Capsulolabral augmentation increases glenohumeral stability in the cadaver shoulder.

Multidirectional instability is not clearly understood. Excessive capsular laxity has been proposed as the key component. However, because ligaments fail to resist humeral head translation until they are tensioned, glenohumeral instability in the mid range of motion cannot be explained by capsuloligamentous pathology alone. Capsulolabral augmentation is designed to increase glenohumeral stability by 2 separate mechanisms: deepening the glenoid concavity and reducing capsular laxity. This is accomplished by shifting the capsule to buttress the glenoid labrum. Hence, the glenolabral concavity in which the humeral head is stabilized by compression throughout the entire range is enhanced. The purposes of this study were to examine glenolabral depth and glenohumeral stability before and after labral augmentation and to measure the effect of diminished capsular laxity on motion in clinically important positions. We compared glenolabral depth, resistance to humeral head displacement, and glenohumeral range of motion before and after capsulolabral augmentation. Glenolabral depth was measured as the lateral displacement of the center of the humeral head translating from the glenoid fossa. We recorded a mean increase in glenoid depth of 1.9 mm inferiorly, 2.0 mm posteroinferiorly, and 0.9 mm posteriorly (P <.02). Resistance to humeral head displacement was measured by use of the stability ratio, defined as the translatory force required to displace the humeral head divided by the force compressing the humeral head into the glenoid fossa. The mean stability ratio was increased by 0.24 inferiorly and 0.24 posteroinferiorly (P <.02). Motion was measured by achieving 30 degrees and 60 degrees elevation in the 0 degrees, 30 degrees, 60 degrees, and 90 degrees planes of elevation and measuring the extent of possible internal rotation for each of these 8 positions when the capsule was tensioned to exert 1000 N-mm of torque. Reduction of internal rotation in these positions was a mean of 15 degrees at 1000 N-mm of torque. This study demonstrates that humeral head stability within the glenolabral fossa is increased by local capsular augmentation. A simultaneous reduction in capsular laxity is achieved, which partially limits glenohumeral motion. Understanding the biomechanical effect of this procedure helps the physician to establish surgical goals and to explain to patients the rationale of why this procedure may be clinically efficacious.

Do shoulder patients insured by workers' compensation present with worse self-assessed function and health status?

The purpose of this study was to test the hypothesis that patients whose shoulder problems are covered by workers' compensation insurance perceive worse shoulder function and health status than do comparable patients whose problem is not covered by workers' compensation. Each of 1063 consecutive patients presenting with shoulder problems to an individual consultant completed 2 questionnaires: the Simple Shoulder Test inventory of shoulder function and the Short Form 36 general health assessment. The patients were divided into 2 groups on the basis of whether care of the shoulder problem was covered by injured workers' compensation insurance. The results indicate that patients whose shoulder condition is covered by workers' compensation have significantly lower self-assessed shoulder function and health status than do those patients whose shoulder conditions are not related to on-the-job injuries. The differences between the workers' compensation and non-workers' compensation groups could not be attributed to differences in age, sex, or diagnosis.

A prospective, multipractice study of shoulder function and health status in patients with documented rotator cuff tears.

A total of 191 patients from 29 orthopedic practices are analyzed in this report. All had full-thickness tears documented by imaging tests and/or surgical observation; 190 had tears of the supraspinatus, 54 had tears of the infraspinatus, and 13 had tears of the subscapularis. The greatest functional deficits were in the ability to place 8 pounds on a shelf at the level of the head (93% unable), the ability to throw overhand (93% unable), and the ability to sleep on the affected side (86% unable). The SF-36 physical role function and comfort scores were 27% and 48%, respectively, of those of age- and sex-matched controls. Of the variables suggested by a review of the literature, only female sex, involvement of the infraspinatus in the cuff tear, and workers' compensation claims were significantly correlated with lower shoulder function in this series of patients.

The Bloch equations in high-gradient magnetic resonance force microscopy: theory and experiment.

We report theory and observations of paramagnetic resonance in a measured field gradient of 44,000 T per meter by the technique of magnetic resonance force microscopy (MRFM). Resonance was induced in a dilute solid solution of diphenylpicrylhydrazyl in polystyrene at 77 and 10 K by an amplitude-modulated microwave field. This modulated the force between resonant sample spins and a micrometer-scale SmCo magnetic tip on a force microscope cantilever. The force signals were typically of order 10 fN, and were detected above a thermal noise floor of 80 aN per root hertz at 10 K, equivalent to a magnetic moment noise of 200 micro(B) per root hertz of bandwidth. Resonance saturation was readily observed. Starting with the Bloch equations, we derived simple analytic expressions for the predicted cantilever signal amplitudes and T(1)-dependent phase lags, valid at low microwave power levels. For power levels below saturation, the data were in good agreement with the Bloch equation predictions, while above saturation the measured force increased more slowly with power than predicted. Several ESR mechanisms which might lead to non-Bloch dynamics in the MRFM environment are reviewed. Spin-relaxation mechanisms are also reviewed. A detailed description of the experimental apparatus is offered.

Simple home program for frozen shoulder to improve patients' assessment of shoulder function and health status.

BACKGROUND: The purpose of this investigation was to test the hypothesis that a simple home program can improve the self-assessed shoulder function and health status of a group of patients with frozen shoulders. METHODS: A case series using a one-group pretest, posttest design analyzing 41 patients from a single orthopedic practice who had a frozen shoulder were included in this study. The patients completed the Simple Shoulder Test (SST) and the Medical Outcomes Study Short-Form Health Survey (SF-36) questionnaire at the time of initial consultation, had treatment consisting of education regarding frozen shoulder and home stretching instructions, and were asked to complete the same questionnaires mailed every 6 months. Initial results were compared with previously published control values to establish level of impairment, and follow-up results were compared with the initial results to determine the extent of improvement. RESULTS: Patients initially had serious deficits in the 12 shoulder functions inventoried by the SST and were also compromised in their general health status as reflected by the SF-36 scores. At follow-up, 4 of 10 SST functions were improved (P < 0.001). The SF-36 health status scores of physical function, comfort, and physical role function were also improved (P < 0.001). CONCLUSION: These data suggest that this home program for frozen shoulder can lead to improved self-assessed shoulder function and health status in patients similar to those in the study population.

Posteroinferior glenoplasty can change glenoid shape and increase the mechanical stability of the shoulder.

The treatment of recurrent posterior glenohumeral instability remains an unsolved clinical problem. Although various types of capsulorraphy have been advocated, outcome studies indicate that it is difficult to achieve a balance between stability and mobility. Alterations of the bony glenoid for posterior instability have been proposed, but are not well understood from a mechanical perspective. This investigation had 2 purposes: (1) to determine in a cadaver model if posteroinferior glenoplasty can change the shape of the glenoid, and (2) to determine if altering the shape of the glenoid can increase the mechanical stability of the glenohumeral joint. We determined the effective glenoid shape in 7 normal cadaver glenoids by tracking the path of the center of the humeral head as it was translated across the glenoid face in 8 different directions. These determinations enabled us to calculate the maximum effective slope of the glenoid in each direction. We then determined the mechanical stability of the glenoids in each of the 8 directions by measuring the tangential force required to dislocate the shoulder under a 50-N compressive load. The ratio of the dislocating force to the compressive load was defined as the stability ratio. All measurements were repeated after a standardized posteroinferior glenoplasty was performed. Posteroinferior glenoplasty increased the posteroinferior glenoid depth from 3.8 +/- 0.6 mm to 7.0 +/- 1.8 mm and shifted the center of the humeral head an average of 2.2 mm anteriorly and 1.8 mm superiorly. These changes in dimension could be directly visualized as an immediate mechanical consequence of the glenoplasty procedure, particularly because of the insertion of the bone wedge. Glenoplasty increased the posteroinferior glenoid slope from 0.55 +/- 0.07 to 0.83 +/- 0.12 and increased the posteroinferior stability ratio from 0.47 +/- 0.10 to 0.81 +/- 0.17. This is a more than 70% increase in the tangential force that can be resisted before dislocation. The increase can be quantitatively understood as a direct mechanical consequence of the altered shape of the glenoid concavity. These numbers indicate that, in this cadaveric model, posteroinferior glenoplasty results in defined changes in the effective glenoid shape and in the mechanical stability of the glenohumeral joint. However, this study does not establish the role of this procedure in the clinical management of posterior glenohumeral instability.

Glenohumeral motion after complete capsular release.

The range of glenohumeral motion is primarily limited by the joint capsule. If the capsule is contracted, greater restriction in glenohumeral motion is exhibited. Release of a tight capsule has been an effective means of managing refractory stiffness of the glenohumeral joint. The effect of a complete capsular release on glenohumeral kinematics has not been previously studied in a cadaver model. Elevation, rotation, and translation of eight cadaveric glenohumeral preparations were studied before and after complete capsular release. As the intact joint was positioned near the limits of motion, glenohumeral torque rose rapidly with relatively small concomitant increases in elevation and rotational angles. Notable torque, due to tension in the capsule or cuff, ensued only after glenohumeral elevation reached approximately 80% of maximal range. After complete capsular release, maximal elevation increased on average 15%, yet retained definitive endpoints due to residual tension in the rotator cuff. Axial humeral rotation with an intact capsule decreased as maximum elevation approached, especially at elevation angles greater than 60 degrees. Maximum internal rotation was less than external, for all planes except +90 degrees. After complete capsular release, the greatest net gains for external rotation tended to be in the posterior scapular planes, whereas gains for internal rotation tended to be in the anterior scapular planes. Maximal translation in an intact vented capsule was 21 mm, 14 mm, and 15 mm in the anterior, posterior, and inferior directions, respectively. After complete capsular release, translation increased in all positions with maximal anterior, posterior, and inferior translations of 28 mm, 25 mm, and 28 mm, respectively. In general, relative gains in translation were greater in planes posterior to the scapula and at extremes of the range of motion. Although large glenohumeral translations were measured, no preparation could be dislocated before or after complete capsular release. Complete capsular release significantly increased glenohumeral range of motion and translation. The intact rotator cuff myotendinous units serves to limit the range of motion and translation after all capsuloligamentous attachments are rendered incompetent by complete capsular release.

The correlation of comorbidity with function of the shoulder and health status of patients who have glenohumeral degenerative joint disease.

We studied the effect of comorbidities on function of the shoulder and health status in a group of eighty-five consecutive patients who had glenohumeral degenerative joint disease of sufficient severity to meet one surgeon's criteria for the performance of shoulder arthroplasty. A questionnaire was used to identify the comorbidities, such as other diseases, social factors, or a work-related injury, for each patient. The number of functions on the Simple Shoulder Test that the patient could perform had a significant negative correlation with the number of comorbidities (r = -0.32, intercept = 4.6 per cent, slope = -0.6, and p = 0.0031). Each parameter on the Short Form-36 (except for physical role function) had a significant negative correlation with the number of comorbidities (p < 0.05). This negative relationship was strongest for general health perception (r = -0.42) and vitality (r = -0.35). We concluded that the number of comorbidities has a quantitative effect on function of the shoulder. In the evaluation of the functional status of patients and the effectiveness of treatment, the effects of comorbidity must be controlled. The results of the present study demonstrate that the scores on the Short Form-36 are quantitatively related to the number of comorbidities. The six parameters that are unrelated to function of the shoulder (physical function, social function, emotional role function, mental health, vitality, and general health perception) may provide a practical way to integrate the effects of all potential comorbidities on individual patients. Future clinical research will be strengthened by efforts to measure the impact of comorbidities and by strategies to control for their effects.

The humeroscapular motion interface.

Motion between the humerus and scapula commonly is described as glenohumeral motion. However, humeroscapular motion occurs at two distinct sites. In addition to the motion at the diarthrodial glenohumeral joint, movement occurs between the proximal humerus and related structures and the surrounding sleeve of structures, including the acromion, deltoid, coracoid, coracoacromial ligament, and the muscles attached to the coracoid. This site of nonarticular shoulder motion is defined as the humeroscapular motion interface. Nonarticular humeroscapular motion can be documented and measured using standard magnetic resonance imaging techniques. The maximum average interfacial motion using axial images was 29.1 mm, which occurred at the level of the maximum diameter of the humeral head. Interfacial motion varied depending on the site measured. If pathologic conditions such as adhesions secondary to trauma or surgery interfere with or obliterate this space at sites of significant sliding motion, overall shoulder motion will be limited. Successful treatment of shoulder stiffness related to humeroscapular restraints is likely to require restoration of the normal sliding motion at the humeroscapular motion interface, in addition to resolving restraints affecting the glenohumeral joint motion.

Arthroscopic management of refractory shoulder stiffness.

Glenohumeral stiffness is a major cause of shoulder disability and pain. Conventional management strategies often fail to yield consistent or prompt return of comfort and function. Over the past 5 years, we have employed a prospective approach to the evaluation and management of glenohumeral stiffness using arthroscopic release of capsular contractures for the most refractory. This report concerns the first 30 patients who failed at least 6 months (28 month mean) of nonoperative management for unilateral refractory shoulder stiffness and who were managed by arthroscopic capsular release. Fourteen patients were diabetic. Follow-up averaged 33 months (range 12 to 56 months). Each patients' motion and strength was documented according to the American Shoulder and Elbow Surgeons standard examination. Functional outcome measures were patient-assessed using the Simple Shoulder test before and after surgery. Before surgery, active range-of-motion of the affected shoulder average 41% of the opposite asymptomatic side. The day after surgery, motion had improved dramatically to a mean of 78%. An additional 15% of motion was gained after discharge from the hospital. The final motion averaged 93% of the opposite side. All Simple Shoulder Test (SST) parameters and six of nine SF-36 health status scores were improved significantly. Only 6% of patients were able to sleep comfortably on their side and 35% could place 1 lb. on a shelf at shoulder height before surgery. After surgery, 73% were able to sleep comfortably on the affected side and 83% were able to place 1 lb. on a shelf at shoulder height. There were no differences among all outcome measures between diabetic or nondiabetic patients. Three patients developed recurrent refractory stiffness. The only complication was a single axillary neuropraxia which resolved spontaneously. No patient developed instability. Arthroscopic capsular release can be a safe and effective tool in the management of refractory shoulder stiffness.

Effect of a chondral-labral defect on glenoid concavity and glenohumeral stability. A cadaveric model.

One of the primary stabilizing mechanisms of the glenohumeral joint is concavity-compression, the maintenance of the humeral head in the concave glenoid fossa by the compressive force generated by the surrounding muscles. This mechanism is active in all glenohumeral positions but it is particularly important in the functional mid-range, in which the capsule and ligaments are slack. The effectiveness of concavity-compression in the stabilization of a joint can be characterized in terms of the ratio between the maximum dislocating force that can be stabilized in a given direction and the load compressing the head into the glenoid (the stability ratio). Glenoid concavity can be described by the lateral humeral displacement during translation across the glenoid. The purpose of the present investigation was to characterize the concavity and stability ratios of normal cadaveric glenoids, to measure the effect of an anteroinferior chondral-labral defect on these parameters, and to measure the effectiveness of a simulated operative reconstruction on the restoration of glenoid concavity and the stability ratio. The chondral-labral defect created in this study reduced the height of the glenoid by approximately 80 per cent and the stability ratio by approximately 65 per cent for translation in the direction of the defect. Reconstruction of the anteroinferior aspect of the glenoid concavity with use of an autogenous biceps-tendon graft restored normal values for these variables.

Optimizing arthroscopic knots.

Arthroscopic repairs, such as those for shoulder instability, are commonly performed. However, the failure rate after arthroscopic repair appears to be higher than with open surgery. These failures may relate to the challenge of tying secure knots arthroscopically. Many knots tied arthroscopically commonly consist of an initial slip knot to remove slack, and a series of half-hitches. Half-hitches, instead of square throws, are difficult to avoid and result when asymmetrical tension is applied to the strands. For this reason, the security of knots tied arthroscopically may not be equivalent to square knots and a greater rate of failure may occur. The purpose of this study was to determine (1) the security of various arthroscopic knots under cyclic and peak loading conditions, (2) how the surgeon can modify the method or sequence of half-hitch throws to minimize knot slippage or breakage, and (3) whether using an arthroscopic knot pusher affects the security of the same knot tied by hand. The most secure knot configurations were achieved by reversing the half-hitch throws and alternating the posts. These knots performed significantly better than all other knots tested (P < .002). Thus the surgeon can control the holding capacity and minimize suture loop displacement by proper alternation of the tying strands and reversal of the loop when placing the hitches.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of articular conformity and the size of the humeral head component on laxity and motion after glenohumeral arthroplasty. A study in cadavera.

We used a cadaveric model to examine the mechanical effects of changes in the conformity of the articular surfaces and the size of the humeral head component in glenohumeral arthroplasty. The experimental system permitted a manual clinical examination of the glenohumeral joint while sensors monitored the humeroscapular position and orientation as well as the forces and torques applied by the examiner. Four preparations were compared: an anatomical humeroscapular preparation and three glenohumeral arthroplasty preparations (one with anatomically sized components and a radius of curvature of the glenoid that was four millimeters larger than that of the humeral head, one with anatomically sized components and a radius of curvature of the glenoid that was equal to that of the humeral head, and one with a non-anatomical, large humeral head component and a radius of curvature of the glenoid that was equal to that of the humeral head). All motions, including flexion, external and internal rotation, and maximum elevation, were diminished with use of the non-anatomical, large humeral head component. Laxity of the joint on drawer and sulcus tests was not affected by the conformity of the articular surfaces but was decreased significantly by implantation of the large humeral head component. The kinematics of the glenohumeral joint were not markedly altered by reduction of the uniformity between the articular surfaces of the prosthetic components. In all preparations, obligate displacement of the humeral head associated with a passive range of motion occurred at smaller angles with the large humeral head component.

Arthroscopic labral repair to the glenoid rim.

The purpose of this study was to develop a new arthroscopic approach for traumatic instability that effectively reattaches avulsed capsulolabral tissue to the glenoid articular rim with sutures. This technique does not depend on fixation devices, trans-scapular drilling, or implantation of suture anchors. We attached a three-dimensional position sensor and force and torque transducer to the humerus and scapula of eight normal cadaveric shoulders to measure the normal, surgically unstable (arthroscopic Bankart lesion), and repaired preparations. We assessed eight motion ranges and six laxity tests. Capsulolabral release increased all passive ranges and allowed significant translational increases on posterior drawer and crank testing. After repair, motion was never decreased and there were no differences in laxity relative to normal. Neurovascular structures were never at risk. Our arthroscopic repair provides anatomic reattachment and effective deepening of the glenoid con-cavity similar to that achieved by open repair. This new method restores joint stability, preserves motion, and can withstand forceful loads. Ongoing clinical trials will substantiate whether the technique is as safe and reliable as shown cadaverically.

A standardized method for the assessment of shoulder function.

The American Shoulder and Elbow Surgeons have adopted a standardized form for assessment of the shoulder. The form has a patient self-evaluation section and a physician assessment section. The patient self-evaluation section of the form contains visual analog scales for pain and instability and an activities of daily living questionnaire. The activities of daily living questionnaire is marked on a four-point ordinal scale that can be converted to a cumulative activities of daily living index. The patient can complete the self-evaluation portion of the questionnaire in the absence of a physician. The physician assessment section includes an area to collect demographic information and assesses range of motion, specific physical signs, strength, and stability. A shoulder score can be derived from the visual analogue scale score for pain (50%) and the cumulative activities of daily living score (50%). It is hoped that adoption of this instrument to measure shoulder function will facilitate communication between investigators, stimulate multicenter studies, and encourage validity testing of this and other available instruments to measure shoulder function and outcome.

Robotic assistance in orthopaedic surgery. A proof of principle using distal femoral arthroplasty.

The term "robot" refers to a precision mechanical device that is accurately controlled by a computer using intelligent software. The term "robotic assistance" refers to the use of such a device to aid a surgeon in the optimal conduct of a procedure, particularly one requiring specified geometrical relationships. The authors have been exploring the application of robotic assistance in situations in which accuracy and precision are required in orthopaedic surgery. The initial application concerned the planning, positioning, and orientation cuts and holes of the bone required for the femoral component of a total knee arthroplasty. A three-dimensional digitizing template allowed the surgeon to specify the desired position and orientation of the component's articular surfaces in relation to the distal femur. The robotic system used this spatial relationship, along with its knowledge of the geometry of the component selected by the surgeon, to plan the precise location of the required bone cuts and holes. Finally, the robotic assistant sequentially positioned saw and drill guides with respect to the distal femur so that the surgeon made these cuts and holes in the locations necessary for optimal component fit, position, and orientation. The robotic assistant functioned easily in the operating room environment; increased the accuracy; and decreased the time, equipment, and personnel required for the conduct of the geometrical part of this surgical procedure.

Glenohumeral stability from concavity-compression: A quantitative analysis.

The purpose of this research was to determine the degree to which compression of the humeral head into the glenoid concavity stabilizes it against translating forces. Ten normal fresh-frozen cadaver glenohumeral joints in which the labrum was preserved were used. A compressive load of 50 N was applied to the humeral head in a direction perpendicular to the glenoid surface. Increasing tangential forces were then applied until the head dislocated over the glenoid lip. The tangential force at dislocation was examined for eight different directions, 45° apart around the glenoid. Concavity-compression stability was then examined for an increased compressive load of 100 N. Finally, the protocol with 50 and 100 N of compressive load was repeated after the glenoid labrum was excised. Concavity-compression of the humeral head into the glenoid is a most efficient stabilizing mechanism. With the labrum intact the humeral head resisted tangential forces of up to 60% of the compressive load. The degree of compression stabilization varied around the circumference of the glenoid with the greatest magnitude superiorly and inferiorly. This may be attributed to the greater glenoid depth in these directions. Resection of the glenoid labrum reduced the effectiveness of compression stabilization by approximately 20%. These results indicate that concavity-compression may be an important mechanism for providing stability in the mid-range of glenohumeral motion where the capsule and ligaments are lax. The effectiveness is enhanced by the presence of an intact glenoid labrum.

Residual motion and function after glenohumeral or scapulothoracic arthrodesis.

The purpose of this study was to characterize humerothoracic motion and function after glenohumeral or scapulothoracic arthrodesis and to compare those results with those from normal shoulders. We evaluated 12 shoulders in 11 patients at an average of 71 months after glenohumeral arthrodesis and seven shoulders in six patients at an average of 32 months after scapulothoracic arthrodesis. The residual motion of the unfused articulation was measured with a spatial position sensor. Various activities of daily living and standard clinical range-of-motion tests were performed. Nearly all humerothoracic motions were significantly decreased in patients after either type of shoulder arthrodesis. Patients with a glenohumeral fusion maintained their scapulothoracic motion at levels comparable with that of normal subjects. Residual glenohumeral extension and external rotation after scapulothoracic fusion were significantly decreased; internal rotation remained unchanged compared with motion in subjects with normal shoulders. Glenohumeral fusion decreased the patients' ability to perform personal care activities requiring extremes of internal rotation or elevation. Although glenohumeral arthrodesis limited total humerothoracic motion considerably, the majority of patients were improved functionally and were relatively free from pain. Most personal care activities were performed successfully by all patients with scapulothoracic fusion.

Humeral head prosthetic arthroplasty: Surgically relevant geometric considerations.

The relationship of the humeral head prosthesis to the humerus is a critical determinant of the result in glenohumeral arthroplasty. With canal-fitting humeral prostheses, the position of the component is largely dictated by the location of the reamed medullary canal. This study explores the geometric relationships of a surgically defined humeral reference, the "orthopedic axis." This is the axis of a cylindric reamer or press-fit prosthetic stem inserted to the appropriate depth for the humeral prosthesis. The orthopedic axis provides a reference for measuring surgically important geometric features of the normal humeral articular surface and comparing them with those available with humeral prosthetic components. In 10 cadaveric proximal humeri, we measured the following seven parameters in a radiologic projection of the humerus on the plane transverse to the orthopedic axis: the surgically-determined reamed diameter of the humeral canal, the diameter of curvature of the humeral head articular surface, the effective humeral neck length, the combined head and neck length, the subtended angle of the humeral joint surface, the anterior/posterior offset of the center of the humeral head, and the biceps-articular surface angle. We then determined the prosthetic geometry of a canal-fitting humeral component necessary to match the stem size, head diameter, head and neck length, and effective humeral neck length. To examine the effect of changing component version, we determined the maximal angle of anteversion and retroversion achievable by rotation of the component about the orthopedic axis without compromising the tuberosities. In the maximal possible anteversion or retroversion, the combined head and neck length changed by only 2 mm. Thus the effect of component version of a press-fit prosthesis on glenohumeral soft-tissue tension is small. The study suggests that the surgeon controls relatively few important variables in a canal-fitting humeral arthroplasty. Kinematics of the arthroplasty are controlled primarily by soft-tissue releases and the selection of the prosthetic head-neck length.

The role of the rotator interval capsule in passive motion and stability of the shoulder.

The purpose of this study was to characterize the role of the capsule in the interval between the supraspinatus and subscapularis tendons with respect to glenohumeral motion, translation, and stability. We used a six-degrees-of-freedom position-sensor and a six-degrees-of-freedom force and torque-transducer to determine the glenohumoral rotations and translations that resulted from applied loads in eight cadaver shoulders. The range of motion of each specimen was measured with the capsule in the rotator interval in a normal state, after the capsule had been sectioned, and after it had been imbricated. Operative alteration of this capsular interval was found to affect flexion, extension, external rotation, and adduction of the humerus with respect to the scapula. Modification of this portion of the capsule also affected obligate anterior translation of the humeral head on the glenoid during flexion. Limitation of motion and obligate translation were increased by operative imbrication and diminished by sectioning of the rotator interval capsule. Passive stability of the glenohumeral joint was evaluated with the use of anterior, posterior, and inferior stress tests. Instability and occasional frank dislocation of the glenohumeral joint occurred inferiorly and posteriorly after section of the rotator interval capsule. Imbrication of this part of the capsule increased the resistance to inferior and posterior translation.