Animal studies can provide important information in the evaluation of new techniques and prosthetic designs in orthopedics. As a prerequisite they must parallel as closely as possible the human conditions they are modeling. An arthritic sheep model simulating the human clinical situation has previously been designed and reported by Phillips and Gurr 10. The present study introduces for the first time an approach that evaluates a prosthetic joint in an arthritic animal hip. Hemiresurfacing following the Tharies technique 1was carried out unilaterally in 12 Suffolk sheep, and followed up for 2 years. Femoral loosening occurred in three cases. Only one of the 12 cases showed postoperative avascularity of the femoral head. Radiologic follow-up and histologic examination showed features consistently and strikingly similar to those seen in human practice. The sheep hip with simulated arthritis provides a sensitive, clinically reproducible model for the future study of other arthroplasty types and problems.
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