Hip resurfacing can be categorized as total hip resurfacing, consisting of an acetabular and femoral shell and partial hip resurfacing, in which a femoral shell is implanted over the femoral head.
Total Hip Resurfacing (THR)
THR has undergone various evolutions over the past several decades, with modifications in prosthetic design and composition and implantation techniques. For example, similar to total hip prostheses, the acetabular components of total hip resurfacing have been composed of polyethylene. However, over the years it became apparent that device failure was frequently related to the inflammatory osteolytic reaction to polyethylene debris wear particles. Metal acetabular components have since been designed to improve implant longevity. Wear particles from metal-on-metal chromium and cobalt implant components are also of potential concern.
Proposed advantages of THR compared to total hip arthroplasty (THA) include preservation of the femoral neck and femoral canal, thus facilitating revision or conversion to a total hip replacement, if required. In addition, the resurfaced head is more similar in size to the normal femoral head, thus increasing the stability and decreasing the risk of dislocation compared to THA. THR, investigated in a broader range of patients including those with osteoarthritis, rheumatoid arthritis, and advanced avascular necrosis, may be considered an alternative to total hip arthroplasty, particularly in young active patients who would potentially outlive a total hip prosthesis. Therefore, THR could be viewed as a time-buying procedure to delay the need for a THA.
The Buechel-Pappas Integrated Total Hip Replacement has received an FDA 510(k) clearance for use in THR. The weight-bearing surfaces of this device are composed of a ceramic femoral component and a polyethylene acetabular component. There has also been interest in metal on metal designs as a technique to reduce the debris wear particles. The Conserve®Plus (Wright Medical Technology) is a metal-on-metal design that is currently undergoing investigation as part of the FDA approval process. This trial will include 300 patients who will be followed up for a minimum of two years. The Cormet® 2000 hemi-arthroplasty device has 510(k) marketing clearance from the FDA. In May 2006, the FDA granted Pre-Market Approval (PMA) to the Birmingham Hip Resurfacing (BHR) system for use in patients requiring primary hip resurfacing arthroplasty for non-inflammatory or inflammatory arthritis.
Partial Hip Resurfacing (PHR)
Partial hip resurfacing is considered a treatment option for avascular necrosis with collapse of the femoral head and preservation of the acetabular. A variety of devices have been cleared by the FDA for partial hip resurfacing under the FDA’s 510(k) mechanism.
In a PHR procedure, a small cobalt-chrome disc is placed over the damaged area of the femur head. The socket or acetabulum is not touched at all. Preservation of bone is especially attractive for young, active patients who are likely to outlive their first hip replacement operation and will most likely need to have another replacement operation during their lifetime. Not everyone is a candidate for resurfacing; the femoral head may be too damaged to hold the resurfacing component. It is important that the patient does not have any risk factors that may increase the risk of failure of the partial surface hip replacement operation.
Unlike a total hip replacement, PHR leaves more bone in place and does not require that the femur neck shaft be removed. During the procedure, usually only the femoral head is reshaped and resurfaced with an artificial shell to help reduce pain and ensure joint stability. The chance of subsequent hip dislocation is also lower in this surgery than in a total hip replacement.