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.     

The potential role of upper extremity muscle fatigue in the generation of extrinsic subacromial impingement syndrome: a kinematic perspective

Abstract

Background:

Subacromial impingement syndrome (SAIS) of the shoulder has a multi-factorial aetiology which includes both intrinsic and extrinsic mechanisms. Upper extremity muscle fatigue has been proposed as a potential causative factor in extrinsic SAIS development.

Objectives:

This review summarises the current state of knowledge regarding fatigue-induced glenohumeral (GH) and scapulothoracic (ST) kinematic changes as they relate to subacromial space reduction and subsequent SAIS. It specifically addresses evidence for mechanisms including superior humeral head translation and scapular reorientation.

Major findings:

Global upper extremity muscle fatigue elicits GH kinematic changes that increase SAIS risk. Concurrent compensatory ST kinematic alterations, primarily scapular upward rotation (UR), lessen this risk. Additionally, fatiguing protocols aimed to selectively exhaust certain muscles or muscle groups without fatiguing the rotator cuff were unsuccessful, suggesting that rotator cuff fatigue is likely for a wide range of fatiguing upper extremity tasks.

Conclusions:

Despite the compensatory response of scapular reorientation in fatigued conditions, the dimensions of the subacromial space still pose increased risk for SAIS development, and the variability in kinematic responses produces highly differential risk, particularly for those exposed to tasks requiring increased rotator cuff muscle demand.     

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.     

Mechanisms of rotator cuff tendinopathy: Intrinsic,extrinsic, or both?

The etiology of rotator cuff tendinopathy is multi-factorial, and has been attributed to both extrinsic and intrinsic mechanisms. Extrinsic factors that encroach upon the subacromial space and contribute to bursal side compression of the rotator cuff tendons include anatomical variants of the acromion, alterations in scapular or humeral kinematics, postural abnormalities, rotator cuff and scapular muscle performance deficits, and decreased extensibility of pectoralis minor or posterior shoulder. A unique extrinsic mechanism, internal impingement, is attributed to compression of the posterior articular surface of the tendons between the humeral head and glenoid and is not related to subacromial space narrowing. Intrinsic factors that contribute to rotator cuff tendon degradation with tensile/shear overload include alterations in biology, mechanical properties, morphology, and vascularity. The varied nature of these mechanisms indicates that rotator cuff tendinopathy is not a homogenous entity, and thus may require different treatment interventions. Treatment aimed at addressing mechanistic factors appears to be beneficial for patients with rotator cuff tendinopathy, however, not for all patients. Classification of rotator cuff tendinopathy into subgroups based on underlying mechanism may improve treatment outcomes.     

The effect of negative intraarticular pressure and rotator cuff force on glenohumeral translation during simulated active elevation

OBJECTIVE: The objective of this study was to determine the effect of negative pressure in the intraarticular space and subacromial bursa, as well as rotator cuff force, on glenohumeral translation during active elevation. DESIGN: Glenohumeral translation during elevation in the scapular plane was measured under greater than, less than, and equal to physiologic rotator cuff muscle force, as well as with and without the subacromial bursa and intraarticular space vented. BACKGROUND: Negative intraarticular pressure has been shown to help stabilize the glenohumeral joint in passive motion, although the effect on translation during active motion has not been investigated.Methods: Eight cadaverous human shoulder specimens were tested in a dynamic shoulder simulator. Forces in the muscles of the rotator as well as the middle deltoid muscle were simulated using servohydraulic cylinders. Joint motion was measured using an ultrasonic motion analysis system. RESULTS: Superior translation of the humerus increased 1.2 mm (SD, 0.4) upon venting of the bursa, and 2.1 mm (SD, 1.7) upon venting of the joint capsule at 25 degrees of glenohumeral elevation in the scapular plane. At 90 degrees elevation, venting the bursa did not change superior translation but increased anterior translation 1.04 mm (SD, 1.0). Venting of the joint capsule increased superior translation by 2.8 mm (SD, 2.5). Decreasing rotator cuff force increased superior translation, while reducing it did not. CONCLUSION: The muscles of the rotator cuff and the negative pressure of the intraarticular space and the subacromial bursa stabilize the glenohumeral joint since they restrict translation in the superior and anterior directions. RelevanceIncreased glenohumeral translation and the resulting asymmetric loading may lead to arthrosis and ultimately rotator cuff arthropathy.     

Anatomical and biomechanical mechanisms of subacromial impingement syndrome

Subacromial impingement syndrome is the most common disorder of the shoulder, resulting in functional loss and disability in the patients that it affects. This musculoskeletal disorder affects the structures of the subacromial space, which are the tendons of the rotator cuff and the subacromial bursa. Subacromial impingement syndrome appears to result from a variety of factors. Evidence exists to support the presence of the anatomical factors of inflammation of the tendons and bursa, degeneration of the tendons, weak or dysfunctional rotator cuff musculature, weak or dysfunctional scapular musculature, posterior glenohumeral capsule tightness, postural dysfunctions of the spinal column and scapula and bony or soft tissue abnormalities of the borders of the subacromial outlet. These entities may lead to or cause dysfunctional glenohumeral and scapulothoracic movement patterns. These various mechanisms, singularly or in combination may cause subacromial impingement syndrome.     

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.     

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.     

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.     

Scapular kinematics during humeral elevation in adults and children

BACKGROUND: Appropriate motion of the scapula is important for dynamic positioning of the glenoid during humeral elevation. A number of studies have described the typical scapular kinematics during humeral elevation in adults. However, children and adults may have differences in scapulothoracic musculature and scapular osteology. To our knowledge, no study has been performed examining scapular kinematics in children with either typical or atypical development. Consequently in children the influence of age and development on scapular motion is currently unknown. The aim of this study was to describe and compare the kinematic patterns of the scapula during humeral elevation in children with typical development and healthy adults. METHODS: Fifteen adults, 7 females, 25-37 years of age, and 14 children, 8 females, 4-9 years of age, participated in this study. Kinematic data were collected using a magnetic tracking device. Subjects were asked to elevate their arm in the scapular plane (40 degrees anterior to the frontal plane) in a sequence of three trials. FINDINGS: Significant differences were seen between the two age groups in the dependent variables. During scapular plane rotation from 25 degrees to 125 degrees , children showed greater upward rotation (43.9 degrees SD 6.39 degrees ) than adults (29.1 degrees SD 10.1 degrees ). The mean glenohumeral to scapulothoracic ratio in the scapular plane was 2.4:1 for adults, 1.3:1 for children. INTERPRETATION: This study demonstrates that there are significant differences in scapular kinematic patterns between children and adults. Children have a greater contribution from the scapulothoracic joint, specifically upward rotation toward humeral elevation. From a clinical perspective, these results can be used to help determine the incorporation of stabilization and mobilization of the scapulothoracic joint during exercises for a child with impairment at the shoulder for improving shoulder function.     

Kinematic patterns in normal and degenerative shoulders. Part II: Review of 3-D scapular kinematic patterns in patients with shoulder pain,and clinical implications

Background

The global range of motion of the arm is the result of a coordinated motion of the shoulder complex including glenohumeral (GH), scapulothoracic, sternoclavicular and acromioclavicular joints.

The specificity of fatiguing protocols affects scapular orientation: Implications for subacromial impingement

Background

Shoulder impairments are often associated with altered scapular kinematics. As muscles control scapular movement, functionally altering muscle performance through fatigue may produce scapular kinematics that mimic those of injured patients. The aim of this study was to examine if changes in scapular tilt, rotation and pro/retraction following two different upper extremity fatiguing protocols have any implications with respect to subacromial impingement.

Methods

Scapular orientation was monitored during posturally constrained static holds (at 0°, 45° and 90° of humeral elevation) before and after two fatiguing protocols, one global and one local. Both protocols are associated with producing changes in shoulder skeletal arrangement.

Findings

Following the global fatiguing protocol, there was significantly more scapular posterior tilt (P < 0.01) and upward rotation (P < 0.02), particularly at 90° humeral elevation. No changes in scapular orientation occurred following the local fatiguing protocol.

Interpretation

Scapular orientation changes following muscle fatigue acted to increase the subacromial space. Thus, the rotator cuff muscles, not the scapular stabilizers, have more influence on actively preventing mechanical subacromial impingement. The lack of evidence of reduction of the subacromial space thus implicates superior humeral head translation as a more likely primary mechanism of the initiation of subacromial impingement.     

Comparison of rotator cuff to glenoid proximity based on scapulothoracic upward rotation classification

BackgroundRecent evidence suggests that internal impingement, or rotator cuff tendon deformation against the glenoid, occurs during overhead motions and may therefore be a mechanism of pathology even in non-athletes. Clinically, knowing how movement impacts potential injury mechanisms would be useful to guide movement-based treatment strategies.ObjectiveTo compare the distance between the glenoid and rotator cuff footprint between two groups classified based on scapulothoracic upward rotation (UR) magnitude (i.e., low, high) at 90° humerothoracic elevation.MethodsShoulder kinematics were quantified during scapular plane abduction in 60 participants using single-plane fluoroscopy. Of these, 40 were subsequently classified as having high or low scapulothoracic UR based on the sample's distribution. The minimum distance between the glenoid and rotator cuff footprint was calculated along with the locations of closest proximity (i.e., proximity centers). Minimum distances and proximity center locations were compared between groups using 2-factor mixed-model ANOVAs. The prevalence of glenoid-to-footprint contact was also compared.ResultsGlenoid-to-footprint distances consistently decreased as humerothoracic elevation angle increased, and the anterior aspect of the footprint was closest to the posterosuperior glenoid. Minimum distances were not significantly different between UR groups (p≥0.16). However, group differences existed in proximity center locations (p<0.01). Glenoid-to-footprint contact was identified in 75.0% of participants at an average (SD) of 133.6° (3.2°) humerothoracic elevation.ConclusionThe results of this study suggest that decreased UR as classified and assessed in this study does not significantly impact glenoid-to-footprint distances but does alter the location of the contact, which occurred in most participants.     

Effects of muscle fatigue on 3-dimensional scapular kinematics

OBJECTIVE: To determine the effects of fatigue during an external rotation task on 3-dimensional scapular kinematics. DESIGN: A single-group, pretest-posttest measurement design. SETTING: Research laboratory. PARTICIPANTS: Thirty healthy subjects. INTERVENTIONS: Not applicable.Main Outcome Measures: Three-dimensional scapular kinematics were recorded with a Polhemus magnetic tracking device during arm elevation in the scapular plane. RESULTS: There was a significant fatigue effect for all scapular rotations in the early to middle phases of humeral elevation. Significantly less posterior tilting (up to 90 degrees of elevation), external rotation (up to 120 degrees of elevation), and upward rotation (up to 60 degrees of elevation) were observed. Additionally, there were fair to good correlations (r range,.39-.60) between the changes in scapular posterior tilting and the amount of muscle fatigue. CONCLUSIONS: Fatigue in shoulder external rotation altered the scapular resting position and the movement of posterior tilting in the early range during arm elevation in the scapular plane. Observed changes in scapular kinematics may affect the amount of area in the subacromial space and facilitate impingement. Data regarding changes produced by fatigue of the external rotators may also help with the development of a model of diminished rotator cuff function.     

Reported mechanisms of shoulder injury during the baseball throw

Abstract

Background: Shoulder complex injuries are common among overhand throwing athletes. These injuries often manifest as a result of habitual sport performance and often lead to time loss injuries. The mechanisms of these injuries are often non-traumatic and theories on how shoulder injuries manifest differ.

Objectives: To describe the proposed mechanisms of commonly reported shoulder injuries as they relate to the phases of the throwing motion.

Major findings: Shoulder injuries commonly involve rotator cuff muscles and tendons, scapulothoracic muscles, glenohumeral joint labrum, proximal humeral epiphysis, glenohumeral joint capsule, biceps muscle and tendon, and subacromial bursa. The injuries found in these tissues and their purported mechanisms of injury during the throw vary.

Conclusions: The late cocking and deceleration phases have been implicated with the largest number of associated pathologies. Multiple injuries were theorized to occur at more than one phase of the throwing motion. Consensus has not been achieved on the provocative events leading to shoulder injury during the throwing motion.     

A stochastic analysis of glenoid inclination angle and superior migration of the humeral head

BACKGROUND: Superior glenoid inclination, which is a relatively upward facing of the glenoid in the plane of the scapula, has been associated with rotator cuff pathology. Increased glenoid inclination may cause superior humeral head migration, which can cause impingement of the supraspinatus tendon. The purpose of this study was to test the hypothesis that inclination angle affects the probability of superior humeral head migration. METHODS: A three-dimensional model of the glenohumeral joint was developed in which muscle forces were modeled as random variables. Monte Carlo simulation was used to compute the probability that the glenohumeral reaction force was directed such that superior humeral head migration should occur. An electromyogram-driven model was used to estimate shoulder muscle forces in healthy volunteers performing arm elevation. FINDINGS: The model predicted that the probability of superior humeral head migration increased as glenoid inclination angle was increased. This finding was independent of the assumed shape of the muscle force probability distributions. INTERPRETATION: The results support the theory that glenoid inclination may be a risk factor for rotator cuff pathology.     

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.     

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.     

Three-dimensional shoulder kinematics during a pressure relief technique and wheelchair transfer

OBJECTIVE: To assess 3-dimensional scapulothoracic and glenohumeral kinematics in able-bodied subjects during a weight-relief raise and while transferring to and from a wheelchair. DESIGN: Repeated-measures analysis of variance. SETTING: Research laboratory. PARTICIPANTS: Twenty-five able-bodied subjects without spinal cord injury or shoulder symptoms (20 men, 5 women; age range, 20-37y). INTERVENTIONS: Completion of weight-relief raise and transfer tasks. Main Outcome Measures: An electromagnetic motion capture system tracked 3-dimensional position and orientation of the thorax, scapula, and humerus. Absolute angular values assessed included scapular downward and upward rotation, internal and external rotation, and posterior and anterior tipping all relative to the thorax, as well as humeral internal and external rotation relative to the scapula. Data were compared across 3 phases of the weight-relief raise and for transfer direction (leading arm, trailing arm). RESULTS: Key findings included significantly increased anterior tipping and internal rotation of the scapula and decreased scapular upward rotation and external rotation of the humerus during the weight-relief raise. The leading arm showed significantly greater scapular anterior tipping and internal rotation and less scapular upward rotation and humeral external rotation than the trailing arm during the final phase of the transfer. CONCLUSIONS: Both the weight-relief raise and transfer result in scapular and humeral positions and directions of motion that may negatively impact the available subacromial space. This may present increased risk for injury or progression of shoulder pain in persons who must routinely perform these tasks.     

In vivo measurement of subacromial space width during shoulder elevation: technique and preliminary results in patients following unilateral rotator cuff repair

BACKGROUND: The shoulder's subacromial space is of significant clinical interest due to its association with rotator cuff disease. Previous studies have estimated the subacromial space width to be 2-17 mm, but no study has measured in vivo subacromial space width during shoulder motion. The purpose of this study was to measure the in vivo subacromial space width during shoulder elevation in patients following rotator cuff repair. METHODS: Biplane X-ray images were collected during shoulder elevation of 11 patients who had undergone rotator cuff repair. Glenohumeral joint motion was measured from the biplane X-ray images for each subject's repaired and asymptomatic, contralateral shoulders. The joint motion data were combined with subject-specific CT models to measure the subacromial space width during shoulder motion. FINDINGS: Subacromial space width decreased with shoulder elevation, ranging from 2.3 to 7.4 mm in the repaired shoulder and 1.2-7.1 mm in the contralateral shoulder. Subacromial space width in the repaired shoulder was only 0.5 mm less than the contralateral shoulder when averaged over 10-60 degrees of glenohumeral elevation. INTERPRETATION: The results indicate that the humerus in the repaired shoulder is positioned more cranially on the glenoid than in the contralateral shoulder. It is unclear if these subtle differences in subacromial space width are due to the surgical procedure or post-operative stiffness, or if subacromial impingement contributed to the development of the rotator cuff tear. Future research will ascertain if these results represent a transient response to the surgery or a more fundamental difference in rotator cuff function between repaired and contralateral shoulders.