Hip Resurfacing

What is the difference between a Hip Resurfacing and a total hip replacement (THR)?

The concept of hip resurfacing provides potential benefits for the surgeon and patient.  Bone preservation is a central concern for younger patients who want to return to an active lifestyle.  By preserving existing bone rather than removing and replacing a large section of the femur, natural anatomical biomechanics can be maintained.  This may also make for an easier revision to conventional stemmed total hip replacement if required.

Not only is bone conserved, but BMD (bone mineral density) may also improve with a hip resurfacing.  The design of hip resurfacing devices transfers load in a more physiological manner than a conventional THR.  Studies have shown significant increases in bone mineral density in the proximal femur with a hip resurfacing compared to a stemmed total hip replacement.

Further studies have also shown improved function, kinematics and faster recovery for patients who have had hip resurfacing versus those who have had total hip replacements.

The fundamental difference between a hip resurfacing and a conventional total hip replacement (THR) is in the femoral (thigh) side. A THR has a long stem inserted into the canal in the thigh bone. Hence the natural femoral head and part of the neck are removed and weight is transmitted through the stem directly into the upper third of the thigh bone. In a resurfacing, the aim is to preserve most of the femoral head and neck. The resurfacing femoral component therefore has a thin (3 to 4 mm) hollow ball surface that directly transmits weight to the femoral head bone underneath it and a very small stem that is not designed to transmit weight. The socket component can be similar in both the THR and a hip resurfacing.

There are other differences between a Conventional THR and a hip resurfacing. Conventional THR sockets are made of polyethylene (PE). Wear-debris generated from PE wear leads to loosening of the components. This is the primary cause of long-term failure of conventional THRs. PE wear and loosening are directly related to activity. Hence these THRs do not last well in younger and more active patients. In addition, the minimum thickness needed for a PE socket required that the femoral head had to be smaller in diameter than what a metal-metal joint would permit. A small diameter head has the potential to dislocate more readily than a normal hip and therefore the dislocation rates with conventional THRs are greater than those with hip resurfacings.

Hip Resurfacing is bone sparing.

A sketch by Patricia Walter illustrates a hip resurfacing device on the left compared to a total hip replacement device on the right.  Which bone sparing device looks more natural and bone conserving to you? According to medical studies, a hip resurfacing provides a more natural gait and loads the hip more naturally than a total hip replacement.