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 mechanism of creation of superior labrum, anterior, and posterior lesions in a dynamic biomechanical model of the shoulder: the role of inferior subluxation.

Lesions of the superior glenoid labrum are a source of shoulder disease. However, the mechanisms of injury to this region are unknown, and controversy exists regarding the role of shoulder instability in creation of this lesion. With a cadaver model that simulates physiologic rotator cuff forces and produces traction on the biceps tendon, the creation of type II superior labrum, anterior, and posterior (SLAP) lesions and the role of glenohumeral subluxation were investigated: Left and right shoulders from each of 8 paired cadavers (age 62 +/- 7.2 years, 5 male and 3 female) were randomized to be tested in either a 20 mm inferiorly subluxed position or in a reduced position. The long head of the biceps tendon was held near the musculotendinous junction with a novel cryogenic clamp. Traction on the long head of the biceps tendon was applied at a fast rate of 12.7 cm/sec with a servohydraulic testing machine. A load cell was used to monitor the biceps tendon load. After testing to failure, the presence or absence of a type II SLAP lesion was determined by 2 experienced shoulder surgeons masked to the test group. The production of type II SLAP lesions differed significantly (P = .03) between reduced shoulders (2 SLAP lesions out of 8 tests) and the shoulders with inferior subluxation (7 SLAP lesions out of 8 tests). This experiment has shown that traction on the biceps tendon in this biomechanical model can reproducibly create type II SLAP lesions, and inferior subluxation facilitates the generation of such lesions.

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.

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.

Active and passive factors in inferior glenohumeral stabilization: a biomechanical model.

This study examines the stabilizing factors of the glenohumeral joint against inferior translation over a range of subluxations. Factors examined included the glenohumeral capsular ligaments, the coracohumeral ligament, the rotator cuff forces, and the long head of the biceps force. Simulated muscle forces were applied to eight shoulder specimens with the arm near 0 degrees abduction. Stability was defined as the force required to inferiorly sublux the joint to a specified translation from the centered position and was evaluated under varying configurations of capsule cuts, humeral rotation, and muscle loads. The supraspinatus and biceps muscle forces were found to be important active stabilizers. Thus, tension in the long head of the biceps did not tend to depress the humeral head. The inferior glenohumeral ligament was an important passive stabilizer in external rotation. Understanding the effects of these factors adds insight into the underlying biomechanics of clinical shoulder instability.

The low incidence of suprascapular nerve injury after primary repair of massive rotator cuff tears.

We measured the incidence of cuff retear and injury to the suprascapular nerve after mobilization and repair of a massive rotator cuff tear. Of one hundred four rotator cuff repairs performed over a 5-year period, 10 patients (7 men and 3 women, age range 22 to 68 years) had primary repairs of massive rotator cuff tears requiring cuff mobilization and an acromioplasty as their only procedure. These patients were evaluated at a mean of 2.5 years (range 2.0 to 3.0 years) after surgery. At follow-up electromyographic examination confirmed that 1 of the 10 patients had an iatrogenic suprascapular nerve injury, whereas ultrasound evaluation revealed that 2 of 10 repairs failed. Pain relief was achieved in the eight patients with intact repairs and not in the two with recurrent tears. All patients had some limitation of active motion or strength, especially in external rotation. Thus 7 of 10 patients had neither evidence of nerve injury nor recurrent rotator cuff tears yet still showed limited active motion or weakness. It appears that operative injury to the suprascapular nerve during cuff mobilization can occur, but other factors such as inadequate cuff muscle function are more frequently responsible for the poor functional outcomes seen after successful repairs of massive rotator cuff tears.

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.

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.

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.

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.

Percutaneous intramedullary pinning of proximal humeral fractures.

Proximal humeral fractures can usually be treated closed. However, even with an adequate closed reduction, these fractures are occasionally unstable, fail to remain reduced, and require operative intervention. A percutaneous intramedullary pinning technique is effective in stabilizing these fractures. Two cases that illustrate the adult and pediatric techniques for pin placement/application are presented. In the pediatric population, however, large multiple pins often cannot be used due to the size of the intramedullary canal, and fewer or smaller diameter pins are used.

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.

Efficacy and safety of enoxaparin to prevent deep venous thrombosis after hip replacement surgery. Enoxaparin Clinical Trial Group.

OBJECTIVE: To determine the most effective and safe dose of enoxaparin to prevent deep venous thrombosis in high-risk surgical patients. DESIGN: A double-blind, randomized, multicenter clinical trial. SETTING: Private, university, and government hospitals in the United States. PATIENTS: 572 patients having elective hip replacement surgery, 568 of whom received study medication and had efficacy data available for evaluation. INTERVENTIONS: Patients were randomly assigned to one of three subcutaneous enoxaparin regimens: 10 mg once daily (161 patients); 40 mg once daily (199 patients); and 30 mg every 12 hours (208 patients). Treatment was initiated within 24 hours after surgery and continued for as long as 7 days. Treatment with 10 mg enoxaparin once daily was discontinued prematurely after an interim analysis showed an increased deep venous thrombosis incidence in this treatment group. MEASUREMENTS: Efficacy was determined by bilateral lower extremity venography, noninvasive vascular imaging methods, or clinical evidence on day 7 of treatment or earlier if clinically indicated. RESULTS: Deep venous thrombosis occurred in 25% (40 of 161) of the patients who received 10 mg of enoxaparin once daily; in 14% (27 of 199) of those receiving 40 mg of enoxaparin once daily; and in 11% (22 of 208) in those receiving 30 mg of enoxaparin every 12 hours. The incidence of deep venous thrombosis was significantly higher in patients who received 10 mg of enoxaparin once daily compared with those who received 40 mg of enoxaparin once daily (P = 0.02) or those who received 30 mg of enoxaparin every 12 hours (P < 0.001). The difference between the patients who received 40 mg once daily and those who received 30 mg every 12 hours was not significant. Only two cases of pulmonary embolism were diagnosed, one in patients receiving 40 mg of enoxaparin and one in those receiving 10 mg once daily. The incidence of hemorrhagic complications differed significantly between patients who received 10 mg of enoxaparin once daily (5%, 8 of 161 patients) and those who received 30 mg of enoxaparin every 12 hours (13%, 26 of 208; P < 0.05). CONCLUSIONS: After surgery, enoxaparin, 40 mg once daily or 30 mg every 12 hours, is more effective than a regimen of 10 mg once daily to prevent deep venous thrombosis in patients having elective hip replacement surgery. The regimens of 40 mg once daily and 30 mg every 12 hours provided prophylaxis similar to the most effective drug treatments previously reported. The incidence of hemorrhagic episodes with the regimens of 40 mg once daily and 30 mg twice daily was higher than that observed with 10 mg once daily; however, major hemorrhage occurred in only 4% to 5% of patients receiving the higher-dose regimens. The risk-to-benefit ratio supports the use of enoxaparin as a therapeutic agent to prevent deep venous thrombosis in these patients.

Shoulder proprioception. Effect of joint laxity, joint position, and direction of motion.

Recently, considerable importance has been ascribed to that portion of shoulder stability which may be provided by active muscle forces. Joint proprioception likely has a considerable role in muscular stabilization of the shoulder by providing information to the central nervous system for the management of muscular activity. Normal human shoulder proprioception has not yet been thoroughly characterized. We have measured shoulder joint proprioception in a population of subjects without known shoulder abnormalities by quantifying the subjects' ability to correctly detect passive shoulder rotation in the abducted shoulder. We have found absolute angular proprioception to range from an average "best" of 0.78 degrees to a "worst" of 1.08 degrees. Individuals who have clinically determined generalized joint laxity are significantly less sensitive in proprioception (P < .002). Detection of external rotation is significantly more sensitive than detection of internal rotation (P < .001). Detection of external rotation becomes significantly more sensitive as the limit of external rotation is approached. We have concluded that these findings suggest capsular tightening as one possible mechanism for shoulder proprioception.