulated, and after repair. At 30 degrees of abduction, anterior translation of the intact vented shoulder joint from anterior loading was 18.7+/-8.5 mm and increased to 26.2+/-6.5 mm after simulation of the type II SLAP lesion ( p< or =0.05). The arthroscopic repair did not restore anterior translation (23.9+/-8.6 mm) to the same degree as the intact joint ( p> or =0.05). At 60 degrees of abduction, anterior translation of 16.6+/-9.6mm in the intact joint was not significantly increased at 19.4+/-10.1 after simulation of the type II SLAP lesion ( p=0.0527). AP loading also resulted in inferior translation. At 30 degrees of abduction it was 3.8+/-4.0 mm in the intact joint and increased to 8.5+/-5.4 mm after the type II SLAP lesion ( p< or =0.05. After repair the inferior translation decreased significantly to 6.7+/-5.3 mm ( p< or =0.05). Although inferior translations were less at 60 degrees of abduction, results were similar to those at 30 degrees after repair. There were no significant increases in translation after SI/AP combined external rotation torque or posterior-anterior combined internal rotation torque loading.In this study the repair of a type II SLAP lesion only partially restored translations to the same degree as an intact vented shoulder joint. Therefore, improved repair techniques or an anteroinferior capsulolabral procedure in addition to the type II SLAP lesion repair might be needed to restore normal joint function.     

Arthroscopic release and latissimus dorsi transfer for shoulder internal rotation contractures and glenohumeral deformity secondary to brachial plexus birth palsy

BACKGROUND: Internal rotation contractures due to external rotation weakness secondary to brachial plexus birth palsy frequently lead to glenohumeral deformity and impaired shoulder function. Our surgical approach to treat these contractures relies on arthroscopic release for young children (less than three years old) and combines arthroscopic release with latissimus dorsi transfer for older children. We report the results for the first thirty-three children followed for a minimum of two years after such treatment. METHODS: Nineteen children with a mean age of 1.5 years (all younger than three years of age) underwent arthroscopic contracture release as the only primary procedure, and fourteen children with a mean age of 6.7 were also treated with a latissimus dorsi transfer. Passive external rotation with the arm at the side and passive and active elevation were measured for all patients preoperatively. Passive and active external rotation, internal rotation, and elevation were measured for all patients postoperatively. Magnetic resonance imaging was performed preoperatively and postoperatively to evaluate the status of the glenohumeral joint. RESULTS: Preoperative passive external rotation averaged -2 degrees for the children who underwent arthroscopic contracture release only and -24 degrees for those who also were treated with a latissimus dorsi transfer. Arthroscopic release achieved a marked increase in passive external rotation and a centered position of the glenohumeral joint at the time of surgery in all but the oldest child in the series, who had severe deformity. The contracture recurred in four of the younger children who had an isolated release, and this was treated with a repeat arthroscopic release and a secondary latissimus dorsi transfer. None of the children who had a primary latissimus dorsi transfer had recurrence of the contracture. At the time of follow-up, the mean passive external rotation was increased by 67 degrees (p < 0.005) in the fifteen children with a successful arthroscopic release, 81 degrees (p < 0.005) in those treated with a primary latissimus dorsi transfer, and 78 degrees in the four patients who were treated with a late latissimus dorsi transfer because the isolated arthroscopic release failed. The mean active elevation increased 12 degrees , 3 degrees , and 10 degrees , respectively, in the three groups. Internal rotation was not measured consistently preoperatively, but when it had been it was found to have decreased substantially postoperatively. Magnetic resonance imaging performed prior to the surgery showed a pseudoglenoid deformity in eighteen of the children. At two years, magnetic resonance images were available for fifteen of those children, and twelve of the images showed marked remodeling of the deformity. CONCLUSIONS: In children who are younger than three years of age, arthroscopic release effectively restores nearly normal passive external rotation and a centered glenohumeral joint at the time of surgery. In most of these children, external rotation strength is sufficient to maintain this range of motion and to improve glenoid development when preoperative deformity was present. The addition of a latissimus dorsi transfer in older children predictably results in similar improvements. Gains in active elevation are minimal. All children have a loss of internal rotation, which is moderate in most of them but is severe in some.     

Rotator interval dimensions in different shoulder arthroscopy positions: a cadaveric study

The rotator interval was defined as a triangular structure, where the base of the triangle was the coracoid base, the upper border was the anterior margin of the supraspinatus, and the lower border was the superior margin of the subscapularis muscle-tendon unit. We evaluated the rotator interval dimensions in 15 shoulders from 10 lightly embalmed adult cadavers in 3 shoulder arthroscopy positions: 0 degrees of abduction and 30 degrees of flexion (beach chair [BC]), 45 degrees of abduction and 30 degrees of flexion (lateral decubitus 1), and 70 degrees of abduction and 30 degrees of flexion (lateral decubitus 2). In each shoulder position, measurements were made in neutral rotation (NR), 45 degrees of external rotation (ER), and 45 degrees of internal rotation (IR). The coracoid base lengthened with IR in all positions and shortened in ER in the lateral decubitus position but not in the BC position. Abduction significantly lengthened the coracoid base, which was shortest in the BC position with ER (24 +/- 4 mm) and longest in the lateral decubitus 2 position with IR (33 +/- 5 mm). The coracoid base, where sutures are placed during plication of the interval, was observed to lengthen and, therefore, loosen with IR and abduction. To prevent postoperative ER restriction, plication should be made in ER or neutral rotation when operating in the BC position and the degree of abduction should be decreased and the shoulder held in ER when operating in the lateral decubitus position.     

Arthroscopic release of the glenohumeral joint in shoulder stiffness: a review of 26 cases. French Society for Arthroscopy.

The purpose of this multicenter retrospective study of arthroscopic release of the glenohumeral joint was to evaluate the technical feasibility, the results, and the potential correlations between results and cause of the stiffness. Twenty-six shoulders in 25 patients (19 women and six men) were re-evaluated 3 to 72 months (mean, 21 months) after arthroscopic release of the glenohumeral joint. Diagnoses were primary frozen shoulder in 13 cases, bipolar stiffness (rotator cuff tear plus capsular contraction) in 3 cases, and postinjury or postsurgery stiffness in 10 cases. Results were evaluated on passive range of motion, Constant's score, and subjective assessment. Anterior or anterior inferior capsular release was done at the anterior rim of the glenoid fossa. Posterior capsule release was not performed in this series. There were no intraoperative complications. Mean range of motion gains were 86 degrees for forward elevation, 72 degrees for abduction, 34 degrees for external rotation, and 6 spinal processes for internal rotation. Constant's range of motion score increased from 12.9 out of 40 to 32 out of 40 points. Thirteen patients were very satisfied, 5 satisfied, 5 improved, and 3 unchanged. Range of motion gains were independent from the cause of shoulder stiffness, but global results were better in the primary frozen shoulder group in terms of pain and strength. Arthroscopic release of the glenohumeral joint is feasible and safe. For primary frozen shoulders, in case of failure of the functional treatment, arthroscopic release is a less traumatic alternative to manipulation under general anesthesia. For bipolar stiffness, arthroscopy provides the opportunity for treating concomitant lesions. For postsurgical stiffness, arthroscopic release improves range of motion, but the shoulder often remains painful.     

A randomized controlled comparison of stretching procedures for posterior shoulder tightness

STUDY DESIGN: Randomized controlled trial, OBJECTIVES: To compare changes in shoulder internal rotation range of motion (ROM), for 2 stretching exercises, the "cross-body stretch" and the "sleeper stretch," in individuals with posterior shoulder tightness. BACKGROUND: Recently, some authors have expressed the belief that the sleeper stretch is better than the cross-body stretch to address glenohumeral posterior tightness because the scapula is stabilized. METHODS: Fifty-four asymptomatic subjects (20 males, 34 females) participated in the study. The control group (n=24) consisted of subjects with a between-shoulder difference in internal rotation ROM of less than 10 degrees, whereas those subjects with more than a 10 degrees difference were randomly assigned to 1 of 2 intervention groups, the sleeper stretch group (n=15) or the cross-body stretch group (n=15). Shoulder internal rotation ROM, with the arm abducted to 90 degrees and scapula motion prevented, was measured before and after a 4-week intervention period. Subjects in the control group were asked not to engage in any new stretching activities, while subjects in the 2 stretching groups were asked to perform stretching exercises on the more limited side only, once daily for 5 repetitions, holding each stretch for 30 seconds. RESULTS: The improvements in internal rotation ROM for the subjects in the cross-body stretch group (mean +/- SD, 20.0 degrees +/- 12.9 degrees) were significantly greater than for the subjects in the control group (5.9 degrees +/- 9.4 degrees, P = .009). The gains in the sleeper stretch group (12.4 degrees +/- 10.4 degrees) were not significant compared to those of the control group (P = .586) and those of the cross-body stretch group (P = .148). CONCLUSIONS: The cross-body stretch in individuals with limited shoulder internal rotation ROM appears to be more effective than no stretching in controls without internal rotation asymmetry to improve shoulder internal rotation ROM. While the improvement in internal rotation from the cross-body stretch was greater than for the sleeper stretch and of a magnitude that could be clinically significant, the small sample size likely precluded statistical significance between groups.     

Arthroscopic treatment of posterior glenohumeral joint subluxation resulting from brachial plexus birth palsy

The purpose of this study is to assess the ability of arthroscopic anterior capsular release, subscapularis tenotomy, and glenohumeral manipulation to reduce glenohumeral joint subluxation resulting from brachial plexus birth palsy. Twenty-two children with a mean age of 3.9 years (range, 1.6-8.3 years) underwent preoperative magnetic resonance imaging, arthroscopic surgery with or without tendon transfers, and postoperative imaging in their spica cast. In the uninvolved shoulders, the mean percentage of the humeral head anterior to the middle of the glenoid fossa (PHHA) was 45.2% +/- 4.8% and the mean glenoid version was -7% +/- 3%. In the involved shoulders, preoperatively, the mean PHHA was 15.6% +/- 13.5% and the mean glenoid version was -37 degrees +/- 15 degrees . Postoperatively, the mean PHHA corrected to 46.9% +/- 11.2% and the mean glenoid version improved to -8 degrees +/- 8 degrees . There was a significant improvement in the mean PHHA (P < .001) and mean glenoid version (P < .001) that approached the values of the uninvolved shoulder. Arthroscopic capsular release and subscapularis tenotomy were successful in obtaining reduction of glenohumeral joint subluxation in all patients. The maintenance of reduction requires continued follow-up over time.     

Shoulder joint position sense after thermal, open, and arthroscopic capsulorrhaphy for recurrent anterior instability

Identifying the optimal surgical treatment for recurrent, anterior glenohumeral instability remains a challenge. Our purpose was to compare shoulder joint position sense among open, arthroscopic, and thermal capsulorrhaphy patients after repair of recurrent anterior instability and to compare these patients to healthy, control subjects. Sixty-seven adults (45 post-surgical patients, 22 controls) volunteered to participate in the study. We evaluated both the surgically repaired and contralateral shoulders of 45 capsulorrhaphy patients (28 men, 17 women) and compared their results with the normal bilateral shoulders of 22 age-matched controls (11 men, 11 women). Accuracy of joint position sense was quantified via passive reproduction of target positions set at 60% and 90% of each subject's maximum passive external rotation (ER(max)). We observed no significant differences in joint position sense between the repaired shoulders and the contralateral normal shoulders of all groups of capsulorrhaphy patients. Open and thermal capsulorrhaphy patients demonstrated significantly better (P 相似文献   

The effect of scapular protraction on isometric shoulder rotation strength in normal subjects

To measure the effect of scapular protraction on isometric shoulder rotation strength, 20 normal subjects completed 2 maximal isometric internal and external rotation contractions in 2 scapular positions (scapula neutral [SN] and scapula protracted [SP]) from 3 arm positions (90 degrees internal rotation [IR], 45 degrees internal rotation [MR], and 90 degrees external rotation [ER]). Scapular protraction reduced shoulder rotation strength in 5 of 6 test positions (P < .0004), with significant interactions between scapular position and arm position (P < .001) and between scapular position and contraction type (P < .0001). Protraction significantly reduced IR strength by 13% to 24% relative to SN. The effect of SP on ER strength was more position-dependent, increasing strength by 6% in the IR position and decreasing it by 7% in the MR position and 20% in the ER position. In conclusion, acute changes in scapular position affect shoulder isometric IR and ER strength. The potential adverse effects of scapular protraction on shoulder rotation strength should be considered during the evaluation and treatment of shoulder pain.     

Traumatic Anterior Glenohumeral Instability: The Role of Arthroscopy

The static and dynamic stabilizers of the glenohumeral joint act together to ensure joint stability throughout the wide range of normal shoulder motion. These structures are functionally altered after a traumatic anterior shoulder dislocation, often resulting in recurrent instability. The arthroscope has enhanced the surgeon's ability to examine and repair the unstable glenohumeral joint. The rate of recurrence of instability after arthroscopic stabilization has historically been unacceptably high compared with that after open stabilization techniques. The authors offer a treatment algorithm and suggest guidelines for the use of arthroscopic techniques in the treatment of the unstable shoulder.     

Relationship Between Maximum Shoulder External Rotation Angle During Throwing and Physical Variables

The amount of stress imposed on shoulder and elbow appears to be directly correlated with the degree of maximum shoulder external rotation (MER) during throwing motions. Therefore, identifying risk factors contributing to the increase of MER angle may help to decrease the throwing injuries occurrence in baseball players. The purpose of the present study was to demonstrate the correlation between MER and the kinematic variables at stride foot contact (SFC) during the early cocking phase, the passive range of motion (ROM), and the shoulder strength. The subjects were 40 high school baseball players. Each subject carried out five throwing tasks with his maximum effort. A three-dimensional analysis was performed to obtain the MER, and the shoulder angles of external rotation (ER), extension and abduction at SFC in the early cocking phase. The ROM and muscle strength of the shoulder ER and internal rotation (IR) were also measured. Significant moderate linear correlations were found between the MER and the ER (r = -0.32, p = 0.04) at SFC, extension angle ( r= 0.35, p = 0.03) at SFC, IR strength (r = -0.30, p = 0.04) and passive ROM of ER (r = 0.46, p = 0.01). The shoulder IR and extension angles at SFC may determine the degree of the MER angle. Furthermore, weak IR muscle strength and excessive ROM of ER might be risk factors for shoulder and elbow injuries. The finding will enable us to establish better prevention and rehabilitation strategies for throwing injuries in baseball players.

Key points

• It has been reported that the amount of stress imposed on shoulder and elbow joints is correlated with the degree of maximum shoulder external rotation angle (MER) during throwing. Therefore, controlling MER within a normal range plays a key role in the prevention for throwing-related injuries in baseball players.
• Physical and biomechanical factors related to the degree of MER must be addressed to advance the current prevention and rehabilitation strategies for the shoulder and elbow injuries.
• The current finding demonstrated that there was a significant moderate leaner correlation between shoulder internal rotation angle at the initial foot contact in the early cocking phase and MER.

Key words: Throwing, shoulder, elbow, injury prevention     

Editorial Commentary: For Shoulder Hill-Sachs Lesion Remplissage,Medial Anchor Position Must Be Optimized to Achieve Stability Yet Minimize External Rotation Loss

An off-track Hill-Sachs lesion (HSL) is a significant risk factor for recurrent shoulder instability after arthroscopic Bankart repair. Bankart repair combined with remplissage can better restore shoulder stability versus isolated Bankart repair when treating a combined Bankart lesion and off-track HSL. However, remplissage may be nonanatomic and associated with limitation of shoulder external rotation (ER), especially when the arm is in a 90° shoulder abduction position. Excessive medial placement of remplissage anchors is associated with postoperative ER loss and increased glenohumeral cartilage degeneration. The use of 2 medial anchors results in lower articular forces. Thus, in patients with shoulder instability, we recommend using 2 remplissage anchors in those with a Bankart lesion plus an off-track HSL. The anchors should be placed medially to achieve stability—but not so medial as to result in postoperative stiffness and significant ER loss.     

Revision anterior capsular shoulder stabilization using hamstring tendon autograft and tibialis tendon allograft reinforcement: minimum two-year follow-up

Surgical treatment of anterior shoulder capsular deficiency has been a challenge for orthopaedic surgeons dealing with failed anterior shoulder stabilization procedures. We have used hamstring tendon autograft or tibialis tendon allograft to reinforce deficient anterior capsular tissue in patients with failed anterior shoulder stabilization. We performed a clinical follow-up of 15 patients at a minimum of 2 years after surgery, using the American Shoulder and Elbow Surgeons questionnaire, a physical examination, and radiographs. Thirteen patients were satisfied with their surgery. The mean American Shoulder and Elbow Surgeons score was 73, (range, 7-100). There were no postoperative dislocations. The operative shoulder had decreased range of motion compared with the contralateral shoulder. The operative arm lacked 10 degrees of forward flexion, 21 degrees of external rotation at the side, 24 degrees of external rotation with the arm in abduction, and 4 spinal levels of internal rotation. Two patients required total shoulder arthroplasty for painful glenohumeral arthritis. Clinical failure was related to glenohumeral arthritis or residual anterior shoulder apprehension. Our results support the use of hamstring autograft or tibialis anterior allograft for the reconstruction of the anterior capsule during revision shoulder stabilization surgery.     

Experimental investigation of reaction forces at the glenohumeral joint during active abduction

Reaction forces at the glenohumeral joint counterbalance the mass moment of the upper extremity during shoulder motion and are directly related to the activity of muscles across the joint. Because stability of the glenohumeral joint depends on compression of the humeral head into the glenoid, reaction forces constitute an important aspect of shoulder biomechanics. The objective of this study was to measure reaction forces at the glenohumeral joint during active scapula plane abduction. Furthermore, to clarify the relationship between the deltoid and supraspinatus muscles throughout abduction, this study investigated the effect of 4 variations of applied muscle forces on the magnitude and direction of glenohumeral reaction forces. We used a dynamic shoulder testing apparatus equipped with a force-moment sensor to directly measure reaction forces. Joint reaction forces increased throughout abduction and peaked at approximately 90 degrees for all testing conditions. The largest reaction forces occurred when the ratio of applied forces favored the supraspinatus tendon, whereas simulated paralysis of the supraspinatus resulted in a significant decrease in joint compression. There were no differences in direction of the reaction force between testing conditions. The results of this study indicate that the magnitude of glenohumeral joint reaction forces varies according to the ratio of forces between the supraspinatus and deltoid muscles. Thus, conditions characterized by either deltoid or supraspinatus dysfunction may result in abnormal loading mechanics at the glenohumeral joint. Understanding the relationship between rotator cuff function and glenohumeral reaction forces will aid in clarifying the importance of muscular activity to shoulder stability and strength as it relates to compression of the humeral head.