Mechanics of elevation of glenohumeral joint. Its application in rehabilitation of flail shoulder in upper brachial plexus injuries and poliomyelitis and in replacement of the upper humerus by prosthesis

Measurement of dynamic scapular kinematics using an acromion marker cluster to minimize skin movement artifact

The measurement of dynamic scapular kinematics is complex due to the sliding nature of the scapula beneath the skin surface. The aim of the study was to clearly describe the acromion marker cluster (AMC) method of determining scapular kinematics when using a passive marker motion capture system, with consideration for the sources of error which could affect the validity and reliability of measurements. The AMC method involves placing a cluster of markers over the posterior acromion, and through calibration of anatomical landmarks with respect to the marker cluster it is possible to obtain valid measurements of scapular kinematics. The reliability of the method was examined between two days in a group of 15 healthy individuals (aged 19-38 years, eight males) as they performed arm elevation, to 120°, and lowering in the frontal, scapular and sagittal planes. Results showed that between-day reliability was good for upward scapular rotation (Coefficient of Multiple Correlation; CMC = 0.92) and posterior tilt (CMC = 0.70) but fair for internal rotation (CMC = 0.53) during the arm elevation phase. The waveform error was lower for upward rotation (2.7° to 4.4°) and posterior tilt (1.3° to 2.8°), compared to internal rotation (5.4° to 7.3°). The reliability during the lowering phase was comparable to results observed during the elevation phase. If the protocol outlined in this study is adhered to, the AMC provides a reliable measurement of upward rotation and posterior tilt during the elevation and lowering phases of arm movement.

Evaluation of three-dimensional glenoid structure using MRI

The tilting angle and the shape of the glenoid cavity are considered to relate closely to shoulder stability. They are also important when planning arthroplasty and developing new designs. This study examines the glenoid cavity using 3-dimensional MRI. Forty volunteers (20 men, 20 women; average age 21.4; range 18-35 y) were enrolled in the study. The tilting angles of the glenoid bone were measured in 5 consecutive axial planes perpendicular to the glenoidal long axis. Cross sections were divided into 3 types (concave, flat, convex) according to the shape on each plane. The average tilting angles for the 5 planes from the bottom to the top were 3.3+/-4.1, 1.4+/-3.8. -0.6+/-1.9, -1.4+/-3.3, and -6.2+/-3.3 degrees anteriorly, indicating that the 3-dimensional bony structure of the glenoid was twisted anteriorly to posteriorly. Images on the bottom plane consisted of 82.5 % concave type, 15% flat type and 2.5% convex type, while only 3 cases (7.5%) showed concave at the top plane. The shape of the glenoid cavity is thought to be conducive to glenohumeral motion and stability.

The effect of negative intraarticular pressure and rotator cuff force on glenohumeral translation during simulated active elevation

OBJECTIVE

The objective of this study was to determine the effect of negative pressure in the intraarticular space and subacromial bursa, as well as rotator cuff force, on glenohumeral translation during active elevation.

DESIGN

Glenohumeral translation during elevation in the scapular plane was measured under greater than, less than, and equal to physiologic rotator cuff muscle force, as well as with and without the subacromial bursa and intraarticular space vented.

BACKGROUND

Negative intraarticular pressure has been shown to help stabilize the glenohumeral joint in passive motion, although the effect on translation during active motion has not been investigated.

METHODS

Eight cadaverous human shoulder specimens were tested in a dynamic shoulder simulator. Forces in the muscles of the rotator as well as the middle deltoid muscle were simulated using servohydraulic cylinders. Joint motion was measured using an ultrasonic motion analysis system.

RESULTS

Superior translation of the humerus increased 1.2 mm (SD, 0.4) upon venting of the bursa, and 2.1 mm (SD, 1.7) upon venting of the joint capsule at 25 degrees of glenohumeral elevation in the scapular plane. At 90 degrees elevation, venting the bursa did not change superior translation but increased anterior translation 1.04 mm (SD, 1.0). Venting of the joint capsule increased superior translation by 2.8 mm (SD, 2.5). Decreasing rotator cuff force increased superior translation, while reducing it did not.

CONCLUSION

The muscles of the rotator cuff and the negative pressure of the intraarticular space and the subacromial bursa stabilize the glenohumeral joint since they restrict translation in the superior and anterior directions. RelevanceIncreased glenohumeral translation and the resulting asymmetric loading may lead to arthrosis and ultimately rotator cuff arthropathy.

Injuries to the glenoid labrum: a diagnostic and treatment challenge

The glenoid labrum contributes to shoulder stability by increasing the glenoid surface and providing attachments for the shoulder capsule and various ligaments and tendons. Overhead arm activities, especially throwing, can stress the shoulder excessively and cause labral injury. Symptoms include poorly localized pain, exacerbated by overhead and behind-the-back motions, and popping, catching, or grinding. Imaging includes AP, outlet, and axillary radiographs, but CT arthrogram or MR arthrogram is also recommended. Fractures and dislocations should be referred. In other labral injuries, 2 to 4 weeks of rest and physical therapy may resolve symptoms. If not, patients should be referred for further testing and possible surgery.

Electromyographic study relating to shoulder motion: control of shoulder joint by functional electrical stimulation

The purpose of this study is to create the standard stimulation patterns of shoulder motion from electromyographic (EMG) data in 13 healthy human volunteers in order to control the movement of the paralyzed shoulder in quadriplegic and hemiplegic patients by functional electrical stimulation (FES). Simultaneous EMG measurement was made at 24 points of 17 major muscles relating to shoulder motion. Since the number of the output channels in the portable FES apparatus is limited, 12 major muscles were selected from statistically processing these EMG data and stimulation patterns were created based on the EMG data of these muscles. Thus three standard stimulation patterns were created to move the shoulder, i.e., (i) 90 degrees flexion to 90 degrees horizontal abduction, (ii) 90 degrees flexion to 20 degrees horizontal adduction, and (iii) 90 degrees abduction to 90 degrees horizontal adduction. With the created stimulation patterns, the restoration of the shoulder motion in plegic patients was successful and it will be reported in the next paper.

Glenoid replacement in total shoulder arthroplasty

The outcome of total shoulder arthroplasty is largely based on the quality of glenoid component fixation, which, in turn, is related to the amount and quality of bone stock, glenohumeral stability, and rotator cuff function. This article discusses the anatomic and pathologic indications for glenoid replacement, surgical techniques, and results.

A dynamic analysis of glenohumeral motion after simulated capsulolabral injury. A cadaver model

We used a dynamic shoulder-testing apparatus and nine fresh-frozen, entire upper extremities from cadavera to evaluate the effects of varying degrees of capsulolabral injury on the kinematics of the glenohumeral joint during abduction in the scapular plane and external rotation. Joint kinematics were recorded with use of a six-degrees-of-freedom magnetic tracking device before and after the creation of each capsulolabral lesion in a progressive manner. Dislocation did not occur after simulation of a large Bankart lesion or even after sectioning of the anterior aspect of the joint capsule. However, division of the entire joint capsule (that is, both the anterior aspect and the posterior aspect) resulted in a significant increase (p < 0.05) in posterior translation during abduction in the scapular plane, and two of the nine shoulders dislocated posteriorly. External rotation of the abducted extremity produced no increase in anterior or posterior translation.

Topography of mechanoreceptors in the shoulder joint region--a computer-aided 3D reconstruction in the laboratory mouse

BACKGROUND

We investigated the pattern of distribution of corpuscular sensory nerve endings in the shoulder region of the laboratory mouse in relation to their functional properties.

METHODS

Twelve adult female white NMRI-F2-mice were used. The topography of sensory nerve endings in the shoulder joint region was reconstructed by three-dimensional image processing by using serial silver-stained sections of paraffin-embedded samples. Semithin sections obtained from additional samples were used for light microscopy.

RESULTS

Within the fibrous layer of the joint capsule, three types of mechanoreceptors were identified: small lamellated corpuscles of the Pacini type, Ruffini corpuscles, and Golgi tendon organs. Intracapsular small lamellated corpuscles of the Pacini type (in an average number of 29/joint) were found mainly in three areas: in the predominantly flaccid tissue of the axillary region, in the denser ventromedial parts of the capsule, close to the scapula, and in the tight texture of the fiber bundles near the glenoid labrum. Ruffini corpuscles were identified only in small numbers (2/joint) in the ventral aspect of the articular capsule of two animals. Golgi tendon organs (14 or 15 receptors/joint) were discovered predominantly in close vicinity to the joint capsule at the muscle tendon junction of the inserting rotator cuff muscles and in the biceps brachii and triceps brachii muscles.

CONCLUSIONS

In view of their location in the shoulder joint capsule and the glenoid labrum, corpuscular mechanoreceptors evidently play an important role in joint control by inducing protective reflex actions in phases of extreme or abnormal movement. The density of sensory receptors in distinct areas of the shoulder joint capsule appears to be related to zones that are subjected to increased biomechanical stress during physical activity.

Clinical findings in competitive swimmers with shoulder pain

We clinically evaluated 36 competitive swimmers who had shoulder pain; the majority were women. Twenty-three swimmers had unilateral shoulder pain and 13 had bilateral pain, making a total of 49 painful shoulders. Shoulder pain had been present significantly longer in swimmers with bilateral shoulder pain (mean, 104 weeks) than in swimmers with unilateral pain (mean, 33 weeks). Twelve shoulders exhibited signs of impingement without excessive humeral head translation. In 25 shoulders, concomitant signs of impingement and increased glenohumeral translation, together with a positive apprehension sign, were found. Four swimmers, who were generally joint hypermobile, exhibited bilateral impingement signs and excessive humeral head translation, most commonly in the anteroinferior direction. Four shoulders had excessive humeral head translation and apprehension without impingement. Lack of coordination in the scapulohumeral joint was seen significantly more often in symptomatic than in asymptomatic shoulders. Hawkin's test for impingement was more sensitive than Neer's test. Swimmers with shoulder pain have variable clinical findings. The majority demonstrate signs of impingement and increased humeral head translation in the anteroinferior direction together with a positive apprehension sign. This nontraumatic instability might result from wearing of the anteroinferior capsuloligamentous complex. The different clinical findings might represent different stages of the same condition.

Glenohumeral translation in the asymptomatic athlete's shoulder and its relationship to other clinically measurable anthropometric variables

To determine the degree of shoulder translation in uninjured athletes, we examined 76 Division I collegiate athletes (44 women and 32 men) for passive range of motion in both shoulders and for knee and elbow hyperextension. Translation was based on a scale of 0 to 3+. Shoulders with symptoms of pain or a history of instability or dislocation were excluded from this study. Forty-six shoulders had 0 anterior translation, 75 had 1+, and 31 had 2+. Thirteen shoulders had 0 posterior translation, 56 had 1+, and 83 had 2+. Thirty-eight shoulders had 0 inferior translation, 105 had 1+, and 9 had 2+. No shoulder had translation of 3+ in any direction. Twenty-four athletes, 12 men and 12 women, had translational asymmetry of a minimum of one grade in at least one direction. No shoulder was asymmetric in all three directions. There was a significant correlation between dominant hand and increased translation; 19 of 24 athletes with asymmetric shoulders had greater translation in the nondominant extremity. There was no relationship between translation and range of motion, knee or elbow hyperextension, thumb-to-forearm distance, or years spent in sports participation. Asymmetry of shoulder translation may exist in the normal shoulder. This review shows that up to 2+ translation in any direction cannot be considered abnormal.

Anterior Shoulder Dislocations

In brief The clinical diagnosis of anterior shoulder dislocations can be made by evaluating the mechanism of injury and noting limited arm adduction and shoulder rotation. In addition, the shoulder loses its normal rounded contour, and the acromion is unusually prominent. Prereduction x-rays are not always necessary but will confirm the clinical diagnosis. Reduction of the dislocation should be performed as quickly, gently, and safely as possible. Linear force via a self-reduction technique or a simple, passive traction technique will lead to a successful reduction in the vast majority of patients.

A dynamic shoulder model: reliability testing and muscle force study

This study introduces a dynamic shoulder model, where forces were applied to individual muscles in ten cadaveric specimens. The model provided reproducible glenohumeral joint motion and thereby allowed the investigation of active, glenohumeral joint mechanics. Forces were created by servo-actuated hydrodynamic cylinders and applied to the deltoid muscle and to the rotator cuff through wire cables. Computerized regulation initiated precise, time controlled cycles of glenohumeral joint motion. The position of the glenohumeral joint in all spatial orientations was measured and recorded using an ultrasonic sensor device. Reproducibility of glenohumeral joint motion was demonstrated on the basis of five cycles of glenohumeral joint elevation. Repeatability variance of position measurements for five cycles of elevation averaged 0.80 degrees for abduction, 0.75 degrees for anteflexion and 1.36 degrees for internal rotation. Arm weight and force distribution at the shoulder musculature were estimated according to the literature. In comparison to estimated physiologic conditions, a one third increase of arm weight led to a significant (p < 0.05) decrease of elevation of 20%, a one third decrease of arm weight to an average increase of elevation of 18% (p < 0.05). Exclusion of the supraspinatus muscle caused a significant (p < 0.05) 6% decrease of elevation of the glenohumeral joint. Without force applied to the subscapularis and infraspinatus/teres minor muscles, elevation decreased 16% (p < 0.05). A decrease of glenohumeral joint elevation of 25% resulted when force was applied to the deltoid muscle alone (p < 0.05).

Clinical implications of secondary impingement of the shoulder in freestyle swimmers

Swimming has become a popular recreational activity as well as a highly competitive sport in the United States. The repetitive nature of swimming can predispose the shoulder to mechanical impingement and microtrauma, which may lead to laxity, rotator cuff fatigue, and subsequent secondary impingement. Improper stroke mechanics can place the swimmer's shoulder at further risk. The purpose of this paper is to describe the pathology of secondary impingement in freestyle swimmers and to discuss the clinical implications for rehabilitation of swimmers with the pathology. A thorough subjective and objective evaluation is necessary to design a successful rehabilitation program. The rehabilitation program for swimmers with secondary impingement includes modification of training, flexibility, range of motion, strengthening, and mobilization as indicated. Functional and proprioceptive training may also be useful techniques in the rehabilitation of swimmer's shoulder. Improper stroke mechanics can also have clinical implications on swimmer's shoulders with secondary impingement. The clinical implication of secondary impingement in freestyle swimmers suggests that the primary goal of rehabilitation is to promote equilibrium of the shoulder complex while accounting for the demands of the sport.

The entire rotator cuff contributes to elevation of the arm

The function of the infraspinatus, teres minor, and subscapularis during elevation of the arm remains poorly defined. These muscles may generate moments that contribute to abduction of the arm, although they frequently are classified as humeral depressors. The purposes of this study were to measure the contributions to abduction made by the more inferiorly positioned rotator cuff muscles relative to the contributions of the supraspinatus and to determine the range of motion at which the muscles are most effective. Five fresh cadaveric shoulder girdles were mounted in an apparatus designed to simulate contraction of the deltoid and rotator cuff while maintaining the normal relationship between glenohumeral and scapulothoracic motions. The deltoid force required for elevation was measured without simulated contraction of the rotator cuff and with simulated contraction of the entire rotator cuff, of the supraspinatus only, and of the infraspinatus-teres minor and subscapularis only. A significant reduction in deltoid force when other muscle activity was added indicated that the additions contributed significantly to abduction. The deltoid force required with concurrent contraction of the entire rotator cuff averaged 41% less than with the deltoid alone but was not significantly different than with the deltoid and supraspinatus or with the deltoid, infraspinatus-teres minor, and subscapularis. Concurrent application of forces to the supraspinatus or the infraspinatus-teres minor and subscapularis significantly reduced the required deltoid force over the range of motion studied by an average of 28 and 36%, respectively. The contributions of the rotator cuff muscles to abduction of the arm were greatest at low abduction angles (30 and 60 degrees) and were insignificant by 120 degrees. The infraspinatus-teres minor and subscapularis contribute significantly to abduction: their contribution was equal to that of the supraspinatus and, like the supraspinatus, they are most effective during the first 90 degrees of abduction.

Functional anatomy of the shoulder complex

Recent research findings are incorporated in this review of the functional anatomy of the shoulder complex. The scapulothoracic mechanism is described, including a review of scapular motion and the structure and function of the sternoclavicular and acromioclavicular joints. New information regarding the resting position of the scapula on the thorax and the effect of aging and spinal posture on position has been presented. In the second part of the paper, the anatomy of the glenohumeral joint is reviewed, with emphasis on the articular, periarticular, and muscular mechanisms responsible for stability of this articulation. The article concludes with a discussion of the integrated function of the scapulothoracic and glenohumeral articulations in upper extremity elevation.

The role of the scapula

The scapular musculature is often neglected in designing a rehabilitation protocol for the shoulder. Weakness of the scapular stabilizers and resultant altered biomechanics could result in: 1) abnormal stresses to the anterior capsular structures of the shoulder, 2) increased possibility of rotator cuff compression, and 3) decreased performance. This article presents known facts about the biomechanics of the scapula and surrounding muscles and suggests methods for evaluation of scapular muscle weakness. Exercise techniques to maximally strengthen the scapular musculature are also described. As our ability to document strength of these muscles improves, we will be able to determine the effect of scapular strengthening on improving symptoms related to impingement and instability. Scapular strengthening exercises are usually nonstressful to the rotator cuff and are easily implemented into a rehabilitation program for the shoulder.

Current concepts in the rehabilitation of the athletic shoulder

The rehabilitative process of the overhead athlete represents a significant challenge to the clinician. Overhead athletes (thrower, tennis player, swimmer) repetitively subject their shoulder joints to high microtraumatic stresses that, due to the accumulative effects, may lead to a variety of shoulder injuries. This type of athletic patient exhibits uniquely specific physical characteristics, such as hypermobility of the anterior shoulder capsule, excessive external rotation, hypomobility of the posterior capsule, limited internal rotation, and generalized ligamentous laxity of the glenohumeral joint. However, the overhead athlete must exhibit functional stability for pain-free sports participation. Functional stability is accomplished through the proficient balance of static (passive) and dynamic (active) stabilizers. During the rehabilitation process, various concepts, such as neuromuscular control, proprioception, force couple efficiency, plyometrics, eccentrics, and scapular stability, can enhance dynamic functional stability for the overhead athlete. The evaluation and treatment of the shoulder patient is in perpetual change, and the purpose of this paper is to discuss several current concepts in the rehabilitative treatment of the athletic shoulder patient.

Function of the glenohumeral ligaments in active stabilisation of the shoulder joint

The joint capsules and the glenohumeral ligaments of 12 human shoulder specimens were histologically investigated by light microscopy. Serial sections of 15 microns thickness were cut. The tissue was stained following the haematoxylin-eosin and van Giesson techniques. For specific identification of neural elements we made use of a special silver impregnation technique, described by Novotny, for staining axons in peripheral nerves. Axons of different diameters ranging from 0.2 microns to 70 microns were discovered within the ligaments. Close to the humeral site we found small nerves forming neurovascular bundles. Within their connective tissue sheaths, the axons exhibited a serpentine configuration, which may give extra length and may allow stretching of the nerve during motion. Most of the axons discovered were located in the subsynovial layer of the ligaments. In general the diameter of these subsynovial axons did not exceed 10 microns. In addition to these axonal structures, we detected nerve endings which can be classified according to Freeman and Wyke as type II mechanoreceptors (Pacinian corpuscles). These mechanoreceptors had a diameter of approximately 150 microns. They were also positioned directly beneath the synovial membrane and close to the humeral site of insertion of the ligaments.

CLINICAL SIGNIFICANCE

The described neural structures in the glenohumeral ligaments are of particular clinical importance in the light of the high incidence of recurrent shoulder dislocation and concomitant Bankart lesions. The mechanoreceptors located in the glenohumeral ligaments may control the stabilising shoulder musculature. On this premise, rupture or detachment of these ligaments will lead to a loss of a feedback mechanism.

Does the glenohumeral joint capsule have proprioceptive capability?

We performed a clinical study examining 60 volunteers with stable shoulder joints randomized to two groups. In group 1 we injected 5 ml lidocaine intra-articularly. In group 2 we injected 5 ml saline with 5 ml contrast dye the same way. After the injection we measured the amount of passive anteroposterior translation that occurred during anterior and posterior drawer tests and the amount of inferior subluxation during downward stress. We documented the extent of the passive glenohumeral translation using ultrasound. We had no complications related to the intra-articular injection or to the stability measurement. After the injection neither group had significant pain, and the patients were not apprehensive about the ensuing stability test. In group 1 (lidocaine) anteroposterior translation of 13.2 +/- 6.3 mm was seen in the anterior and posterior drawer test, whereas in group 2 (no lidocaine) the anteroposterior translation was only 6.8 +/- 3.2 mm. The difference between the two groups was statistically significant (P < 0.05). With downward stress during the sulcus test the distance between the acromion and the humeral head increased by 5.6 mm (+/- 3.2) in group 1 and by 2.7 mm (+/- 2.1) in group 2. This difference was also statistically significant (P < 0.05). Clinical consequences: Taking our preliminary findings into account, the capsule of the glenohumeral joint seems to have proprioceptive capability. Nerve fibres and mechanoreceptors seem to be localized in the capsule tissue, being part of a physiological feedback mechanism. If our conclusions proprioceptive capability. Nerve fibres and mechanoreceptors seem to be localized in the capsule tissue, being part of a physiological feedback mechanism.

Rotation-abduction analysis in 10 normal and 20 pathologic shoulders. Elite system application

Kinematics of shoulder rotation-abduction in the plane of the scapula were analysed using the Elite system. We evaluated 10 asymptomatic subjects and 20 patients with painful conditions affecting the shoulder, 10 adhesive capsulitis and 10 rotator cuff-tears. The last pathologic cases were reexamined after rehabilitation treatment. The Elite system computed on line the trajectories of 8 retro reflective markers glued on the main reference points (3 on the spine, 3 on the scapula and 2 on the humerus). Angles and linear velocities were also evaluated. The lower humeral site displacement and gleno-humeral angle increase allowed differentiation of the normal shoulder rotation-abduction from the abnormal movement. Hence, rehabilitation progress could be followed up.

Anatomic study of the glenoid labrum

Thirty-one shoulder joints from the cadavers of 13 men and four women and from two cadavers of unspecified sex were dissected to investigate the anatomic characteristics of the glenoid labrum. The ages at death ranged from 63 to 90 years with a mean age of 78.5 years. The glenoids were divided with a bone saw along both their long and short axes. The size of the glenoid and the labrum of each specimen was then measured with calipers. No significant correlation existed between the size of the labrum and that of the glenoid. This indicated that even if the glenoid was large, the labrum was not always correspondingly large. If one aspect of the labrum was large, other portions of the labrum tended to be large also. The anterior and inferior portions of the labrum were the largest, and this may have contributed to stability in the anterior and inferior directions.

An electromyographic analysis of the upper extremity in pitching

The upper extremity is vulnerable to injury during the baseball pitch because of the repetitious nature of the action, the extremes in range of motion, and the high angular velocities and torques generated at the shoulder and elbow. Hence this study was designed to describe the muscle-firing patterns through fine-wire electromyography in 29 muscle bellies in the upper extremities of skilled pitchers during the fastball pitch. The results demonstrated that the muscles functioned with precise timing for joint stabilization to prevent injury, joint activation to transfer forces to the ball, and joint deceleration to dissipate forces after ball release. The synchrony of reciprocal and sequential muscle contraction necessary to accomplish these functions was clearly evident. This study provides a better understanding of the coordinated sequence of muscle activity during the throwing motion; this understanding is crucial to the development of exercise protocols and surgical procedures used for treatment and prevention of shoulder and elbow injuries in the throwing athlete.

The stabilizing function of passive shoulder restraints

The static restraints of the scapulohumeral joint provide stability for the humeral head in the glenoid cavity, limit extremes of motion of the glenohumeral joint, and guide positioning of the humerus during normal shoulder movement. Eleven fresh-frozen cadaver shoulders of unknown age were attached to a shoulder motion device that allowed measurement of motion in three planes with an accuracy to 0.5 degrees. Four shoulders underwent motion analysis and seven were used for strain gauge analysis of the static scapulohumeral ligamentous restraints. The results of the motion analysis demonstrated that any attempt at simple motion (flexion, extension, abduction, internal or external rotation) resulted in coupled motion in two additional planes. The strain gauge data, expressed as a percent of total tension for each ligament tested, demonstrated a reciprocal tension-sharing relationship among all ligament components and a transference of tension among these components when original and new joint positions were compared. These data provide an in vitro model of shoulder restraint function to explain primary restraint, tension sharing, and transference of tension functions in the in vivo scapulohumeral joint.

CLINICAL RELEVANCE

These principles of shoulder function have application in the treatment of instability and frozen shoulder syndrome, and provide an in vitro model to better understand static restraint function in the throwing mechanism.

Patterns of flexibility, laxity, and strength in normal shoulders and shoulders with instability and impingement

Imbalance of the internal and external rotator musculature of the shoulder, excess capsular laxity, and loss of capsular flexibility, have all been implicated as etiologic factors in glenohumeral instability and impingement syndrome; however, these assertions are based largely on qualitative clinical observations. In order to quantitatively define the requirements of adequate protective synergy of the internal and external rotator musculature, as well as the primary capsulolabral restraints, we prospectively evaluated 53 subjects: 15 asymptomatic volunteers, 28 patients with glenohumeral instability, and 10 patients with impingement syndrome. Range of motion was evaluated by goniometric technique in all patients with glenohumeral instability and impingement. Laxity assessment was performed and anterior, posterior, and inferior humeral head translation was graded on a scale of 0 to 3+. Isokinetic strength assessment was performed in a modified abducted position using the Biodex Clinical Data Station with test speeds of 90 and 180 deg/sec. Internal and external rotator ratios and internal and external rotator strength deficits were calculated for both peak torque and total work. Patients with impingement demonstrated marked limitation of shoulder motion and minimal laxity on drawer testing. Both anterior and multidirectional instability patients had excessive external rotation as well as increased capsular laxity in all directions. Sixty-eight percent of the patients with instability had significant impingement signs in addition to apprehension and capsular laxity. Isokinetic testing of asymptomatic subjects demonstrated a 30% greater internal rotator strength in the dominant shoulder. Comparison of all three experimental groups demonstrated a significant difference between internal and external rotator ratios for both peak torque and total work. Conclusions are that there appears to be a dominance tendency with regard to internal rotator strength in asymptomatic individuals. Impingement syndrome and anterior instability have significant differences in both strength patterns of the rotator muscles and flexibility and laxity of the shoulder. Isokinetic testing potentially may be helpful in diagnostically differentiating between these two groups in cases where there is clinical overlap of signs and symptoms.

Isokinetic evaluation of shoulder rotational strength between the plane of scapula and the frontal plane

The purpose of this study was to determine whether shoulder rotational strength was greater in the plane of the scapula or the frontal plane. Isokinetic shoulder rotational strength was evaluated in 20 subjects. Using the Merac (Universal Gym Equipment, Inc., Cedar Rapids, IA), test data was gathered in the right shoulders, in 45 degrees abduction, at a speed of 60 deg/sec, in the plane of the scapula and the frontal plane. Each subject returned within 1 week for retests to establish reliability. The average correlational coefficient across tests was 0.87. The Merac computer system was used to analyze data. Mean and standard deviations for peak torque to body weight were calculated. A paired t-test was used to examine the difference in the means for internal and external rotation between the two positions. The results indicated no significant difference between the two positions for shoulder internal rotational strength values. However, shoulder external rotational strength values in the plane of the scapula were statistically significantly higher than in the frontal plane (P less than 0.001). These preliminary results suggest isokinetic strength training and testing may be preferable in the plane of the scapula rather than the frontal plane.

Glenohumeral instability

Glenohumeral instability is an important cause of shoulder pain and disability in an active population. An awareness of the prevalence of recurrent instability, either in the form of dislocation or subluxation, is particularly useful in the assessment of the young athlete presenting with shoulder pain. Young adults presenting with rotator cuff tendinitis may have an underlying instability as the primary cause of their problem. A careful clinical examination should determine whether the instability is voluntary or involuntary, of traumatic or atraumatic onset, and the primary direction of the instability, as these factors have important implications with regard to treatment. Anterior glenohumeral instability is most common and the incidence of recurrent instability following on from an initial dislocation is high in the young active patient. An intensive rehabilitation programme is indicated for all initial dislocations or subluxations but surgery may become necessary after failure of conservative treatment. Care must be taken to determine accurately those patients with voluntary or multi-directional instability and a longer trial of conservative treatment is indicated here, as results of operative treatment in those cases are less favourable. Conservative treatment should be directed at strengthening the dynamic stabilizers of the shoulder joint, notably the rotator cuff muscles. Additional X-ray views are needed to demonstrate all the radiological changes associated with recurrent instability and further evaluation with examination under anaesthesia and arthroscopy is beneficial in the assessment of these patients. Arthroscopic surgery also has a role in the treatment of patients with symptomatic labral pathology and is now being used to perform stabilization procedures in selected cases. Many operative procedures have been described for stabilization of the shoulder and these should be directed at correcting the pathology present. Restoration of the patient's flexibility and strength postoperatively is essential, especially in the athlete in order to allow a full return to sporting activity.

Electromyography in voluntary posterior instability of the shoulder

Electromyographic (EMG) activity of selected shoulder girdle muscles was analyzed during voluntary posterior subluxation of the glenohumeral joint in four subjects. Although there was a great deal of variation in the muscle activation patterns during subluxation, subjects either pushed the humeral head backwards with the anterior muscles (deltoid, biceps) or pulled the humeral head backwards with the infraspinatus and/or posterior deltoid. In all cases, inhibition of the scapular rotators and winging of the scapula accompanied this maneuver. The method used in this study is presented as an objective technique for quantifying EMG activity during subluxation and relocation phases of shoulder instability.

Biomechanical analysis of stability and fixation strength of total shoulder prostheses

The Neer I (polyethylene glenoid), Neer II (plastic glenoid surface with metal backing), Cofield, and Gristina monospherical total shoulder prostheses were tested for joint subluxation resistance and glenoid component fixation strength. Synthetic glenoid models with consistent structural properties and standard under-cutting geometry were used for glenoid component fixation with bone cement. It was found that joint subluxation resistance varied linearly with axial compressive force applied. Higher subluxation strength was associated with the amount of curvature of the glenoid articulating surface. Consequently, joint stability was consistently higher for the Gristina design, and all had lower resistance in the anteroposterior direction. After complete joint dislocation under high axial compressive force, the polyethylene material at the site of subluxation experienced gross plastic deformation. The fixation strength of the glenoid component was lowest for the Neer I design and highest for the Cofield design. Fatigue loading at the joint did not seem to affect the glenoid component fixation strength. In general, all glenoid components appeared to have sufficient fixation strength against normal shoulder joint forces except the Neer I design. Loosening and fracture of the plastic glenoid component may occur under excessive loads.

Anatomic basis of ligamentous control of elevation of the shoulder (reference position of the shoulder joint)

The authors describe in detail the position of greatest stability of the shoulder joint. They review the mechanical importance of this position in the overall physiology of the shoulder-girdle and stress the essential role of two articular ligaments of the shoulder joint (the coracohumeral and inferior glenohumeral ligaments) in arrival at this reference position. There thus exists a passive control, of ligamentous origin, of movements of the shoulder-girdle. The position is essential if the shoulder is to benefit from the full range of movement and full stability which it needs in every day functioning.

Case study: rehabilitation of a stiff and painful shoulder: a biomechanical approach

A review of the literature provides an abundance of information discussing the pathology and management of the painful, stiff shoulder. To the clinician, the treatment approach to shoulder dysfunction is confusing. The research demonstrates there are many different treatment regimes for the management of shoulder dysfunction, none of which indicate overwhelming success. Traditionally, the painful, stiff shoulder, commonly diagnosed as frozen shoulder, is assessed without consideration of the entire shoulder complex. The biomechanics of the shoulder complex must be re-evaluated before each treatment session to determine the appropriate course of treatment. This paper presents a treatment regime for the painful, stiff shoulder. The regime was developed with careful analysis of normal shoulder mechanics. J Ortho Sports Phys Ther 1987;9(3):118-126.

Shoulder pain in industry: an epidemiological study on welders

The occurrence of supraspinatus tendinitis in a group of welders at a shipyard was investigated, and compared with the occurrence of this condition in a group of office clerks. The study showed a prevalence ratio of 18 per cent in the welders, significantly higher than in the clerks. The average age (39 year) in the group with pain did not differ significantly from the average age in the entire group of welders. It is concluded that supraspinatus tendinitis is not exclusively an aging phenomenon, but that welding as an occupation plays an etiological role.