THARIES resurfacing arthroplasty. Evolution and long-term results.

The unsatisfactory results of total hip arthroplasty in the young patient led to the development of the concept of hip resurfacing. Total hip articular replacement by internal eccentric shells (THARIES) resurfacing was introduced in 1975, with the primary goal of bone stock preservation and the hope of increased durability in the young patient. Major changes in design and technique include thicker and more uniform acrylic layers, metal-backed flanged acetabular component, and reduction in femoral size for preservation of acetabular bone stock. Of the 584 hips (average patient age, 48 years) with one- to ten-year follow-up study, there have been 72 failures (revision rate, 12.3%) with 66 cases of loosening (nearly all beginning in or limited to the acetabular side), two neck fractures, and four sepses. Survivorship analysis revealed that the single most important factor related to prosthesis failure is age followed by diagnosis and experience of the surgeon. Osteoarthritis and rheumatoid arthritis were favorable categories with congenital dysplastic hip (CDH), osteonecrosis, and previous failed resurfacing being unfavorable categories. Experience has taught the importance in preserving acetabular bone stock, providing bone graft for socket coverage in severe dysplasia, and removing dead bone in osteonecrosis. While resurfacing did not solve the problems of the young patient, even those patients who failed often gained time for application of the newer techniques and materials. The femoral component infrequently failed. The head remained vascular. This leads the authors to conclude that the surface arthroplasty concept is a viable alternative to total hip arthroplasty and seems to be ideal for the application of porous technology.