Improvement in comfort and function after cuff repair without acromioplasty.

The repair of full thickness rotator cuff tears traditionally has included acromioplasty and coracoacromial ligament section. Acromioplasty can be complicated by deltoid detachment, compromise of the deltoid lever arm, anterosuperior instability, and adhesions of the rotator cuff tendons under the bleeding cancellous bone of the osteotomized acromion. This report concerns the improvement in shoulder function at a minimum of 2 years after 27 full thickness rotator cuff repairs were done without deltoid detachment, acromioplasty, or section of the coracoacromial ligament. The mean number of Simple Shoulder Test functions that the patients could do increased from six of 12 before surgery to 10 of 12 at an average followup of 4 years after surgery. Eight of 12 individual Simple Shoulder Test functions were significantly improved after the procedure. There also was a significant improvement in the Short Form-36 comfort, physical role function, and mental health scores. When done without acromioplasty, cuff repair avoids the possibility of deltoid detachment, altered deltoid mechanics, anterosuperior instability, and tendon scarring to the cancellous undersurface of the acromion.

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.

In vivo quantification of the laxity of normal and unstable glenohumeral joints.

The purpose of this study was to determine whether the magnitude of glenohumeral translation on clinical laxity tests could distinguish between clinically stable shoulders and shoulders with traumatic or atraumatic instability. Subjects included eight male volunteers with no history of symptoms of glenohumeral instability, eight patients with documented traumatic anterior instability and Bankart lesions, and eight patients with documented atraumatic multidirectional instability. The patients in the two instability groups had disabling instability that was refractory to nonoperative management and thus met the indications for surgical repair. All subjects were examined by an experienced shoulder surgeon using five standard manual tests: anterior drawer, posterior drawer, sulcus, push-pull, and fulcrum. The glenohumeral translations occurring during these laxity tests were quantitated with a spatial sensing system that had six degrees of freedom and was rigidly fixed to the scapula and humerus. The result showed substantial overlap in the translations found in members of the three groups for each of the laxity tests. Standard laxity tests demonstrate considerable translation in normal glenohumeral joints and do not reliably differentiate normal shoulders from those with two common forms of glenohumeral instability. This study suggests that assessment of the magnitude of glenohumeral translation on clinical laxity tests is not a specific test for the diagnosis of glenohumeral instability. Healthy subjects without symptoms may have as much translation as patients needing surgical repair for symptomatic shoulder instability. The need for and the type of surgical reconstruction for the unstable shoulder must be based on the patient's history and on duplication of the symptoms of instability on directed physical examination rather than on the magnitude of glenohumeral translation.

Total shoulder arthroplasty: Some considerations related to glenoid surface contact.

The area of prosthetic surface contact is an important surgeon-controlled variable in total shoulder arthroplasty and is related to the geometry of the glenoid and humeral articular surfaces and their relative positions. This study explores some of the factors that affect joint surface contact area. We measured the humeral and the glenoid articular surface angles in the superior-inferior and anteroposterior planes for two prosthesis systems representative of those in common clinical use. On the basis of these data we determined the range of glenohumeral positions providing full glenoid surface contact, a condition in which all of the articular surface of the glenoid component is in contact with the articular surface of the humeral component. We found a wide variability in the range of glenohumeral positions providing full glenoid contact with different prosthetic combinations. Some combinations do not even offer full glenoid surface contact with the joint in the centered position, for example, when the center of the humeral head articular surface is opposed to the center of the glenoid articular surface. The maximal range of glenohumeral positions providing full glenoid surface contact was 117° for a combination with a small radius of head curvature and a large articular surface angle. The relative positions of the humeral and glenoid articular surfaces also have a major influence on the joint contact area. Some combinations offer full glenoid surface contact only in a position of humeral abduction with respect to the scapula. Loss of full glenoid surface contact between the glenoid and humerus may allow for unwanted translations of the humeral head on the glenoid in the direction where contact is lacking. Furthermore, in positions where full surface contact is lacking, humeral bone or soft tissue may make unwanted contact with the glenoid. These results suggest that the design of the humeral articular surface and the surgical procedure should maximize full glenoid surface contact in functionally important positions.

Thermal aspects of the use of polymethylmethacrylate in large metaphyseal defects in bone. A clinical review and laboratory study.

The potential necrotizing effects of the heat produced by the exothermic polymerization process has raised questions regarding the use of polymethylmethacrylate (PMMA) in orthopedic surgery. An experimental model was used to: (1) analyze the amplitude and distribution of heat in bone taken from autopsy specimens when large metaphyseal defects (simulating tumor excision) were filled with curing PMMA and (2) to observe any significant necrotizing temperatures. The experimental design included two experimental groups of five distal femora into which either a small- or large-bore defect was made in the lateral epicondylar region. These defects were filled with either one or two packs of PMMA cement, and temperature probes were used to record temperature elevations at the cement core, the bone-cement interface, and the surrounding 1-, 2-, 3-, and 5-mm bone intervals. To simulate physiologic temperature and fluid environment, the experiment was conducted in a 37 degrees normal saline bath. There is clinical evidence suggesting that the large amounts of PMMA used in tumor reconstructive surgery (often two packs or more) may lead to thermal necrosis of remaining tumor cells in the curetted cavity. This may explain, at least in part, the decrease in recurrence of giant-cell bone tumor after curettage and PMMA cementation.

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.

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.

A system for describing positions of the humerus relative to the thorax and its use in the presentation of several functionally important arm positions.

The function of the shoulder is to position the arm with respect to the thorax. Humerothoracic positions are commonly described in terms of the degrees of humeral elevation in the sagittal plane (flexion) and/or the degrees of elevation in the coronal plane (abduction). This article proposes a more general system for describing positions of the arm based on the plane of humeral elevation and the angle of elevation within this plane. This system is used to present the humerothoracic positions used by eight normal subjects to perform several activities of daily living as well as those achieved in a range-of-motion examination of the shoulder. Eating, hair combing, and maximal elevation were all performed in a plane approximately 60° anterior to the coronal plane. Between reaching the perineum and washing the contralateral axilla, the humerus functioned in a range of planes extending over 180°.

Humeroscapular positions in a shoulder range-of-motion-examination.

Positions of the arm are traditionally described in relation to the thorax. Yet shoulder pathology most often lies in and about the glenohumeral joint, which then becomes the focus of treatment. Little is known about the relative motion between the humerus and the scapula primarily because there is no clinically accepted method for assessing and describing these positions. This paper proposes a clinical method for describing and measuring humeroscapular positions based on an anatomic definition of the plane of the scapula. Humeroscapular positions achieved by 75 normal subiects during a conventional (humerothoracic) shoulder range-of-motion examination are presented. Identification of the plane of the scapula is based on four palpable anatomic landmarks: (7) the inferior pole of the scapula, (2) the medial border of the scapula at the level of the scapular spine, (3) the posterolateral corner of the acromion, and (4) the tip of the coracoid. The plane of the scapula is defined by the line connecting the first two of these points and a point midway between the last two. Humeroscapular positions are specified by the plane of elevation and the angle of elevation in relation to this mobile scapular plane. Measurement of these positions was done with a goniometer facilitated by a "scapula-locating device" designed for this study. Maximal humerothoracic elevation of the arm was achieved with the humerus lust behind the scapular plane at 90° of humeroscapular elevation. Cross-body adduction positioned the humerus in a plane 51° anterior to the plane of the scapula, with most of the cross-body motion occurring between the scapula and thorax. External rotation at 90° of elevation in the coronal plane of the body (the apprehension position) positioned the humerus in a plane 17° posterior to the scapular plane. Humerothoracic extension and reaching up the back took place at very low angles of humeroscapular elevation.