Anterior glenohumeral stabilization factors: progressive effects in a biomechanical model.

The aim of this study was to evaluate the anterior stabilizing factors of the glenohumeral joint over a range of translations. The stabilizers examined included the capsular ligaments, the coracohumeral ligament, the rotator cuff muscles, and the long head of the biceps. Simulated muscle forces were applied to eight shoulder specimens to produce 90 degrees of total elevation of the arm in the scapular plane. Stability, defined as the force required to reach a specified subluxation, then was evaluated under varying configurations of capsule cuts, humeral rotation, and muscular loads. The overall force-displacement relationship of the subluxation was found to increase exponentially in external rotation to 239 N at 10 mm of displacement and to level off in neutral rotation to 172 N at 10 mm of displacement. Among the muscles, the biceps was the most important stabilizer in neutral rotation, providing more than 30 N of stabilization; the subscapularis provided the greatest degree of stabilization in external rotation, increasing to approximately 20 N. The subscapularis and supraspinatus were the most consistently important stabilizers in both types of rotation. In external rotation, the superior, middle, and inferior glenohumeral ligaments were the most effective ligamentous stabilizers, and all provided progressively more stabilization as higher displacements were reached. The stability provided by some of the ligaments reached nearly 50 N at 10 mm of displacement.

Intraoperative positioning for arthrodesis of the hip with the double beanbag technique.

The double beanbag technique allows the surgeon to select the position of the lower limb before an arthrodesis of the hip. During the procedure, the surgeon can freely manipulate the limb, confident that it can be replaced in the exact position that was chosen for the arthrodesis. The technique is not cumbersome, and only commonly available equipment is needed. For the method to be effective, there must be enough residual motion of the hip to allow positioning and preparation of the skin. Also, rigid internal fixation must be used to maintain the selected position of arthrodesis at the conclusion of the operation.

Interlocking intramedullary nailing of pathological fractures of the shaft of the humerus.

We performed a retrospective study of thirteen patients who had had sixteen pathological fractures of the shaft of the humerus secondary to metastatic disease. All but one fracture was stabilized with interlocking intramedullary nailing with use of a closed technique. The mean operative time for the sixteen procedures was ninety-two minutes (range, fifty to 180 minutes), the mean blood loss was 116 milliliters (range, fifty to 200 milliliters), and the mean duration of hospitalization was five days (range, two to ten days). Fourteen extremities had a return to nearly normal function within three weeks after nailing. Relief of pain was rated as good or excellent in all but one patient. Eleven patients (fourteen humeri) received radiation therapy at a mean of seven days (range, three to fourteen days) after the operation. Nine patients died at a mean of four months (range, one to twelve months) postoperatively; the remaining four patients were still alive at a mean of ten months (range, nine to fifteen months). There were no problems related to the wound, deep infections, nerve palsies, or failures of the implant. The fracture was united in all seven of the eleven extremities in patients who survived for at least three months and had radiographs available. Interlocking intramedullary nailing of the humerus for pathological fractures provides immediate stability and can be accomplished with a closed technique, brief operative time, and minimum morbidity, with a resultant early return of function to the extremity.

Posterior glenohumeral subluxation: active and passive stabilization in a biomechanical model.

UNLABELLED: We examined the role of the glenohumeral and coracohumeral ligaments as well as the forces provided by the rotator cuff muscles, the long head of the biceps, the anterior and middle deltoids, and the pectoralis major in the stabilization of the glenohumeral joint in the posterior direction. Simulated muscle forces were mechanically applied to eight shoulder specimens. The humeroscapular position for testing simulated the 90-degree forward-flexion (humerothoracic) position used clinically for the so-called jerk test, which is the most clinically important position with regard to posterior instability of the shoulder. Experiments were performed with a variety of configurations of ligamentous and capsular cuts, humeral rotation, and levels of muscle force. Stability was investigated by measuring the force required to subluxate the humeral head a specified amount from its reduced position. Of the muscles and ligaments tested, the subscapularis muscle contributed the most to this subluxation force. The coracohumeral ligament was an effective contributor in neutral humeral rotation, and the inferior glenohumeral ligament was an effective contributor in internal humeral rotation. The long head of the biceps was found to reduce the subluxation force in certain positions. CLINICAL RELEVANCE: It is widely agreed that a complex interaction of passive and active stabilizing structures and forces is necessary for clinical stability of the shoulder. The present study identified the contributions of ligaments and muscles to posterior stability of the shoulder in the position of greatest clinical importance--posterior subluxation with the shoulder in forward flexion.

The effects of muscle fatigue on shoulder joint position sense.

Proprioception, or joint position sense, probably plays an important role in shoulder joint function. In this study, we assessed the effect of muscle fatigue on shoulder proprioception in 20 volunteers with no shoulder abnormalities. Shoulder proprioception was measured as the threshold to first detection of humeral rotation with the joint at 90 degrees of abduction and 90 degrees of external rotation. Subjects were tested while rested, exercised on a isokinetic testing machine until fatigued, and then retested in an identical fashion. Both shoulders were tested, and the order of dominant and nondominant shoulder was randomized. Shoulder proprioception was analyzed for its dependence on arm dominance, direction of rotation, and muscle fatigue. Subjects detected external rotation after significantly less movement than they did internal rotation. Overall, before exercise, motion was detected after a mean of 0.92 degrees of rotation. After exercise, this threshold to detection of movement increased to 1.59 degrees, an increase of 73%. This significant increase occurred with both internal and external rotation. The decrease in proprioceptive sense with muscle fatigue may play a role in decreasing athletic performance and in fatigue-related shoulder dysfunction. It remains to be determined if training can lessen this loss in position sense.

Ligamentous restraints to external rotation of the humerus in the late-cocking phase of throwing. A cadaveric biomechanical investigation.

The late-cocking phase of throwing is characterized by extreme external rotation of the abducted arm; repeated stress in this position is a potential source of glenohumeral joint laxity. To determine the ligamentous restraints for external rotation in this position, 20 cadaver shoulders (mean age, 65 +/- 16 years) were dissected, leaving the rotator cuff tendons, coracoacromial ligament, glenohumeral capsule and ligaments, and coracohumeral ligament intact. The combined superior and middle glenohumeral ligaments, anterior band of the inferior glenohumeral ligament, and the entire inferior glenohumeral ligament were marked with sutures during arthroscopy. Specimens were mounted in a testing apparatus to simulate the late-cocking position. Forces of 22 N were applied to each of the rotator cuff tendons. An external rotation torque (0.06 N x m/sec to a peak of 3.4 N x m) was applied to the humerus of each specimen with the capsule intact and again after a single randomly chosen ligament was cut (N = 5 in each group). Cutting the entire inferior glenohumeral ligament resulted in the greatest increase in external rotation (10.2 degrees +/- 4.9 degrees). This was not significantly different from sectioning the coracohumeral ligament (8.6 degrees +/- 7.3 degrees). The anterior band of the inferior glenohumeral ligament (2.7 degrees +/- 1.5 degrees) and the superior and middle glenohumeral ligaments (0.7 degrees +/- 0.3 degrees) were significantly less important in limiting external rotation.

The Bankart repair illustrated in cross-section. Some anatomical considerations.

The Bankart repair for chronic anterior shoulder instability effectively addresses the pathologic components responsible for repeated dislocation or subluxation. However, contrary to popular belief, the Bankart repair does not precisely restore the premorbid anatomy. The capsule is reattached to the boney rim of the anterioinferior glenoid deep to and lateral to the torn cartilagenous labrum, thus excluding the labrum from the joint anteriorly. This was demonstrated by cross-sectional cadaver dissections performed to illustrate this complex surgical anatomy to orthopaedic residents in training. In addition, when correlated with double-contrast computerized axial tomography, we noted five predominant patterns of anatomical lesions which by common use have been collectively termed the "Bankart lesion." These are: 1) the rare "classic" Bankart lesion in which the cartilagenous labrum and capsular origin are torn from the glenoid rim; 2) the capsule stripped from the scapular neck and the labrum detached from the glenoid rim remaining fixed to the overlying capsule; 3) the capsule stripped from the scapular neck and the labrum separated from the glenoid rim, but separately; 4) the labrum abraded away and no longer radiographically detectable; and 5) glenoid rim fracture.

Assessment of outcome in shoulder arthroplasty.

This article discusses outcome measures for the patient requiring shoulder arthroplasty and the weakness and strengths of various assessment tools in current use. The optimal method to measure the outcome of patients with shoulder arthroplasty is yet to be defined; however, the ideal assessment should include measures of general health, a shoulder-specific assessment, and an assessment that is specific to the disease state for which shoulder arthroplasty is indicated. The authors also provide appendices with their recommended calculations for the elevation of the shoulder arthroplasty patient.

Fractures of the acromion process: a proposed classification system.

A review of 27 fractures of the acromion process during a 15-year period revealed five distinct types that were classified into three groups. Stress fractures are rare, do not result from acute trauma, and gain little benefit from nonoperative treatment. Type I fractures are minimally displaced. Type IA fractures are avulsion fractures and heal rapidly. Type IB fractures result from direct trauma to the extremity, and are minimally displaced. Most heal with nonoperative treatment. Type II fractures are displaced laterally, superiorly or anteriorly and do not reduce the subacromial space. Most are pain free with full motion after 6 weeks of nonoperative treatment. Type III fractures reduce the subacromial space. This may occur by an inferiorly displaced acromion fracture, or an acromion fracture associated with an ipsilateral, superiorly displaced glenoid neck fracture. Patients in this group sustained significant trauma to the involved extremity. All type III fractures treated nonoperatively develop significant limited shoulder motion with pain, suggesting that early surgical intervention may be indicated.

Cannulated hip screws: a study of fixation integrity, cut-out resistance, and high-cycle bending fatigue performance.

One major advancement in the treatment of femoral neck fractures has been the development of cannulated screws. This study investigates the integrity of five commercially available cannulated screw systems. Transcervical fractures were created in 25 adult femora and repaired by three cannulated hip screws of a randomly assigned design. The repaired specimens were subjected to a triangular loading pattern for 1,000 cycles, then loaded to ultimate failure. Secondly, screws of each type were inserted into femoral heads to a point 5-mm from the chondral surface, then ramp loaded to determine the push-through stiffness and maximum load. Finally, individual screws were tested in high-cycle four-point bending fatigue in a custom fixture. In push-through, the Orthomet screws could withstand a significantly greater maximum load than the Synthes screws. The fatigue life of the Ace screws was significantly longer than the Howmedica, Synthes, and Orthomet screws, whereas the Orthomet screws performed significantly worse than all other screw types. Although cannulated screw systems uniquely address the problems of push-through resistance and high-cycle fatigue failure, certain designs are more susceptible to failure.

Management of humeral nonunion after the failure of locking intramedullary nails.

We reviewed 21 cases of humeral nonunion following the failure of "locking" humeral nails. The nails had been inserted as the primary operative procedure following humeral fracture in fifteen cases or after the failure of closed treatment in six cases. Reconstruction after the failure of these implants was complicated by poor bone stock and difficulty in achieving union. Although technically difficult, open reduction and internal fixation with plating and bone grafting (successful in nine of nine cases) was more consistent than exchange nailing (successful in four of 10 cases) in achieving union (p = 0.01). Two patients refused further surgical intervention. The degree of bone loss associated with a loose nail, the lack of success of exchange nailing, and the insertion site morbidity associated with humeral nail removal differentiate these nonunions from similar lower extremity problems. The degree of bone loss following failed locking nailing of the humerus is a major concern, and exchange nailing alone may not be an acceptable option to deal with this problem.

Measuring outcomes in shoulder arthroplasty.

No standard assessment for the patient with a shoulder arthroplasty has been universally accepted to date. Traditional assessment tools can be divided into three levels of resolution including: (1) assessments of the quality of life and general health, (2) global shoulder assessments, and (3) assessments for a particular disorder of the shoulder. In this article, examples of each of these groups are discussed. Each of these levels of sensitivity offers a different perspective on the outcome of shoulder arthroplasty and until the ideal, universal outcome measure is developed, outcomes should be reported using assessments in each of these levels.

Infantile cortical hyperostosis with osteomyelitis of the humerus.

A case is presented in which a delay in diagnosis and treatment of osteomyelitis occurred because of diagnostic confusion between the patient's osteomyelitis and his coincident infantile cortical hyperostosis.

Simulation of compartment syndrome by rupture of the deep femoral artery from blunt trauma.

Life-threatening hemorrhage of the femoral vasculature from a blunt injury to the thigh without femoral fracture has not been emphasized in the medical literature. Two cases of massive hemorrhage from the deep femoral system resulted from blunt injury to the thigh without femoral fracture. In the first case, a diagnosis of compartment syndrome was based on muscle swelling from the blunt trauma. A fasciotomy uncovered life-threatening bleeding. In the second case, which had a similar history and clinical symptoms, a vascular injury was suspected and an arteriogram was done. Disruption of the deep femoral arterial system was detected, and fluoroscopic embolization controlled the bleeding. A routine fasciotomy was then done. Both patients appeared clinically to have a thigh compartment syndrome, presumably based on injury from the crushed muscle. They both had normal arterial pulsations distal to the injured thigh. The only feature that suggested a vascular injury was a need for transfusion for hemodynamic support in excess of apparent blood loss. Arteriography, with embolization if necessary, is advised for all cases of suspected thigh compartment syndrome in which there is an unexplained need for hemodynamic support by transfusion.