Stability Of Glenohumeral Joint Research Articles

Current Concepts in Rehabilitation for Traumatic Anterior Shoulder Instability.

The objectives of this review are to evaluate the current evidence-based literature and concepts surrounding rehabilitation in patients with anterior shoulder instability injuries and surgical repair. The current literature evidence for shoulder rehabilitation for anterior shoulder instability and labral repair is limited. As a result, there are variations among surgeons and physical therapists in rehabilitation protocols after anterior shoulder instability injuries and repair. While general consensus on certain rehabilitation parameters exists, the evidence for the importance of rehabilitation and functional performance test for return to sport in future injury prevention is still lacking in literature. Rehabilitation after anterior shoulder instability injury and anterior labral repair is paramount in the injured or post-operative shoulder. Restoration of soft tissue mobility, dynamic glenohumeral joint stability, and balance and strength around the shoulder not only protect healing of injured or repaired soft tissues but also potentially minimizes future re-injury or recurrence risk.

Osteochondral Allografts in Shoulder Surgical Procedures.

The use of fresh osteochondral allografts has become popular in many joint-preserving orthopaedic procedures and shows early promising results within the shoulder. Distal tibial allograft contains a stout cartilaginous layer that appears to have highly congruent curvature and concavity to the glenoid, which makes for an optimal allograft option for instability. In the setting of large Hill-Sachs lesions, the use of a humeral-head osteochondral allograft is essential to restore geometry, stability, and mechanics of the native glenohumeral joint. One must be cautious with the treatment of glenoid chondral lesions with osteoarticular grafting procedures because of the depth of the glenoid compared with the depth of subchondral bone on the graft necessary to achieve a press fit, and advanced imaging is recommended when planning an operative intervention. Optimizing joint-preservation treatment with osteochondral allografts will rely on the long-term results of these procedures, and careful patient selection, preoperative discussion, and realistic expectations are necessary.

Paper #17 - Remplissage of an off-track hill-sachs lesion is necessary to restore biomechanical glenohumeral joint stability in a bipolar bone loss model

Purpose: To validate the “glenoid track” concept in a cadaveric bipolar bone loss model and to test whether “on-track” and “off-track” lesions can be adequately stabilized with Bankart or remplissage repair techniques. Methods: Eight fresh-frozen cadaver shoulders were tested in a custom shoulder rig with passive axial rotation and then progressive translational loading (10-40N). The injury conditions included glenoid bone loss of 15% with “on-track” (15%) and “off-track” (30%) Hill-Sachs lesions. Repair conditions included Hill-Sachs remplissage and/or Bankart repair. Engagement of bipolar lesions was noted, and glenohumeral joint stiffness was calculated from force-displacement measurements. Results: As seen in Table 1, for on-track lesions, engagement was rare and stability was adequately restored with Bankart repair only. For off-track lesions, engagement was routine and the addition of Hill-Sachs remplissage was necessary to restore biomechanical stability. As seen in Figure 1, injury conditions had much lower stiffness than the intact shoulder. Stiffness after off-track HS remplissage was much larger than that of the intact shoulder, injury conditions, and Bankart repair only conditions. Bankart repair of the on-track HS injury condition improved stiffness to near intact, while addition of on-track HS remplissage increased stiffness over Bankart repair alone at 90°. Conclusions: The glenoid track concept is supported by this model of two Hill-Sachs lesions with 15% glenoid bone loss. Our results support the paradigm of Bankart repair for on-track lesions and Bankart plus remplissage for off-track lesions. Remplissage of on-track lesions might be considered for increased stability in high-risk patients. Level of Evidence: Biomechanical study. Table 1Force at 60 or 90° causing engagement of the Hill-Sachs lesions with the glenoid. – indicates no engagement. Bold indicates that a given repair affected the engagement of the experimental condition to the left Figure 1Glenohumeral joint stiffness calculated from the translation of the humeral head with applied loads from 10-40 N at two rotation positions for the various injury and repair conditions of the shoulder. View Large Image Figure Viewer Download Hi-res image

Evolution of isokinetic torque ratios of shoulder rotator muscles

Shoulder internal (IR) and external rotator (ER) muscles play an important role in the stability of glenohumeral joint. The ratio between the peak torque of ER and IR in concentric (ER/IRPT) and mixed (ER-ECC/IR-CONPT) are usually measured to evaluate the effects of muscle weakness, sport activities, injury and treatment (Greenfield et al., 1990; Scoville et al., 1997). However, ER/IRPT and ER-ECC/IR-CONPT failed to provide some indication on the evolution of the ER/IR torque ratio (ER/IRTorque) and mixed torque ratio (ER-EC/IR-COTorque) during the range of motion (ROM). The aim of this study was to examine the ER/IRTorque and ER-EC/IR-COTorque during ROM in regard to the ER/IRPT and ER-ECC/IR-CONPT values. Twenty-one healthy trained (23.0 ± 2.7 y) underwent an isokinetic concentric IR and ER strength test on a Cybex Norm ® dynamometer in a seated position (45° shoulder abduction in scapular plane), at 60°.s −1 for both sides. ER/IRTorque and ER-EC/IR-COTorque were continuously recorded (PowerLab ® ) then averaged per range of 10° throughout 110°. ER/IRPT and ER-ECC/IR-CONPT were calculated according conventional method. Repeated Anova test revealed that ER/IRT significantly increased during internal rotation ( P < 0.05) with an inconstant value during ROM. ER/IRT was significantly lower than ER/IRPT in more than 80% of ROM. ER/IRPT and ER-ECC/IR-CONPT are classically determined according the peak torque value of RE and RI, regardless of the difference between angle for which each value is reached. However, we showed a variation of ER/IRTorque and ER-EC/IR-COTorque during the ROM. Coombs (2002) has already reported the effect of angular knee position on the hamstring/quadriceps torque ratio value. ER/IRTorque and ER-EC/IR-COTorque appears an additional indicator on the dynamic glenohumeral strength balance. In addition to PT ratio, ER/IRTorque and ER-EC/IR-COTorque ratios during the range of motion could assess to risk factors for shoulder injuries, specific adaptations to exercise training and rehabilitation.

The effect of the arthroscopic augmentation of the subscapularis tendon on shoulder instability and range of motion: A biomechanical study

BackgroundAnterior shoulder dislocation is common. The treatment of recurrence with glenoid bone defect is still considered controversial. A new arthroscopic subscapularis augmentation has recently been described that functions to decrease the anterior translation of the humeral head. The purpose of the presented study was to examine the biomechanical effect on glenohumeral joint motion and stability. MethodsEight fresh frozen cadaver shoulders were studied by use of a force guided industrial robot fitted with a six-component force-moment sensor to which the humerus was attached. The testing protocol includes measurement of glenohumeral translation in the anterior, anterior-inferior and inferior directions at 0°, 30° and 60° of glenohumeral abduction, respectively, with a passive humerus load of 30N in the testing direction. The maximum possible external rotation was measured at each abduction angle applying a moment of 1Nm. Each specimen was measured in a physiologic state, as well as after Bankart lesion with an anterior bone defect of 15–20% of the glenoid, after arthroscopic subscapularis augmentation and after Bankart repair. FindingsThe arthroscopic subscapularis augmentation decreased the anterior and anterior-inferior translation. The Bankart repair did not restore the mechanical stability compared to the physiologic shoulder group. External rotation was decreased after arthroscopic subscapularis augmentation compared to the physiologic state, however, the limitation of external rotation was decreased at 60° abduction. InterpretationThe arthroscopic subscapularis augmentation investigated herein was observed to restore shoulder stability in an experimental model.

Remplissage of an Off-track Hill-Sachs Lesion Is Necessary to Restore Biomechanical Glenohumeral Joint Stability in a Bipolar Bone Loss Model

To validate the glenoid track concept in a cadaveric bipolar bone loss model and to test whether "on-track" and "off-track" lesions can be stabilized with Bankart repair (BR) with or without Hill-Sachs remplissage (HSR). Eight fresh-frozen cadaveric shoulders were tested in a custom apparatus with passive axial rotation and then progressive translational loading (10 to 40N) at mid-range (60°) and end-range external rotation (90°). Injury conditions included glenoid bone loss of 15% with on-track (15%) and off-track (30%) Hill-Sachs lesions. Repair conditions included BR with HSR and BR without HSR. For on-track lesions, engagement occurred with translation testing in one shoulder (12.5%) at end-range rotation. After BR, engagement was prevented for this shoulder. For off-track lesions, engagement with translation testing occurred in 8 shoulders (100%) at end-range rotation and in 6 (75%) at mid-range rotation. AfterBR, engagement was prevented in 4 of 6 engaging shoulders (67%) at mid-range rotation but was prevented inzero of 8 (0%) at end-range rotation. Adding HSR prevented engagement in all 14 engaging shoulders with off-track lesions (100%). BR with HSR resulted in supraphysiological stiffness for off-track lesions at mid- and end-range rotation(13.3N/m vs 7.0N/m and 10.0N/m vs 5.0N/m, P= .0002) and for on-track lesions at end-range rotation (10.1N/m vs 5.0N/m, P= .0002). Stiffness of BR with HSR was not different from the intact shoulder for on-track lesions at mid-range rotation (7.2N/m vs 7.0N/m, P > .99). The patterns of engagement of Hill-Sachs lesions with a 15% glenoid defect in this model give support to the glenoid track concept. BR plus remplissage resulted in supraphysiological shoulder stiffness but was necessary to prevent engagement of off-track bipolar bone lesions. This biomechanical study provides evidence to aid in surgical decision making by examining the effects of bipolar bone loss and soft-tissue reconstruction on shoulder stability.

Finite element models of the human shoulder complex: a review of their clinical implications and modelling techniques.

SummaryThe human shoulder is a complicated musculoskeletal structure and is a perfect compromise between mobility and stability. The objective of this paper is to provide a thorough review of previous finite element (FE) studies in biomechanics of the human shoulder complex. Those FE studies to investigate shoulder biomechanics have been reviewed according to the physiological and clinical problems addressed: glenohumeral joint stability, rotator cuff tears, joint capsular and labral defects and shoulder arthroplasty. The major findings, limitations, potential clinical applications and modelling techniques of those FE studies are critically discussed. The main challenges faced in order to accurately represent the realistic physiological functions of the shoulder mechanism in FE simulations involve (1) subject‐specific representation of the anisotropic nonhomogeneous material properties of the shoulder tissues in both healthy and pathological conditions; (2) definition of boundary and loading conditions based on individualised physiological data; (3) more comprehensive modelling describing the whole shoulder complex including appropriate three‐dimensional (3D) representation of all major shoulder hard tissues and soft tissues and their delicate interactions; (4) rigorous in vivo experimental validation of FE simulation results. Fully validated shoulder FE models would greatly enhance our understanding of the aetiology of shoulder disorders, and hence facilitate the development of more efficient clinical diagnoses, non‐surgical and surgical treatments, as well as shoulder orthotics and prosthetics. © 2016 The Authors. International Journal for Numerical Methods in Biomedical Engineering published by John Wiley & Sons Ltd.

Influence of rotator cuff tears on glenohumeral stability during abduction tasks.

One of the main goals in reconstructing rotator cuff tears is the restoration of glenohumeral joint stability, which is subsequently of utmost importance in order to prevent degenerative damage such as superior labral anterior posterior (SLAP) lesion, arthrosis, and malfunction. The goal of the current study was to facilitate musculoskeletal models in order to estimate glenohumeral instability introduced by muscle weakness due to cuff lesions. Inverse dynamics simulations were used to compute joint reaction forces for several static abduction tasks with different muscle weakness. Results were compared with the existing literature in order to ensure the model validity. Further arm positions taken from activities of daily living, requiring the rotator cuff muscles were modeled and their contribution to joint kinetics computed. Weakness of the superior rotator cuff muscles (supraspinatus; infraspinatus) leads to a deviation of the joint reaction force to the cranial dorsal rim of the glenoid. Massive rotator cuff defects showed higher potential for glenohumeral instability in contrast to single muscle ruptures. The teres minor muscle seems to substitute lost joint torque during several simulated muscle tears to maintain joint stability. Joint instability increases with cuff tear size. Weakness of the upper part of the rotator cuff leads to a joint reaction force closer to the upper glenoid rim. This indicates the comorbidity of cuff tears with SLAP lesions. The teres minor is crucial for maintaining joint stability in case of massive cuff defects and should be uprated in clinical decision-making. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1628-1635, 2016.

Correlation of the Rotator Interval on Direct CT Arthrography in Shoulder Instability Patients with External Rotation Stress Radiographs

The rotator interval (RI) is defined as the space between the anterior aspect of the supraspinatus tendon (SST) and superior aspect of the subscapularis tendon (SSC), covered by rotator interval capsule (RIC) (1, 2). It represents a region of capsule that is not reinforced by overlying rotator cuff tendon (1) and its components, coracohumeral ligament (CHL) and superior glenohumeral ligament (SGHL), are suggested to have a role in glenohumeral joint (GHJ) stability. The role of different shoulder stabilizers vary according to different shoulder position. For example, the CHL is shown to be a stabilizer in superior-inferior directions with arm in external rotation, whereas, the intra-articular pressure that is maintained by the intact RIC is suggested to act as a stabilizer in superior-inferior directions with the arm in internal and neutral rotations (3). The role of the RI in shoulder mechanopathology remains a much debated subject, with some authors advocating its role as a negative articular pressure inducer (3), whereas others, in resisting posteroinferior glenohumeral translation (4-7). Correlation of the Rotator Interval on Direct CT Arthrography in Shoulder Instability Patients with External Rotation Stress Radiographs 견관절 불안정 환자의 CT 관절 조영술상 회전근개 간격과 외회전 부하 영상과의 연관성

Inclination-dependent changes of the critical shoulder angle significantly influence superior glenohumeral joint stability

BackgroundThe critical shoulder angle combines the acromion index and glenoid inclination and has potential to discriminate between shoulders at risk for rotator cuff tear or osteoarthritis and those that are asymptomatic. However, its biomechanics, and particularly the role of the glenoid inclination, are not yet fully understood. MethodsA shoulder simulator was used to analyze the independent influence of glenoid inclination during abduction from 0 to 60°. Spindle motors transferred tension forces by a cable-pulley on human cadaveric humeri. A six-degree-of-freedom force transducer was mounted directly behind the polyethylene glenoid to measure shear and compressive joint reaction force and calculate the instability ratio (ratio of shear and compressive joint reaction force) with the different force ratios of the deltoid and supraspinatus muscles (2:1 and 1:1). A stepwise change in the inclination by 5° increments allowed simulation of a critical shoulder angle range of 20° to 45°. FindingsTilting the glenoid to cranial (increasing the critical shoulder angle) increases the shear joint reaction force and therefore the instability ratio. A balanced force ratio (1:1) between the deltoid and the supraspinatus allowed larger critical shoulder angles before cranial subluxation occurred than did the deltoid-dominant ratio (2:1). InterpretationGlenoid inclination-dependent changes of the critical shoulder angle have a significant impact on superior glenohumeral joint stability. The increased compensatory activity of the rotator cuff to keep the humeral head centered may lead to mechanical overload and could explain the clinically observed association between large angles and degenerative rotator cuff tears.

Stability of the Glenohumeral Joint with Combined Humeral Head and Glenoid Defects

Objectives:Shoulders with recurrent anterior shoulder instability often have combined defects of the humeral head and glenoid. The aim of this study is to define the relationship of combined humeral head and glenoid defects on anterior shoulder instability. We hypothesize that combined humeral head and glenoid defects will produce greater instability than either defect found alone, and that the size of humeral head and glenoid defects which are “critical” and need to be repaired in order to restore glenohumeral stability will be smaller when the defects are found together than when either defect is found alone.Methods:Eighteen shoulder specimens (mean age 57 years) were tested at 60° of glenohumeral abduction and 80° of glenohumeral external rotation (equivalent to 90° of abduction and 90° of external rotation relative to the trunk). Humeral head defect sizes included 6%, 19%, 31%, and 44% of the humeral head diameter. Glenoid defect sizes included 10%, 20%, and 30% of the glenoid width. Outcome measures included Percent of Intact Stability Ratio (stability ratio for a given trial divided by the stability ratio in the intact state for that specimen) and Percent of Intact Translation (distance to dislocation for a given trial divided by the distance to dislocation in the intact state for that specimen).Results:There was a progressive decrease in stability as humeral head defect size increased and as glenoid defect size increased. The decrease in Percent of Intact Stability Ratio reached statistical significance for humeral head defects of 44%, for glenoid defects of 30%, and additionally for a combined 19% humeral head defect with a 20% glenoid defect. The mean Percent of Intact Stability Ratio was 65% for a combined 19% humeral head defect with a 20% glenoid defect. The decrease in Percent of Intact Translation reached statistical significance for humeral head defects of 31% and 44%, for glenoid defects of 20% and 30%, and additionally for a combined 19% humeral head defect with a 10% glenoid defect. The mean Percent of Intact Translation was 69% for a combined 19% humeral head defect with a 10% glenoid defect.Conclusion:The humeral head and glenoid defect sizes required to produce instability are smaller when the defects are found together than when either defect is found alone. In patients with combined humeral head and glenoid defects bony reconstruction may be indicated for humeral head defects as small as 19% of the humeral head diameter and glenoid defects as small as 10-20% of the glenoid width.

Effect of rotator cuff tears on joint reaction force and muscle force: musculoskeletal model simulation

Background: Rotator cuff tears can cause serious pain and dysfunction in the shoulder joint among adults. Previous reports have indicated the importance of the lesion area in the rotator cuff to shoulder dysfunction, but few have reported its effects on glenohumeral joint stability or muscle force. Purpose: The purpose of this study was to clarify the effects of rotator cuff tears on glenohumeral joint stability and muscle force using a musculoskeletal simulation. Methods: Three young adults participated in this study. Joint reaction force in the glenohumeral jointwas used to estimate joint stability. Arm elevation in the frontal and sagittal plane were measured by a motion capture system. A threemarker cluster attached to the acromion was used to obtain the scapular motion. We analyzed the arm elevation below 120 degree due to skin motion artifact. The AnyBody shoulder model was used to calculate the shoulder joint reaction force andmuscle force frommotion capture data, whichwere estimated in the intact model and four simulated cuff tear models:

Upper limb kinematics after cervical spinal cord injury: a review.

Although a number of upper limb kinematic studies have been conducted, no review actually addresses the key-features of open-chain upper limb movements after cervical spinal cord injury (SCI). The aim of this literature review is to provide a clear understanding of motor control and kinematic changes during open-chain upper limb reaching, reach-to-grasp, overhead movements, and fast elbow flexion movements after tetraplegia. Using data from MEDLINE between 1966 and December 2014, we examined temporal and spatial kinematic measures and when available electromyographic recordings. We included fifteen control case and three series case studies with a total of 164 SCI participants and 131 healthy control participants. SCI participants efficiently performed a broad range of tasks with their upper limb and movements were planned and executed with strong kinematic invariants like movement endpoint accuracy and minimal cost. Our review revealed that elbow extension without triceps brachii relies on increased scapulothoracic and glenohumeral movements providing a dynamic coupling between shoulder and elbow. Furthermore, contrary to normal grasping patterns where grasping is prepared during the transport phase, reaching and grasping are performed successively after SCI. The prolonged transport phase ensures correct hand placement while the grasping relies on wrist extension eliciting either whole hand or lateral grip. One of the main kinematic characteristics observed after tetraplegia is motor slowing attested by increased movement time. This could be caused by (i) decreased strength, (ii) triceps brachii paralysis which disrupts normal agonist–antagonist co-contractions, (iii) accuracy preservation at movement endpoint, and/or (iv) grasping relying on tenodesis. Another feature is a reduction of maximal superior reaching during overhead movements which could be caused by i) strength deficit in agonist muscles like pectoralis major, ii) strength deficit in proximal synergic muscles responsible for scapulothoracic and glenohumeral joint stability, iii) strength deficit in distal synergic muscles preventing the maintenance of elbow extension by shoulder elbow dynamic coupling, iv) shoulder joint ankyloses, and/or v) shoulder pain. Further studies on open chain movements are needed to identify the contribution of each of these factors in order to tailor upper limb rehabilitation programs for SCI individuals.

The influence of various resistance loads on the ratio of activity of the external rotator muscles of the shoulder and the anterior gliding of the humeral head during external rotation exercise.

[Purpose] To quantify the ratio of activation of the infraspinatus and posterior deltoid muscles and the anterior gliding motion of the humeral head during external rotation (ER) motions of the shoulder performed in prone position against different external resistance loads. [Subjects] Twenty healthy women between the ages of 20 and 30 years. [Methods] Activity ratio was quantified as the difference in the root mean square of the smoothed electromyography signal (EMG) of the posterior deltoid to the infraspinatus muscle, and anterior gliding pressure of the humeral head using a pressure biofeedback unit (PBU), for three resistance loads: 0, 1 and 2 kg. [Results] There was a significant correlation among all three variables (load, ratio, and pressure). Anterior gliding pressure correlated with the activity ratio, with activity of the posterior deltoid increasing with the magnitude of the resistance load. [Conclusion] There was a positive association between the magnitude of resistance load, activity of the posterior deltoid and anterior gliding pressure of the humeral head. The PBU could be used to facilitate the recruitment of the infraspinatus muscle at higher loads to improve glenohumeral joint stability during ER exercise against higher resistance.

Evaluating Healing of Allograft Tissues in the Shoulder—Cartilage and Bone

Glenohumeral bone loss and articular defects are often treated by using osseous or osteoarticular allografts. These aid in glenohumeral joint stability and in reconstruction of the native articular surface. Grafts include those such as iliac crest, coracoid, distal tibia, femoral head, or humeral head, depending on the specific surgical pathology. Articular grafts can be further subdivided into viable or nonviable sources. The outcome of grafts that are implemented for stability could be subject to osteolysis, which may portend a poor clinical outcome and recurrent instability. Similarly, grafts required for reconstruction of the articular surface may undergo avascular necrosis, nonunion, and collapse, rendering them useless. The status of these grafts is best assessed with postoperative imaging modalities, which range from plain film radiography to 3-dimensional computed tomography reconstructions. The purpose of this article is to review the current literature regarding the rate of graft resorption, integration, collapse, and union for each of the grafts mentioned using postoperative imaging.

Effects of Varying Locations for Biceps Tendon Tenotomy and Superior Labral Integrity on Shoulder Stability in a Cadaveric Concavity-Compression Model

The purpose of this study was to examine the location of biceps tenotomy and the integrity of the superior labrum as they relate to superior glenohumeral joint stability in a cadaveric concavity-compression model. Eight cadaveric glenoid labrums were mounted individually onto a load cell with the corresponding humerus fixed to the loading arm in the hanging-arm position. All surrounding soft tissue was removed except the labrum and proximal stump of the long head of the biceps (LHB) tendon, simulating a biceps tenotomy. A compressive load of 22N was applied across the glenohumeral joint. The humerus was then translated superiorly until it subluxated over the glenoid labrum. The force resisting superior translation was characterized for each of 50 cycles. Each specimen was tested under the following conditions: (1) with a 4 cm biceps stump after tenotomy, (2) with a 0 cm biceps stump, (3) after full detachment of the superior labrum, and (4) after repair of the labrum. Biceps tenotomy performed at the biceps-labral junction resulted in an average decrease in force required to superiorly subluxate the humeral head by 8.6% (P= .01) when compared with leaving 4cm of biceps stump. Resection of the entire superior labrum resulted in a future decrease to 15.2% (P < .001) from baseline. Repair of the labrum resulted in restoration of stability with a mean of 101.1% (P= .82) and was not statistically different from baseline. The kinematics of the glenohumeral joint was affected by labral repair, with an earlier upslope on the force-to-displacement curve and alteration in the total energy required to cause subluxation of the humeral head noted. In this study, location of the biceps tenotomy and integrity of the superior labrum affected glenohumeral stability during axial loading in the hanging-arm position. Repair of the labrum restored stability for superior subluxation but also changed the kinematics of the subluxation event. Preservation of superior labrum after biceps tenotomy provides increased resistive force to superior translation in a unidirectional biomechanical model.

Arthroscopic Bankart Repair With Knotless Anchors in the Lateral Decubitus Position

Arthroscopic stabilization of the glenohumeral joint has become the treatment of choice for the management of anteroinferior instability of the glenohumeral joint. Arthroscopic treatment affords improved visualization of primary pathology and associated lesions, decreased scarring, improved postoperative motion, as well as decreased postoperative pain. The addition of knotless anchors to a surgeon's armory provides stable fixation of the pathologic labrocapsular complex to the glenoid rim without the technical difficulties associated with arthroscopic knot tying and may further avoid complications from the presence of intraarticular knots that may irritate the articular surface. The key to successful surgery remains the identification and treatment of all associated pathology. Accurate portal placement and careful anchor placement are keys to the anatomical restoration of the labrum. Simple as well as more complex suture configurations allow a surgeon to restore the labral height and position.

Role of Coracoacromial Ligament and Related Structures in Glenohumeral Stability: A Cadaveric Study

This study sought to determine the role of the coracoacromial ligament and related arch structures in glenohumeral joint stabilization. Eight fresh-frozen cadaver specimens were tested at multiple angles of glenohumeral abduction and rotation for translations (in the direction of and perpendicular to a 50-N force) in intact, vented shoulders and after three interventions: coracoacromial veil release, coracoacromial ligament release, and anterior acromioplasty. After releasing the veil, an inferior force significantly increased inferior translation at lower angles of abduction with no additional increase after coracoacromial ligament section or acromioplasty. After ligament release or acromioplasty, a superior force increased superior translation at all angles. Few increases in anterior or posterior translations were observed. The coracoacromial veil interacts with the structures of the coracoacromial arch and glenohumeral capsule to limit inferior humeral translation. Likewise, the coracoacromial ligament and the acromian serve to limit superior translation. Attempts to preserve these structures may help improve surgical outcomes.

Rotator-Cuff Muscle-Recruitment Strategies During Shoulder Rehabilitation Exercises

There are contradictory data on optimal muscle-activation strategies for restoring shoulder stability. Further investigation of neuromuscular-control strategies for glenohumeral-joint stability will guide clinicians in decisions regarding appropriate rehabilitation exercises. To determine whether subscapularis, infraspinatus, and teres minor (anteroposterior force couple) muscle activation differ between 4 shoulder exercises and describe coactivation ratios and individual muscle-recruitment characteristics of rotator-cuff muscles throughout each shoulder exercise. Crossover. Laboratory. healthy, physically active men, age 20.55 ± 2.0 y. 4 rehabilitation exercises: pitchback, PNF D2 pattern with tubing, push-up plus, and slide board. Mean coactivation level, coactivation-ratio patterns, and level (area) of muscle-activation patterns of the subscapularis, infraspinatus, and teres minor throughout each exercise. Coactivation levels varied throughout each exercise. Subscapularis activity was consistently higher than that of the infraspinatus and teres minor combined at the start of each exercise and in end ranges of motion. Individual muscle-recruitment levels in the subscapularis were also different between exercises. Results provide descriptive data for determining normative coactivation-ratio values for muscle recruitment for the functional exercises studied. Differences in subscapularis activation suggest a reliance to resist anteriorly directed forces.

Normal shoulder muscular activation and co‐ordination during a shoulder elevation task based on activities of daily living: An electromyographic study

Studies of normal shoulder function have often failed to consider the inter-relationship between different muscle groups in activities relevant to daily life. Upper limb functional status was assessed in 12 healthy male volunteers using the Functional Impairment Test-Hand, Neck, Shoulder and Arm test (FIT-HaNSA). Electromyography was then used to study the activity and coordination of 13 muscles (10 by surface electrodes, 3 by fine-wire intramuscular electrodes) around the shoulder during a dynamic movement task based on the shelf-lifting task in FIT-HaNSA. Muscles were grouped for analysis into deltoid (anterior, middle, and posterior divisions), adductors (latissimus dorsi and teres major), rotator cuff (supraspinatus, infraspinatus, and subscapularis), and elbow flexor (brachioradialis, biceps brachii) groups. There were no significant inter-session effects. Using cross-correlation analysis to investigate the whole time-course of activation, there were highly significant positive correlations (p < 0.001) between the deltoid and rotator cuff, the deltoid and adductor and the adductor and rotator cuff groups, and a significant negative correlation between the deltoid and elbow flexor groups (p = 0.031). We conclude that the deltoid, adductor, and rotator cuff muscles all contribute to the muscular component of glenohumeral joint stability. Muscular stability can be adapted as required to meet task-specific demands.