A comperative study between two different types of radial head prosthesis regarding effects on radiocapitellar joint (a biomechanical study)

2. SUMMARY A comperative study between two different types of radial head prosthesis regarding effects on radiocapitellar joint ( a biomechanical study) Mehmet Ozan Aşık M.D. Dokuz Eylul University Faculty Of Medicine Department of Orthopaedics and Traumatology Inciralti-IZMIR The goal of stable open reduction and internal fixation could not be achieved in complex radial head fractures. Inspite of ligamentous injury and associated instabilities, radial head excision, worsens the current instability. Recently radial head arthroplasty is the treatment of choice in these kind of fractures. Many kind of materials have been used in radial head arthroplasties. In 1941 after introduction of vitallium caps, silicon and silastic designs have been used. But detoriation of elbow functions and incapabilities of these designs in restoration of elbow kinematics led their withdrawal from the clinical use. Recently metal prosthetic designs have taken their place. Radial head prosthesis designs have been evolved lately, and modular designs have been introduced for ease of surgery. Radiocapitellar erosion, elbow arthrosis and decreased range of motion at the elbow joint are some of the complications that can be seen after radial head arthroplasties. In the last few years bipolar designs were introduced to medical practice, hoping for restoration of elbow functions to a more physiological level. Studies regarding effects of metal prosthesis on radiocapitellar joint are limited in the literature. In this study we compared the loading patterns of two seperate designs, on the radicapitellar joint surface. We aimed to compare the differences of two prosthetic designs in between and with the original radial head during physiological motion ranges. Six formaldehyde embalmed cadavera were used in our study. Cadavera with suitable elbow motion ranges and similar radial head dimensisons were chosen for the study. Radiologically the cadavera were tested for previous elbow arthrosis or forearm fractures. 12Monopolar and bipolar prostheses were designed and produced. For measuring load, load cells were adapted to the prostheses. To measure loads transferred from intact elbow, load cells were designed of the same metal with having the same concavity as the prosthesis did. Same stem size and head diameter were used in the study. For adaptation of cadavera into axial compression device and simulation of elbow motion, ring external fixator systems were used. 100 Newtons of load was applied from the hand. Obtained strain values were mathematically converted to load unit, Newton. Eventually; with bipolar prosthesis design we obtained load values more close to phsyiological loads on capitellum, compared to monopolar design. But could not find statistical difference between designs. Both prosthetic designs exerted more load on the capitellum compared with the native joint. We obtained similar patterns of load transfer through the prosthetic designs with respect to native radial head. Key words: radial head prosthesis,monopolar-bipolar prosthesis designs, radial head fractures, radiocapitellar load transfer, elbow biomechanics. 13