|
Michael J. Dunbar, M.D., FRCSC, PhD
Division of Orthopaedics
Clinical Research Scholar
Dalhousie University
Halifax, NS Hemi-resurfacing arthroplasty (HRA) for osteonecrosis of the hip is not a new concept. For the sake of brevity, the assumption will be made that the reader has a basic understanding of the concept and is referred to an excellent review article by Dr. H. Amstutz1.
 | Figure 1
Intraoperative photograph demonstrating position of HRA given limited surgical exposure. |
HRA has been reported to be efficacious with respect to improvement in physical function and reduction in pain in several papers. However, HRA may not have as predictable an outcome nor as long-lasting a result as total hip arthroplasty. Patients may have the majority of their symptoms relieved, yet still suffer from groin pain from the contact of the metal prosthesis onto the native acetabular bone. This is similar in nature to the results seen in the bipolar population.
With respect to survivorship, it appears that HRA can be viewed conceptually as having parallel results to that of a high tibial osteotomy around the knee. For example, at five years the survivorship rate is approximately 90 percent, decreasing to the 50-60 percent range at the 10-year mark2.
With respect to reliability of the surgical outcome, HRA offers a potential advantage over core decompressions, fibular grafts, and indeed osteotomies, given the difficulty in preoperatively delineating cartilaginous flap tears associated with osteonecrosis. The variability of results in addressing osteonecrosis may be related to unrealized flap tears that cannot be addressed with these more minimal procedures. HRA addresses not only the osteonecrosis, but also the cartilaginous issues by complete removal of the cartilaginous surface intraoperatively. Conversely, variations in the status of acetabular cartilage and the fit and fill of the HRA into the acetabulum may also adversely affect the reliability of the outcome.
 | Figure 2
Postoperative radiograph demonstrating appropriate positioning and sizing of HRA component. | HRA is perhaps the most technically difficult of all the procedures recommended for osteonecrosis of the hip, given that a surgical dislocation of the hip is required. Furthermore, given the limited access to the femoral head, there are technical challenges with proper component positioning. As well, great care must be taken to avoid notching of the femoral neck, which is intimately related to jig placement prior and subsequently a function of surgical exposure.
In order to improve the reliability of the outcome of the operative intervention and to decrease the incidence of groin pain, several prosthetic manufacturers have reintroduced the concept of a HRA with a concomitant cup arthroplasty, resulting in a metal-on-metal bearing surface. Unfortunately, the orthopaedic audience is well aware of previous experience with this concept, subsequently deterring many surgeons from embracing the revisiting of this concept.
One of the major issues that appears to have changed from prior experience is that of improved machining tolerances, which are felt to decrease the frictional forces at the interface and are subsequently hypothesized to improve long-term survivorship of the prosthesis. Nevertheless, long-term outcome studies on the newer prostheses are lacking. A major limitation with respect to acetabular resurfacing with concomitant HRA relates to the amount of host bone that needs to be removed in order to accommodate the acetabular component. The limiting aspect of the surgical intervention is the native size of the femoral neck, which dictates the size of the femoral component utilized in order to avoid notching of the femoral neck and subsequent periprosthetic fracture. However, in doing so, the surgeon is often forced to ream the acetabulum to an extent greater than would be required for a primary total hip arthroplasty. This represents a philosophical problem with respect to the entire concept of HRA combined with cup arthroplasty given the fact that the postulated "conservative" procedure on the femoral side is coupled with an "aggressive" surgical approach to the acetabulum. Again, long-term survivorship and outcomes to guide the surgeon are lacking.
In summary, although the approach is technically demanding, HRA of the hip offers a viable option for the treatment of osteonecrosis of the hip. Nevertheless, outcomes may be more reliable because the variable of cartilaginous flap tears is removed. Combining HRA with cup arthroplasty has entered the modern era, but long-term outcome studies are required before the greater surgical community can embrace this technique.
References
- Amstutz Harlan C. (1991). "Hip Arthroplasty". New York: Churchill Livingstone. xix, 1001p.:ill. (some col.); 29 cm.
- Hungerford M.W., M.A. Mont, et al. (1998). "Surface replacement hemiarthroplasty for the treatment of osteonecrosis of the femoral head." J Bone Joint Surg Am 80(11): 1656-64.
|
Member Services 
