Cranial humerus translation,deltoid activation,adductor co-activation and rotator cuff disease — Different patterns in rotator cuff tears,subacromial impingement and controls

Background

Arm adductor co-activation during abduction has been reported as a potential compensation mechanism for a narrow subacromial space in patients with rotator cuff dysfunction. We assessed differences in acromiohumeral distance at rest and the amount of humerus translation during active abduction and adduction in patients with rotator cuff tears (n = 20) and impingement (n = 30) and controls (n = 10), controlled for deltoid, pectoralis major, latissimus dorsi and teres major activation (electromyography).

Methods

During the acquirement of shoulder radiographs, subjects performed standardized isometric arm abduction and adduction tasks. EMG's were normalized between − 1 and 1 using the “Activation Ratio”, where low values express (pathologic) co-activation, e.g. adductor activation during abduction.

Findings

In patients with cuff tears mean rest acromiohumeral distance was 7.6 mm (SD = 1.6): 3.5 mm narrower compared to patients with impingement (95%-CI: 2.4–4.5) and 1.3 mm narrower compared to controls (95%-CI: − 0.1–2.7). Both during abduction and adduction tasks, cranial translation was observed with equal magnitudes for patients and controls, with average values of 2.3 and 1.7 mm, respectively. Where patients with cuff tears had lower adductor Activation Ratios (i.e. more adductor co-activation during abduction), no association between abductor/adductor muscle activation and acromiohumeral distance was found.

Interpretation

The subacromial space is narrower in patients with rotator cuff tears compared to patients with impingement and controls. We found additional subacromial narrowing during isometric abduction and, to a lesser amount, during adduction in all subjects and more adductor co-activation in patients with cuff tears. We found no association between subacromial space and activation of the deltoid and main adductors.     

Three-dimensional scapular morphology is associated with rotator cuff tears and alters the abduction moment arm of the supraspinatus

BackgroundNumerous studies have reported an association between rotator cuff injury and two-dimensional measures of scapular morphology. However, the mechanical underpinnings explaining how these shape features affect glenohumeral joint function and lead to injury are poorly understood. We hypothesized that three-dimensional features of scapular morphology differentiate asymptomatic shoulders from those with rotator cuff tears, and that these features would alter the mechanical advantage of the supraspinatus.MethodsTwenty-four individuals with supraspinatus tears and twenty-seven age-matched controls were recruited. A statistical shape analysis identified scapular features distinguishing symptomatic patients from asymptomatic controls. We examined the effect of injury-associated morphology on mechanics by developing a morphable model driven by six degree-of-freedom biplanar videoradiography data. We used the model to simulate abduction for a range of shapes and computed the supraspinatus moment arm.FindingsRotator cuff injury was associated with a cranial orientation of the glenoid and scapular spine (P = .011, d = 0.75) and/or decreased subacromial space (P = .001, d = 0.94). The shape analysis also identified previously undocumented features associated with superior inclination and subacromial narrowing. In our computational model, warping the scapula from a cranial to a lateral orientation increased the supraspinatus moment arm at 20° of abduction and decreased the moment arm at 160° of abduction.InterpretationsThree-dimensional analysis of scapular morphology indicates a stronger relationship between morphology and cuff tears than two-dimensional measures. Insight into how morphological features affect rotator cuff mechanics may improve patient-specific strategies for prevention and treatment of cuff tears.     

In vitro kinematics of the shoulder following rotator cuff injury

BACKGROUND: Tears in the rotator cuff may result in altered mechanics of the glenohumeral joint. It is not unusual for some patients with cuff tears to exhibit near normal motion with the injured shoulder, while other patients with the same magnitude of injury are unable to achieve full elevation on the injured side. METHODS: The effect of simulated tears of the rotator cuff on active glenohumeral joint kinematics was investigated by testing eight cadaveric specimens using an in vitro shoulder simulator. Active abduction of the humerus was produced by applying forces to simulate loading of the supraspinatus, subscapularis, infraspinatus/teres minor, and the anterior, middle, and posterior thirds of the deltoid. Three sequential 1cm lesions were created in the rotator cuff, the first two in the supraspinatus tendon and the third in the subscapularis tendon. FINDINGS: The plane of abduction moved posteriorly and became more abnormal throughout abduction with increased tear size. No difference was observed in the internal/external rotation of the humerus or the position of the humeral head on the glenoid during elevation. INTERPRETATION: In order to generate the motions achieved by the intact joint, patients with rotator cuff insufficiency likely employ other muscle groups. Retraining muscle groups surrounding the glenohumeral joint may decrease the need for surgical interventions.     

Kinematics and muscle activation in subacromial pain syndrome patients and asymptomatic controls

BackgroundConflicting theories exist about the underlying cause of chronic subacromial pain in the middle-aged population. We aim to improve our understanding of kinematics and muscle activation in subacromial pain syndrome to provide insight in its pathophysiology.MethodsIn a cross-sectional comparison of 40 patients with subacromial pain syndrome and 30 asymptomatic controls, three-dimensional shoulder kinematics and electromyography-based co-contraction in 10 shoulder muscles were independently recorded. Glenohumeral and scapulothoracic kinematics were evaluated during abduction and forward flexion. Co-contraction was expressed as an activation ratio, specifying the relative agonistic and antagonistic muscle activity in each muscle.FindingsDuring abduction and forward flexion, the contribution of glenohumeral motion to elevation and glenohumeral external rotation was lower in subacromial pain syndrome (at 120⁰ abduction: −9°, 95% CI -14°- -3°; and − 8°, 95% CI -13°--3°, respectively), and was compensated by more scapulothoracic motion. The pectoralis major's activation ratio was significantly lower (Z-score: -2.657, P = 0.008) and teres major's activation ratio significantly higher (Z-score: -4.088, P < 0.001) in patients with subacromial pain syndrome compared to the control group.InterpretationReduced glenohumeral elevation and external rotation in subacromial pain syndrome coincided with less teres major antagonistic activity during elevation. These biomechanical findings provide a scientific basis for intervention studies directed at stretching exercises to reduce glenohumeral stiffness in the treatment of subacromial pain syndrome, and teres major strengthening to improve humeral head depressor function.     

Biomechanical analysis of scapular neck malunion--a simulation study

OBJECTIVE: To explain loss of shoulder function following scapular neck malunion in terms of biomechanical changes around the gleno-humeral joint. DESIGN: Biomechanical modelling study. BACKGROUND: Residual rotation of the scapular neck after fracture can lead to pain and loss of function, and the indications for surgical intervention are contested. METHODS: A 3D, large-scale, musculo-skeletal model of the upper limb was used to compare shoulder biomechanics in the case of scapular neck malunion with normal anatomy. Abduction of the humerus was simulated with three models: normal anatomy, 24 degrees and 40 degrees inferior scapular neck rotation. RESULTS: Predicted muscle activation differed greatly between the control and the fracture cases. The motion required additional muscle effort for the maintenance of gleno-humeral stability in the fracture cases. Higher moments in the plane of abduction were generated by the teres major, pectoralis major and biceps brachii muscles with high humeral elevation angles. The rotator cuff muscles were severely shortened in the post-fracture cases and the forces in these muscles were greatly reduced in a test of loaded abduction with the humerus at 90 degrees. CONCLUSIONS: Given the function of the rotator cuff muscles as stabilisers of the gleno-humeral joint, it is concluded that the loss of force in these muscles, together with other changes in muscle activation, will lead to loss of arm function in patients with scapular neck malunion. RELEVANCE:These findings will contribute to the improved treatment of patients with scapular neck malunion by identifying important factors in the consideration of surgical intervention.     

The effect of a rotator cuff tear and its size on three-dimensional shoulder motion

BackgroundRotator cuff-disease is associated with changes in kinematics, but the effect of a rotator cuff-tear and its size on shoulder kinematics is still unknown in-vivo.MethodsIn this cross-sectional study, glenohumeral and scapulothoracic kinematics of the affected shoulder were evaluated using electromagnetic motion analysis in 109 patients with 1) subacromial pain syndrome (n = 34), 2) an isolated supraspinatus tear (n = 21), and 3) a massive rotator cuff tear involving the supraspinatus and infraspinatus (n = 54). Mixed models were applied for the comparisons of shoulder kinematics between the three groups during abduction and forward flexion.FindingsIn the massive rotator cuff-tear group, we found reduced glenohumeral elevation compared to the subacromial pain syndrome (16°, 95% CI [10.5, 21.2], p < 0.001) and the isolated supraspinatus tear group (10°, 95% CI [4.0, 16.7], p = 0.002) at 110° abduction. Reduced glenohumeral elevation in massive rotator cuff tears coincides with an increase in scapulothoracic lateral rotation compared to subacromial pain syndrome (11°, 95% CI [6.5, 15.2], p < 0.001) and supraspinatus tears (7°, 95% CI [1.8, 12.1], p = 0.012). Comparable differences were observed for forward flexion. No differences in glenohumeral elevation were found between the subacromial pain syndrome and isolated supraspinatus tear group during arm elevation.InterpretationThe massive posterosuperior rotator cuff-tear group had substantially less glenohumeral elevation and more scapulothoracic lateral rotation compared to the other groups. These observations suggest that the infraspinatus is essential to preserve glenohumeral elevation in the presence of a supraspinatus tear. Shoulder kinematics are associated with rotator cuff-tear size and may have diagnostic potential.     

Decreasing glenoid inclination improves function in shoulders with simulated massive rotator cuff tears

BACKGROUND: A massive rotator cuff tear leads to poor shoulder function as evidenced by diminished glenohumeral abduction and superior translation of the humeral head compared to its normal position. The inclination angle of the glenoid has been associated with rotator cuff tears. The objective of this study was to quantify the effect of a decreased glenoid inclination angle on glenohumeral kinematics during active abduction in shoulders with a simulated, massive rotator cuff tear. METHODS: Eight fresh-frozen full upper extremities were tested using a dynamic shoulder testing apparatus. After recording the kinematics of the intact shoulder, a massive rotator cuff tear was surgically simulated. An osteotomy of the glenoid was then performed and the inclination angle was decreased by 30 degrees . The translation of the humeral head during abduction and the maximum abduction angle were recorded. FINDINGS: With an intact rotator cuff minimal humeral head translation on the glenoid occurred and the maximum abduction angle was mean 85.5 degrees (SD 7.4 degrees ). A massive rotator cuff tear resulted in superior translation of the humeral head with impingement on the acromion. The maximum abduction angle was mean 15.5 degrees (SD 9.4 degrees ). Decreasing the inclination angle of the glenoid resulted in a significant reduction of superior humeral head translation during abduction and there was no impingement on the acromion. The maximum abduction achieved was mean 28.5 degrees (SD 17.0 degrees ). INTERPRETATION: From a clinical perspective the reduced superior translation may decrease shoulder pain since the humeral head no longer impinges on the acromion. Further investigations are necessary to assess if the improvement in abduction is clinically significant.     

MR imaging of sports injuries to the rotator cuff

Impingement pain and rotator cuff injury are common in athletes, particularly in overhead throwers. The cuff can be injured in these patients in the typical location in the anterior supraspinatus tendon and near the junction of the supraspinatus and infraspinatus tendons. The cuff tears in athletes are usually small, articular surface partial-thickness tears. The posterior cuff tears in overhead throwers are seen best at MR arthrography with the arm in abduction and external rotation. Other abnormalities, such as instability lesions or labral fraying, can be associated with rotator cuff tears in athletes.     

Rotator cuff pathology and subacromial impingement

Musculoskeletal complaints are one of the most common reasons for primary care office visits, and rotator cuff disorders are the most common source of shoulder pain. Subacromial impingement with subsequent tendinitis and bursitis is frequently found in young adult patients. Rotator cuff tears are a common cause of shoulder pain in patients over age 40. The majority of subacromial impingement and incomplete rotator cuff tears may be successfully managed with conservative treatment. This article discusses anatomic function of the glenohumeral joint and subacromial space, etiology of subacromial impingement and rotator cuff disorders, examination of the shoulder, diagnostic testing, and treatment of subacromial impingement and rotator cuff disorders in the primary care setting.     

In vivo dynamic acromiohumeral distance in shoulders with rotator cuff tears

BackgroundThere are no previous studies on the acromiohumeral distance in shoulders with large-to-massive full-thickness rotator cuff tears. In this study, the acromiohumeral distance in rotator cuff tear and healthy shoulders was measured using 3D-to-2D model-to-image registration techniques.MethodsThe dynamic glenohumeral kinematics during scapular plane abduction and axial rotation were analyzed in 11 rotator cuff tear patients and 10 healthy control subjects. Periodic radiographic images of scapular plane abduction and axial rotation were taken using a flat-panel radiograph image detector. Movements of the shoulder joint were assessed using radiographic images and computed tomography-derived digitally reconstructed radiographs. The acromiohumeral distance was defined as the shortest 3D distance between the acromion and the proximal humerus.FindingsFor scapular plane abduction, the rotator cuff tear group had significantly smaller acromiohumeral distance than the control group at 15°, 30°, 45°, 60°, 75°, 135°, and 150° of humeral abduction (P < 0.05 at each measured angle). For axial rotation in the adducted position, the rotator cuff tear group had significantly smaller acromiohumeral distance than the control group at each point between −20° and 40° of glenohumeral external rotation (P < 0.05 at each measured angle).InterpretationThe minimum measured acromiohumeral distance was 0.9 mm in the rotator cuff tear shoulders and 2.1 mm in the healthy shoulders at 90° of scapular plane abduction. The findings are of clinical relevance because quantitative evaluation of the dynamic acromiohumeral distances in rotator cuff tear and healthy shoulders might provide important insight into subacromial impingement.     

Influence of lever arm and stabilization on measures of hip abduction and adduction torque obtained by hand-held dynamometry

OBJECTIVE: To examine the reliability of clinical techniques for testing hip abductor and adductor muscle performance. DESIGN: Repeated measures. SETTING: Academic laboratory. PARTICIPANTS: A sample of 21 healthy subjects (12 men, 9 women) between 22 and 31 years of age. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Reliability of repeated measures was estimated by calculating intraclass correlation coefficients. Torque production capability was calculated by multiplying force output obtained with a hand-held dynamometer by the length of the resistance lever arm. RESULTS: The reliability of abduction testing was greatest in the long-lever condition. Adduction test reliability was greatest in the long-lever condition with bench stabilization. The maximal hip abduction torque tested in the long-lever position was significantly greater (t(20)=9.21, P<.001) than that in the short-lever position. The maximal hip adduction torque occurred using a long lever for resistance application and a bench to stabilize the nontest leg (F(1,20)=15.64, P=.001). CONCLUSIONS: Muscle performance testing of hip abductors and adductors with a hand-held dynamometer can be performed with good to excellent intratester and intertester reliability. Hip abduction testing is best performed with a long lever. Hip adduction is best performed with a long lever and a bench to stabilize the nontest extremity.     

Shoulder kinematics impact subacromial proximities: a review of the literature

BackgroundAlterations in glenohumeral and scapulothoracic kinematics have been theorized to contribute to rotator cuff pathology by impacting the magnitude of the subacromial space.ObjectiveThe purpose of this review is to summarize what is currently known about the relationship between shoulder kinematics and subacromial proximities.ConclusionsA variety of methods have been used to quantify subacromial proximities including photographs, MR imaging, ultrasonography, and single- and bi-plane radiographs. Changes in glenohumeral and scapulothoracic kinematics are associated with changes in subacromial proximities. However, the magnitude and direction of a particular motion's impact on subacromial proximities often vary between studies, which likely reflects different methodologies and subject populations. Glenohumeral elevation angle has been consistently found to impact subacromial proximities. Plane of humeral elevation also impacts subacromial proximities but to a lesser degree than the elevation angle. The impact of decreased scapulothoracic upward rotation on subacromial proximities is not absolute, but instead depends on the angle of humerothoracic elevation. The effects of scapular dyskinesis and humeral and scapular axial rotations on subacromial proximities are less clear. Future research is needed to further investigate the relationship between kinematics and subacromial proximities using more homogenous groups, determine the extent to which compression and other factors contribute to rotator cuff pathology, and develop accurate and reliable clinical measures of shoulder motion.     

Comparison of scapular upward rotation during arm elevation in the scapular plane in healthy volunteers and patients with rotator cuff tears pre- and post-surgery

BackgroundFunction loss caused by rotator cuff tears alters the scapular orientation, however, few prior studies have reported on scapular movements after rotator cuff repair. The purpose was to determine the scapular orientations before and after rotator cuff repair.MethodsWe recruited 14 healthy controls, 10 small and six massive rotator cuff tear in patients. The scapular upward rotation during arm elevation was analyzed using fluoroscopic imaging.FindingsBefore surgery, both rotator cuff groups demonstrated greater scapular upward rotation compared to healthy controls. Two months postoperation, the analyses showed significant differences between the patients with small rotator cuff tears and healthy controls at arm elevations of 90°, and between patients with both rotator cuff tear groups and healthy controls at arm elevations of 120°. At five months post-operation, significant differences still existed between the healthy controls and both rotator cuff groups. In regard to the temporal effects in the patients with small rotator cuff tears, the scapular upward rotation decreased significantly over time (2–5 months postoperation) at arm elevations of 120°. We did not identify a main effect owing to time in the patients with massive rotator cuff tears.InterpretationIn patients with small rotator cuff tears, scapular upward rotation was reduced over the period of 2–5 months postoperation, however, the patients with massive rotator cuff tears showed greater scapular upward rotation throughout the experimental period. The results suggested that the execution of the rehabilitation program should consider that the tear size could affect scapular motion.     

Immediate effect of scapula-focused exercises performed with kinematic biofeedback on scapular kinematics in individuals with subacromial pain syndrome

BackgroundGiven the changes in the patterns of muscular activation and scapular movement in individuals with subacromial pain syndrome, the use of neuromuscular training has been considered in rehabilitation protocols. There is currently no evidence of the effects of the use of three-dimensional (3D) kinematic biofeedback on individuals with subacromial pain syndrome. This study aimed to determine the immediate effect of scapular motor control exercises using 3D kinematic biofeedback on the scapular kinematics, inter-segment coordination and pain of individuals with subacromial pain syndrome.MethodThe kinematics of the scapulothoracic joint of 26 subjects with subacromial pain syndrome were assessed in the movement arm elevation and lowering in the sagittal plane before and after performance of three scapula-focused exercises using kinematic biofeedback. The individuals were familiarized with the selected exercises to acquire a greater scapular posterior tilt, while kinematic biofeedback, with visual and auditory stimuli, was used in real time. Scapular kinematics, pain, and subjective perception of exertion were the pre- and post-test measures.FindingsIn the movement of arm elevation and lowering, no differences were found in scapular tilt and on coordination between the segments pre- and post-test and the effect size was considered small.InterpretationOur results demonstrate that the performance of scapula-focused exercises using kinematic biofeedback does not cause immediate changes in the magnitude of scapular movement. However, inter-segmental coordination showed evidence of changes for scapular tilt in the lowering of the arm and internal rotation in the elevation and the lowering of the arm in individuals with subacromial pain syndrome.     

The reconstruction of inveterate rotator cuff lesions and lesions of the glenoid labrum of the shoulder with open and arthroscopic techniques

Background. The purpose of the paper is to present the treatment results of patients with injured rotator cuff, based on 6 months study, major limb dysfunction and severe pain.
Material and methods. Study is based on 14 patients, who underwent arthroscopic and open surgery of the shoulder. After arthroscopic repair of coexisting injuries and curbed mobility of the rotator cuff, open method was employed to reinsert rotator cuff with decompression of subacromial space. After the surgery, the arm was immobilised using orthosis with about 20-30 degrees abduction. Limited exercises of mobility range was started in the 4rd week after the surgery, increasing slightly the intensity and character of the exercises. External rotation movement was introduced in the third month after the surgery.
Results. The decrease of pain score has been observed from 6.28 points before surgery to 1.87 points after the treatment. The UCLA score increased after the surgery by about 26 points. In Simple Shoulder Test the score of positive answers increased from 2.2 to 7.6 after surgery. Results of the treatment were lack off pain and restored stability of the shoulder.
Conclusions. Decreased pain and better mobility seem to prove the efficacy of treatment of inveterate massive rotator cuff lesions.     

In vivo measurements of subacromial impingement: substantial compression develops in abduction with large internal rotation

BACKGROUND: Subacromial impingement is a widely recognized mechanism of chronic shoulder pain. The magnitudes of the compressive forces that impinge the subacromial structures were often measured from cadaveric specimens, but it is questionable to use this data as a sole basis to determine the shoulder motions and/or shoulder configurations that induce impingement in live subjects performing active motion. The purpose of the present study was to determine in vivo the magnitude of the compressive force at selected shoulder configurations. METHODS: The subacromial structures may be impinged by the downward-directed forces exerted by the coraco-acromial ligament. The reactions of these forces push the ligament upwards and deform it into a curved shape. A single resultant of these reaction forces was determined with an inverse approach to quantify the magnitude of the impingement force. An ultrasound unit was used to visualize the deformed shape of the coraco-acromial ligament for thirteen subjects with no symptomatic shoulder problem actively holding their shoulders in five configurations. FINDINGS: The impingement force in 90 degrees abduction+maximum internal rotation (mean=21.3N) and that in the Hawkins test position (mean=18.3N) were significantly greater than those in 90 degrees abduction+neutral and external rotation (means < or = 3N). INTERPRETATION: For young asymptomatic shoulders, the motions that induce impingement are not any arm abduction, but the arm abduction with a large internal rotation. Further study is indicated to examine the impingement force among various age groups.     

Three-dimensional in vivo comparative analysis of the kinematics of normal shoulders and shoulders with massive rotator cuff tears with successful conservative treatment

BackgroundThis study used in vivo three-dimensional to two-dimensional image registration techniques to compare the glenohumeral kinematics of shoulders with massive rotator cuff tears that were successfully treated conservatively and those of normal shoulders.MethodsTen patients (age, 67.4 ± 3.63 years) with massive rotator cuff tears on one side and without contralateral tears were enrolled. We performed computed tomography and fluoroscopy on both shoulder joints and created three-dimensional bone models of the humerus and scapula using image registration techniques. We measured the humeral superoinferior translation, angle of humeral external rotation, scapular upward rotation, scapular anteroposterior tilt, and scapular external rotation of the torn shoulders with good range of motion after effective conservative treatment and compared these measurements to those of the contralateral normal shoulders.FindingsThere was a significant difference in the initial position of the humeral head relative to the glenoid in the tear group; it was 2.0 mm higher than that in the normal group (p < .05). This difference disappeared in the range from 40° to full elevation. The scapular motion of the tear group was significantly more upwardly rotated than that of the normal group: by 9.9° at rest (p < .05) and by 11.6° at terminal elevation (p < .05). No significant differences were detected for humeral head external rotation, scapular anteroposterior tilt, and scapular external rotation between the two groups.InterpretationKinematics of shoulders with massive cuff tears could not be recovered completely even though the patients had no significant symptoms after successful conservative treatment.     

肩峰下撞击综合征的经皮超声引导下肩峰下滑囊造影表现

目的 探讨肩峰下撞击综合征（SIS）的经皮超声引导下肩峰下滑囊造影（PUSB）表现。方法 对150例经临床诊断为SIS患者行PUSB检查,动态观察造影剂在滑囊内的弥散情况及是否进入肩袖、关节腔。结果 53例造影剂在滑囊内呈线状均匀分布,诊断为单纯性肩峰下滑囊炎。97例造影剂在滑囊内分布不均匀,诊断为粘连性肩峰下滑囊炎。40例可见造影剂由滑囊进入肩袖肌腱,但未达肱骨头表面;32例可见造影剂由滑囊进入肩袖肌腱,到达肱骨头表面;78例造影剂未进入肩袖肌腱。结论 PUSB可实时动态评估肩峰下滑囊炎、滑囊粘连、肩袖损伤等情况,对SIS的诊断具有较高的应用价值。     

Immediate effect of MWM adductor stretch,myofascial release,and conventional stretching in asymptomatic individuals with hip adductor tightness: A randomized controlled trial

BackgroundHip adductors are the group of muscles that stabilize the pelvis during weight transfer in lower limbs in a gait cycle. As the full range of motion is seldomly used, this group of muscles commonly go into tightness which in turn may be a predisposing factor in development of back pain and knee pain.Methods54 healthy individuals were selected after screening for bilateral hip adductor tightness by measuring hip abduction range of motion using goniometer. They were randomized to either mobilization with movement (MWM) adductor stretch, myofascial release, or conventional stretching group. All subjects were assessed pre and post intervention. Outcome measure used were hip abduction range of motion and bent knee fall out test.ResultsStatistically significant difference was noted between the experimental and the control group in terms of hip abduction range of motion and bent knee fall out test.ConclusionIntervention showed significant results in all three groups; however, MWM adductor stretch when used in conjunction with conventional stretching has proved to be more effective than myofascial release with foam roller and conventional stretching in increasing the abduction range of motion and bent knee fall out test.     

The relevance of the moment arm of shoulder muscles with respect to axial rotation of the glenohumeral joint in four positions

OBJECTIVE: This study was undertaken to determine the efficiency of the shoulder girdle muscles during axial humeral rotation based on measurements of the moment arms. DESIGN: The instantaneous muscle moment arms of 10 shoulder muscles, including the three portions of the deltoid, the rotator cuff muscles, teres major, and the thoracohumeral muscle group, were measured during four specified glenohumeral rotations. BACKGROUND: Axial humeral rotation is a commonly performed movement during activities of daily living and is a targeted motion of shoulder rehabilitation, particularly in those protocols emphasizing rotator cuff strengthening. An understanding of the function of the movers and stabilizers of the shoulder requires such basic information of muscle moment arms. METHODS: The instantaneous moment arm values of the muscles were derived from the slope of the plot of tendon excursion versus glenohumeral joint rotation angle. Motion studied included axial rotation with the humerus elevated 90 degrees in the coronal, scapular, and sagittal planes, as well as in the neutral position with the arm at the side. RESULTS: Based on the findings, with the humerus in both neutral and elevated positions, the infraspinatus is potentially the most powerful external rotator, followed by teres minor and posterior deltoid. Subscapularis and possibly pectoralis major are the most effective internal rotators in this position. CONCLUSIONS: The moment arm in providing axial humeral rotation of 10 shoulder muscles in four planes were obtained. In general, the teres minor and infraspinatus had the largest moment arms in external rotation, and the subscapularis had the largest moment arm in internal rotation. The muscle function for axial humeral rotation was found to be modified by the plane of arm elevation. RELEVANCE: The data could be used for developing exercise programs in physical therapy.