Hip resurfacing is an attractive implant philosophy which has existed since the advent of total hip replacement surgery. The first attempts to resurface the joint were unsuccessful, based on the fact that the tolerance level required for a smooth articulation with acceptable wear rates and no impingement could not be achieved due to machining constraints at that stage. Recently there has been renewed interest in resurfacing procedures and metal-on-metal resurfacing implants were produced by all the major implant companies. The perceived advantages of a resurfacing procedure is preservation of bone stock around the hip, which will allow a revision to a simple primary total hip replacement if required, as well as maintenance of the native biomechanics of the hip joint and a predictably low dislocation rate.
This procedure is no longer performed by any of the surgeons at the Cape Joint Surgery, based on the fact that recent evidence suggests an unacceptable degree of granulation tissue formation around implants (so-called pseudo-tumors – inflammatory tissue, not in any way malignant), which has necessitated revision rates which are unacceptably high compared with available alternative replacement procedures. While it seems intuitively logical that the incidence of granuloma formation should be directly related to the amount of metallosis secondary to wear particles from the implant, this has not been shown to be the case, despite many recent studies in this regard. What this basically means is that even anatomically and biomechanically perfectly positioned implants with documented low blood metal iron levels (i.e. a low wear rate) may develop these granulomatous pseudotumors. In basic terms, no one knows why these pseudotumours are forming and it is impossible to predict in whom they will occur. Total hip replacement is therefore a superior procedure due to predictable results and complications rates which can be directly related to imply positioning and component wear.
A recent worldwide product recall of the ASR (De Puy / Johnson & Johnson) implants was documented in the mainstream media and, while other companies have not gone the same route, there is a definite international trend of movement away from metal on metal resurfacing implants for any and all patient groups.
If a ceramic alternative bearing system can be designed, this implant philosophy will no doubt be revisited.
