Glenohumeral motion in patients with rotator cuff tears: a comparison of asymptomatic and symptomatic shoulders

The purpose of this study was to determine whether there was a relationship between altered scapular plane glenohumeral kinematics end shoulder pain. Subjects were divided into 3 groups: normal volunteers (n = 10), patients with symptomatic rotator cuff tears severe enough to warrant surgery (n = 10), and subjects with no symptoms who had tears documented on magnetic resonance imaging and normal examination (n = 10). Humeral kinematics were observed with a computer-enhanced modification of the Poppen and Walker technique. Scapular plane x-ray films were obtained at 0 degree, 30 degrees, 60 degrees, 90 degrees, 120 degrees, and 150 degrees of elevation. Measurements were made by 3 independent observers blinded to the diagnosis, and data interpretation was performed based on mean values for independent observers. Results showed a high degree of interobserver and intraobserver reliability (coefficients = 0.96 and 0.95, respectively). The symptomatic and asymptomatic groups showed progressive superior translation of the humeral head on the glenoid with increasing arm elevation. The normal group, in contrast, maintained a constant center of rotation along the geometric center of the glenoid. Symptomatic and asymptomatic rotator cuff tear groups showed superior head migration from 30 degrees to 150 degrees, which was significantly different from those seen in the normal group. No significant difference between the symptomatic and asymptomatic groups was demonstrated with the small numbers used in this study. The presence of a rotator cuff tear was associated in a disruption of normal glenohumeral kinematics in the scapular plane. Because significant superior migration of the humeral head was seen in both the asymptomatic and symptomatic rotator cuff groups, painless and normal shoulder motion is possible in the presence of abnormal glenohumeral kinematics. Abnormal glenohumeral kinematics alone was not an independent factor, which could explain the occurrence of symptoms.     

Shoulder kinematics with two-plane x-ray evaluation in patients with anterior instability or rotator cuff tearing

The goals of this study were to define biplanar glenohumeral kinematics and glenohumeral-scapulothoracic motion relationships in normal patients with a two-plane radiograph series and then in patients with anterior shoulder instability or rotator cuff tear both before surgery and after surgical repair and postoperative rehabilitation. A two-plane radiographic series of x-ray films in the scapular and horizontal (axillary) planes was performed. With these films, measurements of the relationship between the centers of the humeral head and glenoid and measurements of the component contributions of glenohumeral and scapulothoracic motion to total arm abduction were made. Six normal adults underwent x-ray evaluation to establish normal control values. Kappa analysis was used to determine reliability of technique. Eighteen patients with confirmed anterior shoulder instability (group A) and 15 with confirmed rotator cuff tears (group B) were studied before surgery. Seven (39%) of 18 of the patients in group A and all 15 (100%) of the patients in group B demonstrated superior translation of the humeral head during scapular plane abduction. In the horizontal plane 14 (78%) of 18 patients in group A (instability) and none in group B (rotator cuff tear) demonstrated abnormal anterior translation of the humeral head on the glenoid. Both groups demonstrated altered glenohumeral-scapulothoracic motion relationships compared with the normal control group. Two years after surgery 12 patients from group A and 14 patients from group B were restudied. All of these patients had demonstrated abnormalities of humeral head translation before surgery. For group A 12 (100%) of 12 patients demonstrated normal glenohumeral kinematics in both planes after open anterior stabilization. For group B 12 (86%) of 14 patients demonstrated normal glenohumeral kinematics in both planes after open rotator cuff repair. In group A the altered glenohumeral-scapulothoracic motion relationships persisted, whereas in group B these relationships became normal.     

The value of radiological examination in the diagnosis of rotator cuff tear]

The aim of this paper was to evaluate the correlation between radiological changes on a-p radiograph of the shoulder and rotator cuff tear on the ground of analysis of 328 patients (360 shoulders) aged between 11 and 73 years suffering from different forms of periarthritis humeroscapularis. Sonographic examination revealed rotator cuff tear in 54 shoulders; 38 confirmed at surgery and 16 at arthrography. There was very strong correlation between rotator cuff tear and irregularities of greater tubercle, narrowing of the distance between humeral head and acromion to 5 mm or less, greater tubercle recession, osteophytes and reverse shape of acromion. Last 3 changes were very strongly correlated with medium and large size rotator cuff tear.     

Differential patterns of muscle activation in patients with symptomatic and asymptomatic rotator cuff tears

Patients with rotator cuff tears have varying degrees of symptom expression. Our purpose was to evaluate the differential firing patterns of the rotator cuff, deltoid, and scapular stabilizer muscle groups in normal control subjects and in patients with symptomatic and asymptomatic 2-tendon rotator cuff tears. Eighteen subjects were evaluated: six normal subjects and twelve with 2-tendon cuff tears (six asymptomatic and six symptomatic). All cuff tear patients had magnetic resonance imaging (MRI) scans documenting superoposterior tear configurations involving the supraspinatus and infraspinatus tendons; all normal subjects had an ultrasound examination confirming the absence of cuff pathology. Subjects were grouped based on shoulder examination and outcomes questionnaires. Asymptomatic patients had minimal pain (<3 on the visual analog scale and no loss of active range of motion compared with the contralateral side); symptomatic patients had pain greater than 3 on the visual analog scale and decreased range of motion compared with the contralateral side (>10 degrees of motion loss). Electromyographic activity from 12 muscles and kinematic data were collected simultaneously during 10 functional tasks. Both symptomatic and asymptomatic cuff subjects demonstrated a trend toward increased muscle activation during all tasks compared with normal subjects. During the internal rotation tasks, asymptomatic patients had significantly greater (P<.05) subscapularis activity than symptomatic patients (65% maximal voluntary contraction [MVC] vs 42% MVC). During the carrying task, asymptomatic patients demonstrated significantly less (P<.03) upper trapezius muscle activation than symptomatic patients (16% MVC vs 50% MVC). During shoulder elevation tasks, symptomatic patients had significantly greater supraspinatus (52% MVC vs 28% MVC, P<.03), infraspinatus (32% MVC vs 16% MVC, P<.05), and upper trapezius (39% MVC vs 20% MVC, P<.04) muscle activation compared with asymptomatic patients. During heavy elevation (8 lb), asymptomatic patients showed a trend toward increased activation (P<.06) of the subscapularis compared with symptomatic patients (34% MVC vs 21% MVC). Differential shoulder muscle firing patterns in patients with rotator cuff pathology may play a role in the presence or absence of symptoms. Asymptomatic subjects demonstrated increased firing of the intact subscapularis, whereas symptomatic subjects continued to rely on torn rotator cuff tendons and periscapular muscle substitution, resulting in compromised function.     

肱骨外展动作中肩袖生物力学的有限元分析

目的构建肩关节有限元模型，用于分析肩袖生物力学。 方法采集1名26岁健康男性志愿者右肩CT、MRI数据，构建肩关节有限元模型，包含肩胛骨、肱骨、锁骨，以及肩袖肌群（冈上肌、冈下肌、小圆肌、肩胛下肌）。模拟肱骨在肩胛骨平面外展，分析肩袖肌肉应力变化。 结果肱骨在肩胛骨平面外展0°~30°过程中，各组肌腱与肱骨头连接处的应力均增大。冈上肌腱应力变化速率较快；肩胛骨前方的肩胛下肌对比肩胛骨后方的冈下肌-小圆肌，两组肌腱的应力变化较为同步。当肱骨在肩胛骨平面外展30°时，冈上肌腱、肩胛下肌腱及冈下肌腱-小圆肌腱与肱骨头连接面的平均应力分别为7.894 8、4.721 7、3.768 8 Mpa，冈上肌腱关节面与滑囊面结点平均应力分别为7.931 4、4.099 0 Mpa。冈上肌腱的关节面与滑囊面应力有明显差异，应力差值随肱骨在肩胛骨平面外展而增大，造成的剪切力可造成冈上肌腱撕裂。 结论肩袖对肩关节的活动与稳定性有重要作用，其受力特点易引起肩袖损伤。     

Analysis of the scapulohumeral rhythm

The movement of the shoulder complex was once aptly described by Codman as the "scapulohumeral rhythm". To demonstrate this rhythm, 20 normal men and four patients with rotator cuff rupture were asked to elevate their arms smoothly in approximately three seconds and five seconds in front of a fluoroscope with or without load. The X-ray was irradiated perpendicularly in the scapular plane. The movements were calculated using a computer. In the normal men, the ratio of the scapular movements to humeral movements was not constant during scapular abduction. The movements of the instant center of the humerus occurred in a small area during abduction, and the result suggested that the movement of the glenohumeral joint was almost rotational. The movements of the instant center of the scapula occurred in a relatively large area during abduction. The movements of the shoulder complex with cuff rupture were quite different from those of normal men.     

Shoulder kinematics in patients with full-thickness rotator cuff tears after a subacromial injection

The purpose of this study was to test the hypothesis that scapulohumeral rhythm (SHR) is altered in patients with full-thickness rotator cuff tears due to pain. Fifteen subjects (mean age, 60.2 +/- 8.9 years; mean height, 1.72 +/- 0.10 m; mean weight, 85.43 +/- 18.32 kg) performed humeral elevation in the 3 planes before and after a lidocaine injection. Pain was assessed by use of a visual analog scale, and data were collected with an electromagnetic tracking system. Three-dimensional scapular kinematics (scapulothoracic motion) and glenohumeral elevation were assessed. A linear regression model was used to calculate SHR (ratio of scapulothoracic motion to glenohumeral elevation) for equal phases of elevation (I, II, and III) and lowering (IV, V, and VI). Pain was significantly reduced (P 相似文献   

Which Risk Factors Are Associated with Pain and Patient-reported Function in Patients with a Rotator Cuff Tear?

BackgroundPatient-reported measures guide physicians in clinical decision making and therefore it is critical to determine what clinical factors are associated with these scores. Psychological and physical factors are commonly studied separately in patients with rotator cuff tears to determine their influence on outcomes. It is well established that psychological distress and scapular motion change in the presence of a symptomatic rotator cuff tear. However, these factors have not been studied simultaneously in a clinical setting to determine their association with shoulder outcome scores.Question/purposeAfter controlling for relevant confounding variables, what physical and psychological factors are associated with better (1) American Shoulder and Elbow Surgeons (ASES) scores for function, (2) ASES pain scores, and (3) total ASES scores?MethodsFifty-nine patients with a potential symptomatic rotator cuff tear were recruited and agreed to participate in this cross-sectional study. Of those, 85% (50 of 59) met eligibility criteria for a primary diagnosis of an MRI-confirmed symptomatic partial-thickness or full-thickness rotator cuff tear without a history of shoulder surgery. Demographics, rotator cuff tear size, arm flexion, and clinical scapular motion during active arm flexion were evaluated by experienced examiners using standardized procedures. Patients completed the ASES questionnaire and the Optimal Screening for Prediction of Referral and Outcomes-Yellow Flag assessment form, which measures 11 different pain-related psychological distress symptoms. Three separate stepwise multiple linear regression analyses were performed for ASES pain, function, and total scores, with significance set at p < 0.05.ResultsThis model found that ASES function scores were associated with four factors: older age, increased arm flexion, increased percentage of scapular external rotation during arm flexion, and increased scores for acceptance of chronic pain (adjusted r² = 0.67; p = 0.01). Those four factors appear to explain 67% of the observed variance in ASES function scores in patients with rotator cuff tears. Furthermore, increased percentage of scapular external rotation during arm flexion and decreased fear-avoidance beliefs related to physical activity scores (adjusted r² = 0.36; p < 0.01) were associated with better ASES pain scores. And finally, better ASES total scores were associated with four factors: increased arm flexion, increased percentage of scapular upward rotation, increased scapular external rotation during arm flexion, and decreased fear-avoidance beliefs related to physical activity scores (adjusted r² = 0.65; p < 0.001).ConclusionOur results favor adopting a comprehensive biopsychological clinical assessment for patients with rotator cuff tears that specifically includes humeral and scapular motion, fear-avoidance behaviors, and pain coping behaviors along with demographics. These particular physical and psychological variables were found to be associated with the ASES and, therefore, should be clinically examined simultaneously and targeted as part of a tailored treatment plan.Level of EvidenceLevel II, prognostic study.     

Quantitation of in situ contact areas at the glenohumeral joint: a biomechanical study.

Glenohumeral arthritis may result from abnormal articular mechanics, and shoulder reconstructive procedures often rely implicitly on the belief that the restoration of normal articular mechanics is required to obtain satisfactory clinical results. Despite this, limited knowledge of normal or pathologic glenohumeral joint articular mechanics and contact is available. This study uses a stereophotogrammetry technique to determine contact areas in normal cadaver glenohumeral joints with intact ligaments and capsule through a large range of motion using simulated forces of the four rotator cuff muscles and three deltoid heads. All shoulders were first elevated to their maximum elevation in the scapular plane at an external rotation (starting rotation = 40 +/- 8 degrees), which allowed each shoulder to attain its maximal elevation in the scapular plane, and then repeated at 20 degrees internal to this rotation. Contact areas consistently increased with increasing elevation until 120 degrees to an average of 5.07 cm2 before decreasing with further increased elevation to an average of 2.59 cm2 at 180 degrees of total arm elevation. At 20 degrees internal to the starting rotation, contact areas reached high values 60 degrees earlier (averaged 4.56 cm2 at 60 degrees of total arm elevation) and then remained fairly constant through 120 degrees before decreasing with further increased elevation to 2.51 cm2 at 180 degrees total arm elevation. With increasing elevation in the external starting rotation, humeral head contact dramatically migrates from an inferior region to a superocentral-posterior region while glenoid contact shifts posteriorly. When the humeral shaft is positioned 20 degrees internal to the starting rotation, humeral head contact shifts from inferocentral-anterior to superocentral-posterior regions. Simultaneously, a similar posterior shift in glenoid contact is observed. Furthermore, whereas only a small portion of the humeral head surface area is in contact in any given position, contact on the glenoid surface is much more uniformly distributed over its entire articulating surface.     

Shoulder prostheses treating cuff tear arthropathy: a comparative biomechanical study.

Painful cuff tear arthropathy (CTA) affects the independence of the elderly. Surgical treatment often consists of joint replacement, the functional outcome of which remains variable. Knowledge of the biomechanical properties of the different prosthetic designs can guide the orthopaedic surgeon in the choice of implant to predict its clinical result. A 3-D computer model of the glenohumeral joint is used to analyse the moment of the deltoid muscle in the scapular plane. A geometrical 3-D ball-and-socket model of the shoulder joint was used to calculate (1) the angle-force relationships, (2) the moment arm of the deltoid muscle and (3) the moment of the deltoid muscle components, for increasing degrees of arm elevation in the scapular plane. In this 3-D model, a clinical thoraco-scapular rhythm analysis was implemented, based on measurements in normal subjects, patients treated with an anatomical prosthesis and patients treated with an inversed delta III prosthesis. These data were compared for 10 different prosthetic treatment options. RESULTS: Muscle angle-force curves show a favourable slope in non-anatomical prosthetic designs, where the centre of rotation of the glenohumeral joint is medialized, the deltoid muscle is elongated and the humeral shaft is lateralized. On the contrary, anatomical prosthetic designs do not perform well in this computer analysis. CONCLUSIONS: From a biomechanical point of view, a shoulder prosthesis which medializes the centre of rotation, lengthens the deltoid muscle and increases the deltoid lever arm, results in a significantly more powerful abduction of the shoulder, despite complete loss of rotator cuff function. RELEVANCE: This study explains why a successful functional outcome can be expected in CTA with a reversed prosthesis.     

Four‐week exercise program does not change rotator cuff muscle activation and scapular kinematics in healthy subjects

Rotator cuff and scapular muscle strengthening exercises are an essential part of shoulder rehabilitation and sports training. Although the effect of exercise training on pain and function have been widely investigated, few studies have focused on the changes in shoulder kinematics and muscle activity after exercise training. Therefore, the purpose of the present study was to investigate the effect of rotator cuff and scapular strengthening exercises on shoulder kinematics and the activation of rotator cuff and scapular muscles in healthy subjects. Thirty‐six healthy subjects were recruited and randomly assigned into either a training or control group. Subjects in the training group were trained with rotator cuff and scapular strengthening exercises for 4 weeks. Scapular kinematics and shoulder muscle activity during arm elevation were measured before and after exercise training. After the 4‐week training protocol, there was an increase in strength and a decrease in upper trapezius activation in the training group, which is consistent with previous studies. However, no difference was found in scapular kinematics and activation of rotator cuff muscles between the control and training groups after the training protocol. Although the exercise protocol resulted in strength gains for the rotator cuff, these gains did not transfer to an increase in muscle activation during motion. These results demonstrate the difficulty in changing activation patterns of the rotator cuff muscles. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:2079–2088, 2016.     

Effect of shoulder tightness on glenohumeral translation, scapular kinematics, and scapulohumeral rhythm in subjects with stiff shoulders.

Shoulder tightness may cause altered kinematics and lead to development of subacromial impingement, tendinitis, and degenerative changes. In this investigation, the humeral head translations, scapular kinematics, and scapulohumeral rhythm were determined with a three-dimensional electromagnetic tracking device during arm elevations in six subjects with anterior shoulder tightness and in six subjects with posterior shoulder tightness to study the effects of anterior/posterior tightness on shoulder kinematics. Subjects with anterior tightness showed lower slopes in curves of glenohumeral elevation plotted against scapular upward rotation (scapulohumeral rhythm, 0.11 to 0.32; p = 0.021) and less posterior scapular tilt (2.9 to 7.5 degrees; p = 0.002) during arm elevations when compared to the group with posterior tightness. The humeral head was positioned less posteriorly (2.2 to 3.4 mm; p = 0.004) and more superiorly (3.8 to 7.0 mm; p < 0.0005) during arm elevation in subjects with posterior tightness. The alternations in shoulder kinematics between subjects with anterior and posterior shoulder tightness may be relevant to the development of subacromial impingement, tendinitis, and degenerative changes as seen in subjects with stiff shoulders.     

Position of the humeral head and rotator cuff tear: an anatomical observation in cadavers

BACKGROUND: The relationship between the humeral head position and rotator cuff tears is not well described. MATERIAL AND METHODS: We performed an anatomical study of 22 cadaveric shoulders to find out the relationship between the normal anatomical position of the humeral head and tears of the rotator cuff. After dissection, the rotator cuff pathology was documented. The position of the humeral head was noted in relation to the acromion. The humeral head with intact acromion and articulated shoulder joint was photographed from the superior aspect of the joint and the area of the humeral head outside the acromion was measured, i.e. the part of the humeral head lateral to the lateral border of the acromion process. The relationship between rotator cuff pathology and uncovering of the humeral head was determined. RESULTS: 9 specimens had a partial cuff tear, while 4 had a complete tear. Those specimens with a rotator cuff tear had a mean area of 83% of the humeral head under the acromion. The specimens that did not show a rotator cuff tear had a mean area of 61% of the humeral head under the acromion. INTERPRETATION: We suggest that there is individual variation in anatomical position of the humeral head in relation to the acromion and that this position correlates with the occurrence of rotator cuff pathology.     

Position of the humeral head and rotator cuff tearAn anatomical observation in cadavers

Background The relationship between the humeral head position and rotator cuff tears is not well described. Material and methods We performed an anatomical study of 22 cadaveric shoulders to find out the relationship between the normal anatomical position of the humeral head and tears of the rotator cuff. After dissection, the rotator cuff pathology was documented. The position of the humeral head was noted in relation to the acromion. The humeral head with intact acromion and articulated shoulder joint was photographed from the superior aspect of the joint and the area of the humeral head outside the acromion was measured, i.e. the part of the humeral head lateral to the lateral border of the acromion process. The relationship between rotator cuff pathology and uncovering of the humeral head was determined. Results 9 specimens had a partial cuff tear, while 4 had a complete tear. Those specimens with a rotator cuff tear had a mean area of 83% of the humeral head under the acromion. The specimens that did not show a rotator cuff tear had a mean area of 61% of the humeral head under the acromion. Interpretation We suggest that there is individual variation in anatomical position of the humeral head in relation to the acromion and that this position correlates with the occurrence of rotator cuff pathology.     

肩肱距减小与肩袖损伤相关性的研究

目的评估肩肱距（acromiohumeral distance,AHD）与肩袖损伤之间的关系,为肩袖疾病的诊断及预后判断提供指导。 方法对2014年9月至2016年3月于上海市第十人民医院就诊的115例肩关节患者进行回顾性分析,在肩关节X线平片上测量肱骨头顶端与肩峰之间的最短距离为AHD。评估术前MRI检查和术中肩关节镜下探查情况,根据肩袖撕裂位置、大小及肌腱挛缩情况分组,并比较AHD在不同亚组与对照组之间的差异。 结果肩袖撕裂组患者115例,平均AHD为9.3 mm,对照组患者50例,平均AHD为10.6 mm,两者之间差异有统计学意义（P <0.05）。通过不同亚组与对照组的比较,发现后方撕裂亚组（8.8 mm）、广泛撕裂亚组（6.7 mm）患者AHD显著小于对照组（P <0.05）;Patte Ⅲ级亚组（7.0 mm）AHD显著小于对照组（P <0.05）。 结论AHD与肩袖撕裂大小、位置及肌腱挛缩程度相关,肩袖后方冈下肌撕裂对肱骨头上移的影响尤为明显。     

Primary anterior shoulder dislocation and rotator cuff tears.

In a prospective controlled study 167 patients with 167 primary traumatic anterior shoulder dislocations underwent early ultrasonograpic evaluation for rotator cuff tears. We found 53 (31.7%) full-thickness cuff tears in this group. Compared with a group of 93 healthy volunteers, we found with statistical significance more cuff tears in the patients aged < 60 years. Women ruptured the cuff more often than men. If the patient is not able to elevate the affected arm more than 90 degrees in the scapular plane 2 weeks after the dislocation, there should be a high suspicion of rotator cuff tear (76.7%). For early detection of relevant rotator cuff lesions, we recommend shoulder ultrasonographic examination and measurement of active elevation after each traumatic shoulder dislocation in the above mentioned age group.     

Hemiarthroplasty for rotator cufftear arthropathy

Treatment of rotator cuff tear arthropathy presents a formidable challenge for the shoulder surgeon. The alteredmechanical and nutritional environment of the shoulder thought to be responsible for the development and progression of the arthropathy also may contribute to the failures of surgical intervention. In the past, several surgical procedures, including total shoulder arthroplasty, have been used to treat rotator cuff tear arthropathy. However, hemiarthroplasty seems to have the most consistent and predictable long-term results. Even so, certain technical points must be considered while performing a hemiarthroplasty to minimize pain and maximize motion and function. These surgical considerations include mobilizing the rotator cuff and attempting to repair the tear whenever possible, appropriate sizing of the humeral head prosthesis, and placing the humeral head in increased retroversion.     

Assessment of scapulohumeral rhythm for scapular plane shoulder elevation using a modified digital inclinometer

AIM: To develop a better understanding of scapulohumeral rhythm during scapular plane shoulder elevation.METHODS: Thirteen healthy, college-aged subjects participated in this study. Subjects were free from any upper extremity, neck or back pathology. A modified digital inclinometer was utilized to measure scapular upward rotation of the subject’s dominant shoulder. Upward rotation was measured statically as subjects performed clinically relevant amounts of shoulder elevation in the scapular plane. Testing order was randomized by arm position. Scapular upward rotation was assessed over the entire arc of motion and over a series of increments. The percent contributions to shoulder elevation for the scapula and glenohumeral joint were calculated. Scapulohumeral rhythm was assessed and represented the ratio of glenohumeral motion to scapulothoracic motion (glenohumeral elevation: scapular upward rotation). A one-way ANOVA was used to compare scapular upward rotation between elevation increments.RESULTS: Scapulohumeral rhythm for the entire arc of shoulder elevation was equal to a ratio of 2.34 :1 and ranged from 40.01:1 to 0.90:1 when assessed across the different increments of humeral elevation. Total scapular motion increased over the arc of shoulder elevation. The scapula contributed 2.53% of total motion for the first 30 degrees of shoulder elevation, between 20.87% and 37.53% for 30^o-90^o of shoulder elevation, and 52.73% for 90^o-120^o of shoulder elevation. Statistically significant differences in scapular upward rotation were identified across the shoulder elevation increments [F_(3,48) = 12.63, P = 0.0001].CONCLUSION: Clinically, we must recognize the usefulness of the inclinometer in documenting the variable nature of scapulohumeral rhythm in healthy and injured shoulders.     

The effect of rotator cuff tears on reaction forces at the glenohumeral joint.

The rotator cuff muscles maintain glenohumeral stability by compressing the humeral head into the glenoid. Disruption of the rotator cuff compromises concavity compression and can directly affect the loads on the glenohumeral joint. The purpose of this study was to quantify the effect of rotator cuff tears on the magnitude and direction of glenohumeral joint reaction forces during active shoulder abduction in the scapular plane using nine cadaveric upper extremities. Motion of the full upper extremity was simulated using a dynamic shoulder testing apparatus. Glenohumeral joint reaction forces were measured by a universal force-moment sensor. Five conditions of rotator cuff tears were tested: Intact, Incomplete Supraspinatus Tear, Complete Supraspinatus Tear, Supraspinatus/Infraspinatus Tear, and Global Tear. Reaction forces at the glenohumeral joint were found to steadily increase throughout abduction and peaked at maximum abduction for all conditions tested. There were no significant differences in reaction force magnitude for the intact condition (337 +/- 88 N) or those involving an isolated incomplete tear (296 +/- 83 N) or complete tear (300 +/- 85 N) of the supraspinatus tendon. Extension of tears beyond the supraspinatus tendon into the anterior and posterior aspect of the rotator cuff led to a significant decrease in the magnitude of joint reaction force (126 +/- 31 N). Similarly, such tears resulted in a significant change in the direction of the reaction force at the glenohumeral joint. These results suggest that joint reaction forces are significantly affected by the integrity of the rotator cuff, specifically, by the transverse force couple formed by the anterior and posterior aspects of the cuff. The quantitative data obtained in this study on the effect of rotator cuff tears on magnitude and direction of the reaction force at the glenohumeral joint helps clarify the relationship between joint motion, joint compression and stability.     

Electromyographic study associated with rotator cuff tears

To determine the pathophysiological condition of rotator cuff tear, 23 cases were observed using electromyogram of the shoulder girdle muscles during elevation of the arm. The correlation between the action potential of these muscles and the angle of the arm was analyzed using computer in order to identify the pattern of that. The pattern of the electromyogram of the affected side with the ability to elevate the arm above 90 degrees was similar to that of the sound side. Differences were seen between the affected side with the inability and the sound side in the electromyogram of trapezius, deltoideus and supraspinatus. However, these differences were disappeared in patients who became able to elevate their arms above 90 degrees after surgery. It seemed that the restriction of joint motion due to rotator cuff tear caused impairment of coordination of muscular activities, and this phenomenon helped us to clarify the scapulohumeral rhythm.