Evolution and future of surface replacement of the hip.

Surface replacement is a bone-conserving alternative to total hip arthroplasty and is a significant development in the evolution of hip arthroplasty. Surface replacement with polyethylene bearings was largely abandoned, primarily because of component aseptic loosening caused by tissue reaction to high-volumetric polyethylene wear. For patients with osteonecrosis and collapse of the femoral head but with preservation of some acetabular articular cartilage, precision fit, hemisurface replacement of the femoral head only has emerged as the treatment of choice. The survivorship of our series of patients, performed in the 1981-84 era (average age, 32 years), has been 85% at 5 years, 67% at 10 years, and 42% at 16 years. In the absence of polyethylene, there has been no loosening. Revisions were for cartilage wear. The procedure is now much improved with instrumentation for non-trochanteric osteotomy approaches and off-the-shelf components in 1-mm increments. For arthritic hips, a new era of surface replacement has emerged. With metal-on-metal bearings, the volumetric wear has been reduced 20-100 times from those with polyethylene, and there is no penalty for the large ball size. The devices are now conservative on the acetabular as well as femoral side. Hybrid or all-cementless fixation is superior to earlier all-cemented devices. In those patients, the results with up to 4 years have been complication-free, with an absence of pain and a return to high functional levels, including participation in sports. Forty patients have received a Conserve Plus with interference fitting of the acetabular component with sintered beads to obtain fixation. Although the follow-up is short, surface replacement with the large ball size is extremely stable, and dislocation is rare.