The combined dynamic and static contributions to subacromial impingement. A biomechanical analysis

Subacromial contact after acromioplasty in the rotator cuff deficient shoulder

Subacromial impingement (SAI) is associated with shoulder pain and dysfunction and is exacerbated by rotator cuff tears; however, the role of acromioplasty in mitigating subacromial contact in the rotator cuff deficient shoulder remains debated. This study aimed to quantify the influence of isolated and combined tears involving the supraspinatus on subacromial contact during abduction; and second, to evaluate the influence of acromioplasty on joint space size and subacromial contact under these pathological conditions. Eight fresh-frozen human cadaveric upper limbs were mounted to a computer-controlled testing apparatus that simulated joint motion by simulated force application. Shoulder abduction was performed while three-dimensional joint kinematics was measured using an optoelectronic system, and subacromial contact evaluated using a digital pressure sensor secured to the inferior acromion. Testing was performed after an isolated tear to the supraspinatus, as well as tears involving the subscapularis and infraspinatus-teres minor, both before and after acromioplasty. Rotator cuff tears significantly increased peak subacromial pressure (p < 0.001), average subacromial pressure (p = 0.001), and contact force (p = 0.034) relative to those in the intact shoulder. Following acromioplasty, significantly lower peak subacromial contact pressure, force and area were observed for all rotator cuff tears involving the supraspinatus at 30° of abduction (p < 0.05). Acromioplasty predominantly reduces acromion thickness anteriorly thereby reducing subacromial contact in the rotator cuff deficient shoulder, particularly in early to mid-abduction where superior glenohumeral joint shear force potential is large. These findings provide a biomechanical basis for acromioplasty as an intervention for SAI syndrome and as an adjunct to rotator cuff repairs.

The long head of the biceps tendon undergoes multiaxial deformation during shoulder motion

The long head biceps tendon (LHBT) is presumed a common source of shoulder joint pain and injury. Despite common LHBT pathologies, diagnosis and preferred treatment remain frequently debated. This Short Communication reports the development of a subject-specific finite element model of the shoulder joint based on one subject's 3D reconstructed anatomy and 3D in vivo kinematics recorded from bone-fixed electromagnetic sensors. The primary purpose of this study was to use the developed finite element model to investigate the LHBT mechanical environment during a typical shoulder motion of arm raising. Furthermore, this study aimed to assess the viability of material models derived from uniaxial tensile tests for accurate simulation of in vivo motion. The findings of our simulations indicate that the LHBT undergoes complex multidimensional deformations. As such, uniaxial material properties reported in the existing body of literature are not sufficient to simulate accurately the in vivo mechanical behavior of the LHBT. Further experimental tests on cadaveric specimens, such as biaxial tension and combinations of tension and torsion, are needed to describe fully the mechanical behavior of the LHBT and investigate its mechanisms of injury.

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 Influence of Age at Pediatric-Onset Spinal Cord Injury and Years of Wheelchair Use on Shoulder Complex Joint Dynamics During Manual Wheelchair Propulsion

Objective

To assess the association of age at pediatric-onset spinal cord injury (SCI) and years of manual wheelchair use with shoulder dynamics.

Design

Upper extremity kinematics and hand-rim kinetics were obtained during manual wheelchair propulsion. An inverse dynamics model computed three-dimensional acromioclavicular, sternoclavicular, and glenohumeral joint dynamics. Linear mixed effects models evaluated the association of age at injury onset and years of wheelchair use with shoulder dynamics.

Setting

Motion laboratory within a children's hospital.

Participants

Seventeen manual wheelchair users (N=17; 6 female, 11 male; mean age: 17.2 years, mean age at SCI onset: 11.5 years) with pediatric-onset SCI (levels: C4-T11) and International Standards for Neurological Classification of SCI grades: A (11), B (3), C (2), and N/A (2).

Interventions

Not applicable.

Main Outcome Measures

Acromioclavicular, sternoclavicular, and glenohumeral angles and ranges of motion, and glenohumeral forces and moments.

Results

We observed a decrease in maximum acromioclavicular upward rotation (ß [95% confidence interval {CI}]=3.02 [0.15,5.89], P=.039) and an increase in acromioclavicular downward/upward rotation range of motion (ß [95% CI]=0.44 [0.08,0.80], P=.016) with increasing age at SCI onset. We found interactions between age at onset and years of use for maximum glenohumeral abduction (ß [95% CI]=0.16 [0.03,0.29], P=.017), acromioclavicular downward/upward rotation range of motion (ß [95% CI]=-0.05 [-0.09,-0.01], P=.008), minimum acromioclavicular upward rotation (ß [95% CI]=-0.34 [-0.64,-0.04], P=.026). A decrease in glenohumeral internal rotation moment (ß [95% CI]=-0.09 [-0.17,-0.009], P=.029) with increasing years of use was found.

Conclusions

Age at injury and the years of wheelchair use are associated with shoulder complex biomechanics during wheelchair propulsion. These results are noteworthy, as both age at SCI onset and years of wheelchair use are considered important factors in the incidence of shoulder pain. These results suggest that investigations of biomechanical changes over the lifespan are critical.

A design tool to estimate maximum acceptable manual arm forces for above-shoulder work

There is a need for design criteria for above-shoulder work to prevent shoulder fatigue and supraspinatus injuries. A tool is developed to estimate maximum acceptable manual arm forces for above-shoulder work based on 25th % female strength with adjustments for supraspinatus tendon impingement and shoulder fatigue. The tool equations are presented along with tables of maximum acceptable manual arm forces in 77 locations in the 3 D space above the shoulder that accommodates a 50th % female reach. The largest acceptable anterior force, 140.3 N, occurs at shoulder height, 0.5 m anterior to the shoulder. The largest acceptable superior force, 84.4 N, occurs at shoulder height, 0.1 m anterior and 0.2 m medial to the shoulder. The new tool provides design criteria for arm exertions at a higher level of detail than prior ergonomic tools, making it useful for engineers. Based on sensitivity analyses, the tool is robust to parameter assumptions. Practitioner summary: Above-shoulder work is associated with increased risk for shoulder fatigue and injuries. A new tool is developed that estimates maximum acceptable manual arm forces for work at or above shoulder height. The tool can be used to design acceptable above-shoulder work so that it can be accomplished by most workers. Abbreviations: AFF: arm force field; AP: anterior/posterior; DC: duty cycle; GH: glenohumeral angle; HT: humerothoracic angle; LM: lateral/medial; MAE: maximum acceptable effort; MAF: maximum acceptable force; MAS: manual arm strength; MVC: maximum voluntary contraction; N: newton; OCRA: occupational repetitive action; R: reach distance; RMS: root means square; RULA: rapid upper limb assessment; SF: scale factor; SI: superior/inferior; ST: scapulothoracic angle; T: thoracicKEY POINTSA new design tool is introduced that estimates maximum acceptable hand forces for specific locations above the shoulder.This above-shoulder tool is based on a 50th percentile female anthropometry and 25th percentile female manual arm strength.These base strengths are multiplied by scaling factors that adjust for subacromial impingement and fatigue.The tool was shown to be robust based on sensitivity analysis.

Changes in Muscle Activation During and After a Shoulder-Fatiguing Task: A Comparison of Elite Female Swimmers and Water Polo Players

This study compared female athletes with different aquatic sports expertise in their neuromuscular activation before, during, and after a shoulder internal rotation fatigue protocol. Eleven water polo players, 12 swimmers, and 14 controls completed concentric maximal voluntary external and internal shoulder rotations before and after a fatigue protocol consisting of concentric internal rotations at 50% of maximal voluntary contraction for at least 3 min or until reporting a rating of perceived effort RPE of 8/10 or higher. Muscle activation was measured for the maximal voluntary contractions, as well as for the first (T1), middle (T2), and third (T3) minute of the fatigue protocol using surface electromyography (EMG) on pectoralis major, anterior and posterior deltoid, upper and middle trapezius, and latissimus dorsi. Intramuscular EMG was used for supraspinatus, infraspinatus, and subscapularis. Pre-fatigue internal rotation torque was significantly correlated with shorter task duration (r = −0.39, p = 0.02), with water polo players producing significantly greater torque than controls but having significantly lower endurance. Swimmers demonstrated decreased latissimus dorsi activation at T3 compared to T2 (p = 0.020, g = 0.44) and T1 (p = 0.029, g = 0.74), differing from water polo players and controls who exhibited increased agonist activation and decreased activation of stabilizers. Comparing the pre-fatigue to the post-fatigue maximal shoulder rotations, water polo players had decreased activation in subscapularis (p = 0.018, g = 0.67); all groups had decreased activation in latissimus dorsi (p < 0.001), though swimmers demonstrated a large effect (g = 0.97); and controls had decreased activation in supraspinatus (p = 0.005, g = 0.71). Together, these results suggest that sports expertise may be associated with different muscle activation both while and after fatigue is induced. Further research should continue to explore sports-specific patterns of muscle recruitment and fatigue adaptations, as well as if certain strategies are adaptive or maladaptive. This may have important consequences for injury prevention among athletes who perform repetitive overhead movements in their sports and who are susceptible to overuse injuries.

Disabled Throwing Shoulder 2021 Update: Part 1-Anatomy and Mechanics

The purpose of this article is to provide updated information for sports health care specialists regarding the Disabled Throwing Shoulder (DTS). A panel of experts, recognized for their experience and expertise in this field, was assembled to address and provide updated information on several topics that have been identified as key areas in creating the DTS spectrum. Each panel member submitted a concise presentation on one of the topics within these areas, each of which were then edited and sent back to the group for their comments and consensus agreement in each area. Part 1 presents the following consensus conclusions and summary findings regarding anatomy and mechanics, including: 1) The current understanding of the DTS identifies internal impingement, resulting from a combination of causative factors, as the final common pathway for the great majority of the labral pathoanatomy; 2) intact labral anatomy is pivotal for glenohumeral stability, but its structure does not control or adapt well to shear or translational loads; 3) the biceps plays an active role in dynamic glenohumeral stability by potentiating "concavity compression" of the glenohumeral joint; 4) the ultimate function of the kinetic chain is to optimize the launch window, the precise biomechanical time, and position for ball release to most effectively allow the ball to be thrown with maximum speed and accuracy, and kinetic chain function is most efficient when stride length is optimized; 5) overhead throwing athletes demonstrate adaptive bony, capsular, and muscular changes in the shoulder with repetitive throwing, and precise measurement of shoulder range of motion in internal rotation, external rotation, and external rotation with forearm pronation is essential to identify harmful and/or progressive deficits. LEVEL OF EVIDENCE: Level V, expert opinion.

Long Head of the Biceps Tendon Ruptures: Biomechanics, Clinical Ramifications, and Management

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Pathology of the long head of the biceps tendon is a common source of shoulder pain and often occurs in combination with other shoulder disorders.

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Nonsurgical management, including rest and activity modification, use of nonsteroidal anti-inflammatory drugs, physical therapy, and corticosteroid injections, is usually the first line of treatment.

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Patients with symptoms that are refractory to nonsurgical management are indicated for biceps tenotomy or various tenodesis procedures.

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Although several studies have reported a higher incidence of "Popeye" deformity, muscle cramping, and pain in the bicipital groove postoperatively with tenotomy compared with tenodesis, there are no substantial differences in functional scores or patient satisfaction between the 2 techniques.

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To date, both tenotomy and tenodesis have been shown to be effective options in the management of long head of the biceps tendinopathy, and there are advantages to each procedure.

Measuring 3D In-vivo Shoulder Kinematics using Biplanar Videoradiography

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

Neuro-mechanical aspects of playing-related mobility disorders in orchestra violinists and upper strings players: a review

Orchestra musicians are at high risk of neuro-mechanical disorders due to the intense stresses their body withstand, leading to pain and injury. This review presents a comprehensive account of the works on the circumstances and types of playing related mobility disorders of upper strings players, as well as on the relevant neuro-mechanical factors and perspectives to those disorders. The following aspects are considered: asymmetry and imbalance in the musculo-skeletal system, muscle-bone-joint interactions, repetitive overloading and fatigue. An additional factor relates to neuro-muscular redundancy in the motor system, whereby more muscles and tendons than strictly necessary are engaged in performing a motor task, thus making the system indeterminate, with no unique solution. This same task can be performed with different muscle combinations. It is thus of interest to verify whether playing disorders may be alleviated by considering alternative techniques of performance.

Pressure Distribution to the Distal Biceps Tendon at the Radial Tuberosity: A Biomechanical Study

PURPOSE

Mechanical impingement at the narrow radioulnar space of the tuberosity is believed to be an etiological factor in the injury of the distal biceps tendon. The aim of the study was to compare the pressure distribution at the proximal radioulnar space between 2 fixation techniques and the intact state.

METHODS

Six right arms and 6 left arms from 5 female and 6 male frozen specimens were used for this study. A pressure transducer was introduced at the height of the radial tuberosity with the intact distal biceps tendon and after 2 fixation methods: the suture-anchor and the cortical button technique. The force (N), maximum pressure (kPa) applied to the radial tuberosity, and the contact area (mm²) of the radial tuberosity with the ulna were measured and differences from the intact tendon were detected from 60° supination to 60° pronation in 15° increments with the elbow in full extension and in 45° and 90° flexion of the elbow.

RESULTS

With the distal biceps tendon intact, the pressures during pronation were similar regardless of extension and flexion and were the highest at 60° pronation with 90° elbow flexion (23.3 ± 53.5 kPa). After repair of the tendon, the mean peak pressure, contact area, and total force showed an increase regardless of the fixation technique. Highest peak pressures were found using the cortical button technique at 45° flexion of the elbow and 60° pronation. These differences were significantly different from the intact tendon. The contact area was significantly larger in full extension and 15°, 30°, and 60° pronation using the cortical button technique.

CONCLUSIONS

Pressures on the distal biceps tendon at the radial tuberosity increase during pronation, especially after repair of the tendon.

CLINICAL RELEVANCE

Mechanical impingement could play a role in both the etiology of primary distal biceps tendon ruptures and the complications occurring after fixation of the tendon using certain techniques.

Isokinetic Fatigue Ratio of Shoulder Rotators in Elite Softball Players With and Without Rotator Cuff Tendinopathy, and its Association With the Subacromial Space

CONTEXT

Fatigue of the shoulder rotators may cause reduction of the subacromial space (SAS) and contribute to rotator cuff tendinopathy.

OBJECTIVES

To compare the isokinetic peak torques and fatigue ratios of shoulder external rotators (ER) and internal rotators (IR) between elite softball athletes with and without rotator cuff tendinopathy and to investigate their associations with the SAS.

DESIGN

Cross-sectional study.

SETTING

University laboratory.

PARTICIPANTS

Twenty-five elite softball players and 31 asymptomatic sedentary controls participated in this study.

MAIN OUTCOME MEASURES

Isokinetic concentric IR and ER peak torque and fatigue ratio were measured at 60°/s and at 180°/s, respectively; and ultrasound measurement of the SAS was measured during 0° and 60° of shoulder abduction.

RESULTS

Athletes with rotator cuff tendinopathy demonstrated lower peak torque in shoulder concentric ER when compared with their healthy counterparts (37.8 [5.8%] vs 43.6 [8.5%]). No significant difference was found in the fatigue ratios of ER, IR, and ER/IR when compared between elite softball athletes with and without rotator cuff tendinopathy (all P > .24). In asymptomatic athletes, greater IR peak torque (r = .583, P = .03), lower ER/IR strength ratio (r = -.605, P = .02), and greater ER/IR fatigue ratio (r = .575, P = .03) were moderately associated with more reduction of the SAS during 0° and 60° of shoulder abduction.

CONCLUSIONS

Decreased strength ratio and fatigue ratio of ER/IR were related to reduction of the SAS.

Arthroscopic rotator cuff repair with and without subacromial decompression is safe and effective: a clinical study

BACKGROUND

Subacromial decompression, that consists of the release of the coracoid-acromial ligament, subacromial bursectomy and anterior-inferior acromioplasty, has traditionally been performed in the management of this pathology. However, the purpose of subacromial decompression procedure is not clearly explained. Our reaserch aimed to analyse the differences among the outcomes of arthroscopic rotator cuff repair (RCR) made with suture anchors, with or without the subacromial decompression procedure.

METHODS

116 shoulders of 107 patients affected by rotator cuff (RC) tear were treated with Arthroscopic RCR. In 54 subjectes, the arthroscopic RCR and the subacromial decompression procedure (group A) were executed, whereas 53 took only arthroscopic RCR (group B). Clinical outcomes were evaluated through the use of the modified UCLA shoulder rating system, Wolfgang criteria shoulder score and Oxford shoulder score (OSS). Functional outcomes were assessed utilizing active and passive range of motion (ROM) of the shoulder, and muscle strength. The duration of the follow up and the configuration of the acromion were used to realize the comparison between the two groups.

RESULTS

In patients with 2 to 5 year follow up, UCLA score resulted greater in group A patients. In subjectes with longer than five years of follow up, group B patients showed considerably greater UCLA score and OSS if related with group A patients. In subjectes that had the type II acromion, group B patients presented a significant greater strength in external rotation.

CONCLUSION

The long term clinical outcomes resulted significantly higher in patients treated only with RCR respect the ones in patients underwent to RCR with subacromial decompression.

Age-Related Changes in Morphology and Function of Scapular Muscles in Asymptomatic People

BACKGROUND

Aging is a contributing factor to rotator cuff tears. Dysfunction of the scapular muscles can be a potential cause of rotator cuff tears. Although aging can contribute to dysfunction of the scapular muscles and subsequently result in rotator cuff tears, the effects of aging on scapular muscles are unclear.

OBJECTIVE

To determine changes in sizes and electromyographic activities of the scapular muscles with age in asymptomatic subjects.

DESIGN

Cross-sectional study.

PATIENTS

Fifty-four asymptomatic subjects without shoulder pain and dysfunction (18 male and 36 female) were recruited for this study. Subjects consisted of 19 people aged 20-39 years (young adult group, 27.2 ± 5.2 years), 17 people aged 40-59 years (middle age group, 49.9 ± 6.6 years), and 18 people aged 60-79 years (elderly group, 68.0 ± 7.1 years).

METHODS

Using ultrasonography, we measured the muscle thickness of the trapezius (upper and lower portions), serratus anterior, and middle deltoid muscles during rest with the subject in a sitting position. Activities of the same muscles were measured with surface electromyography during shoulder elevation in the scapular plane up to 120°. The electromyographic data were analyzed at ranges 0°-30°, 30°-60°, and 60°-90°. Analysis of variance and Bonferroni multiple comparisons were used for statistical analysis.

RESULTS

Muscle thickness of the lower trapezius in the elderly group was decreased significantly compared with that in the young adult group (95% confidence interval -0.40, 2.24; P < .001) and middle age group (95% confidence interval -0.34, 1.89; P = .012). There were no significant differences in muscle activity and activity ratio between groups.

CONCLUSION

In scapular muscles, muscle thickness of the lower trapezius significantly decreased with aging, although there were no decreases in muscle thicknesses of the other muscles between different age groups. For the functional change, aging may not affect the scapular muscle activities and balance of the activities between the deltoid and scapular muscles.

LEVEL OF EVIDENCE

IV.

The effect of coracoacromial ligament excision and acromioplasty on the amount of rotator cuff force production necessary to restore intact glenohumeral biomechanics

HYPOTHESIS AND BACKGROUND

Coracoacromial ligament (CAL) excision and acromioplasty increase superior and anterosuperior glenohumeral translation. It is unknown how much of an increase in rotator cuff force production is required to re-establish intact glenohumeral biomechanics after these surgical procedures. We hypothesized that, after CAL excision and acromioplasty, an increase in rotator cuff force production would not be necessary to reproduce the anterosuperior and superior translations of the intact specimens.

METHODS

Nine cadaveric shoulders were subjected to loading in the superior and anterosuperior directions in the intact state after CAL excision, acromioplasty, and recording of the translations. The rotator cuff force was then increased to normalize glenohumeral biomechanics.

RESULTS

After CAL excision at 150 and 200 N of loading, an increase in the rotator cuff force by 25% decreased anterosuperior translation to the point where there was no significant difference from the intact specimen's translation. After acromioplasty (and CAL excision) at 150 and 200 N, an increase in the rotator cuff force of 25% and 30%, respectively, decreased superior translation to the point where there was no significant difference from the intact specimen's translation.

CONCLUSIONS

At 150 to 200 N of loading, CAL excision and acromioplasty increase the rotator cuff force required to maintain normal glenohumeral biomechanics by 25% to 30%.

CLINICAL RELEVANCE

After a subacromial decompression, the rotator cuff has an increased force production requirement to maintain baseline glenohumeral mechanics. Under many circumstances, in vivo force requirements may be even greater after surgical attenuation of the coracoacromial arch.

LEVEL OF EVIDENCE

Basic Science Study; Biomechanics.

Posterior Capsular Plication Constrains the Glenohumeral Joint by Drawing the Humeral Head Closer to the Glenoid and Resisting Abduction

BACKGROUND

Shoulder pain is a common problem, with 30% to 50% of the American population affected annually. While the majority of these shoulder problems improve, there is a high rate of recurrence, as 54% of patients experience persistent symptoms 3 years after onset.

PURPOSE

Posterior shoulder tightness has been shown to alter glenohumeral (GH) kinematics. Clinically, posterior shoulder contractures result in a significant loss of internal rotation and abduction (ABD). In this study, the effect of a posterior capsular contracture on GH kinematics was investigated using an intact cadaveric shoulder without violating the joint capsule or the rotator cuff.

STUDY DESIGN

Controlled laboratory study.

METHODS

Glenohumeral motion, humeral load, and subacromial contact pressure were measured in 6 fresh-frozen left shoulders during passive ABD from 60° to 100° using an automated robotic upper extremity testing system. Baseline values were compared with the experimental condition in which the full thickness of posterior tissues was plicated without decompressing the joint capsule.

RESULTS

Posterior soft tissue plication resulted in increased compression between the humeral head and the glenoid (axial load) at 90° of ABD. Throughout ABD, the posterior contracture increased the anterior and superior moment on the humeral head, but it did not change the GH kinematics in this intact model. As a result, there was no increase in the subacromial contact pressure during ABD with posterior plication.

CONCLUSION

In an intact cadaveric shoulder, posterior contracture does not alter GH motion or subacromial contact pressure during passive ABD. By tightening the soft tissue envelope posteriorly, there is an increase in compressive load on the articular cartilage and anterior/superior force on the humeral head. These findings suggest that subacromial impingement in the setting of a posterior soft tissue contracture may result from alterations in scapulothoracic motion, not changes in GH kinematics.

CLINICAL RELEVANCE

This investigation demonstrates that posterior capsular plication increases the axial load on the shoulder joint during ABD. While a significant difference from baseline was observed in the plicated condition, posterior capsular plication did not change GH motion or subacromial contact pressure significantly.

Natural History of Rotator Cuff Disease and Implications on Management

Degenerative rotator cuff disease is commonly associated with ageing and is often asymptomatic. The factors related to tear progression and pain development are just now being defined through longitudinal natural history studies. The majority of studies that follow conservatively treated painful cuff tears or asymptomatic tears that are monitored at regular intervals show slow progression of tear enlargement and muscle degeneration over time. These studies have highlighted greater risks for disease progression for certain variables, such as the presence of a full-thickness tear and involvement of the anterior aspect supraspinatus tendon. Coupling the knowledge of the natural history of degenerative cuff tear progression with variables associated with greater likelihood of successful tendon healing following surgery will allow better refinement of surgical indications for rotator cuff disease. In addition, natural history studies may better define the risks of nonoperative treatment over time. This article will review pertinent literature regarding degenerative rotator cuff disease with emphasis on variables important to defining appropriate initial treatments and refining surgical indications.

Evidence-Based Strategies for Preserving Mobility for Elderly and Aging Manual Wheelchair Users

Elderly and aging manual wheelchair (MWC) users have increased risk for accelerated loss of function and mobility that greatly limits independence and affects quality of life. This review paper addresses important issues for preserving function and mobility for elderly and aging individuals who use a MWC by presenting the current available evidence and recommendations. These include recommendations for maximizing function, by decreasing pain, improving the ability to self-propel, and prolonging mobility and endurance through ergonomics, individualized wheelchair selection and configuration, and adaptations for increasing the capacity to handle the daily mobility demands through training, strengthening, and exercise. Each recommendation is supported by current research in each relevant area.

The long head of the biceps tendon has minimal effect on in vivo glenohumeral kinematics: a biplane fluoroscopy study

BACKGROUND

The in vivo stabilizing role of the long head of the biceps tendon (LHB) is poorly understood. While cadaveric studies report that the loaded LHB constrains translations in all directions, clinical data suggest that there is no clinically demonstrable alteration in glenohumeral position after LHB tenodesis or tenotomy. The purpose of this study was to investigate potential alterations in glenohumeral kinematics after LHB tenodesis during 3 dynamic in vivo motions using a biplane fluoroscopy system.

HYPOTHESIS

Our hypothesis was that there would be no difference in glenohumeral translations greater than 1.0 mm between shoulders after biceps tenodesis and healthy contralateral shoulders.

STUDY DESIGN

Controlled laboratory study.

METHODS

Five patients who underwent unilateral, open subpectoral tenodesis performed abduction, a simulated late cocking phase of a throw, and simulated lifting with both their tenodesed shoulder and their contralateral healthy shoulder inside a biplane fluoroscopy system. Dynamic 3-dimensional glenohumeral positions and electromyography activity of the biceps brachii muscle were determined and compared.

RESULTS

Significant glenohumeral translations occurred in both shoulders for abduction (3.4 mm inferiorly; P < .01) and simulated late cocking (2.6 mm anteriorly; P < .01). The mean difference for each motion in glenohumeral position between the tenodesed and the contralateral healthy shoulders was always less than 1.0 mm. The tenodesed shoulders were more anterior (centered) during abduction (0.7 mm; P < .01) and for the eccentric phase of the simulated late cocking motion (0.9 mm; P < .02). No significant differences were found during the simulated lifting motion and in the superior-inferior direction.

CONCLUSION

The effect of biceps tenodesis on glenohumeral position during the motions studied in vivo was minimal compared with physiological translations and interpatient variability.

CLINICAL RELEVANCE

Our findings demonstrated that LHB tenodesis does not dramatically alter glenohumeral position during dynamic motions, suggesting the risk for clinically significant alterations in glenohumeral kinematics after tenodesis is low in otherwise intact shoulders.

Minor or occult shoulder instability: an intra-articular pathology presenting with extra-articular subacromial impingement symptoms

PURPOSE

Disruption in the balance of shoulder stability can produce a widely varied spectrum of clinical symptoms, ranging from minor shoulder instability to frank shoulder dislocation, followed by recurrent instability. In this study, a series of patients suffering from minor shoulder instability, all with clinical signs of preoperative subacromial impingement associated with instability, were treated. The shoulder instability alone was addressed, with the aim of eliminating the clinical symptoms of subacromial impingement and pain.

MATERIAL

In this study, 20 patients with minor shoulder instability, presenting with subacromial impingement symptoms, underwent arthroscopic treatment to address capsule-labral pathology. All patients underwent a preoperative assessment by one independent physiotherapist, using Constant and WOSI scores, as well as the Castagna test, on both the affected and non-affected sides. The Hawkins test and subacromial pain in 90° of abduction and internal rotation were also evaluated. All patients followed the same rehabilitation protocol by a second physiotherapist. All patients were followed up at 6, 12 and 24 months postoperatively by the same independent physiotherapist.

RESULTS

We observed that 20/20 patients had a positive Hawkins sign at >20° of internal rotation preoperatively, while 4/19 had a positive Hawkins sign--all with less pain--at the 24-month follow-up (P < 0.0001). Moreover, 20/20 had a positive Castagna test preoperatively, while 1/20 had a positive Castagna test at the 24-month follow-up. In terms of shoulder scores, at 24 months, the Constant score had improved from a median value of 70 (51-91) preoperatively to a median value of 91 (86-100). The median WOSI score was 48.3 (12.7-78.6) preoperatively and improved to 84.9 (39.5-98.5) at 24 months postoperatively.

CONCLUSION

Minor shoulder instability is an intra-articular pathology presenting with extra-articular subacromial impingement symptoms. By treating the intra-articular pathology, the extra-articular symptoms can be relieved in the vast majority of patients.

Restoration of anterior-posterior rotator cuff force balance improves shoulder function in a rat model of chronic massive tears

The rotator cuff musculature imparts dynamic stability to the glenohumeral joint. In particular, the balance between the subscapularis anteriorly and the infraspinatus posteriorly, often referred to as the rotator cuff "force couple," is critical for concavity compression and concentric rotation of the humeral head. Restoration of this anterior-posterior force balance after chronic, massive rotator cuff tears may allow for deltoid compensation, but no in vivo studies have quantitatively demonstrated an improvement in shoulder function. Our goal was to determine if restoring this balance of forces improves shoulder function after two-tendon rotator cuff tears in a rat model. Forty-eight rats underwent detachment of the supraspinatus and infraspinatus. After four weeks, rats were randomly assigned to three groups: no repair, infraspinatus repair, and two-tendon repair. Quantitative ambulatory measures including medial/lateral forces, braking, propulsion, and step width were significantly different between the infraspinatus and no repair group and similar between the infraspinatus and two-tendon repair groups at almost all time points. These results suggest that repairing the infraspinatus back to its insertion site without repair of the supraspinatus can improve shoulder function to a level similar to repairing both the infraspinatus and supraspinatus tendons. Clinically, a partial repair of the posterior cuff after a two-tendon tear may be sufficient to restore adequate function. An in vivo model system for two-tendon repair of massive rotator cuff tears is presented.

Anatomy, function, injuries, and treatment of the long head of the biceps brachii tendon

Lesions of the long head biceps tendon (LHB) are frequent causes of shoulder pain and disability. Biceps tenotomy and tenodesis have gained widespread acceptance as effective procedures to manage both isolated LHB pathology and combined lesions of the rotator cuff and biceps-labral complex. The function of the LHB tendon and its role in glenohumeral kinematics presently remain only partially understood because of the difficulty of cadaveric and in vivo biomechanical studies. The purpose of this article is to offer an up-to-date review of the anatomy and biomechanical properties of the LHB and to provide an evidence-based approach to current treatment strategies for LHB disorders.

Modified impingement test can predict the level of pain reduction after rotator cuff repair

BACKGROUND

Most patients experience a significant reduction in pain after rotator cuff repair. However, there is currently no method to predict the level of pain reduction that each patient will experience. This report explores the usefulness of the modified impingement test for prognosis in cases of rotator cuff repair.

HYPOTHESIS

The amount of pain reduction after injection of lidocaine into the subacromial space preoperatively correlates with the level of pain reduction after rotator cuff repair.

STUDY DESIGN

Cohort study (prognosis); Level of evidence, 2.

METHODS

Preoperatively, a visual analog scale for pain was measured in 153 patients (59 males and 94 females) with a rotator cuff tear before and after injection of lidocaine into the subacromial space. Subsequently, rotator cuff repair was performed. At least 1 year after surgery, the visual analog scale for pain and satisfaction, Constant score, Simple Shoulder Test, American Shoulder and Elbow Surgeons (ASES) score, and University of California, Los Angeles shoulder rating scale were evaluated. Correlation analyses were performed between the change in visual analog scale after the modified impingement test and after surgery.

RESULTS

The amount of pain reduction after the modified impingement test was significantly related to improvement of pain postoperatively (P < .001), as measured using the visual analog scale for pain. The change in ASES score was also related to the amount of pain reduction after the modified impingement test (P = .001); however, the other tests showed no statistical significance (P > .05). Univariate regression analysis revealed that a 0.621-unit reduction in postoperative pain on the visual analog scale could be expected for each 1 unit (on a scale of 10) reduction in pain after lidocaine injection preoperatively.

CONCLUSION

The amount of pain reduction after the modified impingement test preoperatively correlated with the improvement of pain after rotator cuff repair. This simple preoperative test could help patients understand the subjective level of pain reduction that they may experience after rotator cuff repair.

Subacromial morphometric assessment of the clavicle hook plate

BACKGROUND

Clavicle hook plates are an effective plate fixation alternative for distal clavicle fractures and severe acromioclavicular joint dislocations. However, post-operative complications associated with the subacromial portion of the hook include acromial osteolysis and subacromial impingement. We examine and quantify the three-dimensional position of the subacromial portion of the hook plate relative to surrounding acromial and subacromial structures in a series of cadaveric shoulders to determine if hook positioning predisposes the shoulder to these noted post-operative complications.

MATERIALS AND METHODS

Fifteen cadaveric shoulders (seven males, eight females) were implanted with 15- or 18-mm hook plates. Dimensions of the acromion and hook plate were digitised and reconstructed into a three-dimensional model to measure acromion dimensions and distances of the subacromial hook relative to surrounding acromial and subacromial structures.

RESULTS

Inter-specimen dimensions of the acromion were highly variable. Mean acromion width and thickness were greater in males than in females (p=0.01). The posterior orientation of the subacromial hook varied widely (mean posterior implantation angle=32.5+/-20 degrees, range 0-67 degrees). The hook pierced the subacromial bursa in 13/15 specimens, made contact with the belly of the supraspinatus muscle in 9/15 specimens, and had focal contact at the hook tip with the undersurface of the acromion in 9/15 specimens.

CONCLUSIONS

The wide range of acromial dimensions leads to a high degree of variability in the positioning of the subacromial hook. The observed frequency of hook contact with surrounding subacromial structures in a static shoulder confirms that the position of the hook portion of the implant can predispose anatomic structures to the post-operative complications of subacromial impingement and bony erosion.

The effect of posterior capsular tightening on peak subacromial contact pressure during simulated active abduction in the scapular plane

HYPOTHESIS

Our hypothesis was that tightening of the posterior capsule would lead to increased subacromial pressure and increased superior translation during active abduction in the scapular plane.

BACKGROUND

Subacromial impingement syndrome is a painful condition that occurs during overhead activities as the rotator cuff is compressed in the subacromial space. Unrecognized secondary causes of subacromial impingement may lead to treatment failure. Posterior capsular tightness, believed to alter glenohumeral joint kinematics, is often cited as a secondary cause of SI; however, scientific evidence is lacking. The primary objective of this study was to evaluate the effect of posterior capsular tightening on peak subacromial pressure during abduction in the scapular plane.

MATERIALS AND METHODS

Ten fresh frozen shoulder specimens from deceased donors were mounted on a custom shoulder simulator. With the scapula fixed, the deltoid and rotator cuff muscles were loaded in discrete static steps with a constant ratio to elevate the humerus in the scapular plane. The treatment order (no tightening, 1-cm, and 2-cm tightening of the posterior capsule) was randomly assigned to each specimen. Peak subacromial contact pressure and glenohumeral kinematics at the peak pressure position were compared using a repeated measures analysis of variance.

RESULTS

Peak subacromial pressures (mean +/- standard deviation) were similar between treatment groups: 345 +/- 152, 410 +/- 213, and 330 +/- 164 kPa for no tightening, 1-cm, and 2-cm tightening of the posterior capsule respectively (P > .05). No significant differences were found for superior or anterior translations at the peak pressure position (P > .05).

DISCUSSION

Posterior capsular tightening, as a sole variable, did not contribute to a significant increase in peak subacromial pressure during abduction in the scapular plane. A similar study simulating active forward flexion is necessary to fully characterize the contribution of posterior capsular tightness to subacromial impingement.

CONCLUSION

Tightening of the posterior capsule did not increase subacromial pressure, or increase superior or anterior translation during abduction in the scapular plane.

Effect of posteroinferior capsule tightness on contact pressure and area beneath the coracoacromial arch during pitching motion

BACKGROUND

Tightness of the posteroinferior capsule is assumed to be the cause of internal rotation loss in baseball pitchers. Although the relationship between posterior capsule and subacromial impingement has been recognized, this relationship during the baseball-pitching motion is unclear.

HYPOTHESIS

Contact pressure during baseball-pitching motion increases with posterior capsule tightness.

STUDY DESIGN

Controlled laboratory study.

METHODS

Eight fresh-frozen shoulders were used. The peak contact pressure and area on the coracoacromial arch were measured on a custom-designed shoulder experimental device capable of 6 degrees of freedom motion. Simultaneously, the sites of peak pressure on the coracoacromial arch and humerus were observed from various angles. The posteroinferior capsule tightness was simulated by plicating the capsule in the region from 6 to 8 o'clock. The static testing positions correlated to the early cocking, late cocking, acceleration, deceleration, and follow-through phases of the pitching motion.

RESULTS

The peak contact pressure during the follow-through phase (0.63 + or - 0.50 MPa) significantly increased with posteroinferior capsule tightness (1.00 + or - 0.65 MPa) (P = .014). Additionally, the contact area on the coracoacromial ligament during the follow-through phase (0.98 + or - 0.67 cm(2)) significantly increased with posteroinferior capsule tightness (1.47 + or - 0.91 cm(2)) (P < .001). The site of the peak contact pressure did not change between the 2 conditions.

CONCLUSION

Our findings demonstrate that posteroinferior capsule tightness leads to higher contact pressure under the subacromial arch and increased contact area, particularly on the coracoacromial ligament during the follow-through phase.

CLINICAL RELEVANCE

This tightness may affect risk of injury of the rotator cuff and its surrounding tissues by increasing subacromial contact during pitching.

The impact of latent trigger points on regional muscle function

To date, most investigation of latent myofascial trigger points (LTrPs) has occurred in pain populations. Many have thought that LTrPs are clinically relevant as -potential precursors to developing active myofascial trigger points and spontaneous pain. Nociceptive substances have been found in greater concentrations at LTrP sites compared with non-TrP sites, indicating the potential for group III and IV afferent fibers to provide input to the central nervous system from affected peripheral sites. Fatigue and neurophysiologic studies provide evidence as to the pathways via which group III and IV afferents can alter activity of the motoneuron pool and therefore affect muscle activation and performance. This article offers suggestions as to the mechanisms via which LTrP-related pathophysiology may explain the clinical examination findings associated with LTrP-containing and functionally related muscles.

Current perspectives on rotator cuff anatomy

Understanding the anatomy of the rotator cuff and the surrounding structures that influence its function is essential to treating rotator cuff disease. During the past decade, advances in basic science and surgical technology have improved our knowledge of this anatomy. This review article presents the current concepts on rotator cuff anatomy and how they should be used in the surgical management of rotator cuff tears.

Predictive factors of subtle residual shoulder symptoms after transtendinous arthroscopic cuff repair: a clinical study

BACKGROUND

Transtendinous repair is a well-known technique for the arthroscopic management of partial rotator cuff tear. However, there are not a lot of clinical follow-up studies in the literature reporting data on this approach, and, moreover, potential factors responsible to influence the outcomes have not been investigated.

PURPOSE

To evaluate clinical outcomes after arthroscopic transtendinous repair and to identify predictive factors of residual shoulder symptoms.

STUDY DESIGN

Case series; Level of evidence, 4.

METHODS

Fifty-four patients with a mean age of 56.7 +/- 8.8 years (range, 31-71 years) who had undergone an arthroscopic transtendon repair for a painful articular-sided rotator cuff tear with a minimum of 2 years of follow-up were contacted. Clinical outcomes using a patient-based questionnaire, the Constant score, University of California at Los Angeles score, Simple Shoulder Test, and visual analog scale were evaluated. The influence of patient age, presence or absence of a trauma responsible for the cuff tear, presence of associated shoulder lesions, millimeters of exposed footprint, and millimeters of torn tendon retraction on the outcomes were assessed.

RESULTS

The mean cuff tear exposure footprint was 5.2 mm, and the mean retraction of the torn part of the tendon was 8 mm. Only one patient reported dissatisfaction with surgery because of persistence of pain during overhead activities. After arthroscopic repair, University of California at Los Angeles, Constant, and Simple Shoulder Test scores were significantly improved from 14.1, 45.3, and 9.8 to 32.9, 90.6, and 0.8, respectively (P < .001). Twenty-two patients (41%) reported occasional shoulder discomfort at the extremes of range of motion (particularly at extremes of abduction and internal rotation) occurring during some daily living and sports activities. The best multivariate model showed that residual shoulder discomfort is strongly linked with a partial thickness supraspinatus tendon avulsion-type articular-sided rotator cuff lesion consisting of a large tendon retraction and/or a relatively small exposure footprint area in an older patient in the absence of a specific trauma (P < .001).

CONCLUSION

Arthroscopic transtendon partial articular supraspinatus tendon avulsion-type rotator cuff repair was a reliable procedure that resulted in a good outcome in terms of pain relief and shoulder scores in 98% of the 54 patients. Better results could be expected in patients with less tendon retraction, a larger footprint exposure, of younger age, and with a clinical history of trauma.

Progressive resistance training in patients with shoulder impingement syndrome: a randomized controlled trial

OBJECTIVE

To assess pain, function, quality of life, and muscle strength in patients with shoulder impingement syndrome who participated in muscle strengthening exercises.

METHODS

A total of 60 patients diagnosed with shoulder impingement syndrome were selected from the clinics of the Federal University of São Paulo and randomly distributed into experimental and control groups. Patients were evaluated regarding pain, function, quality of life, muscle strength, and the number of antiinflammatory drugs and analgesics taken. Patients then participated in the progressive resistance training program for the musculature of the shoulder, which was held twice a week for 2 months, while the control group remained on a waiting list.

RESULTS

Sixty patients were randomly allocated to the experimental group (21 women and 9 men, mean age 56.3 years) and control group (25 women and 5 men, mean age 54.8 years). Patients from the experimental group showed an improvement from 4.2 cm to 2.4 cm on a 10-cm visual analog scale (P < 0.001) regarding pain at rest and from 7.4 cm to 5.2 cm (P < 0.001) regarding pain during movement. Function went from 44.0 to 33.2 (P < 0.007) using the Disabilities of the Arm, Shoulder, and Hand assessment and domains from the Short Form 36. There was a statistically significant difference in improvement in pain and function between patients in the experimental group and those in the control group (P < 0.05).

CONCLUSION

The progressive resistance training program for the musculature of the shoulder in patients with shoulder impingement syndrome was effective in reducing pain and improving function and quality of life.

Biomechanics of massive rotator cuff tears: implications for treatment

BACKGROUND

Some individuals with massive rotator cuff tears maintain active shoulder abduction, and some maintain good postoperative active range of motion despite high rates of repeat tears after repair. We devised a biomechanical rationale for these observations and measured the increases in residual muscle forces necessary to maintain active shoulder motion with rotator cuff tears of various sizes.

METHODS

A custom cadaver shoulder controller utilizing position and orientation closed-loop feedback control was used. Six cadaver glenohumeral joint specimens were tested in open-chain scapular plane abduction with equivalent upper extremity weight. The shoulder controller limited superior translation of the humeral head to 3.0 mm while maintaining neutral axial rotation by automatically controlling individual rotator cuff forces. Three-dimensional position and orientation and rotator cuff and deltoid force vectors were recorded. Specimens were tested with an intact rotator cuff and with 6, 7, and 8-cm tears.

RESULTS

All six specimens achieved full abduction with <or=3.0 mm of superior translation of the humeral head for all rotator cuff tear sizes. The effect of rotator cuff tear was significant for all tear sizes (p < 0.01). Compared with the intact condition, the subscapularis force requirements for the 6, 7, and 8-cm tears were increased by 30%, 44%, and 85%, respectively. For the combined infraspinatus and teres minor, the forces were increased by 32%, 45%, and 86%, respectively. The maximum deltoid force for the simulated tear condition never exceeded the deltoid force required at maximum abduction for the intact condition. However, between 10 degrees and 45 degrees of abduction, the average deltoid force requirement increased 22%, 28%, and 45% for the three tear sizes.

CONCLUSIONS

In the presence of a massive rotator cuff tear, stable glenohumeral abduction without excessive superior humeral head translation requires significantly higher forces in the remaining intact portion of the rotator cuff. These force increases are within the physiologic range of rotator cuff muscles for 6-cm tears and most 7-cm tears. Increases in deltoid force requirements occur in early abduction; however, greater relative increases are required of the rotator cuff, especially in the presence of larger rotator cuff tears.

Shoulder muscular demand during lever-activated vs pushrim wheelchair propulsion in persons with spinal cord injury

BACKGROUND/OBJECTIVE

The high demand on the upper limbs during manual wheelchair (WC) use contributes to a high prevalence of shoulder pathology in people with spinal cord injury (SCI). Lever-activated (LEVER) WCs have been presented as a less demanding alternative mode of manual WC propulsion. The objective of this study was to evaluate the shoulder muscle electromyographic activity and propulsion characteristics in manual WC users with SCI propelling a standard pushrim (ST) and LEVER WC design.

METHODS

Twenty men with complete injuries (ASIA A or B) and tetraplegia (C6, n = 5; C7, n = 7) or paraplegia (n = 8) secondary to SCI propelled ST and LEVER WCs at 3 propulsion conditions on a stationary ergometer: self-selected free, self-selected fast, and simulated graded resistance. Average velocity, cycle distance, and cadence; median and peak electromyographic intensity; and duration of electromyography of anterior deltoid, pectoralis major, supraspinatus, and infraspinatus muscles were compared between LEVER and ST WC propulsion.

RESULTS

Significant decreases in pectoralis major and supraspinatus activity were recorded during LEVER compared with ST WC propulsion. However, anterior deltoid and infraspinatus intensities tended to increase during LEVER WC propulsion. Participants with tetraplegia had similar or greater anterior deltoid, pectoralis major, and infraspinatus activity for both ST and LEVER WC propulsion compared with the men with paraplegia.

CONCLUSIONS

Use of the LEVER WC reduced and shifted the shoulder muscular demands in individuals with paraplegia and tetraplegia. Further studies are needed to determine the impact of LEVER WC propulsion on long-term shoulder function.

Arthroscopic rotator cuff repair with and without subacromial decompression: a prospective randomized study

PURPOSE

Our purpose was to evaluate the role of subacromial decompression in the arthroscopic repair of full-thickness rotator cuff tears in a prospective randomized clinical study.

METHODS

Arthroscopic cuff repair was performed in 80 patients with a full-thickness rotator cuff tear. They were divided into 2 groups comprising 40 patients each. In group 1 arthroscopic rotator cuff repair was performed with subacromial decompression. In group 2 the repair was performed without decompression. Rotator cuff tears were repaired via metal suture anchors for tendon-to-bone repair, side-to-side repair, or a combination of the 2 techniques. Results were evaluated by use of the Constant score normalized for age and gender, as well as the Disabilities of the Arm, Shoulder and Hand (DASH) and Work-DASH self-administered questionnaires. On analyzing the results at 2 years' follow-up, we considered the following independent variables: age; gender; dominance; location, shape, area, retraction, and reducibility of cuff tear; fatty degeneration; involvement of subscapularis tendon; treatment of biceps tendon; rotator cuff repair technique; and type of acromion. A univariate and multivariate statistical analysis was performed to determine which variables were independently associated with the outcome.

RESULTS

Comparison between the groups did not show significant differences for each variable considered. The overall results for the Constant score were 103.6 points in group 1 and 96.1 points in group 2; those for the DASH score were 18.2 points and 23.1 points, respectively; and those for the Work-DASH score were 23.7 points and 26.2 points, respectively. Univariate and multivariate analysis showed that the following variables significantly and independently influenced the outcome: age; shape, retraction, and reducibility of cuff tear; fatty degeneration; involvement of subscapularis; and repair technique. Subacromial decompression did not influence the outcome significantly for each scoring system considered.

CONCLUSIONS

At short-term follow-up, subacromial decompression did not seem to significantly affect the outcome of arthroscopic rotator cuff repair. Longer follow-up studies will be necessary to confirm the clinical relevance of these observations.

LEVEL OF EVIDENCE

Level I, randomized controlled trial with no significant difference but narrow confidence intervals.

An investigation into EMG activity in the upper and lower portions of the subscapularis muscle during normal shoulder motion

BACKGROUND AND PURPOSE

The subscapularis (SSc) muscle is considered to perform a variety of roles during normal shoulder movement. The SSc is innervated by two or more discrete motor nerves and previous studies have indicated some difference in electromyographic (EMG) activity between the upper and lower portions of the muscle. The purpose of the present study was to compare EMG activity between the upper and lower portions of the SSc muscle during voluntary shoulder movements in normal healthy subjects.

METHOD

Eight subjects were evaluated. A pair of intramuscular electrodes was inserted into each portion of the muscle. EMG data were recorded during the following movements: sagittal flexion; abduction in the coronal plane; and abduction in the scapular plane.

RESULTS

EMG onset of the upper portion of subscapularis occurred significantly earlier compared to the lower portion. Differences were also seen in the level and pattern of activation between the two portions, with upper SSc demonstrating higher levels of activation than the lower portion.

CONCLUSIONS

These findings suggest that the upper and lower portions of SSc are differentially active during voluntary shoulder movements.

The influence of the acromial coverage index in rotator cuff tears

Several intrinsic and extrinsic factors have been advocated in the pathogenesis of rotator cuff tears, but it is still unclear whether the origin of the tear is related to tendon degeneration itself or induced by several morphologic changes. The purpose of this study is to determine the relationship between the acromial coverage of the humeral head and the presence of a cuff tear. We evaluated 148 shoulders, including 45 that underwent surgical rotator cuff repair (group I), 26 with documented rotator cuff tears treated conservatively (group II), and 77 with no cuff pathology as a control group (group III). The mean acromial coverage index was 0.68 in group I, 0.72 in group II, and 0.59 in group III, giving a highly significant difference (P < .0001) between the control group and both cuff tear groups. Patients with a cuff tear have a significantly higher acromial coverage index than the control group.

Validation of a new model-based tracking technique for measuring three-dimensional, in vivo glenohumeral joint kinematics

Shoulder motion is complex and significant research efforts have focused on measuring glenohumeral joint motion. Unfortunately, conventional motion measurement techniques are unable to measure glenohumeral joint kinematics during dynamic shoulder motion to clinically significant levels of accuracy. The purpose of this study was to validate the accuracy of a new model-based tracking technique for measuring three-dimensional, in vivo glenohumeral joint kinematics. We have developed a model-based tracking technique for accurately measuring in vivo joint motion from biplane radiographic images that tracks the position of bones based on their three-dimensional shape and texture. To validate this technique, we implanted tantalum beads into the humerus and scapula of both shoulders from three cadaver specimens and then recorded biplane radiographic images of the shoulder while manually moving each specimen's arm. The position of the humerus and scapula were measured using the model-based tracking system and with a previously validated dynamic radiostereometric analysis (RSA) technique. Accuracy was reported in terms of measurement bias, measurement precision, and overall dynamic accuracy by comparing the model-based tracking results to the dynamic RSA results. The model-based tracking technique produced results that were in excellent agreement with the RSA technique. Measurement bias ranged from -0.126 to 0.199 mm for the scapula and ranged from -0.022 to 0.079 mm for the humerus. Dynamic measurement precision was better than 0.130 mm for the scapula and 0.095 mm for the humerus. Overall dynamic accuracy indicated that rms errors in any one direction were less than 0.385 mm for the scapula and less than 0.374 mm for the humerus. These errors correspond to rotational inaccuracies of approximately 0.25 deg for the scapula and 0.47 deg for the humerus. This new model-based tracking approach represents a non-invasive technique for accurately measuring dynamic glenohumeral joint motion under in vivo conditions. The model-based technique achieves accuracy levels that far surpass all previously reported non-invasive techniques for measuring in vivo glenohumeral joint motion. This technique is supported by a rigorous validation study that provides a realistic simulation of in vivo conditions and we fully expect to achieve these levels of accuracy with in vivo human testing. Future research will use this technique to analyze shoulder motion under a variety of testing conditions and to investigate the effects of conservative and surgical treatment of rotator cuff tears on dynamic joint stability.

In vivo measurements of subacromial impingement: substantial compression develops in abduction with large internal rotation

BACKGROUND

Subacromial impingement is a widely recognized mechanism of chronic shoulder pain. The magnitudes of the compressive forces that impinge the subacromial structures were often measured from cadaveric specimens, but it is questionable to use this data as a sole basis to determine the shoulder motions and/or shoulder configurations that induce impingement in live subjects performing active motion. The purpose of the present study was to determine in vivo the magnitude of the compressive force at selected shoulder configurations.

METHODS

The subacromial structures may be impinged by the downward-directed forces exerted by the coraco-acromial ligament. The reactions of these forces push the ligament upwards and deform it into a curved shape. A single resultant of these reaction forces was determined with an inverse approach to quantify the magnitude of the impingement force. An ultrasound unit was used to visualize the deformed shape of the coraco-acromial ligament for thirteen subjects with no symptomatic shoulder problem actively holding their shoulders in five configurations.

FINDINGS

The impingement force in 90 degrees abduction+maximum internal rotation (mean=21.3N) and that in the Hawkins test position (mean=18.3N) were significantly greater than those in 90 degrees abduction+neutral and external rotation (means < or = 3N).

INTERPRETATION

For young asymptomatic shoulders, the motions that induce impingement are not any arm abduction, but the arm abduction with a large internal rotation. Further study is indicated to examine the impingement force among various age groups.

Effect of experimental suprascapular nerve block on active glenohumeral translations in vivo

Static superior shoulder instability is associated with long-standing rotator cuff tears. Factors or mechanisms which can prevent superior migration of the humeral head, and therefore allow preservation or restoration of shoulder function despite nonanatomical cuff repair, are poorly understood. The question has therefore arisen, whether centering of the humeral head was the result of active shoulder muscle function. It was the goal of this experimental investigation to (1) determine the pattern of glenohumeral translations during active shoulder abduction measured by open-magnetic resonance imaging (MRI) techniques, and to (2) determine the influence of experimental paralysis of the infra- and supraspinatus muscles on these translations. In contrast to prior experimental investigations, the humeral head remained always centered in the glenoid fossa during active abduction. No superior migration of the humeral head could be provoked with experimental paralysis of the supra- and/or infraspinatus muscles. The hypothesis that static or dynamic superior humeral head displacement is prevented by active-supra- and/or infraspinatus muscle function must therefore be rejected, for the shoulder with a structurally intact muscle-tendon-bone unit.

Effects of shoulder muscle fatigue caused by repetitive overhead activities on scapulothoracic and glenohumeral kinematics

The purpose of this study was to determine the effects of shoulder muscle fatigue on three dimensional scapulothoracic and glenohumeral kinematics. Twenty healthy subjects participated in this study. Three-dimensional scapulothoracic and glenohumeral kinematics were determined from electromagnetic sensors attached to the scapula, humerus, and thorax. Surface electromyographic (EMG) data were collected from the upper and lower trapezius, serratus anterior, anterior and posterior deltoid, and infraspinatus muscles. Median power frequency (MPF) values were derived from the raw EMG data and were used to indicate the degree of local muscle fatigue. Kinematic and EMG measures were collected prior to and immediately following the performance of a shoulder elevation fatigue protocol. Following the performance of the fatigue protocol subjects demonstrated more upward and external rotation of the scapula, more clavicular retraction, and less humeral external rotation during arm elevation. All muscles with the exception of the lower trapezius showed EMG signs of fatigue, the most notable being the infraspinatus and deltoid muscles. In general, greater scapulothoracic motion and less glenohumeral motion was observed following muscle fatigue. Further studies are needed to determine what effects these changes have on the soft tissues and mechanics of the shoulder complex.

Shoulder impingement syndrome

This article deals with the diagnosis and treatment of shoulder impingement syndrome.

Dynamic contributions of the flexor-pronator mass to elbow valgus stability

BACKGROUND

Previous studies have indicated that the demands placed on the medial ulnar collateral ligament of the elbow when it is subjected to valgus torque during throwing exceed its failure strength, which suggests the necessary dynamic contribution of muscle forces. We hypothesized that the flexor-pronator mass assists the medial ulnar collateral ligament in stabilizing the elbow against valgus torque.

METHODS

Six cadaveric elbows were tested at 30 degrees and 90 degrees of flexion with no other constraints to motion. A full medial ulnar collateral ligament tear was simulated in each elbow. Muscle forces were simulated on the basis of the centroids and physiological cross-sectional areas of individual muscles. The biceps, brachialis, and triceps were simulated during flexor carpi ulnaris, flexor digitorum superficialis, flexor digitorum superficialis and flexor carpi ulnaris, and pronator teres-loading conditions. Kinematic data were obtained at each flexion angle with use of a three-dimensional digitizer.

RESULTS

Release of the medial ulnar collateral ligament caused a significant increase in valgus instability of 5.9 degrees +/- 2.4 degrees at 30 degrees of elbow flexion and of 4.8 degrees +/- 2.0 degrees at 90 degrees of elbow flexion (p < 0.05). The differences in valgus angulation between each muscle-simulation condition and the medial ulnar collateral ligament-intact condition were significantly different from each other (p < 0.05), except for the difference between the flexor carpi ulnaris contraction condition and the flexor digitorum superficialis-flexor carpi ulnaris co-contraction condition. This co-contraction provided the most correction of the valgus angle in comparison with the intact condition at both 30 degrees and 90 degrees of elbow flexion (1.1 degrees +/- 1.8 degrees and 0.38 degrees +/- 2.3 degrees , respectively). Simulation of the flexor carpi ulnaris alone provided the greatest reduction of the valgus angle among all individual flexor-pronator mass muscles tested (p < 0.05), whereas simulation of the pronator teres alone provided the least reduction of the valgus angle (p < 0.05).

CONCLUSIONS

The flexor-pronator mass dynamically stabilizes the elbow against valgus torque. The flexor carpi ulnaris is the primary stabilizer, and the flexor digitorum superficialis is a secondary stabilizer. The pronator teres provides the least dynamic stability.

Arthroscopically assisted rotator cuff repair

PURPOSE

The purpose of this study is to analyze the technique and value of arthroscopically assisted rotator cuff repair based on follow-up results after 3 years.

TYPE OF STUDY

Case series.

METHODS

Since the beginning of 1997, 216 patients included in a clinical case series at the Department of Trauma Surgery of the Hospital of the Barmherzigen Brüder Eisenstadt have undergone arthroscopically assisted rotator cuff repair. Radiographic, clinical, and intraoperative parameters were carefully documented. All patients were treated with an arthroscopically assisted transosseous technique, in which bone tunnels are drilled with a target drill unit through the humeral head lateral to the biceps tendon from a third ventrocaudal incision on the humerus. The nonresorbable sutures placed into the cuff with a suture punch are passed transosseously and tied in the incision directly on the humeral head using a knot pusher. In December 2000, 84 patients (average age, 54.8 years; range, 28 to 74 years) underwent a clinical follow-up evaluation after a mean follow-up time of 35 months (28 to 44 months).

RESULTS

The average Constant score improved from a preoperative rating of 44.9 to a postoperative rating of 87.2. University of California, Los Angeles score was improved from 11.3 to 31.1 ( P <.001). Time of preoperative history, tear size, and condition of the long biceps tendon were found to have significant influence on results (P <.05). Thus, 20 patients with chronic, untreated tears of the long biceps tendon showed significantly worse results with a score of 81.8. Patients with curved or hooked acromion types (Bigliani II and III) showed significantly better results (P <.05) and patients with extensive tears had significantly worse results because of a residual strength deficit. The essential determinant was achievement of a stable tear closure with arthroscopic verification and documentation. Thus, 8 patients with a documented small gap between repaired cuff and bone showed a significantly worse rating in the Constant score, with 80.5 (P <.05). The complications encountered included development of seroma in one case and one case with frozen shoulder symptoms.

CONCLUSIONS

Arthroscopically assisted repair of the rotator cuff was shown to be an effective procedure, guaranteeing good clinical results for medium- and large-sized tears with adequate mobility. Advantages include a primary stability comparable to that seen with open repair. Minimized trauma to soft tissue is associated with a lesser degree of postoperative pain and scarring and reduced hospitalization.

LEVEL OF EVIDENCE

Level IV, case series.