[Hip surgery: local tissue reactions]

Present extent of total hip prostheses, protracted course of first operations lead to pathological studies on local tissue reactions, sign of the failure or of the damaging of the artificial hip. Another pathology, often as intricate, is observed after more conservative surgery: high femoral osteotomies, cup arthroplasties, femoral metallic prostheses. Failure of an high femoral osteotomy shows a running of osteoarthritic lesions the topography of which is always modified by the new orientation of the articular bearing segment. Osteosclerosis, osteoarthritic cysts may develop on a preexisting osteophytosis. Osteonecrosis or bone resorption are sometimes found. Anatomical results in case of a successful osteotomy are scarce. Fibrous layer eventually quoted as a guide to the development of fibrocartilage is more often associated with osteoclast mediated bone loss. Efficient bone remodelling is assumed only, today, by radiological proof. Failures of cup arthroplasties induce femoral bone or acetabular cartilage lesions which are different according to the surgical technic. Some are marked by cartilage destruction of the acetabula or by a cup dislodgement. Bone structure in those cases shows under the cup a good remodelling with a fibrous or fibrocartilaginous mantle originating from the bone marrow spaces and the capsular attachment. In other cases, the femoral head presents areas of superficial or total osteonecrosis, signs of intense osteoclastic activity, cleaving of the fibrous surface and eventually metallic debris or cement induced histiocytic granuloma. A fibrous layer may develop between the cup and the acetabula. Femoral metallic prostheses may damage in some years cartilage of the acetabula. Osteoarthritic bone remodelling is sometimes observed in close contact with the metallic collar. Lesions of capsular tissues are eventually represented by metallic debris or an histiocytic granuloma due to cement anchorage. Material received at the time of surgical revision on total hip arthroplasties concerns chiefly the newly formed capsular and synovial tissues. Their appearance is quite similar to the tissular layers found between prosthetic material and bone or cement. For the pathologist, main inquiries are the rule out of an infection, the extent and course of the macrophage or giant cell response, the nature of wear debris or of the products of corrosion and the histological factors contributing to the loosening of the prosthetic components. It should be stressed that any physiopathological schedule of an artificial hip failure is a topographical and dynamic problem only partly resolved by studying autopsy material.