In vivo 3-dimensional analysis of scapular and glenohumeral kinematics: comparison of symptomatic or asymptomatic shoulders with rotator cuff tears and healthy shoulders

Factors determining the short-term clinical outcomes of conservative treatment in patients with supraspinatus tear

INTRODUCTION

To identify factors influencing the better and worse changes in the Western Ontario Rotator Cuff Index of patients undergoing conservative treatment for supraspinatus tendon tear.

METHODS

The study included 30 patients with supraspinatus tendon tear who underwent conservative treatment. The average duration of intervention was 35.4 days. The Western Ontario Rotator Cuff Index, shoulder range of motion, isometric muscle strength, supraspinatus tendon thickness, thickness of the supraspinatus, infraspinatus, and teres minor muscles, and acromiohumeral interval were assessed before and after the intervention. In the statistical analyses, change in the Western Ontario Rotator Cuff Index was the dependent variable, and the amount of change in each measurement variable before and after the intervention was the independent variable.

RESULTS

The average Western Ontario Rotator Cuff Index improved from 1067 at pre-treatment to 997 at post-treatment, but without a significant difference (p = 0.29). A multiple regression analysis revealed that supraspinatus tendon thickness and muscle strength in shoulder external rotation at 90° scaption had a significant effect on the change in the Western Ontario Rotator Cuff Index (R2 = 0.44, p < 0.01).

CONCLUSION

Supraspinatus tendon thickness and muscle strength in shoulder external rotation at 90° scaption were important factors for the Western Ontario Rotator Cuff Index score in the early stages of conservative treatment for patients with supraspinatus tendon tear.

Severity of rotator cuff disorders and additional load affect fluoroscopy-based shoulder kinematics during arm abduction

BACKGROUND

Rotator cuff disorders, whether symptomatic or asymptomatic, may result in abnormal shoulder kinematics (scapular rotation and glenohumeral translation). This study aimed to investigate the effect of rotator cuff tears on in vivo shoulder kinematics during a 30° loaded abduction test using single-plane fluoroscopy.

MATERIALS AND METHODS

In total, 25 younger controls, 25 older controls and 25 patients with unilateral symptomatic rotator cuff tears participated in this study. Both shoulders of each participant were analysed and grouped on the basis of magnetic resonance imaging into healthy, rotator cuff tendinopathy, asymptomatic and symptomatic rotator cuff tears. All participants performed a bilateral 30° arm abduction and adduction movement in the scapular plane with handheld weights (0, 2 and 4 kg) during fluoroscopy acquisition. The range of upward-downward scapular rotation and superior-inferior glenohumeral translation were measured and analysed during abduction and adduction using a linear mixed model (loads, shoulder types) with random effects (shoulder ID).

RESULTS

Scapular rotation was greater in shoulders with rotator cuff tendinopathy and asymptomatic rotator cuff tears than in healthy shoulders. Additional load increased upward during abduction and downward during adduction scapular rotation (P < 0.001 in all groups but rotator cuff tendinopathy). In healthy shoulders, upward scapular rotation during 30° abduction increased from 2.3° with 0-kg load to 4.1° with 4-kg load and on shoulders with symptomatic rotator cuff tears from 3.6° with 0-kg load to 6.5° with 4-kg load. Glenohumeral translation was influenced by the handheld weights only in shoulders with rotator cuff tendinopathy (P ≤ 0.020). Overall, superior glenohumeral translation during 30° abduction was approximately 1.0 mm with all loads.

CONCLUSIONS

The results of glenohumeral translation comparable to control but greater scapular rotations during 30° abduction in the scapular plane in rotator cuff tears indicate that the scapula compensates for rotator cuff deficiency by rotating. Further analysis of load-dependent joint stability is needed to better understand glenohumeral and scapula motion.

LEVEL OF EVIDENCE

Level 2.

TRIAL REGISTRATION

Ethical approval was obtained from the regional ethics committee (Ethics Committee Northwest Switzerland EKNZ 2021-00182), and the study was registered at clinicaltrials.gov on 29 March 2021 (trial registration number NCT04819724, https://clinicaltrials.gov/ct2/show/NCT04819724 ).

The influence of rotator cuff tear type and weight bearing on shoulder biomechanics in an ex vivo simulator experiment

Glenohumeral biomechanics after rotator cuff (RC) tears have not been fully elucidated. This study aimed to investigate the muscle compensatory mechanism in weight-bearing shoulders with RC tears and asses the induced pathomechanics (i.e., glenohumeral translation, joint instability, center of force (CoF), joint reaction force). An experimental, glenohumeral simulator with muscle-mimicking cable system was used to simulate 30° scaption motion. Eight fresh-frozen shoulders were prepared and mounted in the simulator. Specimen-specific scapular anthropometry was used to test six RC tear types, with intact RC serving as the control, and three weight-bearing loads, with the non-weight-bearing condition serving as the control. Glenohumeral translation was calculated using instantaneous helical axis. CoF, muscle forces, and joint reaction forces were measured using force sensors integrated into the simulator. Linear mixed effects models (RC tear type and weight-bearing) with random effects (specimen and sex) were used to assess differences in glenohumeral biomechanics. RC tears did not change the glenohumeral translation (p > 0.05) but shifted the CoF superiorly (p ≤ 0.005). Glenohumeral translation and joint reaction forces increased with increasing weight bearing (p < 0.001). RC and deltoid muscle forces increased with the presence of RC tears (p ≤ 0.046) and increased weight bearing (p ≤ 0.042). The synergistic muscles compensated for the torn RC tendons, and the glenohumeral translation remained comparable to that for the intact RC tendons. However, in RC tears, the more superior CoF was close to where glenoid erosion occurs in RC tear patients with secondary osteoarthritis. These findings underscore the importance of early detection and precise management of RC tears.

Fully automatic algorithm for detecting and tracking anatomical shoulder landmarks on fluoroscopy images with artificial intelligence

OBJECTIVE

Patients with rotator cuff tears present often with glenohumeral joint instability. Assessing anatomic angles and shoulder kinematics from fluoroscopy requires labelling of specific landmarks in each image. This study aimed to develop an artificial intelligence model for automatic landmark detection from fluoroscopic images for motion tracking of the scapula and humeral head.

MATERIALS AND METHODS

Fluoroscopic images were acquired for both shoulders of 25 participants (N = 12 patients with unilateral rotator cuff tear, 6 men, mean (standard deviation) age: 63.7 ± 9.7 years; 13 asymptomatic subjects, 7 men, 58.2 ± 8.9 years) during a 30° arm abduction and adduction movement in the scapular plane with and without handheld weights of 2 and 4 kg. A 3D full-resolution convolutional neural network (nnU-Net) was trained to automatically locate five landmarks (glenohumeral joint centre, humeral shaft, inferior and superior edges of the glenoid and most lateral point of the acromion) and a calibration sphere.

RESULTS

The nnU-Net was trained with ground-truth data from 6021 fluoroscopic images of 40 shoulders and tested with 1925 fluoroscopic images of 10 shoulders. The automatic landmark detection algorithm achieved an accuracy above inter-rater variability and slightly below intra-rater variability. All landmarks and the calibration sphere were located within 1.5 mm, except the humeral landmark within 9.6 mm, but differences in abduction angles were within 1°.

CONCLUSION

The proposed algorithm detects the desired landmarks on fluoroscopic images with sufficient accuracy and can therefore be applied to automatically assess shoulder motion, scapular rotation or glenohumeral translation in the scapular plane.

CLINICAL RELEVANCE STATEMENT

This nnU-net algorithm facilitates efficient and objective identification and tracking of anatomical landmarks on fluoroscopic images necessary for measuring clinically relevant anatomical configuration (e.g. critical shoulder angle) and enables investigation of dynamic glenohumeral joint stability in pathological shoulders.

KEY POINTS

• Anatomical configuration and glenohumeral joint stability are often a concern after rotator cuff tears. • Artificial intelligence applied to fluoroscopic images helps to identify and track anatomical landmarks during dynamic movements. • The developed automatic landmark detection algorithm optimised the labelling procedures and is suitable for clinical application.

Joint Track Machine Learning: An Autonomous Method of Measuring Total Knee Arthroplasty Kinematics From Single-Plane X-Ray Images

BACKGROUND

Dynamic radiographic measurements of 3-dimensional (3-D) total knee arthroplasty (TKA) kinematics have provided important information for implant design and surgical technique for over 30 years. However, current methods of measuring TKA kinematics are too cumbersome, inaccurate, or time-consuming for practical clinical application. Even state-of-the-art techniques require human-supervision to obtain clinically reliable kinematics. Eliminating human supervision could potentially make this technology practical for clinical use.

METHODS

We demonstrate a fully autonomous pipeline for quantifying 3D-TKA kinematics from single-plane radiographic imaging. First, a convolutional neural network (CNN) segmented the femoral and tibial implants from the image. Second, those segmented images were compared to precomputed shape libraries for initial pose estimates. Lastly, a numerical optimization routine aligned 3D implant contours and fluoroscopic images to obtain the final implant poses.

RESULTS

The autonomous technique reliably produces kinematic measurements comparable to human-supervised measures, with root-mean-squared differences of less than 0.7 mm and 4° for our test data, and 0.8 mm and 1.7° for external validation studies.

CONCLUSION

A fully autonomous method to measure 3D-TKA kinematics from single-plane radiographic images produces results equivalent to a human-supervised method, and may soon make it practical to perform these measurements in a clinical setting.

In Vivo Kinematic Analysis of the Axial Shoulder Rotation in the Standing and Supine Positions Using 3D/2D Registration and Electromyography

Background There has been no report comparing shoulder kinematics and muscle activities during axial shoulder rotation in different positions. The purpose of this study was to investigate differences in shoulder kinematics and muscle activities during axial shoulder rotation in healthy subjects between standing and supine positions using three-dimensional/two-dimensional (3D/2D) registration techniques and electromyography (EMG). Methods Eleven healthy males agreed to participate in this study. We recorded the fluoroscopy time during active shoulder axial rotation with a 90° elbow flexion in both standing and supine positions, simultaneously recording surface EMG of the infraspinatus, anterior deltoid, posterior deltoid, and biceps brachii. Three-dimensional bone models were created from CT images, and shoulder kinematics were analyzed using 3D/2D registration techniques. Muscle activities were evaluated as a ratio of mean electromyographic values to 5-sec maximum voluntary isometric contractions.  Results Scapular kinematics during axial shoulder rotation in the supine position showed similar patterns with those in the standing position. The scapula was more posteriorly tilted and more downwardly rotated in the supine posture than in standing (P < 0.001 for both). Acromiohumeral distance (AHD) in the supine posture was significantly larger than in standing. Muscle activities showed no significant differences between postures except for biceps (P < 0.001). Discussion Shoulder kinematics and muscle activities during axial rotation were similar in pattern between standing and supine postures, but there were shifts in scapular pose and AHD. The findings of this study suggest that posture may be an important consideration for the prescription of optimal shoulder therapy following surgery or for the treatment of shoulder disorders.

Effects of elevation on shoulder joint motion: comparison of dynamic and static conditions

BACKGROUND

Although visual examination and palpation are used to assess shoulder motion in clinical practice, there is no consensus on shoulder motion under dynamic and static conditions. This study aimed to compare shoulder joint motion under dynamic and static conditions.

METHODS

The dominant arm of 14 healthy adult males was investigated. Electromagnetic sensors attached to the scapular, thorax, and humerus were used to measure three-dimensional shoulder joint motion under dynamic and static elevation conditions and compare scapular upward rotation and glenohumeral joint elevation in different elevation planes and angles.

RESULTS

At 120° of elevation in the scapular and coronal planes, the scapular upward rotation angle was higher in the static condition and the glenohumeral joint elevation angle was higher in the dynamic condition (P&lt;0.05). In scapular plane and coronal plane elevation 90°- 120°, the angular change in scapular upward rotation was higher in the static condition and the angular change in scapulohumeral joint elevation was higher in the dynamic condition (P&lt;0.05). No differences were found in shoulder joint motion in the sagittal plane elevation between the dynamic and static conditions. No interaction effects were found between elevation condition and elevation angle in all elevation planes.

CONCLUSIONS

Differences in shoulder joint motion should be noted when assessing shoulder joint motion in different dynamic and static conditions. Level of evidence: Level III, diagnostic cross-sectional study.

How does computed tomography inform our understanding of shoulder kinematics? A structured review

The objective of this structured review was to review how computed tomography (CT) scanning has been used to measure the kinematics of the shoulder. A literature search was conducted using Evidence-based Medicine Reviews (Embase) and PubMed. In total, 29 articles were included in the data extraction process. Forty percent of the studies evaluated healthy participants' shoulder kinematics. The glenohumeral joint was the most studied, followed by the scapulothoracic, acromioclavicular, and sternoclavicular joints. Three-dimensional computed tomography (3DCT) and 3DCT with biplane fluoroscopy are the two primary imaging techniques that have been used to measure shoulder joints' motion under different conditions. Finally, many discrepancies in the reporting of the examined motions were found. Different authors used different perspectives and planes to report similar motions, which results in confusion and misunderstanding of the actual examined motion. The use of 3DCT has been widely used in the examination of shoulder kinematics in a variety of populations with varying methods employed. Future work is needed to extend these methodologies to include more diverse populations, to examine the shoulder complex as a whole, and to standardize their reporting of motion examined to make study to study comparisons possible.

Three-dimensional shoulder kinematics: Upright four-dimensional computed tomography in comparison with an optical three-dimensional motion capture system

Although shoulder kinematics have been analyzed by various methods, dynamic shoulder motion is difficult to track. This study aimed to validate the shoulder kinematic analysis using upright four-dimensional computed tomography (4DCT) and to compare the results with optical three-dimensional motion capture. During active elevation, bilateral shoulders of 10 healthy volunteers were tracked using 4DCT and motion capture. The scapulothoracic and glenohumeral rotations and the scapulohumeral rhythm (SHR) at each position were calculated, and the differences between 4DCT and motion capture were compared. During 10-140° of humerothoracic elevation, the scapulothoracic joint showed upward rotation, internal rotation, and posterior tilting, and the glenohumeral joint showed elevation, external rotation, and anterior plane of elevation in both analyses. In scapulothoracic rotations, the mean differences between the two analyses were -2.6° in upward rotation, 13.9° in internal rotation, and 6.4° in posterior tilting, and became significant with humerothoracic elevation ≥110° in upward rotation, ≥50° in internal rotation, and ≥100° in posterior tilting. In glenohumeral rotations, the mean differences were 3.7° in elevation, 9.1° in internal rotation, and -8.8° in anterior plane of elevation, and became significant with humerothoracic elevation ≥110° in elevation, ≥90° in internal rotation, and ≥100° in anterior plane of elevation. The mean overall SHRs were 1.8 in 4DCT and 2.4 in motion capture, and the differences became significant with humerothoracic elevation ≥100°. The 4DCT analysis of in vivo shoulder kinematics using upright computed tomography scanner is feasible, but the values were different from those by skin-based analysis at the elevated arm positions.

Biomechanical comparison of lower trapezius and latissimus dorsi transfer for irreparable posterosuperior rotator cuff tears using a dynamic shoulder model

BACKGROUND

In the setting of irreparable posterosuperior rotator cuff tears (PSRCTs), lower trapezius transfer (LTT) may be anatomically better positioned for restoring the muscular force couple compared with latissimus dorsi transfer (LDT). The purpose of the study was to evaluate the effect of LTT and LDT on glenohumeral kinematics using a dynamic shoulder model.

METHODS

Ten fresh-frozen cadaveric shoulders (mean age: 56.5 ± 17.2 years) were tested using a dynamic shoulder simulator. The maximum abduction angle (MAA), superior humeral head migration (SHM), and cumulative deltoid forces (CDFs) were compared across 4 conditions: (1) native; (2) irreparable PSRCT; (3) LTT using an Achilles tendon allograft; and (4) LDT. MAA and SHM were measured using 3-dimensional motion tracking. CDF was recorded in real time throughout the dynamic abduction motion by load cells connected to actuators.

RESULTS

Compared to the native state, the PSRCT resulted in a significant decrease (Δ-24.1°; P < .001) in MAA, with a subsequent significant increase after LTT (Δ13.1°; P < .001) and LDT (Δ8.9°; P < .001). LTT achieved a significantly greater MAA than LDT (Δ4.2°; P = .004). Regarding SHM, both LTT (Δ-9.4 mm; P < .001) and LDT (Δ-5.0 mm; P = .008) demonstrated a significant decrease compared with the PSRCT state. LTT also achieved significantly less SHM compared with the LDT (Δ-4.4 mm; P = .011). Further, only the LTT resulted in a significant decrease in CDF compared with the PSRCT state (Δ-21.3 N; P = .048), whereas LTT and LDT showed similar CDF (Δ-11.3 N; P = .346). However, no technique was able to restore the MAA, SHM, and CDF of the native shoulder (P < .001, respectively).

CONCLUSION

LTT and LDT both achieved a significant increase in MAA along with significantly less SHM compared with the PSRCT state. Although LTT required significantly less compensatory deltoid forces compared with the PSRCT state, this was not observed for the LDT. Further, the LTT prevented loss of abduction motion and SHM more sufficiently. In the challenging treatment of irreparable PSRCTs, LTT may restore native glenohumeral kinematics more sufficiently, potentially leading to improved postoperative functional outcomes.

Reliability of the Fluoroscopic Assessment of Load-Induced Glenohumeral Translation during a 30° Shoulder Abduction Test

Rotator cuff tears are often linked to superior translational instability, but a thorough understanding of glenohumeral motion is lacking. This study aimed to assess the reliability of fluoroscopically measured glenohumeral translation during a shoulder abduction test. Ten patients with rotator cuff tears participated in this study. Fluoroscopic images were acquired during 30° abduction and adduction in the scapular plane with and without handheld weights of 2 kg and 4 kg. Images were labelled by two raters, and inferior–superior glenohumeral translation was calculated. During abduction, glenohumeral translation (mean (standard deviation)) ranged from 3.3 (2.2) mm for 0 kg to 4.1 (1.8) mm for 4 kg, and from 2.3 (1.5) mm for 0 kg to 3.8 (2.2) mm for 4 kg for the asymptomatic and symptomatic sides, respectively. For the translation range, moderate to good interrater (intra-class correlation coefficient ICC [95% confidence interval (CI)]; abduction: 0.803 [0.691; 0.877]; adduction: 0.705 [0.551; 0.813]) and intrarater reliabilities (ICC [95% CI]; abduction: 0.817 [0.712; 0.887]; adduction: 0.688 [0.529; 0.801]) were found. Differences in the translation range between the repeated measurements were not statistically significant (mean difference, interrater: abduction, −0.1 mm, p = 0.686; adduction, −0.1 mm, p = 0.466; intrarater: abduction 0.0 mm, p = 0.888; adduction, 0.2 mm, p = 0.275). This method is suitable for measuring inferior–superior glenohumeral translation in the scapular plane.

Increased Glenohumeral Joint Loads Due to a Supraspinatus Tear Can Be Reversed With Rotator Cuff Repair: A Biomechanical Investigation

PURPOSE

To evaluate the effect of an isolated full-thickness supraspinatus (SSP) tear on glenohumeral kinematics and contact mechanics, as well as to quantify improvement following rotator cuff repair (RCR).

METHODS

Ten fresh-frozen cadaveric shoulders (mean age: 63.1 ± 4.6 years) were tested using a dynamic shoulder simulator. A pressure-mapping sensor was placed between the humeral head and the glenoid. Each specimen underwent the following three conditions: 1) native, 2) isolated full-thickness SSP tear, and 3) RCR. Maximum abduction angle (MAA) and superior humeral head migration (SHM) were measured using 3D motion tracking software. Cumulative deltoid force (CDF) and glenohumeral contact mechanics, including contact area (GCA) and contact pressure (GCP), were assessed at the resting position, as well as at 15°, 30°, 45°, and 60° of glenohumeral abduction.

RESULTS

Compared to native, the SSP tear resulted in a significant decrease in MAA (Δ-8.3°; P < .001) along with a SHM of 6.4 ± 3.8 mm, while significantly increasing CDF (Δ20.5 N; P = .008), GCP (Δ63.1 kPa; P < .001), and peak GCP (Δ278.6 kPa; P < .001), as well as decreasing GCA (Δ-45.8 mm²; P < .001) at each degree of abduction. RCR reduced SHM to 1.2 ± 2.5 mm, while restoring native MAA, CDF (Δ1.8 N), GCA (Δ4.5 mm²), GCP (Δ-4.5 kPa) and peak GCP (Δ19.9 kPa) at each degree of abduction (P > .999, respectively).

CONCLUSION

In a dynamic biomechanical cadaveric model, increased glenohumeral joint loads due to a full-thickness SSP tear can be reversed with RCR. More specifically, RCR restored native glenohumeral contact area and contact pressure, while preventing superior humeral head migration and decreasing compensatory deltoid forces.

CLINICAL RELEVANCE

These time 0 observations indicate that undergoing rotator cuff repair may prevent the development of degenerative changes by significantly reducing glenohumeral joint loads and ensuring sufficiently stable joint kinematics.

Comparison of glenohumeral joint kinematics between manual wheelchair tasks and implications on the subacromial space: A biplane fluoroscopy study

Scapula and humerus motion associated with common manual wheelchair tasks is hypothesized to reduce the subacromial space. However, previous work relied on either marker-based motion capture for kinematic measures, which is prone to skin-motion artifact; or ultrasound imaging for arthrokinematic measures, which are 2D and acquired in statically-held positions. The aim of this study was to use a fluoroscopy-based approach to accurately quantify glenohumeral kinematics during manual wheelchair use, and compare tasks for a subset of parameters theorized to be associated with mechanical impingement. Biplane images of the dominant shoulder were acquired during scapular plane elevation, propulsion, sideways lean, and weight-relief raise in ten manual wheelchair users with spinal cord injury. A computed tomography scan of the shoulder was obtained, and model-based tracking was used to quantify six-degree-of-freedom glenohumeral kinematics. Axial rotation and superior/inferior and anterior/posterior humeral head positions were characterized for full activity cycles and compared between tasks. The change in the subacromial space was also determined for the period of each task defined by maximal change in the aforementioned parameters. Propulsion, sideways lean, and weight-relief raise, but not scapular plane elevation, were marked by mean internal rotation (8.1°, 10.8°, 14.7°, -49.2° respectively). On average, the humeral head was most superiorly positioned during the weight-relief raise (1.6 ± 0.9 mm), but not significantly different from the sideways lean (0.8 ± 1.1 mm) (p = 0.191), and much of the task was characterized by inferior translation. Scaption was the only task without a defined period of superior translation on average. Pairwise comparisons revealed no significant differences between tasks for anterior/posterior position (task means range: 0.1-1.7 mm), but each task exhibited defined periods of anterior translation. There was not a consistent trend across tasks between internal rotation, superior translation, and anterior translation with reductions in the subacromial space. Further research is warranted to determine the likelihood of mechanical impingement during these tasks based on the measured task kinematics and reductions in the subacromial space.

Improvement in scapular dyskinesis after rotator cuff repair and subacromial decompression

PURPOSE

To investigate the incidence of scapular dyskinesis (SD) in patients with rotator cuff tears using pre- and postoperative 3D computed tomography, analyze the changes in scapular kinematics that occur after arthroscopic rotator cuff repair, and identify the contributing clinical factors.

METHODS

Thirty-five patients (mean age, 62.5 ± 8.4 years) were included. Four scapular angles (upward rotation, internal rotation, protraction, and posterior tilt) were measured. The patients were categorized into three pre-existing SD types according to the difference in measured scapular angles between the affected and unaffected sides (type 1 SD, posterior tilt angle difference <  - 5°; type 2 SD, internal rotation angle difference > 5°; and type 3 SD, upward rotation angle difference > 5°). The prevalence, factors influencing SD, and outcomes were compared between the improved and sustained SD groups.

RESULTS

Twenty three of the 35 patients (65.7%) with rotator cuff tears had SD (type 1, 11; type 2, six; type 3, six). Of the 23 preoperative SD patients, 12 (52.1%) showed improved SD postoperatively. Most of the patients with improved SD (9/12) had type 1 SD (p = 0.021) and a significantly improved posterior tilt angle (p = 0.043). The improvement in SD was correlated with a higher range of motion of forward flexion and higher Constant scores (all p < 0.05). No healing failure occurred in the improved SD group (p = 0.037).

CONCLUSION

The prevalence of SD was high in patients with degenerative rotator cuff tears. More than half of the SD cases, especially type 1 SD, improved postoperatively. SD recovery correlated with better function and successful rotator cuff healing.

LEVEL OF EVIDENCE

IV.

Comparing in vivo three-dimensional shoulder elevation kinematics between standing and supine postures

Background

It is often assumed that body posture, standing vs. supine, changes shoulder muscle activation and range of motion, but these altered shoulder mechanics have not been objectively assessed. We expected the supine posture might facilitate scapular rotation and change subacromial pressure. The purpose of this study is to evaluate the influence of body posture on shoulder kinematics during arm elevation.

Methods

Ten males and eight females with a mean age of 33 years participated in this study. Shoulder kinematics were assessed during scapular plane elevation in the standing and supine postures by using single-plane fluoroscopic images. Kinematics were measured using 3-dimensional to 2-dimensional model-image registration techniques: matching the 3-dimensional bone model derived from computed tomography onto each fluoroscopic image. Glenohumeral superior/inferior translation, acromiohumeral distance, and scapular rotations were compared between the postures. The effect of sex also was evaluated.

Results

With the arm at the side position, the humeral head in the supine posture was located 0.5 mm superior compared to the standing posture (P < .001). During humeral elevation, the humeral head significantly shifted more inferiorly in the supine posture than in standing; the biggest mean difference was 0.6 mm, P = .003. But acromiohumeral distance during elevation was not significantly affected by the body posture (P = .05). Scapular upward rotation and posterior tilt were significantly different between the postures (P < .001). Sex had statistically significant, but quantitatively small, effects on shoulder kinematics.

Conclusions

Body postures affect shoulder kinematics during humeral elevation. This knowledge will be useful to optimize rehabilitation exercises and for diagnostic insight.

The role of scapular dyskinesis on rotator cuff tears: a narrative review of the current knowledge

Scapular dyskinesis can be present in healthy individuals as in patients with shoulder pathology.Altered patterns of scapular kinematics can cause or exacerbate rotator cuff tear pathology. However, more research is needed.Regardless of the cause or the consequence of rotator cuff tear, scapular dyskinesis impairs shoulder function, worsens the symptoms, and compromises the success of clinical intervention.The available literature suggests physical therapy as the first treatment for degenerative cuff tears, and scapular dyskinesis should be addressed if present. Non-responsive cases or traumatic tears may require surgery.Postsurgical physical therapy protocols after rotator cuff repair must consider scapular dyskinesia to improve the outcomes. Cite this article: EFORT Open Rev 2021;6:932-940. DOI: 10.1302/2058-5241.6.210043.

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

BACKGROUND

Patient-reported measures guide physicians in clinical decision making and therefore it is critical to determine what clinical factors are associated with these scores. Psychological and physical factors are commonly studied separately in patients with rotator cuff tears to determine their influence on outcomes. It is well established that psychological distress and scapular motion change in the presence of a symptomatic rotator cuff tear. However, these factors have not been studied simultaneously in a clinical setting to determine their association with shoulder outcome scores.

QUESTION/PURPOSE

After controlling for relevant confounding variables, what physical and psychological factors are associated with better (1) American Shoulder and Elbow Surgeons (ASES) scores for function, (2) ASES pain scores, and (3) total ASES scores?

METHODS

Fifty-nine patients with a potential symptomatic rotator cuff tear were recruited and agreed to participate in this cross-sectional study. Of those, 85% (50 of 59) met eligibility criteria for a primary diagnosis of an MRI-confirmed symptomatic partial-thickness or full-thickness rotator cuff tear without a history of shoulder surgery. Demographics, rotator cuff tear size, arm flexion, and clinical scapular motion during active arm flexion were evaluated by experienced examiners using standardized procedures. Patients completed the ASES questionnaire and the Optimal Screening for Prediction of Referral and Outcomes-Yellow Flag assessment form, which measures 11 different pain-related psychological distress symptoms. Three separate stepwise multiple linear regression analyses were performed for ASES pain, function, and total scores, with significance set at p < 0.05.

RESULTS

This model found that ASES function scores were associated with four factors: older age, increased arm flexion, increased percentage of scapular external rotation during arm flexion, and increased scores for acceptance of chronic pain (adjusted r2 = 0.67; p = 0.01). Those four factors appear to explain 67% of the observed variance in ASES function scores in patients with rotator cuff tears. Furthermore, increased percentage of scapular external rotation during arm flexion and decreased fear-avoidance beliefs related to physical activity scores (adjusted r2 = 0.36; p < 0.01) were associated with better ASES pain scores. And finally, better ASES total scores were associated with four factors: increased arm flexion, increased percentage of scapular upward rotation, increased scapular external rotation during arm flexion, and decreased fear-avoidance beliefs related to physical activity scores (adjusted r2 = 0.65; p < 0.001).

CONCLUSION

Our results favor adopting a comprehensive biopsychological clinical assessment for patients with rotator cuff tears that specifically includes humeral and scapular motion, fear-avoidance behaviors, and pain coping behaviors along with demographics. These particular physical and psychological variables were found to be associated with the ASES and, therefore, should be clinically examined simultaneously and targeted as part of a tailored treatment plan.

LEVEL OF EVIDENCE

Level II, prognostic study.

Scapular motion in the presence of rotator cuff tears: a systematic review

BACKGROUND

Rotator cuff tears (RCTs) remain a significant source of pain and disability in the shoulder. Although much work has been done in the study of the effects of rotator cuff tears on glenohumeral joint motion, much less has been done in understanding the effect of rotator cuff tearing on scapular motion or activation. It remains unknown whether scapular dyskinesis is causative or adaptive. The purpose of this study was to systematically review the literature to determine the relationship between rotator cuff tear presence and size on scapular motion, and if rotator cuff repair restored normal motion.

METHODS

A systematic review using PRISMA guidelines was accomplished to include all studies with biomechanical or clinical outcomes of scapular motion in the presence of RCTs. Studies were excluded if they involved shoulder arthroplasty, rotator cuff tendinopathy, or shoulder impingement without an RCT. From 530 initial references, 42 manuscripts were selected for full review and cross referenced. All studies were evaluated for inclusion and exclusion criteria.

RESULTS

Sixteen studies including 335 rotator cuff tears were included in the final review. There were several findings of interest in the literature. First, although all studies demonstrated scapular dyskinesis, they did not report a consistent pattern of motion in the presence of an RCT. In general, scapular posterior tilt was decreased, and scapular upward rotation was increased, especially in large tears, but the literature was unclear as to whether this was a result of the RCT or an adaptive attempt to maintain elevation. Larger RCTs resulted in more pronounced scapular dysfunction, but there was significant variability within studies. Further, dyskinesis was confounded by pain with more abnormal movement in symptomatic vs. asymptomatic RCTs, the latter of which were not different from normal healthy controls. Four studies addressed the effect of RCT on scapular mechanics and found that repair consistently improved it compared to the normal side, but the time to normalization varied between 5 months and 2 years.

CONCLUSION

Scapular motion is abnormal in the presence of an RCT, but the literature is inconsistent regarding a universally affected variable or consistent degree of scapular dysfunction in this setting. Furthermore, it remains unknown which changes are adaptive vs. pathologic. Understanding the relationship between rotator cuff tearing and scapular dyskinesis will require better biomechanical models that consider scapular dyskinesis in their design.

Dynamic scapulohumeral rhythm: Comparison between healthy shoulders and those with large or massive rotator cuff tear

INTRODUCTION

Assessment of scapular kinematics and the dynamics of the scapulohumeral rhythm (SHR) would be important for understanding pathologies of the shoulder and to inform treatment. Our aim in this study was to evaluate the SHR and scapular kinematics in patients with a rotator cuff tear (RCT), compared to a control group with healthy shoulders using image-matching techniques.

MATERIALS AND METHODS

The shoulder kinematics of large or massive RCT patients were evaluated and compared to a control group with healthy shoulders. Radiographic surveillance was performed throughout the full range of external rotation and scapular plane abduction. Computed tomography imaging of the shoulder complex was performed, with three-dimensional image reconstruction and matching to the radiographs to measure three-dimensional positions and orientations. SHR and angular values of the scapula were measured.

RESULTS

Scapular external rotation in the late phase of external rotation movement was greater in the RCT group than in the control group (p < 0.05), but with no difference in the SHR. During scapular plane abduction, there were significant differences in SHR, scapular posterior tilt and scapular upward rotation between the RCT and control group (p < 0.05).

CONCLUSIONS

Regarding clinical relevance, this study clarified the differences of SHR and angular values of the scapula between the RCT and control group. These results underline the importance of assessment the SHR and scapular kinematics in individuals with a RCT. RCT is associated with specific compensation in the kinematics of the scapula and SHR during external rotation and scapular plane abduction, which could inform treatment.

Investigation of the range of motion of the shoulder joint in subjects with rotator cuff arthropathy while performing daily activities

Background

Patients who have rotator cuff arthropathy experience a limited range of motion (ROM) of the shoulder joint and experience problems in performing their daily activities; however, no evidence is available to suggest the exact ROM of the shoulder joint in this population. Therefore, this study sought to determine the degree of motion of the shoulder joint in three planes during different activities.

Methods

Five subjects with rotator cuff injuries participated in this study. The motion of the shoulder joints on both the involved and normal sides was assessed by a motion analysis system while performing forward abduction (task 1), flexion (task 2), and forward flexion (task 3). The OpenSIM software program was used to determine the ROM of the shoulder joints on both sides. The difference between the ranges of motion was determined using a two-sample t-test.

Results

The ROMs of the shoulder joint in task 1 were 93.5°±16.5°, 72.1°±2.6°, and 103.9°±25.7° for flexion, abduction, and rotation, respectively, on the normal side and 28°±19.8°, 31°±31.56°, and 48°±33.5° on the involved side (p<0.05). There was no significant difference between the flexion/extension and rotation movements of the shoulder joint when performing task 1. However, the difference between flexion and rotation movements of the shoulder joints for the second task was significant (p>0.05).

Conclusions

Those with rotator cuff arthropathy have functional limitations due to muscle weakness and paralysis, especially during the vertical reaching task. However, although these individuals have decreased ROM for transverse reaching tasks, the reduction was not significant.

Three-dimensional kinematic features in large and massive rotator cuff tears with pseudoparesis

BACKGROUND

Although massive rotator cuff tears occasionally lead to severe impairment of shoulder function, the criteria for losing the ability to elevate the arm are unclear. This study aimed to analyze the features of both tear size and 3-dimensional (3D) shoulder kinematics that correspond to the loss of the ability to elevate the arm in patients with large and massive rotator cuff tears.

METHODS

We prospectively enrolled patients with rotator cuff tears, including the supraspinatus and more than half of the subscapularis or more than two-thirds of the infraspinatus, without severe pain. A total of 13 patients (15 shoulders) were divided into 2 groups: 9 shoulders in the pseudoparesis (P) group and 6 shoulders in the non-pseudoparesis (NP) group. Fluoroscopic images were collected during active scapular-plane elevation, and 3D shoulder kinematics was analyzed using 2-dimensional-3D registration techniques. The radiographic findings and 3D kinematic results were compared between the groups. The correlation between tear size and 3D kinematics was also investigated.

RESULTS

The most superior position of the humeral head center was significantly higher in the P group (6.7 ± 3.0 mm in P group vs. 3.6 ± 1.3 mm in NP group, P = .0321). Superior migration, which was defined as the most superior position > 5 mm, was significantly more frequent in the P group (7 shoulders and 1 shoulder in the P and NP groups, respectively; P = .0201). Thoracohumeral external rotation was significantly smaller in the P group (16° ± 31° in P group vs. 91° ± 21° in NP group, P < .0001). The total tear size and the tear sizes of the anterior and posterior rotator cuffs were significantly correlated with the superior (r = 0.68, P = .0056), anterior (r = 0.68, P = .0058), and posterior (r = -0.80, P = .0004) positions of the humeral head center. The tear size of the posterior rotator cuff also tended to be correlated with glenohumeral external rotation (r = -0.48, P = .0719).

CONCLUSION

Anterior and posterior rotator cuff tears cause significant superior and anteroposterior translations of the humeral head, and posterior cuff tears may lead to loss of glenohumeral external rotation. With these abnormal kinematics, superior migration and loss of thoracohumeral external rotation were identified as features of pseudoparesis.

Limitation of the external glenohumeral joint rotation is associated with subacromial impingement syndrome, especially pain

Background

Subacromial impingement syndrome is a common disorder associated with functional impairment and disability of the shoulder. Internal/external glenohumeral rotation is important for shoulder function. However, because it is difficult to measure the glenohumeral joint rotation angle physically, the relationship between this angle and the clinical symptoms of subacromial impingement syndrome is still largely unknown. Using advanced cine-magnetic resonance imaging techniques, we designed a study to improve our understanding of the nature of this relationship.

Methods

We evaluated 100 shoulders with subacromial impingement syndrome. Patients underwent cine-magnetic resonance imaging during axial rotation with the arm adducted. During imaging, patients rotated their shoulder from maximum internal rotation to maximum external rotation over 10 seconds and then to maximum internal rotation over 10 seconds. The rotation angles were then evaluated using a series of axial images. The Constant–Murley (Constant) and UCLA scores for each patient were determined, and the correlation between the scores and rotational angles was assessed. Patients were divided into 3 groups according to the Constant pain score, and the rotational angles of each group were compared. Rotational angles were also compared between shoulders with and without night pain.

Results

The external rotation angle showed a significant but low correlation with the Constant and UCLA scores (ρ = 0.24 and 0.24, respectively), whereas the internal rotation angle did not. In comparing the pain groups of Constant score and UCLA score, the external rotation angle significantly decreased as pain increased (P < .01), demonstrating a negative correlation (ρ = −0.47, −0.41, respectively). Additionally, the shoulders of patients with night pain showed significantly more restriction of external rotation angles than the shoulders of those without night pain (P = .01).

Conclusions

Limitation of the glenohumeral joint’s external rotation is correlated with pain, for which we explore possible explanations. The results suggest that night pain can be effectively reduced using therapeutic interventions that target external rotational dysfunction.

Differences in scapular motion and parascapular muscle activities among patients with symptomatic and asymptomatic rotator cuff tears, and healthy individuals

Background

Altered scapular motion is thought to be one of the factors associated with the development of symptomatic rotator cuff tears. However, the differences in kinematics and muscle activities of scapular upward/downward rotation between patients with symptomatic and asymptomatic tears are unclear. The purpose of this study was to compare the differences in kinematics and muscle activities of scapular rotation among patients with symptomatic and asymptomatic tears, and healthy individuals.

Methods

Twenty-three patients with rotator cuff tears and 9 healthy individuals (healthy group) participated in this study. Based on a visual analog scale (VAS, 0-100 mm), the patients were divided into symptomatic (13 patients; VAS ≥20 mm) and asymptomatic (10 patients; VAS <20 mm) groups. Scapular upward rotation was measured with a digital inclinometer. Elasticities of the upper trapezius, levator scapulae, and rhomboid major were assessed by using ultrasound real-time tissue elastography to quantify their muscle activities. All measurements were performed at 0°, 60°, 90°, and 120° of active arm elevation in the scapular plane.

Results

Scapular upward rotation was significantly less in the symptomatic group (9.4° ± 5.6°) compared with the asymptomatic group (15.7° ± 6.0°; P = .022) at 90° of arm elevation. The activity of the levator scapulae was significantly higher in the symptomatic group compared with the asymptomatic and healthy groups (P = .013 and P = .005, respectively) at 90° of arm elevation. The activity of the upper trapezius was significantly higher in the symptomatic group compared with the healthy group (P = .015) at 120° of arm elevation.

Conclusion

Patients with symptomatic rotator cuff tears showed less scapular upward rotation and higher activity of the levator scapulae at 90° of arm elevation compared to patients with asymptomatic rotator cuff tears.

Examining assessment methods of scapular motion: Comparing results from planar elevations and functional task performance

BACKGROUND

Scapular kinematics of breast cancer survivors are most often evaluated during arm elevation. However, known compensations exist during functional task performance. The purpose of this study was to determine if scapular kinematics of breast cancer survivors during arm elevation are related to scapular kinematics during functional task performance.

METHODS

Scapular kinematics of 25 non-cancer controls and 25 breast cancer survivors (split by presence of impingement pain) during arm elevation in 3 planes and 3 reaching and lifting functional tasks were measured. Scapular upward rotation and scapulohumeral rhythm (SHR) at 30° increments of arm elevation were calculated. Between-group differences of upward rotation during arm elevation were evaluated with one-way ANOVAs (p < 0.05). The association of upward rotation angle and SHR during arm elevation and functional tasks was tested with Pearson correlations (p < 0.05).

FINDINGS

Scapular upward rotation was reduced for the breast cancer survivor with pain at lower levels of arm elevation in each plane by up to 7.1° (p = .014 to 0.049). This is inconsistent with functional task results, in which upward rotation decrements occurred at higher levels of arm elevation. Upward rotation angles and SHR during arm elevation had an overall weak-to-moderate relationship (r = 0.003 to 0.970, p = .001 to 0.048) to values from functional tasks. Arm elevation during sagittal plane elevation demonstrated scapular upward rotation that was most closely associated to upward rotation during functional task performance.

INTERPRETATION

Inconsistent relationships suggests that clinical evaluations should adopt basic functional movements for scapular motion assessment to complement simple arm elevations.

Comparison of shoulder muscle strength, cross-sectional area, acromiohumeral distance, and thickness of the supraspinatus tendon between symptomatic and asymptomatic patients with rotator cuff tears

BACKGROUND

The purpose of this study was to demonstrate the differences in shoulder muscle strength, cross-sectional area of the rotator cuff muscles, acromiohumeral distance, and supraspinatus tendon thickness between symptomatic and asymptomatic patients with rotator cuff tears.

METHODS

Thirty-two symptomatic patients and 23 asymptomatic patients with rotator cuff tears participated in this study. Data of the patients with any type of tear and supraspinatus tear were analyzed. We evaluated the isometric torque, cross-sectional area of the rotator cuff muscles, supraspinatus tendon thickness, acromiohumeral distance, range of motion, and Western Ontario Rotator Cuff Index.

RESULTS

Asymptomatic patients showed greater isometric torque of shoulder abduction and internal rotation than symptomatic patients with any type of tear (P ≤ .01). Asymptomatic patients also demonstrated greater cross-sectional area of the supraspinatus (P < .01); however, there was no significant difference in the cross-sectional area of the other cuff muscles. There was also no significant difference in the supraspinatus tendon thickness (P = .10). The acromiohumeral distance at 90° of shoulder abduction was larger (P = .04) in asymptomatic patients. Additionally, similar tendencies were observed in the results of patients with supraspinatus tears, except for the isometric torque of shoulder external rotation. This torque was greater (P < .01) in asymptomatic patients.

CONCLUSION

Asymptomatic patients showed greater shoulder range of motion, muscle strength of shoulder abduction and internal rotation, small occupation ratio of supraspinatus tendon thickness as a percentage of acromiohumeral distance, and large cross-sectional area of supraspinatus.

Association of Both Scapular Upward Rotation and Scapulothoracic Muscle Lengths With Shoulder Pain, Function, and Range of Movement

OBJECTIVE

Our aim was to analyze whether shoulder pain is related to scapular upward rotation (SUR) or to the lengths of the pectoralis minor and levator scapulae muscles.

METHODS

This cross-sectional, observational study was carried out in 3 primary-care centers; 54 individuals with chronic shoulder pain participated. Scapular upward rotation and the lengths of the pectoralis minor and levator scapulae muscles were assessed.

RESULTS

The level of association was small between shoulder pain and function and (1) the lengths of the pectoralis minor (r = 0.08, P = .93) and levator scapulae (r = -0.01, P = .57) muscles and (2) SUR at 45° (r = 0.17, P = .21), 90° (r = 0.08, P = .57), and 135° (r = 0.10, P = 0.45) of shoulder elevation.

CONCLUSION

The relationship was small between shoulder pain and function and (1) SUR (45°, 90°, and 135° of shoulder elevation) and (2) the lengths of the pectoralis minor and levator scapulae muscles. Thus, the use of SUR and pectoralis minor and levator scapulae lengths in shoulder assessment should be undertaken with caution. Other factors such as psychological factors, central/peripheral sensitization, and intrinsic properties of the tissue have to be taken into account.

Motion quality in rotator cuff tear using an inertial measurement unit: new parameters for dynamic motion assessment

PURPOSE

This study aimed to (1) figure out the difference in motion smoothness between a nonpathologic shoulder and the other with a rotator cuff tear by measuring the angular velocity using an inertial measurement unit (IMU) sensor and (2) propose the parameters to describe the difference because there is no literature on this topic.

MATERIAL AND METHODS

We enrolled patients with rotator cuff disease diagnosed by magnetic resonance imaging. The intact shoulder of participants was compared with the shoulder with rotator cuff tear by using IMU on the basis of the parameters that establish motion smoothness: the number of peaks, the peak velocity-to-mean velocity ratio (PV/MV), and the number of sign reversals. In addition, subgroup analysis was performed with respect to tear size (small to medium vs. large to massive). In addition, correlations with the American Shoulder and Elbow Surgeons score and symptom duration (months) were evaluated.

RESULTS

Among 24 patients (15 males, 9 females), all 3 parameters for the motion quality of patients with a rotator cuff tear exhibited significant difference. The parameters showed a significant difference between the small to medium tear group and the large to massive tear group. A negative correlation was found between symptom duration and parameters of motion quality, except for PV/MV.

CONCLUSIONS

Motion quality assessment using IMU showed a marked difference in the shoulder with a rotator cuff tear compared with the intact shoulder. Hence, IMU-based parameters for dynamic motion quality could be considered as an option for assessing the function of the shoulder.

Comparison of scapular kinematics and muscle strength between those with a positive and a negative Scapular Assistance Test

BACKGROUND

The Scapular Assistance Test was suggested to directly assess the influence of scapular motion on pain and indirectly measure the function of the scapular rotators. However, it is still not clear if individuals with a positive Scapular Assistance Test actually present changes in scapular motion and muscle strength. This study compared scapular kinematics and muscle strength between those with a positive Scapular Assistance Test and those with a negative Scapular Assistance Test.

METHODS

Fifty individuals with shoulder pain were randomly allocated to: positive (n = 25) or negative Scapular Assistance Test (n = 25) group. Scapular kinematics was measured during elevation and lowering of the arm. Strength of the serratus anterior and lower trapezius was also measured. Two-way analysis of variance was used to compare kinematics between groups. Unpaired Student's t-test and Mann-Whitney test were used to compare strength of serratus anterior and lower trapezius, respectively.

FINDINGS

There were no differences (P > 0.05) in scapular internal rotation and upward rotation between both groups. For scapular tilt, there was group main effect (P < 0.05) during elevation and lowering of the arm, whereas the positive Scapular Assistance Test group presented greater scapular anterior tilt. There was no difference (P > 0.05) in strength between groups.

INTERPRETATION

Individuals with a positive Scapular Assistance Test are more likely to present decreased scapular posterior tilt in those with shoulder pain. Strength of the scapular muscles seems to be same in those with a positive and a negative Scapular Assistance Test.

Radiographic evaluation of the glenohumeral joint space in patients undergoing arthroscopic shoulder surgery in the beach-chair position

Background

Shoulder arthroscopy can be performed with the patient in the lateral decubitus or beach-chair position, but in both cases, glenohumeral (GH) joint spaces must be increased to improve visualization and allow access of the optical instrument. The aim of this study was to determine the effects of limb setup and longitudinal traction on the opening of the GH space with patients placed in the beach-chair (dorsal decubitus) position.

Methods

GH spaces at 3 test points corresponding to the anatomic locations of Bankart lesions were determined indirectly from radiographic images obtained from 67 patients presenting shoulder pathology with an indication for arthroscopic surgery. Measurements were made with the operative limb in neutral rotation and positioned in relation to the coronal plane in adduction, 45° of abduction, or adduction with an axillary spacer, in each case with and without longitudinal traction.

Results

GH spaces were optimized at 2 of 3 test points when the operative limb was positioned in adduction or neutral rotation and manual longitudinal traction was applied with or without a polystyrene spacer placed under the axilla, but use of the spacer was essential to maximize the GH space at all 3 locations. In contrast, 45° of abduction proved to be the least appropriate position because it afforded the smallest GH space values with or without traction.

Conclusion

Appropriate positioning of the patient on the operating table is a critical aspect of shoulder arthroscopy. Radiographic images revealed that adducted upper-limb traction with the use of an axillary spacer in patients in the beach-chair position generates a significant increase in the GH space in the lower half of the glenoid cavity, thereby facilitating visualization and access of the optical equipment to the GH compartments.

Scapulothoracic rhythm affects glenohumeral joint force

Hypothesis

Musculoskeletal computer models provide valuable insights into shoulder biomechanics. The shoulder is a complex joint composed of glenohumeral, scapulothoracic, acromioclavicular, and sternoclavicular articulations, whose function is largely dependent on the many muscles spanning these joints. However, the range of patient-to-patient variability in shoulder function is largely unknown. We therefore assessed the sensitivity of glenohumeral forces to population-based model input parameters that were likely to influence shoulder function.

Methods

We constructed musculoskeletal models of the shoulder in the AnyBody Modeling System (AnyBody Technology, Aalborg, Denmark). We used inverse dynamics and static optimization to solve for glenohumeral joint forces during a simulated shoulder elevation. We generated 1000 AnyBody models by uniformly distributing the following input parameters: subject height, scapulohumeral rhythm, humeral head radius, and acromiohumeral interval.

Results

Increasing body height increased glenohumeral joint forces. Increasing the ratio of scapulothoracic to glenohumeral elevation also increased forces. Increasing humeral head radius and acromiohumeral interval decreased forces. The relative sensitivity of glenohumeral joint forces to input parameters was dependent on the angle of shoulder elevation. We developed an efficient method of generating and simulating musculoskeletal models representing a large population of shoulder arthroplasty patients. We found that scapulohumeral rhythm had a significant influence on glenohumeral joint force.

Conclusions

This finding underscores the importance of more accurately measuring and simulating scapulothoracic motion rather than using fixed ratios or average scapulothoracic motion. This modeling approach can be used to generate virtual populations for conducting efficient simulations and generating statistical conclusions.

Differences in scapular upward rotation, pectoralis minor and levator scapulae muscle length between the symptomatic, the contralateral asymptomatic shoulder and control subjects: a cross-sectional study in a Spanish primary care setting

OBJECTIVE

To determine the potential differences in both scapular positioning and scapular movement between the symptomatic and asymptomatic contralateral shoulder, in patients with unilateral subacromial pain syndrome (SAPS), and when compared with participants free of shoulder pain.

SETTING

Three different primary care centres.

PARTICIPANTS

A sample of 73 patients with SAPS in their dominant arm was recruited, with a final sample size of 54 participants.

PRIMARY OUTCOME MEASURES

The scapular upward rotation (SUR), the pectoralis minor and the levator scapulae muscles length tests were carried out.

RESULTS

When symptomatic shoulders and controls were compared, an increased SUR at all positions (45°, 90° and 135°) was obtained in symptomatic shoulders (2/3,98/8,96°, respectively). These differences in SUR surpassed the minimal detectable change (MDC95) (0,91/1,55/2,83° at 45/90/135° of shoulder elevation). No differences were found in SUR between symptomatic and contralateral shoulders. No differences were found in either pectoralis minor or levator scapulae muscle length in all groups.

CONCLUSIONS

SUR was greater in patients with chronic SAPS compared with controls at different angles of shoulder elevation.

Asymptomatic Rotator Cuff Tears

Asymptomatic rotator cuff tears (RCTs) are prevalent in the general population; they are positively associated with age and are common in the contralateral shoulder of individuals who are being treated for shoulder pain or a symptomatic RCT. Asymptomatic RCTs are likely to become symptomatic over time, corresponding with decreased patient-reported function, strength, and range of motion. Previous studies have largely reported inconsistent findings regarding patient-reported outcomes, strength, range of motion, and kinematics in individuals with asymptomatic RCTs. Future research would benefit from characterizing any functional alteration that is associated with asymptomatic rotator cuff pathology, including determining whether such alterations are detrimental or compensatory and understanding the mechanism by which an asymptomatic RCT becomes symptomatic.

Results measured by means of a motion capture system in proximal humerus fractures treated by osteosynthesis with locking plate

OBJECTIVE

To evaluate the results after locking plate internal fixation of proximal humerus fractures by means of a motion capture system, and functional scales.

MATERIAL AND METHOD

Retrospective study of a cohort of 47 elderly patients undergoing surgery from January 2010 to December 2014. After a minimum follow-up of two years, two functional scales (Constant-Murley and Quick DASH), and a quality of life scale (EQ-5D) were used for clinical evaluation. For objective evaluation of the range of motion a kinematic marker-free analysis with cameras was performed.

RESULTS

The average age was 74.85 years. Average functional scores were: Constant-Murley 70.06 points, Quick DASH 35.74 points and EQ-5D 6.79 points. The average range of motion was: flexion, 111.49°; extension: 24.13°; abduction: 109.40°; adduction: 15.13°; external rotation: 38.96°, and internal rotation: 49.28°. Correlation was found between the two functional scales, between them and the EQ-5D, and between range of motion and functional scales (except for external rotation) as well as between range of motion and EQ-5D (except for flexion and external rotation).

CONCLUSION

Locking plate osteosynthesis in proximal humerus fragility fractures achieved good functional and quality of life scores. Motion capture systems can be a useful tool for the functional assessment of shoulder pathology allowing an objective evaluation of range of motion.

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

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.

Electromyographic analysis of infraspinatus and scapular muscles during external shoulder rotation with different weight loads and positions

BACKGROUND

Strengthening the infraspinatus is important in shoulder rehabilitation. Changes in infraspinatus activity with changing load and position have not been quantified. We sought to determine the most appropriate load and posture for early infraspinatus strengthening by assessing for changes in electromyographic activity in the healthy infraspinatus and other shoulder girdle muscles during isometric external rotational exercise under different loads with the shoulder adducted in the supine and seated positions.

METHODS

Sixteen healthy adults (30 shoulders) performed isometric shoulder external rotation in the sitting and supine positions, starting with the shoulder and forearm in neutral position and the elbow flexed 90°. Loads (0.5 kg, 1 kg, and 2 kg) were applied at rest. We assessed the infraspinatus, upper trapezius, posterior deltoid, and biceps brachii. For analysis, we used the mean percentage of maximum voluntary muscle contraction (%MVC) value measured during each isometric contraction divided by the maximum voluntary muscle contraction (MVC) of each muscle.

RESULTS

In the infraspinatus and posterior deltoid, significant interaction was observed between body position and load. Compared to the sitting position, an increase in activity in the supine position was attenuated as load increased, especially at 2 kg. The supine values of the upper trapezius and biceps brachii were always significantly lower than those in the sitting position regardless of load.

CONCLUSION

The activity of the infraspinatus can be increased gradually during rehabilitation by beginning in the supine position, which assures low activity of the upper trapezius and biceps brachii. Exercise with the shoulder adducted in the supine position can strengthen the infraspinatus gradually and avoid compensatory mobility.

LEVEL OF EVIDENCE

Level 3.

Relationship Between Deltoid and Rotator Cuff Muscles During Dynamic Shoulder Abduction: A Biomechanical Study of Rotator Cuff Tear Progression

BACKGROUND

Previous biomechanical studies regarding deltoid function during glenohumeral abduction have primarily used static testing protocols.

HYPOTHESES

(1) Deltoid forces required for scapular plane abduction increase as simulated rotator cuff tears become larger, and (2) maximal abduction decreases despite increased deltoid forces.

STUDY DESIGN

Controlled laboratory study.

METHODS

Twelve fresh-frozen cadaveric shoulders with a mean age of 67 years (range, 64-74 years) were used. The supraspinatus and anterior, middle, and posterior deltoid tendons were attached to individual shoulder simulator actuators. Deltoid forces and maximum abduction were recorded for the following tear patterns: intact, isolated subscapularis (SSC), isolated supraspinatus (SSP), anterosuperior (SSP + SSC), posterosuperior (infraspinatus [ISP] + SSP), and massive (SSC + SSP + ISP). Optical triads tracked 3-dimensional motion during dynamic testing. Fluoroscopy and computed tomography were used to measure critical shoulder angle, acromial index, and superior humeral head migration with massive tears. Mean values for maximum glenohumeral abduction and deltoid forces were determined. Linear mixed-effects regression examined changes in motion and forces over time. Pearson product-moment correlation coefficients ( r) among deltoid forces, critical shoulder angles, and acromial indices were calculated.

RESULTS

Shoulders with an intact cuff required 193.8 N (95% CI, 125.5 to 262.1) total deltoid force to achieve 79.8° (95% CI, 66.4° to 93.2°) of maximum glenohumeral abduction. Compared with native shoulders, abduction decreased after simulated SSP (-27.2%; 95% CI, -43.3% to -11.1%, P = .04), anterosuperior (-51.5%; 95% CI, -70.2% to -32.8%, P < .01), and massive (-48.4%; 95% CI, -65.2% to -31.5%, P < .01) cuff tears. Increased total deltoid forces were required for simulated anterosuperior (+108.1%; 95% CI, 68.7% to 147.5%, P < .01) and massive (+57.2%; 95% CI, 19.6% to 94.7%, P = .05) cuff tears. Anterior deltoid forces were significantly greater in anterosuperior ( P < .01) and massive ( P = .03) tears. Middle deltoid forces were greater with anterosuperior tears ( P = .03). Posterior deltoid forces were greater with anterosuperior ( P = .02) and posterosuperior ( P = .04) tears. Anterior deltoid force was negatively correlated ( r = -0.89, P = .01) with critical shoulder angle (34.3°; 95% CI, 32.0° to 36.6°). Deltoid forces had no statistical correlation with acromial index (0.55; 95% CI, 0.48 to 0.61). Superior migration was 8.3 mm (95% CI, 5.5 to 11.1 mm) during testing of massive rotator cuff tears.

CONCLUSION

Shoulders with rotator cuff tears require considerable compensatory deltoid function to prevent abduction motion loss. Anterosuperior tears resulted in the largest motion loss despite the greatest increase in deltoid force.

CLINICAL RELEVANCE

Rotator cuff tears place more strain on the deltoid to prevent abduction motion loss. Fatigue or injury to the deltoid may result in a precipitous decline in abduction, regardless of tear size.

Scapular kinematic alterations during arm elevation with decrease in pectoralis minor stiffness after stretching in healthy individuals

BACKGROUND

Pectoralis minor tightness may be seen in individuals with scapular dyskinesis, and stretching is used for the treatment of altered scapular motion in sports and clinical fields. However, few researchers have reported on the effects of pectoralis minor stiffness on scapular motion during arm elevation. This study investigated whether an acute decrease of pectoralis minor stiffness after stretching changes the scapular motion during arm elevation.

METHODS

The study allocated 15 dominant and 15 nondominant upper limbs in healthy men as control and interventional limbs, respectively. In the intervention limb group, the shoulder was passively and horizontally abducted at 150° of elevation for 5 minutes to stretch the pectoralis minor muscle. Before and after stretching, an electromagnetic sensor was used to examine 3-dimensional scapular motion during abduction and scaption. Ultrasonic shear wave elastography was used to measure pectoralis minor stiffness before and immediately after stretching and after arm elevation.

RESULTS

In the interventional limb, pectoralis minor stiffness decreased by 3.2 kPa immediately after stretching and by 2.5 kPa after arm elevation. The maximal changes in scapular kinematics after stretching were 4.8° of external rotation and 3.3° of posterior tilt in abduction, and 4.5° of external rotation and 3.7° of posterior tilt in scaption. Upward rotation in abduction or scaption did not change.

CONCLUSIONS

Stretching for the pectoralis minor muscle increases external rotation and posterior tilt of the scapula during arm elevation.

Scapular kinematics during manual wheelchair propulsion in able-bodied participants

BACKGROUND

Altered scapular kinematics have been associated with shoulder pain and functional limitations. To understand kinematics in persons with spinal cord injury during manual handrim wheelchair propulsion, a description of normal scapular behaviour in able-bodied persons during this specific task is a prerequisite for accurate interpretation. The primary aim of this study is to describe scapular kinematics in able-bodied persons during manual wheelchair propulsion.

METHODS

Sixteen able-bodied, novice wheelchair users without shoulder complaints participated in the study. Kinematic and kinetic data were collected during a standardized pose in the anatomic posture, frontal-plane arm elevation and low-intensity steady-state handrim wheelchair propulsion and upper-body Euler angles were calculated.

FINDINGS

Scapulothoracic joint orientations in a static position were 36.7° (SD 5.4°), 6.4° (SD 9.1°) and 9.1° (SD 5.7°) for respectively protraction, lateral rotation and anterior tilt. At 80° of arm elevation in the frontal plane, the respective values of 33.4° (SD 8.0°), 23.9° (SD 5.4°) and 4.1° (SD 11.3°) were found. During the push phase of manual wheelchair propulsion, the mean scapular rotations were respectively 32.7° (SD 7.1°), 7.1° (SD 9.2°) and 9.8° (SD 8.3°).

INTERPRETATION

The orientation of the scapula in a static pose, during arm elevation and in manual wheelchair propulsion in able-bodied participants showed similar patterns to a previous study in persons with para- and tetraplegia. These values provide a reference for the investigation of the scapular movement pattern in wheelchair-dependent persons and its relation to shoulder complex abnormalities.

Rehabilitation of symptomatic atraumatic degenerative rotator cuff tears: A clinical commentary on assessment and management

STUDY DESIGN

Clinical Commentary.

INTRODUCTION

Atraumatic rotator cuff (RC) disease, is one of the most common cause of shoulder pain, which encompasses a continuum from tendinopathy to full thickness cuff tears. Extrinsic, intrinsic and environmental factors have been implicated in the pathophysiology of this disorder, affecting the clinical presentation of symptoms including pain and irritability. Successful rehabilitation of symptomatic atraumatic degenerative rotator cuff (SADRC) tears must address the underlying mechanisms causing dysfunction and correct modifiable factors.

PURPOSE OF THE STUDY

The purpose of this paper is to review the shoulder complex anatomy, introduce atraumatic degenerative RC pathology, differentiate between symptomatic and asymptomatic degenerative RC tears, propose an assessment and introduce the Rotator Cuff Protocol 1 (RCP1) designed by the clinical reasoning of one of the lead authors (LW) as a rehabilitation management approach for those clients who present with SADRC tears.

METHODS/RESULTS/DISCUSSION

N/A for clinical commentary.

CONCLUSIONS

The ability to identify SADRC tears should consider shoulder anatomy, extrinsic, intrinsic and environmental factors, and the consideration for the natural history of atraumatic partial and full thickness tears in the general population. A thorough clinical history and examination, which includes shoulder symptom modification tests, allows the examiner to determine at what phase the patient may start their exercise program. The RCP1 is a program that has been used clinically by many therapists and clients over the years and research is underway to test this protocol in atraumatic rotator cuff disease including SADRC tears.

LEVEL OF EVIDENCE

5.

Dynamic kinematics of the glenohumeral joint in shoulders with rotator cuff tears

Background

No clear trend has emerged from the literature regarding three-dimensional (3D) translations of the humerus relative to the scapula in shoulders with rotator cuff tears (RCTs). The purpose of this study was to evaluate the kinematics of RCT shoulders using 3D-to-two-dimensional (2D) model-to-image registration techniques.

Methods

Dynamic glenohumeral kinematics during scapular plane abduction and axial rotation were analyzed in 11 RCT patients and 10 healthy control subjects. We measured the 3D kinematic parameters of glenohumeral joints using X-ray images and CT-derived digitally reconstructed radiographs.

Results

For scapular plane abduction, the humeral head center was positioned significantly more medially in shoulders with RCTs than in controls at 135° of humeral abduction (p = 0.02; RCTs versus controls: − 0.9 ± 1.6 versus 0.3 ± 1.3 mm). There was no significant difference in the superior/inferior translation of the humeral head center (p = 0.99). For axial rotation in adducted position, the humeral head center was positioned significantly more anteriorly in shoulders with RCTs than in controls at − 30° of glenohumeral external rotation (p < 0.0001; RCTs versus controls: 3.0 ± 1.7 versus 0.3 ± 1.5 mm).

Conclusions

This study revealed the kinematics of shoulders with large to massive full-thickness RCTs: the humeral head center showed a medial shift at the late phase of scapular plane full abduction, and an anterior shift at the internal rotation position during full axial rotation. The kinematic data in this study, which describe the patterns of movement of shoulders with large to massive full-thickness RCTs, provide valuable information for future studies investigating glenohumeral translations in other pathological conditions of the shoulder. For clinical relevance, quantitative assessment of the dynamic kinematics of shoulders with RCTs might be a therapeutic indicator for achieving functional restoration.

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.

METHODS

This study is a non-systematic review of kinematic patterns in degenerated shoulders. It is a based on our own research on the kinematics of the shoulder complex and clinical experience.

RESULTS

For patients with subacromial impingement syndrome without rotator-cuff tears, most kinematic studies showed a small superior humeral translation relative to the glenoid and decreased scapular lateral rotation and posterior tilt. These scapular kinematic modifications could decrease the subacromial space and favor rotator-cuff tendon injury. For patients with shoulder pain and restricted mobility, the studies showed a significant increase in scapular lateral rotation generally seen as a compensation mechanism of GH decreased range of motion. For patients with multidirectional GH instability, the studies found an antero-inferior decentering of the humeral head, decreased scapular lateral rotation and increased scapular internal rotation.

CONCLUSION

The clinical or instrumented assessment of the shoulder complex with a degenerative pathology must include the analysis of scapula-clavicle and trunk movements complementing the GH assessment. Depending on the individual clinical case, scapular dyskinesis could be the cause or the consequence of the shoulder degenerative pathology. For most degenerative shoulder pathologies, the rehabilitation program should take into account the whole shoulder complex and include first a scapular and trunk postural-correcting strategy, then scapulothoracic muscle rehabilitation (especially serratus anterior and trapezius inferior and medium parts) and finally neuromotor techniques to recover appropriate upper-limb kinematic schemas for daily and/or sports activities.

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.

Shoulder Strength Requirements for Upper Limb Functional Tasks: Do Age and Rotator Cuff Tear Status Matter?

Understanding upper limb strength requirements for daily tasks is imperative for early detection of strength loss that may progress to disability due to age or rotator cuff tear. We quantified shoulder strength requirements for 5 upper limb tasks performed by 3 groups: uninjured young adults and older adults, and older adults with a degenerative supraspinatus tear prior to repair. Musculoskeletal models were developed for each group representing age, sex, and tear-related strength losses. Percentage of available strength used was quantified for the subset of tasks requiring the largest amount of shoulder strength. Significant differences in strength requirements existed across tasks: upward reach 105° required the largest average strength; axilla wash required the largest peak strength. However, there were limited differences across participant groups. Older adults with and without a tear used a larger percentage of their shoulder elevation (p < .001, p < .001) and external rotation (p < .001, p = .017) strength than the young adults, respectively. Presence of a tear significantly increased percentage of internal rotation strength compared to young (p < .001) and uninjured older adults (p = .008). Marked differences in strength demand across tasks indicate the need for evaluating a diversity of functional tasks to effectively detect early strength loss, which may lead to disability.

In vivo kinematic analysis of the glenohumeral joint during dynamic full axial rotation and scapular plane full abduction in healthy shoulders

PURPOSE

The purpose of this study was to evaluate the kinematics of healthy shoulders during dynamic full axial rotation and scapular plane full abduction using three-dimensional (3D)-to-two-dimensional (2D) model-to-image registration techniques.

METHODS

Dynamic glenohumeral kinematics during axial rotation and scapular plane abduction were analysed in 10 healthy participants. Continuous radiographic images of axial rotation and scapular plane abduction were taken using a flat panel radiographic detector. The participants received a computed tomography scan to generate virtual digitally reconstructed radiographs. The density-based digitally reconstructed radiographs were then compared with the serial radiographic images acquired using image correlations. These 3D-to-2D model-to-image registration techniques determined the 3D positions and orientations of the humerus and scapula during dynamic full axial rotation and scapular plane full abduction.

RESULTS

The humeral head centre translated an average of 2.5 ± 3.1 mm posteriorly, and 1.4 ± 1.0 mm superiorly in the early phase, then an average of 2.0 ± 0.8 mm inferiorly in the late phase during external rotation motion. The glenohumeral external rotation angle had a significant effect on the anterior/posterior (A/P) and superior/inferior (S/I) translation of the humeral head centre (both p < 0.05). 33.6 ± 15.6° of glenohumeral external rotation occurred during scapular plane abduction. The humeral head centre translated an average of 0.6 ± 0.9 mm superiorly in the early phase, then 1.7 ± 2.6 mm inferiorly in the late phase, and translated an average of 0.4 ± 0.5 mm medially in the early phase, then 1.6 ± 1.0 mm laterally in the late phase during scapular plane abduction. The humeral abduction angle had a significant effect on the S/I and lateral/medial (L/M) translation of the humeral head centre (both p < 0.05).

CONCLUSION

This study investigated 3D translations of the humerus relative to the scapula: during scapular plane full abduction, the humerus rotated 33.6° externally relative to the scapula, and during external rotation motion in the adducted position, the humeral head centre translated an average of 2.5 mm posteriorly. Kinematic data will provide important insights into evaluating the kinematics of pathological shoulders. For clinical relevance, quantitative assessment of dynamic healthy shoulder kinematics might be a physiological indicator for the assessment of pathological shoulders.

Shoulder horizontal abduction stretching effectively increases shear elastic modulus of pectoralis minor muscle

BACKGROUND

Stretching maneuvers for the pectoralis minor muscle, which involve shoulder horizontal abduction or scapular retraction, are performed in clinical and sports settings because the tightness of this muscle may contribute to scapular dyskinesis. The effectiveness of stretching maneuvers for the pectoralis minor muscle is unclear in vivo. The purpose of this study was to verify the effectiveness of stretching maneuvers for the pectoralis minor muscle in vivo using ultrasonic shear wave elastography.

METHODS

Eighteen healthy men participated in this study. Elongation of the pectoralis minor muscle was measured for 3 stretching maneuvers (shoulder flexion, shoulder horizontal abduction, and scapular retraction) at 3 shoulder elevation angles (30°, 90°, and 150°). The shear elastic modulus, used as the index of muscle elongation, was computed using ultrasonic shear wave elastography for the 9 aforementioned stretching maneuver-angle combinations.

RESULTS

The shear elastic modulus was highest in horizontal abduction at 150°, followed by horizontal abduction at 90°, horizontal abduction at 30°, scapular retraction at 30°, scapular retraction at 90°, scapular retraction at 150°, flexion at 150°, flexion at 90°, and flexion at 30°. The shear elastic moduli of horizontal abduction at 90° and horizontal abduction at 150° were significantly higher than those of other stretching maneuvers. There was no significant difference between horizontal abduction at 90° and horizontal abduction at 150°.

CONCLUSIONS

This study determined that shoulder horizontal abduction at an elevation of 90° and horizontal abduction at an elevation of 150° were the most effective stretching maneuvers for the pectoralis minor muscle in vivo.

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.