John A. Sidles

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.

Translation of the humeral head on the glenoid with passive glenohumeral motion

We have demonstrated that certain passive motions of the glenohumeral joint are reproducibly accompanied by translation of the head of the humerus on the glenoid. We investigated the relationship of these translations to the position of the glenohumeral joint and to applied torques and forces in seven isolated glenohumeral joints from fresh cadavera, using a six-degrees-of-freedom position sensor and a six-axis force and torque transducer. Reproducible and significant translation occurred in an anterior direction with glenohumeral flexion and in a posterior direction with extension. We also observed translation with cross-body movement. The translation occurring with flexion was obligate in that it could not be prevented by the application of an oppositely directed force of thirty to forty newtons. Operative tightening of the posterior portion of the capsule increased the anterior translation on flexion and cross-body movement and caused it to occur earlier in the arc of motion compared with the intact glenohumeral joint. Operative tightening of the posterior part of the capsule also resulted in significant superior translation with flexion of the glenohumeral joint.

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.

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.

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. CLINICAL RELEVANCE: Loss of glenoid concavity may be an important factor in glenohumeral instability, and reconstruction of this concavity may effectively restore stability.

Laxity of the normal glenohumeral joint: A quantitative in vivo assessment.

It is critical that surgeons comprehend the normal laxity of the glenohumeral joint (1) to assist them in diagnosing conditions of clinical instability and (2) to help define a therapeutic end point for the management of shoulders with excessive stiffness. In clinical practice this joint laxity is judged by standard manual tests. We report a quantitative study of the clinical in vivo laxity of the normal shoulders of eight male volunteers. To our knowledge this is the first time that the laxity revealed on standard manual clinical tests has been quantified in vivo. The relative motions of the humerus and scapula were determined with an electromagnetic spatial tracker. This device was pinned percutaneously to the humerus and scapula of each of eight normal male volunteers of ages 25 to 45 years. An experienced shoulder surgeon carried out standard manual clinical tests of glenohumeral laxity while the resulting displacements of the humeral head relative to the glenoid were measured. Spatial tracker data indicated that for each of the different tests, the positions of the glenohumeral and scapulothoracic joints were reproducible for a given subject and among subjects. Substantial glenohumeral translations were measured during those manual laxity tests in which the joint was not at the limit of its range of motion: the drawer test, 7.8 ± 4.0 mm anterior and 7.9 ± 5.6 mm posterior; the sulcus test, 10.6 ± 3.8 mm inferior; and the push-pull test, 9.0 ± 6.3 mm posterior. A minimal translation of 0.3 ± 2.5 mm was measured during the fulcrum test in which the glenohumeral ligaments were under tension. The observed translations were reproducible in each subjects shoulder. On the other hand, there was marked variability among subjects. Even though manual laxity tests are a standard part of the clinical evaluation of the shoulder, our finding that normal glenohumeral joints show substantial translations indicates that translation on clinical manual laxity testing is not in and of itself a sufficient indication for surgical stabilization.

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)

Edge displacement and deformation of glenoid components in response to eccentric loading. The effect of preparation of the glenoid bone.

The effect of different methods of preparation of glenoid bone on displacement and deformation of a glenoid component under eccentric loading was investigated in a series of scapulae of cadavera. Handburring of the osseous surface was associated with less displacement and deformation than simple removal of cartilage with a curet. Reaming resulted in the least displacement and deformation. Substantial posterior deficiency of the bone of the reamed glenoid was not associated with significant increases of displacement and deformation.

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.

A prospective multipractice investigation of patients with full-thickness rotator cuff tears: the importance of comorbidities, practice, and other covariables on self-assessed shoulder function and health status.

Background: Rotator cuff tears are among the most common conditions of the shoulder. One of the major difficulties in studying patients with rotator cuff tears is that the clinical expression of these tears varies widely and different practices may have substantially different patient populations. The goals of the present prospective multipractice study were to use patient self-assessment questionnaires (1) to identify some of the characteristics of patients with rotator cuff tears, other than the size of the cuff tear, that are correlated with shoulder function, and (2) to determine whether there are significant differences in these characteristics among patients from the practices of different surgeons.Methods: Ten surgeons enrolled a total of 333 patients with a full-thickness tear of the supraspinatus tendon into this prospective study. Each patient completed self-assessment questionnaires that included items regarding demographic characteristics, prior treatment, medical and social comorbidities, general health status, and shoulder function.Results: As expected, patients who had an infraspinatus tendon tear as well as a supraspinatus tendon tear had significantly worse ability to use the arm overhead compared with those who had a supraspinatus tear alone (p < 0.005). However, shoulder function and health status were correlated with patient characteristics other than the size of the rotator cuff tear. The number of shoulder functions that were performable was correlated with the subscales of the Short Form-36 and was inversely associated with medical and social comorbidities. The patients from the ten different surgeon practices showed significant differences in almost every parameter, including age, gender, method of tear documentation, tear size, prior treatment, medical and social comorbidities, general health status, and shoulder function.Conclusions: Clinical studies on the natural history of rotator cuff tears and the effectiveness of treatment must control for a wide range of variables, many of which do not pertain directly to the shoulder. Patients from the practices of different surgeons cannot be assumed to be similar with respect to these variables. Patient self-assessment questionnaires appear to offer a practical method of uniform assessment across different practices.Level of Evidence: Prognostic study, Level I-1 (prospective study). See Instructions to Authors for a complete description of levels of evidence.