Resurfacing is a type of hip replacement that preserves bone in the proximal femur.
In a standard total hip, the entire femoral head and a large part of the femoral neck are removed and replaced with the femoral component. In resurfacing, only the articular cartilage and the outer portion of the femoral head are removed. The inner portion of the head and the femoral neck are left in place. A cup shaped femoral component is seated over the remaining portion of the femoral head. A small stem extends into part of the femoral neck. In a standard total hip replacement, a much broader and longer femoral stem is inserted well into the proximal shaft of the femur.
Both the femoral and acetabular components are made of a cobalt-chromium metal alloy. Thus, the bearing surfaces are metal on metal. The acetabular component is press fit into the socket. The femoral component is cemented onto the remaining portion of the femoral head. Resurfacing is therefore a hybrid arthroplasty. Resurfacing procedures have been done for approximately 30 years. The initial procedures had metal on polyethylene surfaces and met with limited success. The high failure rate may have been due to polyethylene wear caused by the large diameter femoral component. It was also felt that early failures were due to poor technique.
The demand for a bone sparing procedure in younger patients has led to renewed interest in resurfacing. Better component design and surgical technique have improved results. Ideally, the procedure is performed on a young patient with good bone suffering from either osteoarthritis or post-traumatic arthritis. Adequate bone stock is necessary for the success of the procedure. Patients with a leg length discrepancy are not good candidates. Unlike a conventional total hip, leg lengths cannot be adjusted or corrected by a resurfacing procedure.
Resurfacing has several advantages. The large size femoral head is very stable. Dislocation is a rare event. It is much easier to revise a resurfacing than a standard total hip. If revision is necessary, the femoral head and femoral neck can be removed at the normal level and a conventional femoral stem inserted. The large surface area of the components lessens the risk of impingement on the edge of the acetabulum.
Resurfacing may be a useful option in patients who have a high risk of dislocation, such as those with neurologic disease and poor muscle control. It is also an option for patients with a deformed hip where placement of a standard femoral stem is difficult. Resurfacing may be done through a standard anterior (front) or posterior (rear) approach to the hip. Since the femoral head is not removed, it must be retracted after it has been dislocated. This requires a longer surgical exposure and more dissection than a conventional total hip. Once the femoral head is exposed, a guide wire is placed at the proper angle through the surface of the head into the femoral neck.
A milling or reaming device is placed over the guide wire to shape the femoral head. The acetabular side is reamed and pre-pared in the same way as a conventional total hip. The all metal acetabular component is impacted into place. The femoral component is cemented onto the remaining surface of the femoral head. The joint is then reduced and checked for alignment and stability. Resurfacing is best done in young patients with good bone and a normal shaped femoral head. Patients who should not have the procedure are patients with:
- osteoporosis
- poor bone quality in the femoral head or femoral neck
- metabolic bone disease
- avascular necrosis with femoral head collapse
- large degenerative cysts in the femoral head or femoral neck
The procedure is also not ideal for patients who are overweight, have abnormal metal sensitivity, or have kidney problems. It is not known if the kidneys are affected by the metallic ion particles given off by wear of the metal on metal bearing. Resurfacing is also difficult in patients such as those who have had Perthes disease in childhood and have residual deformities of the femoral head and neck.
Recent studies have shown that with modern surgical technique and good patient selection, short-term clinical success rates have been high. Since the procedure is relatively new, long-term results and survivorship are not yet available.
The most common cause for revision of a resurfacing procedure is femoral neck fracture. This usually occurs in the first few months after surgery and may be technique dependent. In some cases, a fracture of the femoral neck may be treated by limited weight bearing and no surgery. Most of the time, conversion to a conventional total hip is required. Studies show the incidence of femoral neck fracture following resurfacing to be in the range of 1% to 1.5%.
Limited resurfacing is one more option for younger patients. In limited resurfacing, only the femoral component is applied. The acetabulum is left untouched. This can be done if the hip disease involves the femoral head only and there are no degenerative changes in the acetabulum. While this preserves the acetabulum, patients may sometimes complain of groin pain. This is caused by pressure of the metal femoral head on the native articular cartilage of the socket.
Hip resurfacing is gaining in popularity. As more procedures are done, techniques will improve, and we will have a greater understanding of the long-term survivorship and complications.