Stabilizing characteristics of rotator cuff muscles: a systematic review

Application of multidisciplinary team-based integrated traditional Chinese medicine and Western medicine in rotator cuff injury patients undergoing arthroscopic surgery

BACKGROUND

Arthroscopic rotator cuff repair is a common surgical treatment for rotator cuff injuries (RCIs). Although this procedure has certain clinical advantages, it requires rehabilitation management interventions to ensure therapeutic efficacy.

AIM

To investigate the effect of integrated traditional Chinese medicine and Western medicine (TCM-WM) under the multidisciplinary team (MDT) model on the postoperative recovery of patients undergoing arthroscopic surgery for RCIs.

METHODS

This study enrolled 100 patients who underwent arthroscopic rotator cuff repair for RCIs at the Seventh People's Hospital of Shanghai University of Traditional Chinese Medicine between June 2021 and May 2024. They were divided into a control group (n = 48) that received routine rehabilitation treatment and an experimental group (n = 52) that received TCM-WM under the MDT model (e.g., acupuncture, TCM traumatology and orthopedics, and rehabilitation). The results of the Constant-Murley Shoulder Score (CMS), Visual Analogue Scale (VAS), Shoulder Pain and Disability Index (SPADI), muscular strength evaluation, and shoulder range of motion (ROM) assessments were analyzed.

RESULTS

After treatment, the experimental group showed significantly higher CMS scores in terms of pain, functional activity, shoulder joint mobility, and muscular strength than the baseline and those of the control group. The experimental group also exhibited significantly lower VAS and SPADI scores than the baseline and those of the control group. In addition, the experimental group showed significantly enhanced muscular strength (forward flexor and external and internal rotator muscles) and shoulder ROM (forward flexion, abduction, and lateral abduction) after treatment compared with the control group.

CONCLUSION

TCM-WM under the MDT model improved shoulder joint function, relieved postoperative pain, promoted postoperative functional recovery, and facilitated the recovery of muscular strength and shoulder ROM in patients with RCIs who underwent arthroscopic rotator cuff repair.

Altered Cervical Spine Position Results in Decreased Eccentric Shoulder Rotation Strength

Overhead athletes require strenuous shoulder activity in nonneutral cervical spine positions to eccentrically decelerate the throwing/striking arm following ball release/contact. We therefore aimed to compare eccentric shoulder rotation strength through a 90° arc between neutral and rotated positions. Fifty-two participants (19 M, 34 F 170±10 cm; 73±18 kg, 21.9±2.9 years) without shoulder or cervical spine pathology participated. Isokinetic eccentric shoulder rotation strength was measured through a 90° arc with the shoulder elevated 90° in frontal plane (frontal plane), and 45° anterior to the frontal plane (scapular plane) in neutral and rotated cervical spine positions. Cervical spine position was obtained by instructing participants to maximally rotate their respective side. Frontal plane eccentric external rotated strength differed between neutral and contralaterally positions in the first 10° of the motion, near forearm vertical (p+=+0.029). Internal rotation strength differed between neutral and contralaterally rotated positions from 55-60° external rotation (p+=+0.004). Scapular plane eccentric external rotation differed between cervical positions between 21-67° shoulder external rotation (p<0.001). Scapular plane internal rotation strength differed between cervical positions between 22-60° shoulder external rotation (p<0.001). In populations requiring strenuous use of their shoulders in altered cervical spine positions, sports medicine clinicians should consider including strength testing that reflects the functional positions of their patients during an orthopedic examination.

Stabilizing Mechanisms in Patients Treated Using Hill-Sachs Remplissage With Bankart Repair in Abduction-External Rotation Position

BACKGROUND

Hill-Sachs lesion (HSL) remplissage with Bankart repair (RMBR) provides a minimally invasive solution for treating HSLs and glenoid bone defects of <25%. The infraspinatus tendon is inserted into the HSL during the remplissage process, causing the infraspinatus to shift medially, leading to an unknown effect on glenohumeral alignment during the resting abduction-external rotation (ABER) and muscle-active states.

PURPOSE/HYPOTHESIS

The purpose of this study was to evaluate the possible check-rein effect and muscle-active control in stabilizing the glenohumeral joint after RMBR in vivo. We hypothesized that the check-rein effect and active control would stabilize the glenohumeral joint in the ABER position in patients after RMBR.

STUDY DESIGN

Controlled laboratory study.

METHODS

We included 42 participants-22 patients in group A who met the inclusion criteria after RMBR and 20 healthy participants in group B without shoulder laxity. Three-dimensional magnetic resonance imaging was performed to analyze the alignment relationship of the glenohumeral joint with and without muscular activity. Ultrasonic shear wave elastography was used to evaluate the elastic properties of the anterior capsule covered with the anterior bands of the inferior glenohumeral ligament.

RESULTS

Patients who underwent RMBR demonstrated more posterior (-1.81 ± 1.19 mm vs -0.76 ± 1.25 mm; P = .008) and inferior (-1.05 ± 0.62 mm vs -0.45 ± 0.48 mm; P = .001) shifts of the humeral head rotation center and less anterior capsular elasticity (70.07 ± 22.60 kPa vs 84.01 ± 14.08 kPa; P = .023) than healthy participants in the resting ABER state. More posterior (-3.17 ± 0.84 mm vs -1.81 ± 1.19 mm; P < .001) and less-inferior (-0.34 ± 0.56 mm vs -1.05 ± 0.62 mm; P < .001) shifts of the humeral head rotation center and less anterior capsular elasticity (36.57 ± 13.89 kPa vs 70.07 ± 22.60 kPa; P < .001) were observed in the operative shoulder during muscle-active ABER than in resting ABER states.

CONCLUSION

The check-rein effect and muscle-active control act as stabilizing mechanisms in RMBR during the ABER position.

CLINICAL RELEVANCE

Stabilizing mechanisms in RMBR during the ABER position include the check-rein effect and muscle-active control.

To allow or avoid pain during shoulder rehabilitation exercises for patients with chronic rotator cuff tendinopathy-Study protocol for a randomized controlled trial (the PASE trial)

BACKGROUND

Rotator cuff (RC) tendinopathy is the most reported shoulder disorder in the general population with highest prevalence in overhead athletes and adult working-age population. A growing body of evidence support exercise therapy as an effective intervention, but to date there are no prospective randomized controlled trials addressing pain as an intervention variable.

METHODS

A single-site, prospective, pragmatic, assessor-blinded randomized controlled superiority trial. Eighty-four patients aged 18-55 years with chronic (symptom duration over 3 months) RC tendinopathy are randomized 1:1 to receive shoulder exercise during which pain is either allowed or avoided. The intervention period lasts 26 weeks. During that period, participants in both groups are offered 8 individual on-site sessions with an assigned sports physiotherapist. Participants perform home exercises and are provided with a pain and exercise logbook and asked to report completed home-based exercise sessions and reasons for not completing sessions (pain or other reasons). Patients are also asked to report load and the number of sets and repetitions per sets for each exercise session. The logbooks are collected continuously throughout the intervention period. The primary and secondary outcomes are obtained at baseline, 6 weeks, 26 weeks, and 1 year after baseline. The primary outcome is patient-reported pain and disability using the Shoulder PAin and Disability Index (SPADI). Secondary outcomes are patient-reported pain and disability using Disability Arm Shoulder and Hand short-form (Quick DASH), and shoulder pain using Numeric Pain Rating Scale. Objective outcomes are shoulder range of motion, isometric shoulder muscle strength, pain sensitivity, working ability, and structural changes in the supraspinatus tendon and muscle using ultrasound.

DISCUSSION

The results of this study will contribute knowledge about the treatment strategies for patients with RC tendinopathy and help physiotherapists in clinical decision-making. This is the first randomized controlled trial comparing the effects of allowing pain versus avoiding pain during shoulder exercises in patients with chronic RC tendinopathy. If tolerating pain during and after exercise proves to be effective, it will potentially expand our understanding of "exercising into pain" for this patient group, as there is currently no consensus.

TRIAL REGISTRATION

ClinicalTrials.gov NCT05124769. Registered on August 11, 2021.

Movement pattern and upper extremity muscle activation during fast and slow continuous steering movement

Continuous steering movement (CSM) is an essential component of the upper extremity (UE) task during vehicle driving, and could be a suitable candidate for multi-joint rehabilitation programs for patients with UE disabilities. This study aims to evaluate the UE muscle activation during CSM and how the rotating speed and direction affect CSM's kinematic and kinetic performance. Surface electromyography (EMG), hand contact information, and steering torque were measured under fast (180°/s) and slow (60°/s) constant-velocity CSM to reveal the activation of shoulder and elbow muscles, temporal characteristics, and force exertion during the stance and swing phases of a CSM cycle. Data from 24 normal young adults showed that shorter contact duration but higher force exertion occurred in the hand moving in an outward steering direction during only fast CSM in either the clockwise (CW) or counterclockwise (CCW) direction. During a steering cycle (either fast or slow speed), the triceps brachii, sternal part of the pectoralis major (PS), and posterior deltoid play major roles in generating steering torque in the CW direction of the CSM. In contrast, the PS, clavicular part of the pectoralis major (PC), and anterior deltoid (AD) largely contribute to torque generation during the CCW CSM. During the swing phase of CSM, AD, PC, and PS are the major muscles that move the hand for the next grasping of the steering wheel in all four conditions. Using the mean activation profiles of the major contributing muscles, the functional roles of these elbow and shoulder muscles were analyzed and are discussed herein. These findings help us to further understand the activation patterns of UE muscles and the kinematic and kinetic changes during two rotating directions and two speeds of CSM, and suggest important implications for future practice in clinical training.

Altered Cervical Spine Position Results in Decreased Shoulder Rotation Strength

BACKGROUND

Strength testing of shoulder rotation is commonly used in clinical examinations of the shoulder. People prone to shoulder injury, such as overhead athletes and manual trade workers, place their shoulders under tremendous amounts of stress when the cervical spine is in nonneutral positions. If these nonneutral cervical spine positions result in decreased shoulder strength, it may help explain the etiology of the high prevalence of shoulder injuries in these populations. Given standard clinical strength assessments are performed with a neutral cervical spine, an investigation into the effects of cervical spine rotation is warranted.

QUESTIONS/PURPOSES

We sought to compare isokinetic shoulder rotation strength while in a neutral position with rotated cervical spine positions, specifically (1) with the cervical spine rotated contralaterally with the shoulder elevated in the frontal plane and (2) with the cervical spine rotated ipsilaterally and the shoulder elevated in the scapular plane.

METHODS

A convenience sample of 52 individuals (height 170 ± 10 cm; weight 73 ± 18 kg, age 21 ± 2 years; 18 males, 34 females), without shoulder or cervical spine pathology participated in this study. Participants were screened for eligibility via questionnaire. Concentric shoulder internal and external rotation torque was measured through a 90° arc on an isokinetic dynamometer with the shoulder elevated 90° in the frontal plane, and again 45° anterior to the frontal plane (scapular plane). Two repetitions were performed in a single testing session with the participant's cervical spine in neutral in both planes, maximally rotated contralaterally in the frontal plane, and maximally rotated ipsilaterally with the shoulder in the scapular plane; the second repetition was used for analysis. The testing order was randomized. Data were imported into a platform for statistical parametric mapping analysis (a technique that allows data from the entire arc of motion to be compared with data from another arc to identify differences in the wave form) to compare strength between positions throughout 90° arc of motion.

RESULTS

Rotating the cervical spine contralaterally with the shoulder in the frontal plane resulted in a decrease in external (2.24 Nm or 12% average difference; p < 0.001) and internal (2.22 Nm or a 6% average difference; p = 0.02) rotation strength with the forearm within 15° and 20° of the vertical position. Rotating the cervical spine ipsilaterally with the shoulder in the scapular plane resulted in a decrease in external rotation strength (1.27 Nm or a 6% average difference; p < 0.001) throughout nearly all the motion, with peaks approximately 20° and 60° from the horizontal position, and internal rotation strength (1.78 Nm or 5% average difference; p < 0.001) the last 60° towards the horizontal position.

CONCLUSION

Patient populations who require strenuous use of their shoulders in altered cervical spine positions may be at increased risk for injury from decreased shoulder rotator strength.

CLINICAL RELEVANCE

Clinicians should assess shoulder strength in the position the patient requires to use their shoulder because cervical spine position may cause weakness that would be missed in standard testing positions.

The Subscapularis Muscle: A Proposed Classification System

Background

On the basis of the available literature, we proposed the hypothesis that the number of muscle bellies is morphologically constant. The main purpose of this study was to examine the morphological variability of the SM and to create a new classification of it based on number of muscle bellies.

Methods

Sixty-six adult cadavers of Central European population (45 females, 21 males) were obtained and fixed in 10% formalin before examination.

Results

The SM was found in all 66 specimens (45 females, 21 males, 31 left and 35 right sides). After meticulous dissection, we distinguished nine types on the basis of number of bellies. Type I was characterized by single belly and occurred in 1.5%. Type II had a double belly and was present in 3%. Type III, the most common type, occurring in almost 32% of the studied population, had three bellies. The frequency of type IV, characterized by four bellies, was also high, just over 30%. The following types were less frequent: type V with five bellies (18.2%), type VI with six bellies (7.6%), type VII with seven bellies (3%), type VIII with eight bellies (1.5%), and type IX with nine bellies (3%). All of the types had origin on the anterior surface of the scapula.

Conclusions

The SM is morphologically variable in the number of its bellies. Evolutionary changes are probably the reason. The most common type was the SM with three bellies, in line with Larson's model of the division of the SM into three parts. Subsequent studies should be carried out based on MRI or ultrasonography examination to confirm if it is possible to show all types (presented in this study) among group of patients during MRI.

Physiotherapy Rehabilitation in Subjects Diagnosed with Subacromial Impingement Syndrome Does Not Normalize Periscapular and Rotator Cuff Muscle Onset Time of Activation

Clinicians suggest that rehabilitation of Subacromial Impingement Syndrome (SIS) should target improving movement patterns to ensure better clinical outcomes. Understanding changes in onset time of activation patterns and associated changes in clinical outcomes could improve our understanding of rehabilitation strategies. In this prospective longitudinal study, we examined neuromuscular firing patterns and clinical features before and after a standardized physiotherapy program in subjects diagnosed with SIS. Electromyography (EMG) recordings of eleven shoulder muscles were taken at the initial and discharge consultation in 34 male volunteers diagnosed with SIS. EMG recording was performed during flexion, scaption, and abduction at slow, medium, and fast speeds with a loaded (3 kg) and unloaded arm, as well as rotational motion, rotational strength, pain, and shoulder function. Completion of standardized shoulder physiotherapy program for SIS resulted in improvements in clinical outcomes. Resulted showed inconsistent differences of onset time of activation mainly in some of the periscapular muscles for all movements. No differences were seen on the EMG recordings for rotator cuff muscles. Differences in range of motion, strength and function were shown. Despite some changes in onset time of activation, this study was not able to demonstrate consistent changes of onset time of activation of the periscapular and rotator cuff muscles.

Glenohumeral joint and muscles functions during a lifting task

The mobility of the healthy shoulder depends on complex interactions between the muscles spanning its glenohumeral joint. These interactions ensure the stability of this joint. While previous studies emphasized the complexity of the glenohumeral stability, it is still not clear how the kinematics and muscles interact and adapt to ensure a healthy function of the glenohumeral joint. To understand the function of each muscle and degree of freedom of the glenohumeral joint in executing an above-the shoulder box handling task while ensuring stability, we adapted an index-based approach previously used to characterize the functions of the lower limb joints and muscles during locomotion. Forty participants lifted two loads (6 Vs. 12 kg) from hip to eye level. We computed the mechanical powers of the glenohumeral joint and its spanning muscles. We characterized the function of muscles and degrees of freedom using function indices. The function of the glenohumeral joint underlined its compliancy and design for a large range of motion, while the rotator cuff indices emphasized their stabilizing function. The overall muscle functions underlined the complexity of the glenohumeral stability that goes beyond the rotator cuff. Additionally, the load increase was compensated with changes in the functions that seem to favor joint stability. The implemented approach represents a synthetized tool that could quantify the glenohumeral joint and muscles behavior during tridimensional upper limb tasks, which might offer additional insight into motor control strategies and functional alterations related to pathologies or external parameters (e.g., load).

Line Hops and Side Hold Rotation Tests Load Both Anterior and Posterior Shoulder: A Biomechanical Study

BACKGROUND

Clinical tests should replicate the stressful positions encountered during sport participation. Evaluating the kinetic and electromyographical demands of clinical tests enables clinicians to choose appropriate tests for specific sports.

PURPOSE

To describe the shoulder forces and muscle activation levels during closed chain functional tests of Line Hops (LH) and Side Hold Rotation (SHR).

STUDY DESIGN

Descriptive biomechanical study.

METHODS

Ten asymptomatic participants were examined in a university laboratory. Two functional tests were evaluated using three-dimensional video analysis and electromyography to measure shoulder forces, moments, and muscular activity levels.

RESULTS

SHR produced a peak average posterior translation force of 4.84 N/kg (CI95 4.32-5.36N/kg) and a peak average anterior translational force of 1.57 N/kg (CI95 1.10-2.01N/kg). High levels of serratus anterior (98% maximum voluntary isometric contraction (MVIC) and infraspinatus (52 %MVIC) were recorded during SHR. LH produced a posterior translational force of 4.25 N/kg (CI95 3.44-5.06N/kg). High levels of serratus anterior (105 %MVIC) and infraspinatus (87 %MVIC) were recorded during the push off phase of this activity.

CONCLUSIONS

LH and SHR placed large posterior translational forces that approached half of a person's bodyweight on shoulder structures. SHR produced an anterior translation force at extremes of horizontal abduction placing approximately 18% of bodyweight on shoulder structures. The LH test required the serratus anterior to provide power to push the upper torso of the ground while both the serratus and the infraspinatus provides scapular and humeral stability, respectively.

LEVEL OF EVIDENCE

4: Case series.

Effect of rotator cuff muscle activation on glenohumeral kinematics: A cadaveric study

Healthy shoulder function requires the coordination of the rotator cuff muscles to maintain the humeral head's position in the glenoid. While glenohumeral stability has been studied in various settings, few studies have characterized the effect of dynamic rotator cuff muscle loading on glenohumeral translation during shoulder motion. We hypothesize that dynamic rotator cuff muscle activation decreases joint translation during continuous passive abduction of the humerus in a cadaveric model of scapular plane glenohumeral abduction. The effect of different rotator cuff muscle activity on glenohumeral translation was assessed using a validated shoulder testing system. The Dynamic Load profile is a novel approach, based on musculoskeletal modeling of human subject motion. Passive humeral elevation in the scapular plane was applied via the testing system arm, while the rotator cuff muscles were activated according to the specified force profiles using stepper motors and a proportional control feedback loop. Glenohumeral translation was defined according to the International Society of Biomechanics. The Dynamic load profile minimized superior translation of the humeral head relative to the conventional loading profiles. The total magnitude of translation was not significantly different (0.805) among the loading profiles suggesting that the compressive forces from the rotator cuff primarily alter the direction of humeral head translation, not the magnitude. Rotator cuff muscle loading is an important element of cadaveric shoulder studies that must be considered to accurately simulate glenohumeral motion. A rotator cuff muscle activity profile based on human subject muscle activity reduces superior glenohumeral translation when compared to previous RC loading profiles.

The supporting role of the teres major muscle, an additional component in glenohumeral stability? An anatomical and radiological study

Muscle coordination plays an important role in glenohumeral stability. The rotator cuff and the long head of the biceps are considered the primary dynamic stabilizers muscles. However, the fact that a subgroup of patients with a massive tear in the rotator cuff were able to keep a normal function, should make us question this traditional view. We hypothesize that the teres major which is also a monoarticular scapulohumeral muscle, although it is not part of the conjoined tendon of the rotator cuff, can play a role in glenohumeral stability by a direct support of the humeral head generated by the particular posteroanterior location of this muscle under the humeral head and which, as far as we know, has not been written up previously. This particular effect could appear while the arm is being lifted and the humeral head could be leaning on against the teres major muscle belly underneath it. An anatomical a radiological study was carried out to substantiate our hypothesis. Two cadaver specimens were used for the anatomical study. Frist body was studied through conventional dissection. The second body was analysed through sectional anatomy. Then a radiological study was carried out using magnetic resonance imaging in a healthy male volunteer. Both anatomically and radiologically, the anteroinferior surface of the humeral head was showed firmly resting against the muscle belly of the teres major, to the point of misshaping it from 110 degrees of arm elevation with external rotation. The specific contribution of this effect to the glenohumeral stability needs to be confirmed by further studies and can help us to prevent the high incidence of glenohumeral dislocations.

Are Patients Who Undergo the Latarjet Procedure Ready to Return to Play at 6 Months? A Multicenter Orthopaedic Outcomes Network (MOON) Shoulder Group Cohort Study

BACKGROUND

The Latarjet procedure is growing in popularity for treating athletes with recurrent anterior shoulder instability, largely because of the high recurrence rate of arthroscopic stabilization, particularly among contact athletes with bone loss.

PURPOSE

(1) To evaluate return of strength and range of motion (ROM) 6 months after the Latarjet procedure and (2) to determine risk factors for failure to achieve return-to-play (RTP) criteria at 6 months.

STUDY DESIGN

Case-control study; Level of evidence, 3.

METHODS

A total of 65 athletes (83% contact sports, 37% overhead sports; mean ± SD age, 24.5 ± 8.2 years; 59 male, 6 female) who enrolled in a prospective multicenter study underwent the Latarjet procedure for anterior instability (29% as primary procedure for instability, 71% for failed prior stabilization procedure). Strength and ROM were assessed preoperatively and 6 months after surgery. RTP criteria were defined as return to baseline strength and <20° side-to-side ROM deficits in all planes. The independent likelihood of achieving strength and motion RTP criteria at 6 months was assessed through multivariate logistic regression modeling with adjustment as needed for age, sex, subscapularis split versus tenotomy, preoperative strength/motion, percentage bone loss, number of prior dislocations, preoperative subjective shoulder function (American Shoulder and Elbow Surgeons and Western Ontario Shoulder Instability Index percentage), and participation in contact versus overhead sports.

RESULTS

Of the patients, 55% failed to meet ≥1 RTP criteria: 6% failed for persistent weakness and 51% for ≥20° side-to-side loss of motion. There was no difference in failure to achieve RTP criteria at 6 months between subscapularis split (57%) versus tenotomy (47%) (P = .49). Independent risk factors for failure to achieve either strength or ROM criteria were preoperative American Shoulder and Elbow Surgeons scores (per 10-point decrease: adjusted odds ratio [aOR], 1.61; 95% CI, 1.14-2.43; P = .006), Western Ontario Shoulder Instability Index percentage (per 10% decrease: aOR, 0.61; 95% CI, 0.38-0.92; P = .01), and a preoperative side-to-side ROM deficit ≥20° in any plane (aOR, 5.01; 95% CI, 1.42-21.5; P = .01) or deficits in external rotation at 90° of abduction (per 10° increased deficit: aOR, 1.64; 95% CI, 1.06-2.88; P = .02).

CONCLUSION

A large percentage of athletes fail to achieve full strength and ROM 6 months after the Latarjet procedure. Greater preoperative stiffness and subjective disability are risk factors for failure to meet ROM or strength RTP criteria.

Anatomy of the Subscapularis: A Review

The subscapularis is the largest and most powerful muscle of the rotator cuff. Occupying the vast majority of the subscapular fossa, it is the only internal rotator of the rotator cuff. The subscapularis innervation is classically taught as a dual innervation of 1 upper subscapular and 1 lower subscapular nerve arising from the posterior cord of the brachial plexus. However, there is a large amount of research that suggests there is significant variance in the innervation of the muscle from multiple upper subscapular nerves to multiple lower subscapular nerves arising from various portions of the plexus. Although one of the main functions of the subscapularis is to internally rotate the humerus, there is substantial evidence that displays its importance in glenohumeral stability as well. The insertion of the subscapularis is both tendinous as well as muscular. The more superior tendinous portion inserts on the lesser tuberosity while the more muscular portion inserts inferior to the less tuberosity. The medial to lateral spread of the insertion is quite variable ranging from only on the lesser tuberosity to merging with fibers from the supraspinatus. Understanding the anatomy of the subscapularis improves subscapularis management during shoulder arthroplasty including techniques for takedown, release, and repair.

Shoulder muscle onset timing during clinical assessment movements is the same in elite handball players as non-athletes: Implications for clinical assessment

OBJECTIVES

This study examines neuromuscular firing patterns in overhead athletes and non-athletes of the periscapular, prime-moving, and rotator cuff muscles during "clinical" cardinal plane physiological movements.

DESIGN

Cohort prospective study.

SETTING

EMG recordings were taken of the periscapular, prime-moving, and rotator cuff muscles during flexion, scaption, and abduction performed at fast, medium, and slow speeds with a loaded (3 kg) and unloaded arm.

PARTICIPANTS

14 Handball players and 20 non-athletes. Differences in firing patterns between groups were analyzed by fitting mixed linear models with random intercepts per subject, and fixed factors for group, muscle, movement type, speed, and load.

MAIN OUTCOME MEASURES

No difference in timing of activation was seen between the professional athletes and non-athletes.

RESULTS

Speed and load appear to independently vary muscle activation timing in a non-intuitive manner in both athletes and non-athletes. Onset timing of periscapular, prime movers and rotator cuff muscles are prior to movement in all scenarios studied, with rotator cuff muscles firing last.

CONCLUSIONS

Onset activation patterns in overhead athletes are not different to non-athletes during cardinal plane movements.

A Systematic Summary of Systematic Reviews on the Topic of the Rotator Cuff

BACKGROUND

The number of systematic reviews and meta-analyses published on the rotator cuff (RC) has increased markedly.

PURPOSE

To quantify the number of systematic reviews and meta-analyses published on the RC and to provide a qualitative summary of the literature.

STUDY DESIGN

Systematic review; Level of evidence, 4.

METHODS

A systematic search for all systematic reviews and meta-analyses pertaining to the RC published between January 2007 and September 2017 was performed with PubMed, MEDLINE, and the Cochrane Database of Systematic Reviews. Narrative reviews and non-English language articles were excluded.

RESULTS

A total of 1078 articles were found, of which 196 met the inclusion criteria. Included articles were summarized and divided into 15 topics: anatomy and function, histology and genetics, diagnosis, epidemiology, athletes, nonoperative versus operative treatment, surgical repair methods, concomitant conditions and surgical procedures, RC tears after total shoulder arthroplasty, biological augmentation, postoperative rehabilitation, outcomes and complications, patient-reported outcome measures, cost-effectiveness of RC repair, and quality of randomized controlled trials.

CONCLUSION

A qualitative summary of the systematic reviews and meta-analyses published on the RC can provide surgeons with a single source of the most current literature.

Effect of glenohumeral stabilization exercises combined with scapular stabilization on shoulder function in patients with shoulder pain: A randomized controlled experimenter-blinded study

BACKGROUND

Shoulder stabilization exercises consisted of a glenohumeral stabilization and scapular stabilization. No studies have been assessed the superiority of shoulder stabilization until now.

OBJECTIVE

To compare the effect of a glenohumeral stabilization exercise (GSE) combined with a scapular stabilization exercise (SSE) on changes in shoulder function in patients with shoulder painMETHODS: Shoulder stability, scapular alignment, pain, muscle power, and range of motion (ROM) were measured before and after the intervention in both groups.

RESULTS

Forty subjects with shoulder pain were randomly assigned to an experimental or control group. GSE in the experimental group (n= 20) resulted in significantly better shoulder stability (P= 0.020, from 9.00 ± 6.90 score to 14.25 ± 8.58) and pain intensity (P= 0.042, 7.40 ± 2.44 score to 4.60 ± 2.06) compared to SSE in the controls (n= 20). However, no significant effects were observed for scapular symmetric alignment including the angles of inferior scapular distance (P= 0.555) and inferior scapular height difference (P= 0.770), muscle power including shoulder flexion (P= 0.942) and shoulder abduction (P= 0.551), or ROM including shoulder flexion (P= 0.852) and shoulder abduction (P= 0.622).

CONCLUSION

This study suggests that GSE positively affects shoulder stability and pain control in patients with shoulder pain, probably through a centralization effect on the shoulder mechanism.

Return to Play Criteria Following Surgical Stabilization for Traumatic Anterior Shoulder Instability: A Systematic Review

PURPOSE

To identify and describe in the existing literature any criteria used for return to play following surgical stabilization for traumatic, anterior shoulder instability.

METHODS

We performed a systematic review evaluating surgical stabilization for primary traumatic anterior shoulder instability in skeletally mature patients with a minimum of 1-year follow-up using Level I to IV studies in PubMed and EMBASE from January 1994 to January 2017.

RESULTS

Fifty-eight studies with at least 1 explicitly stated criterion for return to play were identified from a review of more than 5,100 published articles. Seven different categories of return to play criteria were identified, the most common of which were time from surgery (89.6%), strength (18.9%), and range of motion (13.8%). Pain, stability, proprioception, and postoperative radiographic evaluation were also used. As hypothesized, in 75.8% of the included studies (44/58), time was the only criterion explicitly used. The most commonly used time for return to play was 6 months.

CONCLUSIONS

This systematic review identifies 7 criteria that have been used in the available literature to determine when patients are ready to return to play; however, consistent with our hypothesis, 75% of studies used time from surgery as the sole listed criterion, with the most commonly used time point of 6 months postoperative. All of these criteria can be used in future research to develop a comprehensive checklist of functional criteria in hopes of reducing recurrent injury.

LEVEL OF EVIDENCE

Level IV, systematic review.

Evolution of muscular fatigue in periscapular and rotator cuff muscles during isokinetic shoulder rotations

To this day, how shoulder muscles react to a strong fatigue stimulus during dynamic shoulder rotations remains unknown. The aims of this study were to assess the effect of repeated maximal internal-external isokinetic shoulder rotations on shoulder strength and muscle activity. Twenty-four individuals completed a 50-repetition fatiguing isokinetic protocol while electromyography was recorded on eleven muscles of the shoulder girdle. Time-frequency transformation and an ANOVA model using statistical parametric mapping methods were used to analyze shifts in instantaneous median frequency (MDF) between each 10-repetition Blocks. Peak torques decreased in both internal and external rotation (P < 0.01) by 24.8% on average which indicated the presence of fatigue. Significant decrease in MDF (P < 0.01) was observed for pectoralis, middle deltoid, upper, middle and lower trapezius, infraspinatus and subscapularis muscles. The observed fatigue to the periscapular and rotator cuff muscles suggests that shoulder stability could be compromised during repeated shoulder rotations, which could underlie the increased risk of scapular dyskinesis and shoulder impingement during fatiguing tasks. The present study provides a deeper understanding on the manifestations of fatigue within muscles of the shoulder girdle and the results could be applied toward improvements in athlete shoulder injury prevention and rehabilitation programs.

Muscle function in glenohumeral joint stability during lifting task

Ensuring glenohumeral stability during repetitive lifting tasks is a key factor to reduce the risk of shoulder injuries. Nevertheless, the literature reveals some lack concerning the assessment of the muscles that ensure glenohumeral stability during specific lifting tasks. Therefore, the purpose of this study was to assess the stabilization function of shoulder muscles during a lifting task. Kinematics and muscle electromyograms (n = 9) were recorded from 13 healthy adults during a bi-manual lifting task performed from the hip to the shoulder level. A generic upper-limb OpenSim model was implemented to simulate glenohumeral stability and instability by performing static optimizations with and without glenohumeral stability constraints. This procedure enabled to compute the level of shoulder muscle activity and forces in the two conditions. Without the stability constraint, the simulated movement was unstable during 74%±16% of the time. The force of the supraspinatus was significantly increased of 107% (p<0.002) when the glenohumeral stability constraint was implemented. The increased supraspinatus force led to greater compressive force (p<0.001) and smaller shear force (p<0.001), which contributed to improved glenohumeral stability. It was concluded that the supraspinatus may be the main contributor to glenohumeral stability during lifting task.

Muscle recruitment patterns of the subscapularis, serratus anterior and other shoulder girdle muscles during isokinetic internal and external rotations

The aims of this study were to investigate the differences in peak muscle activity and recruitment patterns during high- and low-velocity, concentric and eccentric, internal and external isokinetic shoulder rotations. Electromyographic activity of the rotator cuff and eight superficial muscles of the shoulder girdle was recorded on 25 healthy adults during isokinetic internal and external shoulder rotation at 60°/s and 240°/s. Peak muscle activity, electromyographic envelopes and peak isokinetic moments were analyzed using three-factor ANOVA and statistical parametric mapping. The subscapularis and serratus anterior showed moderate to high peak activity levels during each conditions, while the middle and posterior deltoids, upper, middle and lower trapezius, infraspinatus and supraspinatus showed higher peak activity levels during external rotations (+36.5% of maximum voluntary activation (MVA)). The pectoralis major and latissimus dorsi were more active during internal rotations (+40% of MVA). Only middle trapezius and pectoralis major electromyographic activity decreased with increasing velocity. Peak muscle activity was similar or lower during eccentric contractions, although the peak isokinetic moment increased by 35% on average. The subscapularis and serratus anterior appear to be important stabilizers of the glenohumeral joint and scapula. Isokinetic eccentric training at high velocities may allow for faster recruitment of the shoulder girdle muscles, which could improve joint stability during shoulder internal and external rotations.

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

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

A larger critical shoulder angle requires more rotator cuff activity to preserve joint stability

Shoulders with rotator cuff tears (RCT) tears are associated with significantly larger critical shoulder angles (CSA) (RCT CSA = 38.2°) than shoulders without RCT (CSA = 32.9°). We hypothesized that larger CSAs increase the ratio of glenohumeral joint shear to joint compression forces, requiring substantially increased compensatory supraspinatus loads to stabilize the arm in abduction. A previously established three dimensional (3D) finite element (FE) model was used. Two acromion shapes mimicked the mean CSA of 38.2° found in patients with RCT and that of a normal CSA (32.9°). In a first step, the moment arms for each muscle segment were obtained for 21 different thoracohumeral abduction angles to simulate a quasi-static abduction in the scapular plane. In a second step, the muscle forces were calculated by minimizing the range of muscle stresses able to compensate an external joint moment caused by the arm weight. If the joint became unstable, additional force was applied by the rotator cuff muscles to restore joint stability. The model showed a higher joint shear to joint compressive force for the RCT CSA (38.2°) for thoracohumeral abduction angles between 40° and 90° with a peak difference of 23% at 50° of abduction. To achieve stability in this case additional rotator cuff forces exceeding physiological values were required. Our results document that a higher CSA tends to destabilize the glenohumeral joint such that higher than normal supraspinatus forces are required to maintain modeled stability during active abduction. This lends strong support to the concept that a high CSA can induce supraspinatus (SSP) overload. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:961-968, 2016.