A THR involves removal of the femoral head (the ball part of the joint) and replacement of the ball and socket with prosthetic implants. There are many different designs, but they almost all consist of a stem, which is placed, in the thigh bone (femur), on top of which is placed a new ball, and a socket, which is placed into the original socket in the pelvis. Fixation is achieved either with acrylic cement, or by means of a tight press-fit which is augmented by a surface coating on the prosthesis which encourages either bone ingrowth (osseointegration) or induces bone growth up to the prosthesis (osseoinduction) which further improves the quality of the press-fit.

What type am I going to have?

The choice of fixation and therefore the type of hip replacement depends on a number of factors. For the majority of patients, a standard cemented stem is the best option.

To replace the socket, I usually use a cementless metal socket coated with hydroxyapatite (HA), which is a constituent of normal bone and induces bone cells to adhere to it.

For some younger patients I use cementless stems, since it is possible to achieve good fixation in this way in younger bones, and consideration needs to be given to the future (see below). Some patients have abnormalities of the bones that require replacement with modular stems that allow reconstruction of the femur and make the replacement more like a mechanically normal hip.

Resurfacing

For a small number of patients, it may be appropriate to discuss a resurfacing procedure. This is somewhat different to a THR, in that instead of a stem being inserted into the thigh bone, a metal cap is fitted over the ball part of the hip, and a metal socket is fixed into the pelvis. Because of the much greater size of the ball, dislocation is highly unlikely, and the hip may allow a greater range of motion than a standard hip replacement. It may be appropriate to have this operation if you intend to continue to play vigorous sport for example.

Resurfacing is only feasible for those patients who have completely normal anatomy. If your arthritis has been caused by inherited, childhood or traumatic disorders, it is unlikely that a resurfacing will be possible.

Extravagant claims have been made about the longevity of resurfacing arthroplasty. These are not substantiated by long-term studies.

There are some potential drawbacks peculiar to resurfacing. One is that is impossible to see the bone inside the metal cap on an X-ray, and therefore difficult to predict failure. Secondly, metal-to-metal bearing showers metal debris into the body, especially in the early months after surgery. Such debris can be found in cells throughout the body. No harmful effects have yet been demonstrated, but as a precaution I do not advise women of chid-bearing age to have this operation. More importantly, there is a 1.6% risk of fracture of the neck of the femur with resurfacing which cannot happen with a standard type of hip replacement.

Click here for more information on specialist hip consultants at London Bridge Hospital