Dynamic glenohumeral joint stability

Effect of patient-specific scapular morphology on the glenohumeral joint force and shoulder muscle force equilibrium: a study of rotator cuff tear and osteoarthritis patients

Introduction: Osteoarthritis (OA) and rotator cuff tear (RCT) pathologies have distinct scapular morphologies that impact disease progression. Previous studies examined the correlation between scapular morphology and glenohumeral joint biomechanics through critical shoulder angle (CSA) variations. In abduction, higher CSAs, common in RCT patients, increase vertical shear force and rotator cuff activation, while lower CSAs, common in OA patients, are associated with higher compressive force. However, the impact of the complete patient-specific scapular morphology remains unexplored due to challenges in establishing personalized models. Methods: CT data of 48 OA patients and 55 RCT patients were collected. An automated pipeline customized the AnyBody™ model with patient-specific scapular morphology and glenohumeral joint geometry. Biomechanical simulations calculated glenohumeral joint forces and instability ratios (shear-to-compressive forces). Moment arms and torques of rotator cuff and deltoid muscles were analyzed for each patient-specific geometry. Results and discussion: This study confirms the increased instability ratio on the glenohumeral joint in RCT patients during abduction (mean maximum is 32.80% higher than that in OA), while OA patients exhibit a higher vertical instability ratio in flexion (mean maximum is 24.53% higher than that in RCT) due to the increased inferior vertical shear force. This study further shows lower total joint force in OA patients than that in RCT patients (mean maximum total force for the RCT group is 11.86% greater than that for the OA group), attributed to mechanically advantageous muscle moment arms. The findings highlight the significant impact of the glenohumeral joint center positioning on muscle moment arms and the total force generated. We propose that the RCT pathomechanism is related to force magnitude, while the OA pathomechanism is associated with the shear-to-compressive loading ratio. Overall, this research contributes to the understanding of the impact of the complete 3D scapular morphology of the individual on shoulder biomechanics.

Arthroscopic superior capsule reconstruction augmentation using a semitendinosus autograft in massive reparable rotator cuff tears

Background

Arthroscopic superior capsule reconstruction (SCR) augmentation is a viable treatment option for massive reparable cuff tears. This study aimed to retrospectively compare clinical and imaging outcomes of patients with reparable massive rotator cuff tears after arthroscopic rotator cuff repair (ARCR) with those after SCR augmentation using a semitendinosus autograft.

Methods

We retrospectively compared 50 patients with massive reparable rotator cuff tears who underwent ARCR and SCR augmentation (n = 25 each). Patients were clinically followed up for at least 2 years, and the American Shoulder and Elbow index, other patient-reported outcomes, active range of motion, and radiography and magnetic resonance imaging findings were assessed.

Results

At the final follow-up, both patient groups showed significant improvements in forward elevation in range of motion and visual analog scale scores. Improvements in the American Shoulder and Elbow scores in the SCR augmentation group were significantly superior to those in the ARCR group (48.3 and 28.9, P < .01). There was a significant difference in the retear rate between the SCR augmentation group and ARCR group (20% and 56%, respectively; P = .009).

Conclusion

Our study demonstrated that patient-reported outcomes and retear rates in patients who underwent SCR augmentation with rotator cuff repair for massive rotator cuff tears significantly improved compared with those in patients who underwent ARCR without augmentation. Augmentation with semitendinosus autografting during rotator cuff repair represents a solution for patients with massive reparable rotator cuff tears.

A standardized protocol for needle placement in the infraspinatus muscle: an anatomical perspective

PURPOSE

This study aimed to evaluate the morphology of the three parts of the infraspinatus muscle based on surface landmarks for precise and effective access, and to propose the most effective fine-wire electrode insertion technique and sites.

METHODS

Fifteen Asian fresh cadavers were used. We investigated the probability of the presence of the superior, middle, and inferior parts in each infraspinatus muscle based on surface landmarks. Based on the positional characteristics of the muscle, we determined the needle insertion method and confirmed its effectiveness by dissection.

RESULTS

The superior part was mostly observed near the spine of the scapula. The middle part was broadly observed within the infraspinous fossa. The inferior part showed variable location within the infraspinous fossa. The injection accuracy of the superior, middle, and inferior parts in the infraspinatus muscle was 95.8%, 100%, and 91.7%, respectively. Targeting the superior and middle parts for injection of the infraspinatus muscle is relatively more straightforward than targeting the inferior part. Targeting the inferior part of the infraspinatus muscle in this study was more challenging than targeting the superior and middle parts.

CONCLUSION

Needling for electromyography should be performed with special care to avoid unintended muscle parts, which could lead to inaccurate data acquisition and affect the conclusions about muscle function.

Short-Term Effects of Centralization of the Glenohumeral Joint and Dynamic Humeral Centering on Shoulder Pain, Disability, and Grip Strength in Patients with Secondary Subacromial Impingement Syndrome

Subacromial impingement syndrome (SIS) is one of the most common causes of shoulder pain in adults and is caused by muscle imbalance around the shoulder joint, which is referred to as secondary SIS. Centralization of the glenohumeral joint (CGH), one of the intervention methods for this, targets strengthening the control ability of the rotator cuff. Dynamic humeral centering (DHC) targets the learning of selective contractile function of the pectoralis major and latissimus dorsi as depressors of the humeral head. This study aims to determine the short-term effects of CGH and DHC on pain, disability, and grip strength in patients with secondary SIS. Forty-eight patients with secondary SIS participated in the study and were randomly allocated into three groups (CGH group (n = 16), DHC group (n = 16), and simple exercise group (n = 16)) and received the intervention for 50 min. The Constant-Murley score was used to assess shoulder pain and disability (primary outcome), and a hand-held dynamometer was used to assess grip strength (secondary outcome). Measurements were performed before the intervention and one day after the intervention. The results showed that the Constant-Murley score improved in the CGH and DHC groups. In addition, pain and disability (range of motion scores) improved in both the CGH and DHC groups. Improvements in disability (shoulder strength) and grip strength were seen only in the CGH group. Both CGH and DHC can be used as methods for short-term pain release and disability recovery in secondary SIS. In particular, CGH appears to be more effective in the short-term improvement in shoulder strength and grip strength.

Ex vivo experimental strategies for assessing unconstrained shoulder biomechanics: A scoping review

BACKGROUND

Biomechanical studies of the shoulder often choose an ex vivo approach, especially when investigating the active and passive contribution of individual muscles. Although various simulators of the glenohumeral joint and its muscles have been developed, to date a testing standard has not been established. The objective of this scoping review was to present an overview of methodological and experimental studies describing ex vivo simulators that assess unconstrained, muscular driven shoulder biomechanics.

METHODS

All studies with ex vivo or mechanical simulation experiments using an unconstrained glenohumeral joint simulator and active components mimicking the muscles were included in this scoping review. Static experiments and humeral motion imposed through an external guide, e.g., a robotic device, were excluded.

RESULTS

Nine different glenohumeral simulators were identified in 51 studies after the screening process. We identified four control strategies characterized by: (a) using a primary loader to determine the secondary loaders with constant force ratios; (b) using variable muscle force ratios according to electromyography; (c) calibrating the muscle path profile and control each motor according to this profile; or (d) using muscle optimization.

CONCLUSION

The simulators with the control strategy (b) (n = 1) or (d) (n = 2) appear most promising due to its capability to mimic physiological muscle loads.

The development and evaluation of an in-vitro shoulder simulator with active muscle simulation

The purpose of the present study was to develop a novel active in-vitro shoulder simulator to emulate all forms of planar and non-planar glenohumeral motions with active muscle simulation on cadaver specimens or shoulder models and to critically evaluate its performance. A physiologic shoulder simulator, driven using simulated muscle force, was developed to dynamically realize accurate kinematic control in all three rotational degrees of freedom (DOF) under physiological kinetic boundaries. The control algorithm of the simulator was implemented using three parallel running independent control loops, which regulate the forces of individual muscles in the respect DOF and work asynchronously in disparate sequences adapted to specific motions (abduction, flexion/extension and rotation). Three cadaveric specimens were used to evaluate the kinematic and kinetic performance of the simulator during simulated motions. High kinematic accuracy (maximum mean deviation ≤ 2.35° and RMSE 1.13°) and repeatability (maximum and average SD of ≤ 1.21° and 0.67°) were observed in all three rotational DOF investigated. The reliabilities of all individual muscle forces actuated in the simulator during planar and non-planar motions were generally excellent, with the 95% CIs of ICC estimates of > 0.90 for most instances (30/36). A novel shoulder simulator with active muscle simulation was developed and evaluated. Its capability to reproduce kinematics and kinetics in a physiological range for all DOF was systematically evaluated for multiple kinetic and kinematic outcome variables. The presented simulator is a powerful tool for investigating the biomechanics of physiological and pathological shoulder joints and to evaluate various surgical interventions. Acquisition of reliable data in joint kinetics and translational kinematics during active motions is critical to assess shoulder pathologies and appropriate treatments. We provide a unique muscle activated physiologic shoulder simulator, which allows the comprehensive acquisition of joint kinematic and kinetic data during repeated realistic planar and non-planar motions.

Effect of intraarticular pressure on glenohumeral kinematics during a simulated abduction motion: a cadaveric study

BACKGROUND

The current understanding of glenohumeral joint stability is defined by active restrictions and passive stabilizers including naturally-occurring negative intraarticular pressure. Cadaveric specimens have been used to evaluate the role of intraarticular pressure on joint stability, although, while the shoulder's negative intraarticular pressure is universally acknowledged, it has been inconsistently accounted for.

HYPOTHESIS

During continuous, passive humeral abduction, releasing the native intraarticular pressure increases joint translation, and restoring this pressure decreases joint translations.

STUDY DESIGN

Descriptive Laboratory Study.

METHODS

A validated shoulder testing system was used to passively abduct the humerus in the scapular plane and measure joint translations for seven (n = 7) cadaveric specimens. The pressure within the glenohumeral joint was measured via a 25-gauge needle during passive abduction of the arm, which was released and subsequently restored. During motion, the rotator cuff muscles were loaded using stepper motors in a force feedback loop and electromagnetic sensors were used to continuously measure the position of the humerus and scapula. Joint translation was defined according to the instant center of rotation of the glenohumeral head according to the recommendations by the International Society of Biomechanics.

RESULTS

Area under the translation versus abduction angle curve suggests that releasing the pressure within the capsule results in significantly less posterior translation of the glenohumeral head as compared to intact (85-90˚, p < 0.05). Posterior and superior translations were reduced after 70˚ of abduction when the pressure within the joint was restored.

CONCLUSION

With our testing system employing a smooth continuous passive motion, we were able to show that releasing intraarticular pressure does not have a major effect on the path of humeral head motion during glenohumeral abduction. However, both violating the capsule and restoring intraarticular pressure after releasing alter glenohumeral translations. Future studies should study the effect of simultaneous external rotation and abduction on the relationship between joint motion and IAP, especially in higher degrees of abduction.

CLINICAL RELEVANCE

Thoroughly simulating the glenohumeral joint environment in the cadaveric setting may strengthen the conclusions that can be translated from this setting to the clinic.

Variability of Time- and Frequency-Domain Surface Electromyographic Measures in Non-Fatigued Shoulder Muscles

OCCUPATIONAL APPLICATIONSLocalized Muscle Fatigue (LMF) can be monitored or predicted based on the relative change in the values of surface electromyography (sEMG) measures with respect to the "fresh" or no-fatigue condition. Quantification of LMF based on relative change, though, relies on the assumption that the sEMG measures recorded in a no-fatigue condition can serve as an appropriate reference. Results of this study indicate that sEMG measures in a no-fatigue condition are affected by various work-related factors and provide further guidance on the variability of commonly used time- and frequency-domain sEMG measures to assist the ergonomist in improving the accuracy of LMF assessment.

In Vitro Simulation of Shoulder Motion Driven by Three-Dimensional Scapular and Humeral Kinematics

In vitro simulation of three-dimensional (3D) shoulder motion using in vivo kinematics obtained from human subjects allows investigation of clinical conditions in the context of physiologically relevant biomechanics. Herein, we present a framework for laboratory simulation of subject-specific kinematics that combines individual 3D scapular and humeral control in cadavers. The objectives were to: (1) robotically simulate seven healthy subject-specific 3D scapulothoracic and glenohumeral kinematic trajectories in six cadavers, (2) characterize system performance using kinematic orientation accuracy and repeatability, and muscle force repeatability metrics, and (3) analyze effects of input kinematics and cadaver specimen variability. Using an industrial robot to orient the scapula range of motion (ROM), errors with repeatability of ±0.1 mm and <0.5 deg were achieved. Using a custom robot and a trajectory prediction algorithm to orient the humerus relative to the scapula, orientation accuracy for glenohumeral elevation, plane of elevation, and axial rotation of <3 deg mean absolute error (MAE) was achieved. Kinematic accuracy was not affected by varying input kinematics or cadaver specimens. Muscle forces over five repeated setups showed variability typically <33% relative to the overall simulations. Varying cadaver specimens and subject-specific human motions showed effects on muscle forces, illustrating that the system was capable of differentiating changes in forces due to input conditions. The anterior and middle deltoid, specifically, showed notable variations in patterns across the ROM that were affected by subject-specific motion. This machine provides a platform for future laboratory studies to investigate shoulder biomechanics and consider the impacts of variable input kinematics from populations of interest, as they can significantly impact study outputs and resultant conclusions.

Effects of a Novel Rotator Cuff Rehabilitation Device on Shoulder Strength and Function

ABSTRACT

Savitzky, JA, Abrams, LR, Galluzzo, NA, Ostrow, SP, Protosow, TJ, Liu, SA, Handrakis, JP, and Friel, K. Effects of a novel rotator cuff rehabilitation device on shoulder strength and function. J Strength Cond Res 35(12): 3355-3363, 2021-The glenohumeral joint, a multiaxial ball and socket joint, has inherent instability counterbalanced by the muscular stability of the rotator cuff (RC) and connective tissue. Exercise has been shown to alleviate pain and disability arising from degenerative changes of the RC due to overuse, trauma, or poor posture. This study compared the training effects of ShoulderSphere (SS), an innovative device that uses resistance to centrifugal force, to TheraBand (TB), a traditional device that uses resistance to elasticity. Thirty-five healthy male and female adults (24.2 ± 2.4 years) were randomized into 3 groups: SS, TB, and control. Five outcomes were assessed before and after the twice-weekly, 6-week intervention phase: strength (shoulder flexion [Fx], extension [Ext], external rotation [ER], and internal rotation [IR]), proprioception (6 positions), posterior shoulder endurance (ShEnd), stability (Upper Quarter Y-Balance Test [YBal] (superolateral [YBalSup], medial [YBalMed], and inferolateral [YBalInf]), and power (seated shot put [ShtPt]). Data were analyzed using a 3 (group: SS, TB, and control) × 2 (time: pre and post) generalized estimating equation. Analyses demonstrated a main effect of time for all strength motions (p < 0.01): YBalInf (p < 0.0001), ShtPt (p < 0.05), and ShEnd (p < 0.0001) but no interaction effects of group × time. There were no main or interaction effects for proprioception. Both SS and TB groups had significant within-group increases in Ext, IR, YBalInf, and ShEnd. Only the SS group had significant increases in ER, Fx, and ShtPt. ShoulderSphere demonstrated comparable conditioning effects with TB and may afford additional strength gains in Fx and ER, and power. ShoulderSphere should be considered a viable alternative in RC conditioning.

Muscle Contraction Has a Reduced Effect on Increasing Glenohumeral Stability in the Apprehension Position

PURPOSE

Glenohumeral instability accounts for 23% of all shoulder injuries among collegiate athletes. The apprehension position-combined shoulder abduction and external rotation-commonly reproduces symptoms in athletes with instability. Rehabilitation aims to increase glenohumeral stability by strengthening functional positions. However, it is unclear how much glenohumeral stability increases with muscle contraction in the apprehension position. The purpose of this study was to determine whether the ability to increase translational glenohumeral stiffness, a quantitative measure of glenohumeral stability, with muscle contraction is reduced in the apprehension position.

METHODS

Seventeen asymptomatic adults participated. A precision-instrumented robotic system applied pseudorandom, anterior-posterior displacements to translate the humeral head within the glenoid fossa and measured the resultant forces as participants produced isometric shoulder torques. Measurements were made in neutral abduction (90° abduction/0° external rotation) and apprehension (90° abduction/90° external rotation) positions. Glenohumeral stiffness was estimated from the relationship between applied displacements and resultant forces. The ability to increase glenohumeral stiffness with increasing torque magnitude was compared between positions.

RESULTS

On average, participants increased glenohumeral stiffness from passive levels by 91% in the neutral abduction position and only 64% in the apprehension position while producing 10% of maximum torque production. The biggest decrease in the ability to modulate glenohumeral stiffness in the apprehension position was observed for torques generated in abduction (49% lower, P < 0.001) and horizontal abduction (25% lower, P < 0.001).

CONCLUSION

Our results demonstrate that individuals are less able to increase glenohumeral stiffness with muscle contraction in the apprehension position compared with a neutral shoulder position. These results may help explain why individuals with shoulder instability more frequently experience symptoms in the apprehension position compared with neutral shoulder positions.

The forgotten radial nerve: A conceptual framework for treatment of lateral elbow pain

BACKGROUND

Lateral elbow pain is a prevalent musculoskeletal overuse disorder that has serious consequences for musculoskeletal health, occupational performance, and overall healthcare burden. Available treatment options (traditional therapy and steroid injections) have been studied rigorously, yet supporting evidence is weak. The majority of treatment options available are targeted at the local pathology of the common extensor tendon as the apparent source of pain, and do not adequately address the cause, the source of overuse, and mechanism of injury.

PURPOSE

The purpose of this paper is to describe a novel approach, a regional interdependence model, to reduce symptoms of upper extremity musculoskeletal overuse in populations at risk by addressing a broader systematic approach versus a localized symptom driven approach for the assessment and treatment of lateral elbow pain.

METHODS

The proposed framework - Think in nerve length and layers (TINLL)- accounts for nerve tension and muscle balance in the entire extremity. In this paper we describe the application of the TINLL model for assessment and treatment of SRSN irritation in individuals with lateral elbow pain and propose a method for treatment and for further studies. The proposed treatment approach combines mobilization with movement, elastic taping, and isometric exercises to address impairment at each level: joint alignment, neural tension, and the superficial sensory nervous system.

RESULTS

Our findings of reduced pain with a relatively small number of therapy sessions in a small retrospective cohort of patients using the TINLL framework for assessment and treatment supports further formal study of this approach in a larger cohort with longer follow-up to determine effectiveness compared to current treatments.

CONCLUSION

Future studies will test and compare the efficacy of the TINLL framework and model of treatment on the short- and long-term outcomes in individuals with chronic lateral elbow pain compared to traditional therapy.

Effect of Match Play on Shoulder Strength in Amateur Rugby Union Players

ABSTRACT

Zelinski, S, Manvell, JJ, Manvell, N, Callister, R, and Snodgrass, SJ. Effect of match play on shoulder strength in amateur rugby union players. J Strength Cond Res 35(9): 2584-2590, 2019-The purpose of this study was to determine the effect of match play on shoulder internal rotation (IR) and external rotation (ER) strength in amateur Australian rugby union players. Maximal isometric shoulder IR and ER strength was measured in 18 male players using hand-held dynamometry before match, at half-time, after match, and 1, 3, and 7 days after match. Match stress was measured intrinsically (rating of perceived exertion) and extrinsically (number of shoulder events). Linear mixed regression modeling determined differences in strength measures while exploring possible confounders, including history of pain, pain on testing, player position, exposure, height, body mass, and body mass index. From the models, IR strength decreased from before match to after match (adjusted mean difference 1.96 kg; 95% confidence interval [CI]: 0.63-3.29, p = 0.004), 1 day after match (2.47; 1.14-3.80, p < 0.001), and 3 days after match (1.75; 0.42-3.09, p = 0.010). External rotation strength decreased from before match to half-time (adjusted mean difference 1.54 kg, 95% CI: 0.65-2.42, p = 0.001), but no other time points demonstrated significant changes in ER strength compared with before match. None of the possible confounding variables significantly affected strength changes over time. Rugby union match play is associated with reduced shoulder strength, particularly IR. Future research is required to establish whether strength changes are associated with shoulder pain and injury.

Recurrent anterior shoulder instability in patients 40-60 years old. Accompanying injuries and patient outcomes of arthroscopic repair

BACKGROUND

Accompanying injuries are frequently seen in middle aged patients with recurrent instability. The aim of this study was to elucidate the associated injuries, report patient outcomes of the following arthroscopic instability surgery regarding 40-60 years old patients with recurrent shoulder instability.

METHODS

Patients that underwent arthroscopic instability surgery due to recurrent shoulder instability between February 2008 and November 2015, and which were 40-60 years old were included and evaluated retrospectively. Minimum follow-up duration was 24 months. Anterior-inferior labral injuries and accompanying pathologies such as rotator cuff tears and SLAP lesions were documented. Postoperative patient-reported outcome evaluation was made using Oxford Shoulder Instability Score.

RESULTS

Among 355 patients that underwent arthroscopic instability surgery, 88 patients which had pathology of recurrent instability were in the range of 40-60 years old. Patients who had previous shoulder surgery or fracture (n = 8) epileptic seizure history (n = 3), neurologic deficit (n = 2) were excluded from the study. 75 patients were included with a mean follow-up 69 ± 23 months (32-125). The percentage of middle-aged and elderly (40-60 years old) was 24.8% among recurrent shoulder instability patients. 44% had isolated Bankart lesion whereas 56% revealed multiple pathologies. Bankart + SLAP lesions were found in 32%, whereas Bankart + Rotator Cuff tears in 26.7% (13 isolated supraspinatus, 4 supraspinatus + subscapularis, 1 isolated subscapularis full-thickness and 2 partial-thickness supraspinatus tears). The mean Oxford Shoulder Instability Score was 38.4 ± 5.2 (26-48). The scores of patients which were treated with labrum and rotator cuff repair (median 42, range 30-48) were significantly better than the patients who were treated with isolated labrum repair (median 39, range 20-46) (p = 0.015). There was no difference regarding patients with or without SLAP repair (median 39 vs 39 and range 30-48 vs 20-48, respectively) (p = 0.702).

CONCLUSIONS

Arthroscopic repair of capsulolabral lesions is a safe and successful technique in 40-60 years old patients. Furthermore, the presence of repaired rotator cuff tears led to even superior results. Accompanying SLAP lesions did not affect the results.

STUDY DESIGN

Retrospective Case Series.

LEVEL OF EVIDENCE

4, Retrospective Case Series.

The glenohumeral ligaments: Superior, middle, and inferior: Anatomy, biomechanics, injury, and diagnosis

The three glenohumeral ligaments (superior, middle, and inferior) are discrete thickenings of the glenohumeral joint capsule and are critical to shoulder stability and function. Injuries to this area are a cause of significant musculoskeletal morbidity. A literature search was performed by a review of PubMed, Google Scholar, and OVID for all relevant articles published up until 2020. This study highlights the anatomy, biomechanical function, and injury patterns of the glenohumeral ligaments, which may be relevant to clinical presentation and diagnosis. A detailed understanding of the normal anatomy and biomechanics is a necessary prerequisite to understanding the injury patterns and clinical presentations of disorders involving the glenohumeral ligaments of the shoulder.

Sub-regional activation of supraspinatus and infraspinatus muscles during activities of daily living is task dependent

The supraspinatus and infraspinatus muscles each have multiple sub-regions that may activate differentially in activities of daily living. Awareness of these differential demands critically informs rehabilitation of rotator cuff muscle following injury, particularly if centered on recovering and strengthening the rotator cuff to perform daily tasks. This study quantified muscle activation of supraspinatus and infraspinatus sub-regions during the performance of six activities of daily living. Twenty-three participants (mean: 22.6 ± 2.6 years) completed the following tasks: opening a jar, reaching at shoulder height, overhead reaching, pouring water from a pitcher, eating with a spoon, and combing hair. Indwelling electromyography was collected from the anterior and posterior supraspinatus and superior, middle, and inferior infraspinatus. Tasks requiring high arm elevations (e.g. reaching at shoulder and overhead height) activated anterior supraspinatus between 21 and 28% MVC. The posterior supraspinatus consistently activated between 10 and 30% MVC across all tasks. All sub-regions of infraspinatus activated highly (between 18 and 25% MVC) in tasks requiring high arm elevations in flexion. These findings may be leveraged to define effective measures to increase rotator cuff function in daily tasks.

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.

A Robotic Glenohumeral Simulator for Investigating Prosthetic Implant Subluxation

Total shoulder arthroplasty (TSA) is an effective treatment for glenohumeral (GH) osteoarthritis. However, it still suffers from a substantial rate of mechanical failure, which may be related to cyclic off-center loading of the humeral head on the glenoid. In this work, we present the design and evaluation of a GH joint robotic simulator developed to study GH translations. This five-degree-of-freedom robot was designed to replicate the rotations (±40 deg, accuracy 0.5 deg) and three-dimensional (3D) forces (up to 2 kN, with a 1% error settling time of 0.6 s) that the humeral implant exerts on the glenoid implant. We tested the performances of the simulator using force patterns measured in real patients. Moreover, we evaluated the effect of different orientations of the glenoid implant on joint stability. When simulating realistic dynamic forces and implant orientations, the simulator was able to reproduce stable behavior by measuring the translations of the humeral head of less than 24 mm with respect to the glenoid implant. Simulation with quasi-static forces showed dislocation in extreme ranges of implant orientation. The robotic GH simulator presented here was able to reproduce physiological GH forces and may therefore be used to further evaluate the effects of glenoid implant design and orientation on joint stability.

Quantifying acromiohumeral distance in elite male field hockey players compared to a non-athletic population

BACKGROUND

Shoulders of elite field hockey players are loaded continuously during play. Frequent high shoulder loading is known to influence certain shoulder variables, such as acromiohumeral distance. However, the influence of elite field hockey play on acromiohumeral distance is not examined yet.

OBJECTIVE

To examine the acromiohumeral distance in elite male field hockey players compared to a non-athletic control group.

DESIGN

Cross-sectional study.

METHODS

Fifty male participants were included; 25 elite field hockey players (age: 24.0±2.72 years; weight: 77.2±5.29kg; height; 180.5±5.37cm) and 25 age- and gender matched non-athletes (23.0±2.29 years; weight: 75.7±9.53kg; height: 181.8±5.52cm). A Telemed-Colormaster-128 EXT-IZ device was used to bilaterally obtain ultrasound acromiohumeral distance images at 3 different angles of shoulder abduction in the frontal plane.

RESULTS

Field hockey players showed a bilateral larger acromiohumeral distance at 45° (mean difference: 1.46mm [95% CI 0.46; 2.46]; p=0.005) and 60° (mean difference: 1.07mm [95% CI 0.21; 1.93]; p=0.016) compared to controls. In both groups, a significant but clinically less relevant, side difference was established for the acromiohumeral distance at 60° (mean difference: 0.79mm [95% CI 0.21; 1.34]; p=0.009).

CONCLUSION

With active shoulder abduction, elite field hockey players show a larger acromiohumeral distance in comparison to non-athletic participants. This may be a protective sport-specific adaptation, to better guard the shoulder from injury. Thus, acromiohumeral distance measurement may help physical therapists/coaches decide which athletes could benefit from specific, additional exercises aimed at enlarging the subacromial space.

Postural differences in shoulder dynamics during pushing and pulling

Assessments of shoulder dynamics (e.g. the inertial, viscous, and stiffness properties of the joint) can provide important insights into the stability of the joint at rest and during volitional contraction. The purpose of this study was to investigate how arm posture influences shoulder dynamics while generating pushing or pulling torques in the horizontal plane. Sixteen healthy participants were examined in seven postures encompassing a large workspace of the shoulder. At each posture, the participant's shoulder was rapidly perturbed while measuring the resultant change in shoulder torque about the glenohumeral axis. Participants were examined both at rest and while producing horizontal flexion and extension torques scaled to 15% of a maximum voluntary contraction. Shoulder stiffness, viscosity, and damping ratio were estimated using impedance-based matching, and changes in these outcome measures with torque level, elevation angle, and plane of elevation angle were explored with a linear mixed effects model. Shoulder stiffness was found to decrease with increasing elevation angles (p < 0.001) without subsequent changes in viscosity, leading to a greater damping ratios at higher elevation angles (p < 0.001). Shoulder stiffness, viscosity, and damping ratio (all p < 0.05) were all found to significantly increase as the plane of elevation of the arm was increased. The relationship between the viscosity, stiffness and the damping ratio of the shoulder is one that the central nervous system must regulate in order to maintain stability, protect against injury, and control the shoulder joint as the inertial and muscle contributions change across different arm postures.

Shoulder Glenohumeral Elevation Estimation based on Upper Arm Orientation

In this paper, the shoulder glenohumeral displacement during the movement of the upper arm is studied. Four modeling approaches were examined and compared to estimate the humeral head elevation (vertical displacement) and translation (horizontal displacement). A biomechanics-inspired method was used firstly to model the glenohumeral displacement in which a least squares method was implemented for parameter identification. Then, three Gaussian process regression models were used in which the following variable sets were employed: i) shoulder adduction/abduction angle, ii) combination of shoulder adduction/abduction and flexion/extension angles, iii) overall upper arm orientation in the form of quaternions. In order to test the respective performances of these four models, we collected motion capture data and compared the models' representative capabilities. As a result, Gaussian process regression that considered the overall upper arm orientation outperformed the other modeling approaches; however, it should be noted that the other methods also provided accuracy levels that may be sufficient depending on task requirements.

The Stabilizing Function of Superficial Shoulder Muscles Changes Between Single-Plane Elevation and Reaching Tasks

OBJECTIVE

The goal of this study was to determine whether and how much the stabilizing role of the shoulder muscles changes as a function of humeral elevation and the plane of elevation.

METHODS

A musculoskeletal model, comprising a personalized scapulohumeral rhythm, was used to calculate the ratio of shear over compressive force (stability ratio) of three rotator cuff muscles (supraspinatus, infraspinatus and subscapularis) and three superficial shoulder muscles (middle deltoid, clavicular part of pectoralis major and latissimus dorsi) during abduction, flexion and reaching movements in 10 healthy adults.

RESULTS

The range of the stability ratios was [Formula: see text] for the rotator cuff muscles compared to [Formula: see text] for the superficial shoulder muscles. In the superior-inferior direction, the stability ratios of all muscles changed with humeral elevation and for infraspinatus, subscapularis, latissimus dorsi and deltoid also with the plane of elevation. In the anterior-posterior direction, the stability ratios of all muscles changed with humeral elevation, except for the deltoid, and with the plane of elevation, except for the supraspinatus, with interaction effects in all muscles.

CONCLUSION

The rotator cuff muscles provide greater compression than shear forces during all tasks. The stabilizing function of the superficial shoulder muscles examined in this study varies during tasks.

SIGNIFICANCE

The findings can be used to predict in which movements the shoulder joint becomes more unstable and can be applied to understand how shear and compressive forces change in populations with abnormal shoulder motion.

Mapping glenohumeral laxity: effect of capsule tension and abduction in cadaveric shoulders

BACKGROUND

Shoulder capsular plication aims to restore the passive stabilization of the glenohumeral capsule; however, high reported recurrence rates warrant concern. Improving our understanding of the clinical laxity assessment across 2 dimensions, capsular integrity and shoulder position, can help toward the standardization of clinical tools. Our objectives were to test and describe glenohumeral laxity across 5 capsular tension levels and 4 humeral position levels and describe tension-position interplay.

METHODS

We tested 14 dissected cadavers for glenohumeral laxity in 5 directions: anterior, posterior, and inferior translation, and internal and external axial rotation. Laxity was recorded across capsule tension (baseline, stretched, 5 mm, 10 mm, and 15 mm of plication) and position (0°, 20°, 40°, 60° of scapular abduction). Repeated-measures analysis of variance with post hoc contrasts tested the effect of tension, position, and composite tension × position on laxity.

RESULTS

Capsule tension, position, and composite interplay had a statistically significant, although unequal, effect on laxity in each direction. Laxity was consistently overconstrained in 15-mm plication and was overall greatest in 20° and lowest in 60°. Restoration occurred most in 10 mm, but this depended on the position. The composite effect was significant for external and internal rotation and inferior laxity, but laxity at the middle range (20° or 40°) was different than at the end range (0° or 60°) for all directions.

CONCLUSIONS

On average, laxity was restored to baseline tension after 10-mm plication, but this determination varied depending on shoulder position. Middle-range laxity behaved differently than end-range laxity across plication tensions. This information is useful in understanding the unstable shoulder as well as for standardizing clinical laxity assessment.

Electromyographic investigation of anterior and posterior regions of supraspinatus: a novel approach based on anatomical insights

Supraspinatus is composed of anterior and posterior regions that are distinct. To date, the relative electromyographic (EMG) activity of these regions during different tasks has not been investigated. This work, thus, evaluated activity of the anterior and posterior regions of supraspinatus during isometric actions in different postures. Data were analyzed from 11 healthy participants. Fine-wire electrodes were inserted into the anterior and posterior regions of supraspinatus. EMG activity was recorded during isometric abduction and external rotation exertions against 5% of body weight resistance. Three postures for abduction (30°, 60°, and 90° of humeral abduction, scapular plane) and two for external rotation (0° and 90° humeral abduction) were tested. Each participant’s data were normalized to the peak root mean square (RMS) values for the corresponding region. The RMS of the anterior region was divided by that of the posterior to calculate muscle activation ratios. Non-parametric statistics were used for analyses. The median ratio was lower during external rotation at 90° abduction compared to abduction at 30° (P = 0.003). These results suggest that the two regions of supraspinatus are functionally distinct during isometric tasks. The posterior region may play a more dominant role in postures with higher degrees of abduction and during external rotation exertions.

The effect of short-term isometric training on core/torso stiffness

"Core" exercise is a basic part of many physical training regimens with goals ranging from rehabilitation of spine and knee injuries to improving athletic performance. Core stiffness has been proposed to perform several functions including reducing pain by minimising joint micro-movements, and enhancing strength and speed performance. This study probes the links between a training approach and immediate but temporary changes in stiffness. Passive and active stiffness was measured on 24 participants; 12 having little to no experience in core training (inexperienced), and the other 12 being athletes experienced to core training methods; before and after a 15 min bout of isometric core exercises. Passive stiffness was assessed on a "frictionless" bending apparatus and active stiffness assessed via a quick release mechanism. Short-term isometric core training increased passive and active stiffness in most directions for both inexperienced and experienced participants, passive left lateral bend among experienced participants being the exception (P < 0.05). There was no difference between the inexperienced and experienced groups. The results confirm that the specific isometric training exercise approach tested here can induce immediate changes in core stiffness, in this case following a single session. This may influence performance and injury resilience for a brief period.

Three-dimensional scapular kinematics during open and closed kinetic chain movements in asymptomatic and symptomatic subjects

The combination of open kinetic chain (OKC) and closed kinetic chain (CKC) exercises is commonly recommended in shoulder rehabilitation, aiming at improving strength and sport-specific performance. This study aimed to investigate the three-dimensional (3-D) scapular kinematics and bilateral symmetry of scapular motion during dynamic OKC and CKC movements in asymptomatic and symptomatic shoulders. Fifty subjects with unilateral shoulder pain (symptomatic subjects diagnosed with subacromial impingement syndrome, n=20) or without shoulder pain during active shoulder elevation (asymptomatic subjects, n=30) participated in the study. Furthermore, 3-D scapular kinematics were recorded using an electromagnetic tracking device in the sagittal plane of shoulder elevation for both the OKC and CKC conditions performed with slings. Data for scapular kinematics and symmetry angle (SA) were analyzed at 30°, 45°, 60°, 90°, and 120° of humerothoracic elevation. Analysis of variance models and Student׳s t-test were used to make comparisons between conditions. In general, the scapula was more externally rotated, upwardly rotated and anteriorly tilted for asymptomatic shoulders, and more upwardly rotated for symptomatic shoulders during CKC shoulder elevation. Further, comparisons of SA obtained during OKC and CKC movements revealed that during CKC, scapular motion was more symmetrical for upward-downward rotation and anterior-posterior tilt in asymptomatic shoulders and for anterior-posterior tilt in symptomatic shoulders, especially above 90° humerothoracic elevation. Differences in scapular motion during the CKC condition were in a specific pattern and enhanced symmetry, which would be considered to be a position less likely to produce compression of the rotator cuff tendons for both training in asymptomatic populations and for treatment in early rehabilitation of patients, such as those who have shoulder impingement syndrome.

Glenohumeral joint reaction forces increase with critical shoulder angles representative of osteoarthritis-A biomechanical analysis

Osteoarthritis (OA) of the glenohumeral joint constitutes the most frequent indication for nontraumatic shoulder joint replacement. Recently, a small critical shoulder angle (CSA) was found to be associated with a high prevalence of OA. This study aims to verify the hypothesis that a small CSA leads to higher glenohumeral joint reaction forces during activities of daily living than a normal CSA. A shoulder simulator with simulated deltoid (DLT), supraspinatus (SSP), infraspinatus/teres minor (ISP/TM), and subscapularis (SSC) musculotendinous units was constructed. The DLT wrapping on the humerus was simulated using a pulley that could be horizontally adjusted to simulate the 28° CSA found in OA or the 33° CSA found in disease-free shoulders. Over a range of motion between 6° and 82° of thoracohumeral abduction joint forces were measured using a six-axis load cell. An OA-associated CSA yielded higher net joint reaction forces than a normal CSA over the entire range of motion. The maximum difference of 26.4 N (8.5%) was found at 55° of thoracohumeral abduction. Our model thus suggests that a CSA typical for OA predisposes the glenohumeral joint to higher joint reaction forces and could plausibly play a role in joint overloading and development of OA. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1047-1052, 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.

Shoulder proprioception - lessons we learned from idiopathic frozen shoulder

Background

Of all the most frequent soft tissue disorders of the shoulder, idiopathic frozen shoulder (IFS) offers the greatest potential for studying proprioception. Studies concerning the presence of proprioception dysfunctions have failed to determine the potential for spontaneous healing of passive shoulder stabilizers (anterior and posterior capsule, middle and inferior gleno-humeral ligaments), its relationship with passive (PJPS) and active (AJPS) shoulder proprioception for internal and external rotation (IR, ER), as well as the isokinetic muscle performance of the internal and external rotators. This study investigates these dependencies in the case of arthroscopic release of IFS.

Methods

The study group comprised 23 patients (average aged 54.2) who underwent arthroscopic release due to IFS and 20 healthy volunteers. The average follow-up time was 29.2 months. The Biodex system was used for proprioception measurement in a modified neutral arm position and isokinetic evaluation. The results were analysed using the T-test, Wilcoxon and interclass correlation coefficient. P-values lower than 0.05 were considered significant.

Results

Statistically significant differences were found between involved (I) and uninvolved (U) shoulders only in the cases of PJPS and AJPS, peak torque, time to peak torque and acceleration time for ER (p < 0.05). No statistically significant difference was noted between PJPS IR and PJPS ER or between AJPS IR and AJPS ER (p > 0.05) for the U shoulders.

Conclusions

The anatomical structure of anterior (capsule, middle and anterior band of inferior gleno-humeral ligament) and posterior (capsule and posterior band of inferior gleno-humeral ligament) passive shoulder restraints has no impact on the difference in PJPS values between ER and IR in a modified neutral shoulder position. The potential for spontaneous healing of the anterior and posterior passive shoulder restraints influences PJPS recovery after arthroscopic release of IFS. ER peak torque deficits negatively affect AJPS values. PJPS and AJPS of ER and IR can be measured with a high level of reproducibility using an isokinetic dynamometer with the arm in a modified neutral shoulder position. Differences greater than 15 % for PJPS and >24 % for AJPS for ER and IR can be helpful for future studies as baseline data for identification of particular passive and active shoulder stabilizers at risk.

The effect of defect orientation and size on glenohumeral instability: a biomechanical analysis

PURPOSE

The purpose of this study was to determine the relationship between bony stability and percentage of anterior glenoid bone loss and the effect of bone loss orientation.

METHODS

Twelve cadaveric shoulders were studied. Glenoid bone defects were simulated in two different osteotomy angles: 0° and 45° to the superoinferior (SI) axis of the glenoid. The force and displacement required for dislocation were measured under two compressive forces of 40 and 60N. Testing was performed for the intact glenoid and glenoid defects of 2, 4, 6, 8, and 10 mm from the anterior margin.

RESULTS

The maximum force for dislocation with the 2-mm glenoid defect was significantly decreased compared with intact glenoid (p = 0.01), and this force also significantly decreased with each increase in defect size (p < 0.05). The dislocation force for 45° osteotomy was significantly higher than that for 0° osteotomy for all defect widths up to 8 mm with 40N compression and 6 mm with 60N compression (p < 0.001). The displacement at dislocation did not significantly decrease until the 8-mm defect with the 45° osteotomy but significantly decreased with the 4-mm defect with the 0° osteotomy. The required force for dislocation with 60N compression was significantly higher than that with 40N compression for all osteotomy sizes and orientations.

CONCLUSIONS

The decrease in stability even with glenoid bone loss as small as 2 mm or 7.5 % of the glenoid width suggests that bony restoration is recommended whenever any bone loss exists. Bone defects parallel to SI axis may be more susceptible to recurrent instability, and shoulder muscle strengthening exercises may increase glenohumeral compressive force and thus improve glenohumeral stability. Bony restoration is recommended whenever bone loss exists even with small bone fragments particularly those in line with the superior-inferior axis of the glenoid.

Nerve Transfers for Treatment of Isolated Axillary Nerve Injuries

BACKGROUND

The most common neurological defect in traumatic anterior glenohumeral dislocation is isolated axillary nerve palsy. Most recover spontaneously; however, some have persistent axillary neuropathy. An intact rotator cuff may compensate for an isolated axillary nerve injury; however, given the high rate of rotator cuff pathology with advancing age, patients with an axillary nerve injury are at risk for complete shoulder disability.

OBJECTIVE

To review reconstruction of the axillary nerve to alleviate shoulder pain, augment shoulder stability, abduction and external rotation to alleviate sole reliance on the rotator cuff to move and stabilize the shoulder.

METHODS

A retrospective review of 10 patients with an isolated axillary nerve injury and an intact rotator cuff who underwent a triceps nerve branch to axillary nerve transfer was performed. Patient demographics, surgical technique, deltoid strength, donor-site morbidity, complications and time to surgery were evaluated.

RESULTS

Ten male patients, mean age 38.3 years (range 18 to 66 years), underwent a triceps to axillary nerve transfer for isolated axillary nerve injury 7.4 months (range five to 12 months) post-traumatic shoulder dislocation. Deltoid function was British Medical Research Council grade 0/5 in all patients preoperatively and ≥3/5 deltoid strength in eight patients at final follow-up (14.8 months [range 12 to 25 months]). There were no complications and no donor-site morbidity.

CONCLUSION

A triceps to axillary nerve transfer for isolated axillary neuropathy following traumatic shoulder dislocation improved shoulder pain, stability and deltoid strength, and potentially preserves shoulder function with advancing age by alleviating sole reliance on the rotator cuff for shoulder abduction and external rotation.

Verification of a standardized method for inserting intramuscular electromyography electrodes into teres minor using ultrasound

The close proximity of the infraspinatus to the teres minor and their functional similarity in producing external rotation of the glenohumeral joint make accurate insertion of electromyographic (EMG) electrodes into the teres minor difficult and questionable even when published guidelines are followed. The primary aim of this study was to examine the anatomical support for the current guidelines for inserting intramuscular EMG electrodes into the teres minor muscle. The secondary aim was to provide a technical description for ultrasound-guided electrode insertion into the teres minor. Intramuscular electrodes were inserted into four cadaveric shoulders using markings based on the current guidelines. EMG electrodes were also inserted into the teres minor of four healthy male participants using real-time ultrasound (RTUS) guidance. Systematic dissections of the cadaver specimens revealed that the electrode had been successfully inserted into the teres minor muscle in only one out of the four. In the remaining three specimens, the needle lodged in the infraspinatus muscle belly at distances ranging from 3 to 17 mm medial to the teres minor. Using RTUS guidance, the electrodes were successfully inserted into the teres minor in all participants, as confirmed by visual inspection with RTUS. This study confirms that the current EMG electrode insertion guidelines for the teres minor are not accurate and RTUS ensures the placement of electrodes into the teres minor rather than the adjacent infraspinatus muscle.

Nerve transfers for treatment of isolated axillary nerve injuries

Background

The most common neurological defect in traumatic anterior glenohumeral dislocation is isolated axillary nerve palsy. Most recover spontaneously; however, some have persistent axillary neuropathy. An intact rotator cuff may compensate for an isolated axillary nerve injury; however, given the high rate of rotator cuff pathology with advancing age, patients with an axillary nerve injury are at risk for complete shoulder disability.

Objective

To review reconstruction of the axillary nerve to alleviate shoulder pain, augment shoulder stability, abduction and external rotation to alleviate sole reliance on the rotator cuff to move and stabilize the shoulder.

Method

A retrospective review of 10 patients with an isolated axillary nerve injury and an intact rotator cuff who underwent a triceps nerve branch to axillary nerve transfer was performed. Patient demographics, surgical technique, deltoid strength, donor-site morbidity, complications and time to surgery were evaluated.

Result

Ten male patients, mean age 38.3 years (range 18 to 66 years), underwent a triceps to axillary nerve transfer for isolated axillary nerve injury 7.4 months (range five to 12 months) post-traumatic shoulder dislocation. Deltoid function was British Medical Research Council grade 0/5 in all patients preoperatively and ≥3/5 deltoid strength in eight patients at final follow-up (14.8 months [range 12 to 25 months]). There were no complications and no donor-site morbidity.

Conclusion

A triceps to axillary nerve transfer for isolated axillary neuropathy following traumatic shoulder dislocation improved shoulder pain, stability and deltoid strength, and potentially preserves shoulder function with advancing age by alleviating sole reliance on the rotator cuff for shoulder abduction and external rotation.

Effect of Selective Muscle Training Using Visual EMG Biofeedback on Infraspinatus and Posterior Deltoid

We investigated the effects of visual electromyography (EMG) biofeedback during side-lying shoulder external rotation exercise on the EMG amplitude for the posterior deltoid, infraspinatus, and infraspinatus/posterior deltoid EMG activity ratio. Thirty-one asymptomatic subjects were included. Subjects performed side-lying shoulder external rotation exercise with and without visual EMG biofeedback. Surface EMG was used to collect data from the posterior deltoid and infraspinatus muscles. The visual EMG biofeedback applied the pre-established threshold to prevent excessive posterior deltoid muscle contraction. A paired t-test was used to determine the significance of the measurements between without vs. with visual EMG biofeedback. Posterior deltoid activity significantly decreased while infraspinatus activity and the infraspinatus/posterior activity ratio significantly increased during side-lying shoulder external rotation exercise with visual EMG biofeedback. This suggests that using visual EMG biofeedback during shoulder external rotation exercise is a clinically effective training method for reducing posterior deltoid activity and increasing infraspinatus activity.

Functional evaluation of patient after arthroscopic repair of rotator cuff tear

BACKGROUND

Rotator cuff tear is a common problem either after trauma or after degenerative tear in old age group. Arthroscopic repair is the current concept of rotator cuff repair. Here, we are trying to evaluate the functional outcome after arthroscopic repair of full thickness rotator cuff tear (single row) in Indian population.

MATERIALS AND METHODS

Twenty five patients (14 males and 11 females) who underwent arthroscopic repair of full thickness rotator cuff tear at a single institution were included in the study. Postoperatively patient's shoulder was rated according to UCLA score, pain was graded according to the visual analog score. The range of motion was analysed and documented.

RESULTS

The mean age of the patients were 50.48 years. The preoperative VAS score mode was 7 and post operative VAS was 1 (p value <0.001). The UCLA grading was good in 80% (n = 20), fair in 12% (n = 3), excellent in 8% (n = 2) and poor results were seen in none of the patients. The mean UCLA improved from a score of 15.84 to 30.28 with a p value <0.001. Mean postoperative forward flexion was 161.6°, mean abduction was 147.6° and mean external rotation was 45.4°.

CONCLUSION

Arthroscopic repair is a good procedure for full thickness rotator cuff tear with minimal complications. The newer double row repair claims to be biomechanically superior with faster healing rates without functional advantages, hence we used a single row repair considering the Indian population and the cost effectiveness of the surgery with good to excellent results.

Management of disorders of the rotator cuff: proceedings of the ISAKOS upper extremity committee consensus meeting

The goal of this article is to consolidate the International Society of Arthroscopy, Knee Surgery & Orthopaedic Sports Medicine (ISAKOS) Upper Extremity Committee's (UEC's) current knowledge on rotator cuff disease and management, as well as highlight key unresolved issues. The rotator cuff is an anatomically complex structure important for providing glenohumeral function and stability as part of a closed chain system. Current consensus suggests rotator cuff injuries are most accurately diagnosed, at levels similar to diagnosis by magnetic resonance imaging, with a combination of cuff- and impingement-specific clinical tests. Updates in the understanding of acromion morphology, the insertional anatomy of the rotator cuff, and the role of suprascapular nerve release may require changes to current classification systems and surgical strategies. Although initial management focuses on nonoperative protocols, discussion continues on whether surgery for isolated impingement is clinically more beneficial than rehabilitation. However, clear indications have yet to be established for the use of single- versus double-row repair because evidence confirms neither is clinically efficacious than the other. Biceps tenodesis, however, in non-isolated cuff tears has proven more successful in addressing the etiology of shoulder pain and yields improved outcomes over tenotomy. Data reviewing the benefits of tendon transfers, shoulder prostheses, and mechanical scaffolds, as well as new research on the potential benefit of platelet-rich plasma, pluripotential stem cells, and gene therapies, will also be presented.

Effects of different movement directions on electromyography recorded from the shoulder muscles while passing the target positions

PURPOSE

We compared electromyography (EMG) recorded from the shoulder joint muscles in the same position for different movement directions.

METHODS

Fifteen healthy subjects participated. They performed shoulder elevation from 0° to 120°, shoulder depression from 120° to 0°, shoulder horizontal adduction from -15° to 105°, and shoulder horizontal abduction from 105° to -15°. The target positions were 90° shoulder elevation in the 0°, 30°, 60°, and 90° planes (0°, 30°, 60°, and 90° positions). EMG signals were recorded from the supraspinatus (SSP) muscle by fine-wire electrodes. EMG signals from the infraspinatus (ISP), anterior deltoid, middle deltoid, and posterior deltoid muscles were recorded using active surface electrodes.

RESULTS

During elevation and horizontal abduction, the SSP showed significantly higher activity than that shown during depression and during horizontal adduction in the 0°, 30°, and 60° positions. During elevation, the ISP showed significantly higher activity than during depression and during horizontal adduction in the 90° position. During horizontal abduction, the ISP showed significantly higher activity than during depression in the 90° position.

CONCLUSIONS

When the movement tasks were performed in different movement directions at the same speed, each muscle showed characteristic activity.

Rotator Cuff Weakness Is Not a Risk Factor for First-Time Anterior Glenohumeral Instability

Background:

Shoulder instability is a common problem in young athletes and can lead to pain and decreased ability to participate in high-level activities. Little is known about the modifiable risk factors for glenohumeral joint instability.

Hypothesis:

Isometric shoulder strength at baseline would be a modifiable risk factor associated with subsequent first-time anterior instability events.

Study Design:

Cohort study.

Methods:

Study participants were freshmen entering the United States Military Academy in June 2006. All participants completed bilateral isometric strength evaluations with a hand-held dynamometer at baseline upon entry into the study. Variables measured included internal and external rotation at 0° (IR0, ER0) and internal and external rotation at 45° of abduction (IR45, ER45). All subjects were followed for subsequent glenohumeral joint instability events until graduation in May 2010. Independent t tests were used to analyze the data.

Results:

Baseline strength data were available for 1316 shoulders with no prior history of instability, of which 26 went on to have an acute first-time anterior shoulder instability event while the individuals were at the academy. There were no significant differences in mean strength between shoulders that did not go on to develop instability (uninjured; n = 1290) and those that did develop anterior instability (injured; n = 26). The mean strength values in pounds of force for uninjured and injured shoulders, respectively, were as follows: IR0 (49.80 vs 49.29; P = .88), ER0 (35.58 vs 33.66; P = .27), IR45 (47.38 vs 46.93; P = .88), and ER45 (40.08 vs 38.98; P = .59).

Conclusion:

No association was found between isometric shoulder strength measures at baseline and subsequent first-time anterior glenohumeral joint instability within the high-risk athletic population studied in this prospective cohort.

A Systematic Literature Review of the Resistance Exercises That Promote Maximal Muscle Activity of the Rotator Cuff in Normal Shoulders

Background

There are numerous resistance exercises that can be used to activate the rotator cuff. However, the optimal exercises to achieve maximal muscle activation in supraspinatus, infraspinatus, subscapularis and teres minor remain unclear. Thus, the aim of this systematic review is to identify the optimal resistance exercises for producing maximal muscle activation of the rotator cuff in normal shoulders. Methods A literature search was completed using six key databases - MEDLINE, EMBASE, CINAHL, PEDro, SPORTdiscus and Cochrane Library (from inception to January 2012). The search yielded 452 records using terms relating to rotator cuff, exercise, and electromyography. Eighteen papers remained after duplicates were removed and selection criteria applied. Quality assessment, data extraction and data synthesis of included papers was undertaken.

Results

Prone horizontal abduction at 90–100° with external rotation, push-up-plus, empty can and full can produced greatest activity in supraspinatus; prone horizontal abduction at 90–100° with full external rotation, standing external rotation at 0° abduction and the push-up-plus exercise produced greatest activity in infraspinatus and push-up-plus and shoulder flexion exercise in subscapularis. There was limited data for teres minor.

Discussion

Exercises to elicit maximal activity of supraspinatus, infraspinatus and subscapularis in normal shoulders were identified.

Glenohumeral contact pressure in a simulated active compression test using cadaveric shoulders

BACKGROUND

The active compression test has been described to detect superior labrum anterior and posterior (SLAP) lesions. Some have speculated that contact between the lesser tuberosity and the superior glenoid in the testing position causes a positive test. This study evaluated the location of peak glenohumeral contact pressures during a simulated active compression test in a cadaveric model with and without SLAP lesions.

MATERIALS AND METHODS

Six specimens were tested. A pressure sensor was used to record glenohumeral contact, and a motion analysis system was used to measure humeral head translation. Contact pressures and translations were measured during serial deltoid and biceps loads. These were repeated for small and large SLAP lesions.

RESULTS

There was a notable shift in the location of peak contact pressure from the anterior-inferior glenoid to the anterior-superior glenoid with increasing deltoid load. Deltoid loading translated the humeral head posteriorly relative to the glenoid. Conversely, biceps loads countered the pull of the deltoid only when the biceps load was greater than the deltoid load. The SLAP tears did not significantly alter the degree of humeral head translation or location of the contact pressures.

CONCLUSIONS

In the active compression test, the posterior capsule is taut and the anterior capsule is lax, which permits the deltoid to translate the humeral head posteriorly. This shift in the peak contact pressure to the superior glenoid may elicit a positive active compression test.

LEVEL OF EVIDENCE

Basic Science Study, Biomechanics, Cadaver Model.

An 8-stage model for evaluating the tennis serve: implications for performance enhancement and injury prevention

BACKGROUND

The tennis serve is a complex stroke characterized by a series of segmental rotations involving the entire kinetic chain. Many overhead athletes use a basic 6-stage throwing model; however, the tennis serve does provide some differences.

EVIDENCE ACQUISITION

To support the present 8-stage descriptive model, data were gathered from PubMed and SPORTDiscus databases using keywords tennis and serve for publications between 1980 and 2010.

RESULTS

An 8-stage model of analysis for the tennis serve that includes 3 distinct phases-preparation, acceleration, and follow-through-provides a more tennis-specific analysis than that previously presented in the clinical tennis literature. When a serve is evaluated, the total body perspective is just as important as the individual segments alone.

CONCLUSION

The 8-stage model provides a more in-depth analysis that should be utilized in all tennis players to help better understand areas of weakness, potential areas of injury, as well as components that can be improved for greater performance.