The load transfer effect of monopolar and bipolar radial head prosthesis designs on capitellar cartilage: A comparative biomechanical cadaver study.

OBJECTIVE: The aim of this study was to determine whether bipolar radial head arthroplasty may transfer less load to the capitellum than monopolar radial head arthroplasty and native radial heads. METHODS: Six human elbow joints were obtained from six fresh frozen cadavers (3 males, 3 females; mean age = 78 years, age range = 66-80). None of the elbow joints had a previous osseous injury, a chondral defect, osteoarthritis, or instability. In group 1, load transfer of the native radial head was measured in each specimen under 100 N of compression force using a custom-made load cell at 0°, 30°, 60°, 90°, and 120° flexion of the elbow in supination, neutral rotation, and pronation, respectively. After excision of the radial heads, the same testing protocol was first applied for monopolar radial head arthroplasty (Group 2) and then for bipolar radial head arthroplasty (Group 3). RESULTS: The mean load transfer on the capitellum was significantly higher in each forearm rotation and all angles of the elbow flexion in the arthroplasty groups than the native radial head group. Mean load transfer values of bipolar prostheses were between the values of native radial heads and monopolar prostheses in all positions. Bipolar prostheses showed similar load transfer characteristics compared to those of the native radial head in supination at 60° flexion; in neutral rotation at 0°, 30°, 60°, and 120° flexion; and in pronation at 90° and 120° flexion. CONCLUSION: The results of this study have revealed that bipolar radial head arthroplasty transfers similar loading as the native radial head on the capitellum in certain forearm positions and at elbow flexion angles. No significant differences could be found between load transfer values of bipolar head design and monopolar head design except in the pronation at full extension.

Pigmented villonodular synovitis of the thoracic vertebra presenting with progressive spastic paraparesis.

Pigmented villonodular synovitis (PVNS) is a proliferative benign lesion originating from the synovium and commonly affects large joints of the extremities. PVNS can arise from any synovium in the whole body and rarely affects the zygapophyseal joints of the spine. Spinal PVNS is diagnosed mostly after resection of the mass. In our case we present a 22-year-old male patient showing progressive spastic paraparesis with insidious onset of back pain and difficulty of walking in a relatively short period of 1 month. After gross excision of the mass, diagnosis was established through histopathology. Two years of follow-up period reveals complete resolution of the patient's complaints and no recurrence on radiologic images.