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Effect of hemiarthroplasty on acetabular cartilage

Marjolein C. H. van der Meulen, PhD; William A. Allen, BS; Virginia L. Giddings, ME; Kyriacos A. Athanasiou, PhD; Robert D. Poser, DVM; Stuart B. Goodman, MD, PhD; R. Lane Smith, PhD; Gary S. Beaupré, PhD

One third of all hip replacements performed in the U.S. annually are hemiarthroplasties. A hemiarthroplasty, as opposed to a total hip replacement, involves the replacement of the femoral side of the hip joint by a rigid metal implant which rests in the patient?s acetabulum against the natural cartilage (Fig. 1). Compared to a total hip replacement, hemiarthroplasty procedures involve shorter surgical times and lower medical and prosthesis costs. Cost considerations make it likely that the number of hemiarthroplasties performed will increase in the future. Hemiarthroplasty success, however, is often limited by pain from extensive cartilage erosion and loss of joint space. The severe cartilage degradation resulting from articulation with a metal implant is of great concern if hemiarthroplasty is to be a more successful surgical procedure.

Figure 1. Schematics of (a) total hip arthroplasty with prosthetic replacements of both sides of the hip joint; (b) hemiarthroplasty with femoral prosthesis only. The purpose of the present research is to fully characterize the changes that occur in the acetabulum following hemiarthroplasty, and to also examine surgical variables which may contribute to this degradation. We hypothesize that the altered loading environment created by the introduction of the rigid spherical prosthesis head will result in cartilage changes in the acetabulum.

We examined the morphological, biochemical, material and histologic changes of acetabular articular cartilage after one year of hemiarthroplasty in nineteen sheep. Visual examination of the left acetabulum determined the extent of cartilage erosion (% loss of cartilage area) and the condition of the remaining cartilage (% fibrillation). Cartilage degradation was assessed biochemically by examining the primary constituents of cartilage: proteoglycans and collagen. Material properties and thickness were determined from creep indentation experiments. Histologic appearance was graded from thin sections. Differences between the acetabulum pairs were analyzed by paired t-tests.

From visual examination, twelve sheep demonstrated moderate loss of cartilage (10-50%), and seven sheep had widespread cartilage loss (50-90%). In fifteen sheep, the remaining cartilage exhibited widespread or complete fibrillation. Both the biochemistry and the material property data indicate severe degradation of the remaining cartilage. We are currently in the process of confirming these results with the histology. Upon completion of the cartilage characterization, we will examine the correlation of the degradative changes with surgical parameters, including head size, leg length, and neck angle.

Republished from the 1996 Rehabilitation R&D Center Progress Report. For current information about this project, contact: Marjolein C. H. van der Meulen.