In vivo shoulder function after surgical repair of a torn rotator cuff: glenohumeral joint mechanics, shoulder strength, clinical outcomes, and their interaction

In Vivo 3-Dimensional Dynamic Evaluation of Shoulder Kinematics After the Latarjet Procedure: Comparison With the Contralateral Healthy Shoulder

Background

Researchers have attempted to understand the underlying mechanism of the Latarjet procedure; however, its effects on shoulder kinematics have not been well studied.

Purpose/Hypothesis

The purpose was to analyze shoulder kinematics after the Latarjet procedure. It was hypothesized that the nonanatomic transfer of the coracoid process during the procedure would affect normal shoulder kinematics.

Study Design

Controlled laboratory study.

Methods

The study included 10 patients (age range, 20-52 years) who underwent the modified Latarjet procedure between June 2016 and November 2021. Computed tomography and fluoroscopy were conducted on both shoulder joints of all patients, and 3-dimensional models were reconstructed. The 3-dimensional coordinates were encoded on the reconstructed models, and shoulder kinematics were analyzed through a 3-dimensional-2-dimensional model-image registration technique. Scapular rotation parameters (scapular upward rotation, posterior tilt, external rotation, and scapulohumeral rhythm) were compared between the Latarjet and the nonsurgical contralateral sides during humeral abduction, as was anteroposterior (AP) translation relative to the glenoid center during active humeral external rotation.

Results

The Latarjet side displayed significantly higher values of scapular upward rotation at higher degrees of humeral elevation (130°, 140°, and 150°) compared with the nonsurgical side (P = .027). Posterior tilt, external rotation, and scapulohumeral rhythm were not significantly different between sides. AP translation at maximal humeral rotation was not significantly different between sides (Latarjet, -0.06 ± 5.73 mm vs nonsurgical, 5.33 ± 1.60 mm; P = .28). Interestingly, on the Latarjet side, AP translation increased until 40° of humeral rotation (4.27 ± 4.64 mm) but began to decrease from 50° of humeral rotation.

Conclusion

The Latarjet side demonstrated significant changes in scapular upward rotation during higher degrees of humeral elevation compared with the contralateral shoulder. Posterior movement of the humeral head at >50° of humeral rotation could be the desired effect of anterior stabilization; however, researchers should evaluate long-term complications such as osteoarthritis.

Clinical Relevance

Analysis of shoulder kinematics after the Latarjet procedure could provide information regarding long-term outcomes and whether the procedure would affect the daily activities of patients.

Improved joint function when reaching behind the back is associated with patient reported outcomes in individuals with rotator cuff tears following exercise therapy

BACKGROUND

Reaching behind the back is painful for individuals with rotator cuff tears. The objectives of the study were to determine changes in glenohumeral kinematics when reaching behind the back, passive range of motion (RoM), patient reported outcomes and the relationships between kinematics and patient reported outcomes following exercise therapy.

METHODS

Eighty-four individuals with symptomatic isolated supraspinatus tears were recruited for this prospective observational study. Glenohumeral kinematics were measured using biplane radiography during a reaching behind the back movement. Passive glenohumeral internal rotation and patient reported outcome measures were collected. Depending on data normality, appropriate tests were utilized to determine changes in variables. Spearman's correlations were utilized for associations, and Stuart-Maxwell tests for changes in distributions.

FINDINGS

Maximum active glenohumeral internal rotation increased by 3.2° (P = 0.001), contact path length decreased by 5.5% glenoid size (P = 0.022), passive glenohumeral internal rotation RoM increased by 4.9° (P = 0.001), and Western Ontario Rotator Cuff Index and American Shoulder and Elbow Surgeons scores increased by 29.8 and 21.1 (P = 0.001), respectively. Changes in Western Ontario Rotator Cuff Index scores positively associated with changes in maximum active glenohumeral internal rotation and negatively associated with changes in contact path lengths (P = 0.008 and P = 0.006, respectively).

INTERPRETATION

The reaching behind the back movement was useful in elucidating in-vivo mechanistic changes associated with patient reported outcomes. Glenohumeral joint function and patient reported outcomes improved, where changes in Western Ontario Rotator Cuff Index scores were associated with kinematics. These findings inform clinicians of functional changes following exercise therapy and new targetable treatment factors.

Test-retest reliability of isometric shoulder muscle strength during abduction and rotation tasks measured using the Biodex dynamometer

BACKGROUND

The Constant score (CS) is often used clinically to assess shoulder function and includes a muscle strength assessment only for abduction. The aim of this study was to evaluate the test-retest reliability of isometric shoulder muscle strength during various positions of abduction and rotation with the Biodex dynamometer and to determine their correlation with the strength assessment of the CS.

METHODS

Ten young healthy subjects participated in this study. Isometric shoulder muscle strength was measured during 3 repetitions for abduction at 10° and 30° abduction in the scapular plane (with extended elbow and hand in neutral position) and for internal and external rotation (with the arm at 15° abduction in the scapular plane and elbow flexed at 90°). Muscle strength tests with the Biodex dynamometer were measured in 2 different sessions. The CS was acquired only in the first session. Intraclass correlation coefficients (ICCs) with 95% confidence interval, limits of agreement, and paired t tests for repeated tests of each abduction and rotation task were calculated. Pearson's correlation between the strength parameter of the CS and isometric muscle strength was investigated.

RESULTS

Muscle strength did not differ between tests (P > .05) with good to very good reliabilities for abduction at 10° and 30°, external rotation and internal rotation (ICC >0.7 for all). A moderate correlation of the strength parameter of the CS with all isometric shoulder strength parameters was observed (r > 0.5 for all).

CONCLUSION

Shoulder muscle strength for abduction and rotation measured with the Biodex dynamometer are reproducible and correlate with the strength assessment of the CS. Therefore, these isometric muscle strength tests can be further employed to investigate the effect of different shoulder joint pathology on muscle strength. These measurements consider a more comprehensive functionality of the rotator cuff than the single strength evaluation in abduction within the CS as both abduction and rotation are assessed. Potentially, this would allow for a more precise differentiation between the various outcomes of rotator cuff tears.

Fully automatic tracking of native glenohumeral kinematics from stereo-radiography

The current work introduces a system for fully automatic tracking of native glenohumeral kinematics in stereo-radiography sequences. The proposed method first applies convolutional neural networks to obtain segmentation and semantic key point predictions in biplanar radiograph frames. Preliminary bone pose estimates are computed by solving a non-convex optimization problem with semidefinite relaxations to register digitized bone landmarks to semantic key points. Initial poses are then refined by registering computed tomography-based digitally reconstructed radiographs to captured scenes, which are masked by segmentation maps to isolate the shoulder joint. A particular neural net architecture which exploits subject-specific geometry is also introduced to improve segmentation predictions and increase robustness of subsequent pose estimates. The method is evaluated by comparing predicted glenohumeral kinematics to manually tracked values from 17 trials capturing 4 dynamic activities. Median orientation differences between predicted and ground truth poses were 1.7∘ and 8.6∘ for the scapula and humerus, respectively. Joint-level kinematics differences were less than 2∘ in 65%, 13%, and 63% of frames for XYZ orientation DoFs based on Euler angle decompositions. Automation of kinematic tracking can increase scalability of tracking workflows in research, clinical, or surgical applications.

Empirical joint contact mechanics: A comprehensive review

Empirical joint contact mechanics measurement (EJCM; e.g. contact area or force, surface velocities) enables critical investigations of the relationship between changing joint mechanics and the impact on surface-to-surface interactions. In orthopedic biomechanics, understanding the changes to cartilage contact mechanics following joint pathology or aging is critical due to its suggested role in the increased risk of osteoarthritis (OA), which might be due to changed kinematics and kinetics that alter the contact patterns within a joint. This article reviews and discusses EJCM approaches that have been applied to articulating joints such that readers across different disciplines will be informed of the various measurement and analysis techniques used in this field. The approaches reviewed include classical measurement approaches (radiographic and sectioning, dye staining, casting, surface proximity, and pressure measurement), stereophotogrammetry/motion analysis, computed tomography (CT), magnetic resonance imaging (MRI), and high-speed videoradiography. Perspectives on approaches to advance this field of EJCM are provided, including the value of considering relative velocity in joints, tractional stress, quantification of joint contact area shape, consideration of normalization techniques, net response (superposition) of multiple input variables, and establishing linkages to regional cartilage health status. EJCM measures continue to provide insights to advance our understanding of cartilage health and degeneration and provide avenues to assess the efficacy and guide future directions of developing interventions (e.g. surgical, biological, rehabilitative) to optimize joint's health and function long term.

Associations between range of motion, strength, tear size, patient-reported outcomes, and glenohumeral kinematics in individuals with symptomatic isolated supraspinatus tears

BACKGROUND

Clinical failure associated with nonoperative treatment of rotator cuff tears may be due to inadequate characterization of the individual's functional impairments. Clinically, restricted passive range of motion (ROM) (restrictions imply capsular tightness), limitations in muscle strength, and larger rotator cuff tears are hypothesized to be related to altered glenohumeral kinematics. Understanding these relationships, as well as the relationship between glenohumeral kinematics and patient-reported outcomes (PROs) prior to exercise therapy, may help characterize functional impairments in individuals with rotator cuff tears. The objectives of the study were to describe the baseline presentation of individuals with an isolated supraspinatus tear, including passive ROM, rotator cuff muscle strength, tear size, PROs, and glenohumeral kinematics, and to determine associations among these variables.

METHODS

One hundred one individuals with symptomatic isolated supraspinatus tears were recruited for the study and underwent assessments of passive glenohumeral ROM, isometric muscle strength, and ultrasonography to assess anterior-posterior tear size. Glenohumeral kinematics during scapular-plane abduction were measured using biplane radiography. Furthermore, PROs including the American Shoulder and Elbow Surgeons (ASES) score and the Western Ontario Rotator Cuff Index (WORC) score were collected.

RESULTS

Individuals presented with decreased ROM, external rotation weakness compared with the uninvolved side, and pain and disability as measured by the ASES and WORC scores. These findings were not associated with glenohumeral kinematics, with the exception of a weak positive association between glenohumeral contact path lengths and WORC scores (ρ = 0.25, P = .03). Tear size was 11.7 ± 5.7 mm, and maximum anterior translation, superior translation, and contact path length were 3.0% ± 3.8% of glenoid width, 3.5% ± 3.8% of glenoid height, and 38.2% ± 20.7% of glenoid size, respectively.

CONCLUSION

Individuals with a symptomatic isolated supraspinatus tear presented with decreased ROM, external rotation weakness, and pain and disability as measured by the ASES and WORC scores. However, no abnormal kinematics associated with these limitations were observed. Thus, given that the tear is isolated to the supraspinatus tendon and no capsular restrictions are present, normal function of the glenohumeral joint may be possible during scapular-plane abduction.

In Vivo Static Retraction and Dynamic Elongation of Rotator Cuff Repair Tissue After Surgical Repair: A Preliminary Analysis at 3 Months

Background:

Rotator cuff repair is a common orthopaedic procedure that provides pain relief for many patients, but unfortunately, an estimated 20% to 70% of repair procedures will fail. Previous research has shown that elongation (ie, retraction) of a repaired tendon is common even in patients with a repair construct that appears intact on magnetic resonance imaging. However, it is unknown how this repair tissue functions under dynamic conditions.

Purpose:

To quantify static retraction and maximum dynamic elongation of repair tissue after rotator cuff repair.

Study Design:

Case series; Level of evidence, 4.

Methods:

Data from 9 patients were analyzed for this study. During surgery, a 3.1-mm tantalum bead was sutured to the supraspinatus tendon, medial to the repair site. Glenohumeral kinematics were assessed at 1 week (static) and 3 months (static and during scapular-plane abduction) after surgery using a biplanar videoradiographic system. The 3-dimensional position of the bead was calculated relative to the tendon’s insertion on the humerus (ie, bead-to-insertion distance). Static retraction was calculated as the change in the bead-to-insertion distance under static conditions between 1 week and 3 months after surgery, and maximum dynamic elongation was calculated as the maximal positive change in the bead-to-insertion distance during dynamic motion relative to the start of motion. The magnitudes of static retraction and maximum dynamic elongation were assessed with 1-sample t tests.

Results:

At 3 months after surgery, static retraction occurred in all patients by a mean of 10.0 ± 9.1 mm (P = .01 compared with no elongation). During scapular-plane abduction, maximum dynamic elongation averaged 1.4 ± 1.0 mm (P < .01 compared with no elongation). Descriptively, dynamic elongation consistently took 1 of 2 forms: an initial increase in the bead-to-insertion distance (mean, 2.0 ± 0.6 mm) before decreasing until the end of motion or an immediate and substantial decrease in the bead-to-insertion distance at the onset of motion.

Conclusion:

Repair tissue elongation (static retraction and maximum dynamic elongation) appeared to be a common and significant finding at 3 months after arthroscopic rotator cuff repair. Dynamic elongation of repair tissue during scapular-plane abduction exhibited 1 of 2 distinct patterns, which may suggest different patterns of supraspinatus mechanical and neuromuscular function.

Four-dimensional computed tomography evaluation of shoulder joint motion in collegiate baseball pitchers

The purpose of this study is to evaluate the glenohumeral contact area, center of glenohumeral contact area, and center of humeral head during simulated pitching motion in collegiate baseball pitchers using four-dimensional computed tomography (4D CT). We obtained 4D CT data from the dominant and non-dominant shoulders of eight collegiate baseball pitchers during the cocking motion. CT image data of each joint were reconstructed using a 3D reconstruction software package. The glenohumeral contact area, center of glenohumeral contact area, center of humeral head, and oblateness of humeral head were calculated from 3D bone models using customized software. The center of glenohumeral contact area translated from anterior to posterior during maximum external rotation to maximum internal rotation (0.58 ± 0.63 mm on the dominant side and 0.99 ± 0.82 mm on the non-dominant side). The center of humeral head translated from posterior to anterior during maximum external rotation to maximum internal rotation (0.76 ± 0.75 mm on the dominant side and 1.21 ± 0.78 mm on the non-dominant side). The increase in anterior translation of the center of glenohumeral contact area was associated with the increase in posterior translation of the center of humeral head. Also, the increase in translation of the center of humeral head and glenohumeral contact area were associated with the increase in oblateness of the humeral head. 4D CT analyses demonstrated that the center of humeral head translated in the opposite direction to that of the center of glenohumeral contact area during external rotation to internal rotation in abduction in the dominant and non-dominant shoulders. The oblateness of the humeral head may cause this diametric translation. 4D CT scanning and the software for bone surface modeling of the glenohumeral joint enabled quantitative assessment of glenohumeral micromotion and be used for kinematic evaluation of throwing athletes.

Improved Outcomes Following Arthroscopic Superior Capsular Reconstruction May Not Be Associated With Changes in Shoulder Kinematics: An In Vivo Study

PURPOSE

To determine the in vivo effects of superior capsule reconstruction (SCR) on glenohumeral kinematics during abduction and to compare those kinematics results with patient-reported outcomes, range of motion, and strength.

METHODS

Dynamic biplane radiography was used to image 10 patients with irreparable rotator cuff tears while performing scapular plane abduction pre- and 1-year post-surgery. Shoulder kinematics were determined by matching subject-specific computed tomography-based bone models to the radiographs using a validated tracking technique.

RESULTS

No change was detected in static acromiohumeral distance (-0.7 ± 2.1 mm; P = .35); however, average dynamic acromiohumeral distance decreased (2.7 ± 1.2 mm to 2.3 ± 1.0 mm; P = .035) from pre- to 1-year post-surgery, respectively. The humeral head position was 0.5 ± 0.5 mm more superior 1-year post-surgery compared with pre-surgery (P = .01). Glenohumeral abduction increased from pre-surgery (150 ± 20°) to 1-year post-surgery (165 ± 10°) (P = .04) and all patient-reported outcomes improved from pre-surgery to 1-year post-surgery (all P < .002). A more posterior shift in humeral head position was associated with improved American Shoulder and Elbow Surgeons Shoulder Score from pre-surgery to 1-year post-surgery (r = 0.71, P = .02).

CONCLUSIONS

These data suggest that SCR may not depress the humeral head during functional abduction, as previously postulated, and postoperative improvements in subjective and clinical outcomes may be affected by mechanisms other than changes in shoulder kinematics.

CLINICAL RELEVANCE

In vivo kinematics changes after SCR are small and do not correspond to previously postulated changes.

Time-course changes in active stiffness of the supraspinatus muscle after arthroscopic rotator cuff repair

PURPOSE

This study aimed to investigate the time-course changes in the active stiffness of the supraspinatus muscle after arthroscopic rotator cuff repair.

METHODS

Eight male patients (mean age 61.5 ± 9.4 years) who underwent arthroscopic rotator cuff repair for small to medium tears were recruited for this study. Movement tasks included 30° shoulder isometric abduction and maximal voluntary isometric contraction of shoulder abduction in the scapular plane. The stiffness of the supraspinatus (anterior superficial, anterior deep, posterior superficial, and posterior deep regions), upper trapezius, and middle deltoid muscles in bilateral shoulders was recorded using ultrasound shear wave elastography. For each subject, the measurement was performed preoperatively and 3, 6, and 12 months postoperatively.

RESULTS

The stiffness of the affected anterior superficial region of the supraspinatus muscle 12 months postoperatively was significantly higher than that measured preoperatively and 3 months postoperatively (p < 0.05); it was significantly higher at 6 months postoperatively than at 3 months postoperatively (p < 0.05). Further, the maximal voluntary isometric contraction had significantly improved 12 months postoperatively compared to that measured preoperatively and 3 months postoperatively (p < 0.05). The stiffness of the affected upper trapezius and middle deltoid muscles 12 months postoperatively was significantly lower than that preoperatively (p < 0.05).

CONCLUSION

The maximal voluntary isometric contraction 12 months postoperatively possibly increased because of improvement in the active stiffness of the anterior superficial region. Active stiffness of the anterior superficial region may improve 6 months rather than 3 months postoperatively because of the different stages of muscle force, structural repair tendon strength, and remodeling.

Presurgical tear characteristics and estimated shear modulus as predictors of repair integrity and shoulder function one year after rotator cuff repair

Background

Rotator cuff repair provides pain relief for many patients; however, retears are relatively common and affect approximately 20%-70% of patients after repair. Although magnetic resonance imaging (MRI) offers the ability to assess tissue characteristics such as tear size, retraction, and fatty infiltration, it provides little insight into the quality of the musculotendinous tissues the surgeon will encounter during surgery. However, shear wave elastography (SWE) could provide an indirect assessment of quality (ie, stiffness) by measuring the speed of shear waves propagating through tissue. The objective of this study was to determine the extent to which estimated shear modulus predicts repair integrity and functional outcomes 1 year after rotator cuff repair.

Methods

Thirty-three individuals scheduled to undergo arthroscopic rotator cuff repair were enrolled in this study. Before surgery, shear modulus of the supraspinatus tendon and muscle was estimated using ultrasound SWE. MRIs were obtained before and 1 year after surgery to assess tear characteristics and repair integrity, respectively. Shoulder strength, range of motion, and patient-reported pain and function were assessed before and after surgery. Functional outcomes were compared between groups and across time using a two-factor mixed model analysis of variance. Stepwise regression with model comparison was used to investigate the extent to which MRI and shear modulus predicted repair integrity and function at 1 year after surgery.

Results

At 1 year after surgery, 56.5% of patients had an intact repair. No significant differences were found in any demographic variable, presurgical tear characteristic, or shear modulus between patients with an intact repair and those with a recurrent tear. Compared with presurgical measures, patients in both groups demonstrated significant improvements at 1 year after surgery in pain (P < .01), self-reported function (P < .01), range of motion (P < .01), and shoulder strength (P < .01). In addition, neither presurgical MRI variables (P > .16) nor shear modulus (P > .52) was significantly different between groups at 1 year after surgery. Finally, presurgical shear modulus generally did not improve the prediction of functional outcomes above and beyond that provided by MRI variables alone (P > .22).

Conclusion

Although SWE remains a promising modality for many clinical applications, this study found that SWE-estimated shear modulus did not predict repair integrity or functional outcomes at 1 year after surgery, nor did it add to the prediction of outcomes above and beyond that provided by traditional presurgical MRI measures of tear characteristics. Therefore, it appears that further research is needed to fully understand the clinical utility of SWE for musculoskeletal tissue and its potential use for predicting outcomes after surgical rotator cuff repair.

Measuring 3D In-vivo Shoulder Kinematics using Biplanar Videoradiography

The shoulder is one of the human body's most complex joint systems, with motion occurring through the coordinated actions of four individual joints, multiple ligaments, and approximately 20 muscles. Unfortunately, shoulder pathologies (e.g., rotator cuff tears, joint dislocations, arthritis) are common, resulting in substantial pain, disability, and decreased quality of life. The specific etiology for many of these pathologic conditions is not fully understood, but it is generally accepted that shoulder pathology is often associated with altered joint motion. Unfortunately, measuring shoulder motion with the necessary level of accuracy to investigate motion-based hypotheses is not trivial. However, radiographic-based motion measurement techniques have provided the advancement necessary to investigate motion-based hypotheses and provide a mechanistic understanding of shoulder function. Thus, the purpose of this article is to describe the approaches for measuring shoulder motion using a custom biplanar videoradiography system. The specific objectives of this article are to describe the protocols to acquire biplanar videoradiographic images of the shoulder complex, acquire CT scans, develop 3D bone models, locate anatomical landmarks, track the position and orientation of the humerus, scapula, and torso from the biplanar radiographic images, and calculate the kinematic outcome measures. In addition, the article will describe special considerations unique to the shoulder when measuring joint kinematics using this approach.

Biplanar Videoradiography to Study the Wrist and Distal Radioulnar Joints

Accurate measurement of skeletal kinematics in vivo is essential for understanding normal joint function, the influence of pathology, disease progression, and the effects of treatments. Measurement systems that use skin surface markers to infer skeletal motion have provided important insight into normal and pathological kinematics, however, accurate arthrokinematics cannot be attained using these systems, especially during dynamic activities. In the past two decades, biplanar videoradiography (BVR) systems have enabled many researchers to directly study the skeletal kinematics of the joints during activities of daily living. To implement BVR systems for the distal upper extremity, videoradiographs of the distal radius and the hand are acquired from two calibrated X-ray sources while a subject performs a designated task. Three-dimensional (3D) rigid-body positions are computed from the videoradiographs via a best-fit registrations of 3D model projections onto to each BVR view. The 3D models are density-based image volumes of the specific bone derived from independently acquired computed-tomography data. Utilizing graphics processor units and high-performance computing systems, this model-based tracking approach is shown to be fast and accurate in evaluating the wrist and distal radioulnar joint biomechanics. In this study, we first summarized the previous studies that have established the submillimeter and subdegree agreement of BVR with an in vitro optical motion capture system in evaluating the wrist and distal radioulnar joint kinematics. Furthermore, we used BVR to compute the center of rotation behavior of the wrist joint, to evaluate the articulation pattern of the components of the implant upon one another, and to assess the dynamic change of ulnar variance during pronosupination of the forearm. In the future, carpal bones may be captured in greater detail with the addition of flat panel X-ray detectors, more X-ray sources (i.e., multiplanar videoradiography), or advanced computer vision algorithms.

Age-related differences in humerothoracic, scapulothoracic, and glenohumeral kinematics during elevation and rotation motions

Age affects gross shoulder range of motion (ROM), but biomechanical changes over a lifetime are typically only characterized for the humerothoracic joint. Suitable age-related baselines for the scapulothoracic and glenohumeral contributions to humerothoracic motion are needed to advance understanding of shoulder injuries and pathology. Notably, biomechanical comparisons between younger or older populations may obscure detected differences in underlying shoulder motion. Herein, biplane fluoroscopy and skin-marker motion analysis quantified humerothoracic, scapulothoracic, and glenohumeral motion during 3 static poses (resting neutral, internal rotation to L4-L5, and internal rotation to maximum reach) and 2 dynamic activities (scapular plane abduction and external rotation in adduction). Orientations during static poses and rotations during active ROM were compared between subjects <35 years and >45 years of age (N=10 subjects per group). Numerous age-related kinematic differences were measured, ranging 5–25°, where variations in scapular orientation and motion were consistently observed. These disparities are on par with or exceed mean clinically important differences and standard error of measurement of clinical ROM, which indicates that high resolution techniques and appropriately matched controls are required to avoid confounding results of studies that investigate shoulder kinematics. Understanding these dissimilarities will help clinicians manage expectations and treatment protocols where indications and prevalence between age groups tend to differ. Where possible, it is advised to select age-matched control cohorts when studying the kinematics of shoulder injury, pathology, or surgical/physical therapy interventions to ensure clinically important differences are not overlooked.

Instantaneous helical axis estimation of glenohumeral kinematics: The impact of rotator cuff pathology

The rotator cuff is theorized to contribute to force couples required to produce glenohumeral kinematics. Impairment in these force couples would theoretically result in impaired ball-and-socket kinematics. Although less frequently used than traditional kinematic descriptors (e.g., Euler angles, joint translations), helical axes are capable of identifying alterations in ball-and-socket kinematics by quantifying the variability (i.e., dispersion) in axis orientation and position during motion. Consequently, assessing glenohumeral helical dispersion may provide indirect evidence of rotator cuff function. The purpose of this exploratory study was to determine the extent to which rotator cuff pathology is associated with alterations in ball-and-socket kinematics. Fifty-one participants were classified into one of five groups based on an assessment of the supraspinatus using diagnostic imaging: asymptomatic healthy, asymptomatic tendinosis, asymptomatic partial-thickness tear, asymptomatic full-thickness tear, symptomatic full-thickness tear. Glenohumeral kinematics were quantified during coronal plane abduction using a biplane x-ray system and described using instantaneous helical axes. The degree to which glenohumeral motion coincided with ball-and-socket kinematics was described using the angular and positional dispersion about the optimal helical axis and pivot, respectively. No statistically significant difference was observed between groups in angular dispersion. However, symptomatic individuals with a full-thickness supraspinatus tear had significantly more positional dispersion than asymptomatic individuals with a healthy supraspinatus or tendinosis. These findings suggest that symptomatic individuals with a full-thickness supraspinatus tear exhibit impaired ball-and-socket kinematics, which is believed to be associated with a disruption of the glenohumeral force couples.

Surgical repair of the supraspinatus: architectural changes in the muscle pre- and postoperatively

INTRODUCTION

Shortening of the tendon and muscle is recognised as a strong predictor for surgical failure of supraspinatus tendon tears. Changes in muscle architecture following repair have not been thoroughly investigated. We aimed to compare the architecture of the supraspinatus pre- and postoperatively.

METHODS

We recruited eight participants with full-thickness supraspinatus tears. Images of the supraspinatus were captured preoperatively (pre-op) and postoperatively at one (post-op1), three (post-op2) and six (post-op3) months in relaxed and contracted states (0° and 60° glenohumeral abduction). Fibre bundle length (FBL), pennation angle (PA) and muscle thickness (MT) were quantified. Self-reported function, and maximal isometric abduction and external rotation strengths were assessed.

RESULTS

Mean FBL increased from pre-op to post-op1 (p = 0.001) in the relaxed state and from pre-op to post-op2 (p = 0.002) in the contracted state. Decrease in FBL was observed from post-op2 to post-op3 in the relaxed state. Mean PA decreased from pre-op to post-op1 (p < 0.001) in the relaxed state, but increased from post-op2 to post-op3 in both relaxed (p = 0.006) and contracted (p = 0.004) states. At post-op3, external rotation (p = 0.009) and abduction (p = 0.005) strengths were greater than at post-op2. Overall function increased by 47.67% from pre-op to post-op3.

CONCLUSION

Lengthening of the supraspinatus occurs with surgery, altering the length-tension relationship of the muscle, which can compromise muscle function and lead to inferior surgical outcomes. These findings may guide clinicians to optimise loads, velocities and shoulder ranges for effective postoperative rehabilitation.

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

BACKGROUND

Function 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.

METHODS

We 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.

FINDINGS

Before 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.

INTERPRETATION

In 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.

Factors Affecting the Cost and Profitability of Arthroscopic Rotator Cuff Repair

PURPOSE

To examine the cost metrics and profitability of rotator cuff repairs (RCRs) in a large health care system.

METHODS

A retrospective study was performed using value analysis team data from 2 hospitals within a large metropolitan health system from 2010 to 2014. Cost and profit metrics were collected and compared against surgeon volume, surgeon subspecialty training, implant costs, Current Procedural Terminology (CPT) coding, length of stay, and hospital site.

RESULTS

A total of 5,899 RCRs were identified with a mean contribution margin of $2,133. Surgical supplies were the largest contributor to direct costs. Hospital site also significantly affected contribution margin ($1,912 at hospital 1 vs $3,129 at hospital 2, P < .001). The number of billed CPT codes was not significantly correlated to contribution margin; however, significant differences were noted in contribution margin and direct cost associated with different CPT code combinations, with arthroscopic RCR with subacromial decompression and distal clavicle excision being the most profitable, at an average contribution margin of $2,147. There was no correlation between surgeon volume and contribution margin or direct cost.

CONCLUSIONS

Our overall findings show that improvement in the profitability of arthroscopic RCR for hospital systems is possible, both by examining institutions' direct costs and by providing individual surgeons with cost breakdowns and contribution margin information to improve the profitability of their practice.

LEVEL OF EVIDENCE

Level IV, economic and decision analysis.

In vivo dynamic acromiohumeral distance in shoulders with rotator cuff tears

BACKGROUND

There 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.

METHODS

The 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.

FINDINGS

For 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).

INTERPRETATION

The 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.

In Vivo Assessment of Exercise-Induced Glenohumeral Cartilage Strain

BACKGROUND

The human shoulder joint is the most mobile joint in the body. While in vivo shoulder kinematics under minimally loaded conditions have been studied, it is unclear how glenohumeral cartilage responds to high-demand loaded exercise.

HYPOTHESIS

A high-demand upper extremity exercise, push-ups, will induce compressive strain in the glenohumeral articular cartilage, which can be measured with validated magnetic resonance imaging (MRI)-based techniques.

STUDY DESIGN

Descriptive laboratory study.

METHODS

High-resolution MRI was used to measure in vivo glenohumeral cartilage thickness before and after exercise among 8 study participants with no history of upper extremity injury or disease. Manual MRI segmentation and 3-dimensional modeling techniques were used to generate pre- and postexercise thickness maps of the humeral head and glenoid cartilage. Strain was calculated as the difference between pre- and postexercise cartilage thickness, normalized to the pre-exercise cartilage thickness.

RESULTS

Significant compressive cartilage strains of 17% ± 6% and 15% ± 7% (mean ± 95% CI) were detected in the humeral head and glenoid cartilage, respectively. The anterior region of the glenoid cartilage experienced a significantly higher mean strain (19% ± 6%) than the posterior region of the glenoid cartilage (12% ± 8%). No significant regional differences in postexercise humeral head cartilage strain were observed.

CONCLUSION

Push-ups induce compressive strain on the glenohumeral joint articular cartilage, particularly at the anterior glenoid. This MRI-based methodology can be applied to further the understanding of chondral changes in the shoulder under high-demand loading conditions.

CLINICAL RELEVANCE

These results improve the understanding of healthy glenohumeral cartilage mechanics in response to loaded upper extremity exercise. In the future, these methods can be applied to identify which activities induce high glenohumeral cartilage strains and deviations from normal shoulder function.

Exercise therapy for treatment of supraspinatus tears does not alter glenohumeral kinematics during internal/external rotation with the arm at the side

PURPOSE

Rotator cuff tears are a significant clinical problem, with exercise therapy being a common treatment option for patients. Failure rates of exercise therapy may be due to the failure to improve glenohumeral kinematics. Tears involving the supraspinatus may result in altered glenohumeral kinematics and joint instability for internal/external rotation with the arm at the side because not all muscles used to stabilize the glenohumeral joint are functioning normally. The objective of the study is to assess in vivo glenohumeral kinematic changes for internal/external rotation motions with the arm at the side of patients with a symptomatic full-thickness supraspinatus tear before and after a 12-week exercise therapy programme.

METHODS

Five patients underwent dynamic stereoradiography analysis before and after a 12-week exercise therapy protocol to measure changes in glenohumeral kinematics during transverse plane internal/external rotation with the arm at the side. Patient-reported outcomes and shoulder strength were also evaluated.

RESULTS

No patient sought surgery immediately following exercise therapy. Significant improvements in isometric shoulder strength and patient-reported outcomes were observed (p < 0.05). No significant changes in glenohumeral kinematics following physical therapy were found.

CONCLUSION

Isolated supraspinatus tears resulted in increased joint translations compared to healthy controls from the previous literature for internal/external rotation with the arm at the side. Despite satisfactory clinical outcomes following exercise therapy, glenohumeral kinematics did not change. The lack of changes may be due to the motion studied or the focus of current exercise therapy protocols being increasing shoulder strength and restoring range of motion. Current exercise therapy protocols should be adapted to also focus on restoring glenohumeral kinematics to improve joint stability since exercise therapy may have different effects depending on the motions of daily living.

LEVEL OF EVIDENCE

Prognostic study, Level II.

The effect of Medicaid payer status on patient outcomes following repair of massive rotator cuff tears

BACKGROUND

The influence of socioeconomic status and insurance type has not been studied extensively for RCR, particularly not in the high risk massive RCT population. The purpose of this study is to identify relationships between Medicaid payer status and patient outcomes following massive RCR.

METHODS

A retrospective review of shoulder surgery database identified 29 patients undergoing massive rotator cuff repair. Patients were stratified based on insurance type into two cohorts, Medicaid (14 patients) and non-Medicaid (15 patients). Missed routine follow-up appointments and comorbidities were recorded and compared between groups. Group comparisons were made for pre- and postoperative patient-reported and functional outcomes. Outcome scores included American Shoulder and Elbow Shoulder Score (ASES), the Penn Shoulder Score, and the Subjective Shoulder Value (SSV). A p value of < 0.05 was considered significant for all statistical analyses.

RESULTS

Medicaid patients were on average 7.1 years younger than non-Medicaid patients (49.8 vs. 56.9 years, respectively), and remaining demographics were comparable between groups. Preoperative patient-reported outcomes were only significantly different for ASES and ASES pain (p = 0.010, 0.037). There was excellent average improvement for Medicaid patients but no significant differences compared to non-Medicaid patients for ASES (p = 0.630), PENN scores (p = 0.395), and SSV (p = 0.198). Medicaid patients also had a higher number of missed and canceled appointments (28%) compared to non-Medicaid patients (18%).

CONCLUSION

Medicaid coverage will expand to millions of uninsured Americans under current healthcare reform. Medicaid patients with massive RCT appear to significantly improve with surgical treatment.

Impaired contractile function of the supraspinatus in the acute period following a rotator cuff tear

Background

Rotator cuff (RTC) tears are a common clinical problem resulting in adverse changes to the muscle, but there is limited information comparing histopathology to contractile function. This study assessed supraspinatus force and susceptibility to injury in the rat model of RTC tear, and compared these functional changes to histopathology of the muscle.

Methods

Unilateral RTC tears were induced in male rats via tenotomy of the supraspinatus and infraspinatus. Maximal tetanic force and susceptibility to injury of the supraspinatus muscle were measured in vivo at day 2 and day 15 after tenotomy. Supraspinatus muscles were weighed and harvested for histologic analysis of the neuromuscular junction (NMJ), intramuscular lipid, and collagen.

Results

Tenotomy resulted in eventual atrophy and weakness. Despite no loss in muscle mass at day 2 there was a 30% reduction in contractile force, and a decrease in NMJ continuity and size. Reduced force persisted at day 15, a time point when muscle atrophy was evident but NMJ morphology was restored. At day 15, torn muscles had decreased collagen-packing density and were also more susceptible to contraction-induced injury.

Conclusion

Muscle size and histopathology are not direct indicators of overall RTC contractile health. Changes in NMJ morphology and collagen organization were associated with changes in contractile function and thus may play a role in response to injury. Although our findings are limited to the acute phase after a RTC tear, the most salient finding is that RTC tenotomy results in increased susceptibility to injury of the supraspinatus.

Glenohumeral and scapulohumeral kinematic analysis of patients with traumatic anterior instability wearing a shoulder brace: a prospective laboratory study

PURPOSE

To assess the effectiveness of a novel glenohumeral joint immobilizer, the S2 Shoulder Stabilizer^®, by evaluating shoulder kinematics with a stereophotogrammetry system.

METHODS

Participants in this prospective laboratory study were recruited from patients with anterior traumatic instability awaiting arthroscopic glenohumeral stabilization. Glenohumeral and scapulohumeral kinematic data (arm abduction-adduction and internal-external rotation, and scapular pronation-retraction and mediolateral rotation) were collected twice, without and with the brace, using a VICON™ motion capture system, and processed with MATLAB^® software.

RESULTS

The tests showed a significantly lower joint angle during abduction-adduction (p = 0.0022) and external rotation (p = 0.0076) and a significantly lower (p = 0.0022) mediolateral scapular rotation angle in the limbs wearing the immobilizer. Humeral head translation during abduction-adduction and internal-external rotation was also lower in the patients wearing the brace.

CONCLUSIONS

The immobilizer significantly limited joint excursion in all planes of movement except internal rotation. The narrower humeral head translation with respect to the trunk, measured in the tests with the brace, demonstrates that the immobilizer achieves the goal of preserving joint stability in the movements that are at risk of dislocation.

Effects of asymptomatic rotator cuff pathology on in vivo shoulder motion and clinical outcomes

BACKGROUND

The incidence of asymptomatic rotator cuff tears has been reported to range from 15% to 39%, but the influence of asymptomatic rotator cuff pathology on shoulder function is not well understood. This study assessed the effects of asymptomatic rotator cuff pathology on shoulder kinematics, strength, and patient-reported outcomes.

METHODS

A clinical ultrasound examination was performed in 46 asymptomatic volunteers (age: 60.3 ± 7.5 years) with normal shoulder function to document the condition of their rotator cuff. The ultrasound imaging identified the participants as healthy (n = 14) or pathologic (n = 32). Shoulder motion was measured with a biplane x-ray imaging system, strength was assessed with a Biodex (Biodex Medical Systems, Inc., Shirley, NY, USA), and patient-reported outcomes were assessed using the Western Ontario Rotator Cuff Index and visual analog scale pain scores.

RESULTS

Compared with healthy volunteers, those with rotator cuff pathology had significantly less abduction (P = .050) and elevation (P = .041) strength, their humerus was positioned more inferiorly on the glenoid (P = .018), and the glenohumeral contact path length was longer (P = .007). No significant differences were detected in the Western Ontario Rotator Cuff Index, visual analog scale, range of motion, or acromiohumeral distance.

CONCLUSIONS

The differences observed between the healthy volunteers and those with asymptomatic rotator cuff pathology lend insight into the changes in joint mechanics, shoulder strength, and conventional clinical outcomes associated with the early stages of rotator cuff pathology. Furthermore, these findings suggest a plausible mechanical progression of kinematic and strength changes associated with the development of rotator cuff pathology.

Comparison of dynamics in 3D glenohumeral position between primary dislocated shoulders and contralateral healthy shoulders

BACKGROUNDS

After shoulder dislocation, kinematic changes in shoulder, including translation of the humeral head, ensue. There have been many attempts to measure these changes using motion measurement techniques, but in vivo three-dimensional (3D) glenohumeral changes have not been appreciated until now. The purpose of this study was to measure and analyze changes in glenohumeral translation in patients with shoulder dislocation and compare these changes with healthy shoulder.

METHODS

We included 20 subjects who had suffered shoulder dislocation for first time, and 3D models of their humerus and scapula were obtained using computed tomography and fluoroscopic images during scapular plane abduction and external rotation of shoulder with elbow flexed at 90° and arm abducted at 90°. We measured the superior/inferior (SI) and anterior/posterior (AP) translations for both shoulders.

RESULTS

No statistically significant difference between healthy and dislocated shoulders was detected in SI translation for scapular plane abduction with increasing elevation angles. In AP translation, the humeral head was located 2.29 mm more anteriorly in the dislocated shoulder than in the healthy shoulder. However, no statistically significant difference was seen. For internal to external rotation, the angle of the rotated arm had an effect on AP translation. However, no statistically significant difference was detected. In the apprehension test, there was no significant difference in the mean value of AP translation.

CONCLUSION

Compared with the contralateral healthy shoulder, changes in glenohumeral translation during in vivo movement after shoulder dislocation were found to be non-significant.

Assessment of Kinematics and Electromyography Following Arthroscopic Single-Tendon Rotator Cuff Repair

BACKGROUND

The increasing demand for rotator cuff (RC) repair patients to return to work as soon as they are physically able has led to exploration of when this is feasible. Current guidelines from our orthopedic surgery clinic recommend a return to work at 9 weeks postoperation. To more fully define capacity to return to work, the current study was conducted using a unique series of quantitative tools. To date, no study has combined 3-dimensional (3D) motion analysis with electromyography (EMG) assessment during activities of daily living (ADLs), including desk tasks, and commonly prescribed rehabilitation exercise.

OBJECTIVE

To apply a quantitative, validated upper extremity model to assess the kinematics and muscle activity of the shoulder following repair of the supraspinatus RC tendon compared to that in healthy shoulders.

DESIGN

A prospective, cross-sectional comparison study.

SETTING

All participants were evaluated during a single session at the Medical College of Wisconsin Department of Orthopaedic Surgery's Motion Analysis Laboratory.

PARTICIPANTS

Ten participants who were 9-12 weeks post-operative repair of a supraspinatus RC tendon tear and 10 participants with healthy shoulders (HS) were evaluated.

METHODS

All participants were evaluated with 3D motion analysis using a validated upper extremity model and synchronized EMG. Data from the 2 groups were compared using multivariate Hotelling T² tests with post hoc analyses based on Welch t-tests.

MAIN OUTCOME MEASUREMENTS

Participants' thoracic and thoracohumeral joint kinematics, temporal-spatial parameters, and RC muscle activity were measured by applying a quantitative upper extremity model during 10 ADLs and 3 rehabilitation exercises. These included tasks of hair combing, drinking, writing, computer mouse use, typing, calling, reaching to back pocket, pushing a door open, pulling a door closed, external rotation, internal rotation, and rowing.

RESULTS

There were significant differences of the thoracohumeral joint motion in only a few of the tested tasks: comb maximal flexion angle (P = .004), pull door internal/external rotation range of motion (P = .020), reach abduction/adduction range of motion (P = .001), reach flexion/extension range of motion (P = .001), reach extension minimal angle (P = .025), active external rotation maximal angle (P = .012), and active external rotation minimal angle (P = .004). The thorax showed significantly different kinematics of maximal flexion angle during the call (P = .011), mouse (P = .007), and drink tasks (P = .005) between the 2 groups. The EMG data analysis showed significantly increased subscapularis activity in the RC repair group during active external rotation.

CONCLUSIONS

Although limited abduction was expected due to repair of the supraspinatus tendon, only a single ADL (reaching to back pocket) had a significantly reduced abduction range of motion. Thoracic motion was shown to be used as a compensatory strategy during seated ADLs. Less flexion of the thorax may create passive shoulder flexion at the thoracohumeral joint in efforts to avoid active flexion. The RC repair group participants were able to accomplish the ADLs within the same time frame and through thoracohumeral joint kinematics similar to those in the healthy shoulder group participants. In summary, this study presents a quantification of the effects of RC repair and rehabilitation on the ability to perform ADLs. It may also point to a need for increased rehabilitation focus on either regaining external rotation strength or range of motion following RC repair to enhance recovery and return to the workforce.

LEVEL OF EVIDENCE

III.

Effects of Rotator Cuff Pathology and Physical Therapy on In Vivo Shoulder Motion and Clinical Outcomes in Patients With a Symptomatic Full-Thickness Rotator Cuff Tear

BACKGROUND

Physical therapy (PT) is often prescribed for patients with rotator cuff tears. The extent to which PT influences strength, range of motion (ROM), and patient-reported outcomes has been studied extensively, but the effect of PT on in vivo joint kinematics is not well understood.

PURPOSE

To assess the influence of symptomatic rotator cuff pathology and the effects of PT on shoulder motion, strength, and patient-reported outcomes.

STUDY DESIGN

Controlled laboratory study.

METHODS

Twenty-five patients with a symptomatic rotator cuff tear and 25 age-matched asymptomatic control subjects were recruited. Shoulder motion was measured using a biplane radiography imaging system, strength was assessed with a Biodex dynamometer, and patient-reported outcomes were assessed using the Western Ontario Rotator Cuff Index and visual analog scale (VAS) pain scores. Data were acquired from the patients before and after 8 weeks of physical therapy. Data were acquired at 1 time point for the control subjects.

RESULTS

Compared with the control subjects, patients with a symptomatic rotator cuff tear had significantly worse pain/function scores (P < .01); less ROM (P < .01); lower abduction (ABD), external rotation (ER), and internal rotation (IR) strength (P < .01); less scapulothoracic posterior tilt (P = .05); and lower glenohumeral joint elevation (P < .01). Physical therapy resulted in improved pain/function scores (P < .01), increased ROM (P < .02), increased scapulothoracic posterior tilt (P = .05), increased glenohumeral joint elevation (P = .01), and decreased acromiohumeral distance (AHD) (P = .02).

CONCLUSION

Compared with age-matched controls, patients had worse pain/function scores, less ROM, and lower ABD, ER, and IR strength. Patients also had less scapulothoracic anteroposterior tilt, less glenohumeral joint elevation, and an altered glenohumeral joint contact path. PT resulted in improved pain/function scores, increased ROM, greater posterior scapulothoracic tilt, increased glenohumeral joint elevation, an increased range of superoinferior joint contact, and a lower mean AHD. Of these differences, PT only returned scapulothoracic tilt to control levels.

CLINICAL RELEVANCE

This study documents the effects of PT on shoulder motion and conventional clinical outcomes. It is expected that understanding how changes in joint motion are associated with conventional clinical outcomes will lead to improved nonoperative interventions for patients with rotator cuff tears.

Measuring Three-Dimensional Thorax Motion Via Biplane Radiographic Imaging: Technique and Preliminary Results

Measures of scapulothoracic motion are dependent on accurate imaging of the scapula and thorax. Advanced radiographic techniques can provide accurate measures of scapular motion, but the limited 3D imaging volume of these techniques often precludes measurement of thorax motion. To overcome this, a thorax coordinate system was defined based on the position of rib pairs and then compared to a conventional sternum/spine-based thorax coordinate system. Alignment of the rib-based coordinate system was dependent on the rib pairs used, with the rib3:rib4 pairing aligned to within 4.4 ± 2.1 deg of the conventional thorax coordinate system.

Dynamic Three-Dimensional Shoulder Mri during Active Motion for Investigation of Rotator Cuff Diseases

Background

MRI is the standard methodology in diagnosis of rotator cuff diseases. However, many patients continue to have pain despite treatment, and MRI of a static unloaded shoulder seems insufficient for best diagnosis and treatment. This study evaluated if Dynamic MRI provides novel kinematic data that can be used to improve the understanding, diagnosis and best treatment of rotator cuff diseases.

Methods

Dynamic MRI provided real-time 3D image series and was used to measure changes in the width of subacromial space, superior-inferior translation and anterior-posterior translation of the humeral head relative to the glenoid during active abduction. These measures were investigated for consistency with the rotator cuff diseases classifications from standard MRI.

Results

The study included: 4 shoulders with massive rotator cuff tears, 5 shoulders with an isolated full-thickness supraspinatus tear, 5 shoulders with tendinopathy and 6 normal shoulders. A change in the width of subacromial space greater than 4mm differentiated between rotator cuff diseases with tendon tears (massive cuff tears and supraspinatus tear) and without tears (tendinopathy) (p = 0.012). The range of the superior-inferior translation was higher in the massive cuff tears group (6.4mm) than in normals (3.4mm) (p = 0.02). The range of the anterior-posterior translation was higher in the massive cuff tears (9.2 mm) and supraspinatus tear (9.3 mm) shoulders compared to normals (3.5mm) and tendinopathy (4.8mm) shoulders (p = 0.05).

Conclusion

The Dynamic MRI enabled a novel measure; ‘Looseness’, i.e. the translation of the humeral head on the glenoid during an abduction cycle. Looseness was better able at differentiating different forms of rotator cuff disease than a simple static measure of relative glenohumeral position.

Differences in glenohumeral translations calculated with three methods: Comparison of relative positions and contact point

Several published articles have reported 3-dimensional glenohumeral kinematics using model-image registration techniques. However, different methods to compute the translations were used in these articles. The purpose of this study was to compare glenohumeral translations calculated with three different methods. Fifteen healthy males with a mean age of 31 years (range, 27-36 years old) were enrolled in this study. Fluoroscopic images during scapular plane elevation were recorded at 30 frames per second for the right shoulder in each subject, and CT-derived models of the humerus and the scapula were matched with the silhouette of the bones in the fluoroscopic images using model-image registration techniques. Glenohumeral translations were computed with three methods: relative position of the origins of the humeral and scapular models, contact points of the two models, and relative positions based upon the calculated glenohumeral center of rotation (CoR). In the supero-inferior direction, translations calculated with the three methods were roughly parallel, with the maximum difference of 1.6mm (P<0.001). In the antero-posterior direction, translations with the origins and CoR were parallel; however, translations computed with the origins and contact point describe arcs that differ by almost 2mm at low humeral elevation angles and converge at higher degrees of humeral elevation (P<0.001). Glenohumeral translations calculated using three methods showed statistically significant differences that may be important when comparing detailed results of different studies. However, these relatively small differences are likely subclinical, so that all three methods can reasonably be used for description of glenohumeral translations.

Effects of exercise therapy for the treatment of symptomatic full-thickness supraspinatus tears on in vivo glenohumeral kinematics

BACKGROUND

The high incidence of rotator cuff disease combined with high failure rates for nonoperative treatment of full-thickness rotator cuff tears underlines the importance of improving nonoperative management of rotator cuff tears. The study objective was to assess changes in in vivo glenohumeral kinematics of patients with a symptomatic full-thickness supraspinatus tear before and after a 12-week exercise therapy program. It was hypothesized that successful exercise therapy would result in improved kinematics (smaller translations and increased subacromial space).

MATERIALS AND METHODS

Five patients were recruited for the study and underwent dynamic stereoradiography analysis before and after a 12-week exercise therapy protocol to measure changes in glenohumeral joint translations and subacromial space during coronal plane abduction. Strength and patient-reported outcomes (American Shoulder and Elbow Surgeons; Disabilities of the Arm, Shoulder and Hand; Western Ontario Rotator Cuff Index) were also evaluated.

RESULTS

After therapy, no subject went on to receive surgery. It was found that the contact path length of the humerus translating on the surface of the glenoid was reduced by 29% from 67.2% ± 36.9% glenoid height to 43.1% ± 26.9% glenoid height (P = .036) after therapy. Minimum acromiohumeral distance showed a small increase from 0.9 ± 0.6 mm to 1.3 ± 0.8 mm (P = .079). Significant improvements in strength and patient-reported outcomes were also observed (P < .05).

CONCLUSIONS

Successful exercise therapy for treatment of small full-thickness supraspinatus tears results in improvements in glenohumeral joint kinematics and patient-reported outcomes through increases in rotator cuff muscle strength and joint stability. This study may enable identification of prognostic factors that predict the response of a patient with a rotator cuff tear to exercise therapy.

Alterations in Glenohumeral Kinematics in Patients With Rotator Cuff Tears Measured With Biplane Fluoroscopy

PURPOSE

To quantitatively measure the 3-dimensional (3D) glenohumeral translations during dynamic shoulder abduction in the scapular plane, using a biplane fluoroscopy system, in patients with supraspinatus rotator cuff tears.

METHODS

A custom biplane fluoroscopy system was used to measure the 3D position and orientation of the scapula and humerus of 14 patients with full-thickness supraspinatus or supraspinatus and infraspinatus rotator cuff tears and 10 controls as they performed shoulder abduction over their full range of motion. The 3D geometries of the scapula and humerus were extracted from a computed tomography scan of each shoulder. For each frame, the 3D bone position and orientation were estimated using a contour-based matching algorithm, and the 3D position of the humeral head center was determined relative to the glenoid. For each subject the superior-inferior and anterior-posterior translation curves were determined from 20° through 150° of arm elevation.

RESULTS

The humeral head in shoulders with rotator cuff tears was positioned significantly inferior compared with controls for higher elevation angles of 80° to 140° (P < .05). For both groups the humeral head translated inferiorly during shoulder abduction from 80° (P = .044; rotator cuff tear v controls: -0.2 ± 1.3 v 1.2 ± 1.4 mm) up to 140° (P = .047; rotator cuff tear v controls: -1.3 ± 2.2 v 0.44 ± 1.4 mm). There was no significant translation in the anterior- posterior direction.

CONCLUSIONS

Patients with well-compensated single or 2-tendon rotator cuff tears show no dynamic superior humeral head migration but unexpectedly show an inferior shift during active elevation. It is unclear whether the size of the translational differences found in this study, while statistically significant, are also of clinical significance.

LEVEL OF EVIDENCE

Level III, comparative study.

Effect of Arthroscopic Stabilization on In Vivo Glenohumeral Joint Motion and Clinical Outcomes in Patients With Anterior Instability

BACKGROUND

Glenohumeral joint (GHJ) dislocations are common, and the resulting shoulder instability is often treated with arthroscopic stabilization. These procedures result in favorable clinical outcomes, but abnormal GHJ motion may persist, which may place patients at risk for developing osteoarthritis. However, the effects of shoulder instability and arthroscopic stabilization on GHJ motion are not well understood.

HYPOTHESIS

GHJ motion is significantly influenced by anterior instability and arthroscopic stabilization, but postsurgical measures of GHJ motion are not different from those of control subjects.

STUDY DESIGN

Controlled laboratory study.

METHODS

In vivo GHJ motion was measured by applying a computed tomographic model-based tracking technique to biplane radiographic images acquired during an apprehension test in healthy control subjects (n = 11) and anterior instability patients (n = 11). Patients were tested before surgery and at 6 months after surgery. Control subjects were tested once. Shoulder strength, active range of motion (ROM), and the Western Ontario Shoulder Instability (WOSI) index were also measured.

RESULTS

Before surgery, the humerus of the instability patients during the apprehension test was located significantly more anteriorly on the glenoid (7.9% of glenoid width; 2.1 mm) compared with that of the controls (P = .03), but arthroscopic stabilization moved this joint contact location posteriorly on the glenoid (4.7% of glenoid width; 1.1 mm; P = .03). After surgery, GHJ excursion during the apprehension test was significantly lower (14.7% of glenoid width; 3.6 mm) compared with presurgical values (19.4% of glenoid width; 4.7 mm; P = .01) and with that of the controls (22.4% of glenoid width; 5.7 mm; P = .01). The external and internal rotation strength of patients was significantly lower than that of the controls before surgery (P < .05), but differences in strength did not persist after surgery (P > .17). External rotation ROM in patients was significantly lower than that in control subjects both before and after arthroscopic stabilization (P < .01). The WOSI score improved significantly, from 48.3 ± 13.1 presurgery to 86.3 ± 16.5 after surgery (P = .0002).

CONCLUSION

In patients with anterior instability, arthroscopic stabilization significantly improves measures of strength, ROM, and clinical outcome. However, GHJ excursion is not fully restored to levels seen in the control subjects.

CLINICAL RELEVANCE

Although arthroscopic stabilization satisfactorily restores most clinical outcome measures, GHJ excursion and external rotation ROM remain compromised compared with healthy control subjects and may contribute to the development of osteoarthritis in patients with anterior instability.

Adaptation of the AnyBody™ Musculoskeletal Shoulder Model to the Nonconforming Total Shoulder Arthroplasty Context

Current musculoskeletal inverse dynamics shoulder models have two limitations to use in the context of nonconforming total shoulder arthroplasty (NC-TSA). First, the ball and socket glenohumeral (GH) joint simplification avoids any humeral head translations. Second, there is no contact at the GH joint to compute the contact area and the center of pressure (COP) between the two components of NC-TSA. In this paper, we adapted the AnyBody™ shoulder model by introducing humeral head translations and contact between the two components of an NC-TSA. Abduction in the scapular plane was considered. The main objective of this study was to adapt the AnyBody™ shoulder model to a NC-TSA context and to compare the results of our model (translations, COP, contact area, GH joint reaction forces (GH-JRFs), and muscular forces) with previous numerical, experimental, and clinical studies. Humeral head translations and contact were successfully introduced in our adapted shoulder model with strong support for our findings by previous studies.

Associations between in-vivo glenohumeral joint motion and morphology

Joint morphology has a significant influence on joint motion and may contribute to the development of rotator cuff pathology, but the relationships between glenohumeral joint (GHJ) morphology and in-vivo GHJ motion are not well understood. The objectives of this study were to assess measures of joint morphology and their relationship with in-vivo joint motion in two populations: shoulders with intact rotator cuffs (n=48) and shoulders with rotator cuff pathology (n=36, including 5 symptomatic tears, 9 asymptomatic tears and 22 repaired tears). GHJ morphology was measured from CT-based three-dimensional models of the humerus and scapula. In-vivo GHJ motion was measured during shoulder abduction using biplane x-ray imaging. Associations between GHJ morphology and motion were assessed with univariate and best subsets regression. The only morphological difference identified between the populations was the critical shoulder angle (intact: 34.5 ± 4.7°, pathologic: 36.9 ± 5.0°, p=0.03), which is consistent with previous research. In intact shoulders, the superior/inferior (S/I) position of the humerus on the glenoid during shoulder abduction was significantly associated with the glenoid's S/I radius of curvature (p<0.01), conformity index (p<0.01), and stability angle (p<0.01). Furthermore, the S/I position of the humerus on the glenoid was negatively associated with the critical shoulder angle (p=0.04), which contradicts previous research. No significant associations between GHJ morphology and GHJ motion were detected in shoulders with rotator cuff tears. It is unknown if rotator cuff pathology compromises the relationships between GHJ morphology and motion, or if the absence of this relationship is a pre-existing condition that increases the likelihood of pathology.

The effect of supraspinatus tears on glenohumeral translations in passive pitching motion

BACKGROUND

Supraspinatus tears are common in pitchers. However, the effect of these tears on glenohumeral (GH) mechanics is incompletely understood.

PURPOSE/HYPOTHESIS

To describe the effect of supraspinatus tears and repairs on GH kinematics during an abbreviated throwing motion using the intact shoulder girdle. The hypothesis was that supraspinatus tears would lead to an increase of GH translation in the coronal plane and supraspinatus repairs would restore GH kinematics.

STUDY DESIGN

Controlled laboratory study.

METHODS

Six shoulders from 3 fresh-frozen cadavers were tested in a novel 7 degrees of freedom robotic testing system. Torsos were mounted and the wrist was pinned to an actuator mounted on an upper frame. After the deltoid was removed, the shoulders were studied during an abbreviated throwing motion (ATM) from maximum external rotation to the midcoronal plane to establish a baseline. The ATM was repeated after creation of a 1-cm supraspinatus tear, after creation of a 3-cm supraspinatus tear, and after repair with a transosseous equivalent (TOE) technique. Retroreflective bone markers and high-speed infrared cameras were used to measure GH kinematics and calculate the center of rotation of the GH joint (CORGH) instantaneously.

RESULTS

The 1- and 3-cm supraspinatus tears did not significantly alter GH translation. The TOE repair shifted the CORGH posteriorly, as evidenced by a significant decrease in the overall GH translation in all 3 planes (P = .003, .019, and .026, for x-y, y-z, and x-z planes, respectively).

CONCLUSION

In contrast to a TOE repair of the supraspinatus tendon, isolated supraspinatus tears did not perturb GH kinematics in this cadaveric model of the throwing shoulder.

CLINICAL RELEVANCE

In throwing athletes, treatment of rotator cuff tears should be addressed with caution to avoid an unintended alteration in GH kinematics due to overtightening of the tendon.

Effects of footwear on three-dimensional tibiotalar and subtalar joint motion during running

Running is a popular form of recreation, but injuries are common and may be associated with abnormal joint motion. The objective of this study was to determine the effect of three footwear conditions - barefoot (BF), an ultraflexible training shoe (FREE), and a motion control shoe (MC) - on 3D foot and ankle motion. Dynamic, biplane radiographic images were acquired from 12 runners during overground running. 3D rotations of the tibiotalar and subtalar joints were quantified in terms of plantarflexion/dorsiflexion (PF/DF), inversion/eversion (IN/EV) and internal/external rotation (IR/ER). Across the early stance phase (defined as footstrike to heel-off), BF running demonstrated greater tibiotalar joint range of motion for PF/DF (28.2 ± 8.3°) and IR/ER (7.0 ± 1.4°) than the shod conditions (FREE: PF/DF=15.1 ± 5.9°, IR/ER=4.8 ± 2.1°; MC: PF/DF=15.0 ± 6.2°, IR/ER=4.3 ± 0.7°). Also at the tibiotalar joint, BF running resulted in a position significantly more plantarflexed (BF: 2.0 ± 12.5°, FREE: 15.7 ± 12.2°, MC: 16.5 ± 9.3°) and internally rotated (BF: 12.9 ± 4.5°, FREE: 10.7 ± 4.3°, MC: 10.6 ± 3.9°) at footstrike compared to both shod conditions. No differences were detected between the shod conditions at any point in the early stance phase at the tibiotalar joint. The MC condition demonstrated significant differences compared to FREE at several points throughout the early stance phase at the subtalar joint, with the greatest differences seen at 30% in PF/DF (MC -1.4 ± 8.8°: FREE: -0.5 ± 9.0°), IN/EV (MC -8.1 ± 5.7°: FREE -6.3 ± 5.5°) and IR/ER (MC -9.5 ± 5.3°: FREE: -8.7 ± 5.2°). These findings indicate that footwear has subtle effects on joint motion mainly between BF and shod conditions at the tibiotalar joint and between shod conditions at the subtalar joint.

Glenohumeral relationships at different angles of abduction

PURPOSE

The objective of this study was to clarify the relationships among anatomical landmarks of the glenohumeral joint at different angles of abduction.

METHODS

Fifteen volunteers (ten men, five women; mean age 29 years) were enrolled in this study. Images of externally and internally rotated positions at 45°, 90°, and 135° of abduction in the plane 30° anterior to the trunk were taken using an open magnetic resonance imaging system. Landmarks including the glenoidal long axis with its center, bicipital groove, center of the head, and humeral shaft axis were determined. Using a line set on the surface of the head in the plane parallel to the humeral axis (including the head center and bicipital groove with its parallel and perpendicular lines), the glenoid location and rotational relationships were investigated in each position.

RESULTS

The average angles of axial rotation were 48° ± 27° at 45º of abduction, 71° ± 20° at 90° of abduction, and 40° ± 27° at 135° of abduction. The trajectories of the glenoid center primarily extended over the anterior portion of the humeral head at 45° of abduction and over the posterior portion at 90° of abduction, while those at 135° of abduction were localized on a small upper portion of the head.

CONCLUSIONS

The glenohumeral relationships demonstrated that arm abduction might influence shoulder function through its effects on the portion of the humeral surface in contact with the glenoid during rotation and the resultant changes in the glenohumeral relationships.

Associations among shoulder strength, glenohumeral joint motion, and clinical outcome after rotator cuff repair

Rotator cuff tears are a common condition causing pain and disability, but the relationships among clinical measures of shoulder function and measures of glenohumeral joint (GHJ) function are not well known. In the study reported here, dynamic in vivo GHJ motion was measured during abduction from biplane radiographs in 22 rotator cuff repair (RCR) patients and 36 control subjects. Isometric shoulder strength was measured and clinical outcomes were assessed using the Western Ontario Rotator Cuff (WORC) Index. Associations among WORC, GHJ motion, and several shoulder strength ratios were assessed with linear regression. An association was detected between higher ER/ABD (external rotation/coronal-plane abduction) strength ratio and a humerus positioned more inferiorly relative to the glenoid in control subjects and RCR patients. Higher ER/ABD strength ratio was also associated with better clinical outcome in RCR patients. These findings suggest a relationship between ER/ABD strength ratio and a more centrally located average superior/inferior contact center in RCR patients and control subjects. The ER/ABD strength ratio can be easily measured in a clinical setting and therefore can be used in larger studies to investigate its relation to clinical outcomes over time or perhaps to predict superior migration of the humeral head.

Rehabilitation following arthroscopic rotator cuff repair: a review of current literature

Physical rehabilitation following arthroscopic rotator cuff repair has conventionally involved a 4- to 6-week period of immobilization; there are two schools of thought regarding activity level during this period. Some authors encourage early, more aggressive rehabilitation along with the use of a continuous passive motion device; others propose later, more conservative rehabilitation. Although some studies report trends in improved early range of motion, pain relief, and outcomes scores with aggressive rehabilitation following rotator cuff repair, no definitive consensus exists supporting a clinical difference resulting from rehabilitation timing in the early stages of healing. Rehabilitation timing does not affect outcomes after 6 to 12 months postoperatively. Given the lack of information regarding which patient groups benefit from aggressive rehabilitation, individualized patient care is warranted.

Arthroscopic treatment for cuff tear: strength recovery at 12 months of follow-up

The rotator cuff tear is one of the most frequent musculoskeletal disorders, but the real incidence is not clearly known because it's usually asymptomatic, even if it's more common in patients with shoulder pain (36%). The prevalence of the complete tear among general population is estimated approximately around 20.7% and it is more usual with the increasing of the age. The aim of this study is to evaluate a group of patients with any size of full-thickness cuff tear treated by arthroscopic technique, comparing the clinical and functional recovery (isokinetic, isotonic and isometric strength) with the un-operated side. Between October 2009 and June 2011, 74 patients, mean age 59 (20-72) years old, underwent arthroscopic treatment for rotator cuff tear. Forty-two patients were finally included in the study, 20 men and 22 women, mean age of 55 (20-68) years old. The mean follow-up was 12 months (6-23 months). The strength of each patient's shoulder, both operated and un-operated, was evaluated using isokinetic, isotonic and isometric tests (BIODEX Medical System). The functional outcome showed no significant differences between operated and un-operated shoulder, confirmed by Constant-Murley score and DASH score. The isokinetic, isotonic and isometric tests are valid support to clinical evaluation in order to obtain an objective data on shoulder recovery.