Charnleys initial attempts at developing total hip replacements were limited by the properties of the available bearing surfaces and difficulties with fixation. He therefore moved from a resurfacing implant towards a femoral stem in order to gain satisfactory stability. In order to reduce the amount of wear he used small femoral heads.  Technology has moved on since and we are now able to take advantage of better biomechical knowledge, improved fixation techniques and superior manufacture of metal on metal resurfacing prostheses.

Over the past decade there has been a resurgence of interest in hip resurfacing prostheses as a mode of treatment for the younger more active patient with hip pathology. Previous hip resurfacing implants have utilised cement fixation and metal on polyethylene bearings. Historically, this combination has produced poor results due to the production of polyethylene wear debris and subsequent osteolysis.  By switching to a metal on metal bearing the issue of polyethylene wear debris is eliminated at the expense of metallic debris, whose systemic effects have yet to be fully defined. The concept of a metal on metal bearing with an uncemented acetabular component and a cemented femoral component would appear to have produced the most reliable combination.

The early failures in the development of hip resurfacing would appear to be due to a failure of materials, rather than a failure of concept. Improved technology, allowing more precise and reproducible manufacture and quality control has eliminated many of the problems. Moreover previous problems with metal on metal articulations seem to have been overcome by manufacturing techniques that allow for better finishes, greater sphericity and tolerance and hence afford the opportunity of fluid film lubrication and extremely low wear rates

A larger femoral head size has a number of advantages.  It is biomechanically closer to the natural state of the hip.  There is good evidence to show there is a greater range of movement before impingement and before dislocation with larger femoral heads. At the recent American Academy of Orthopaedic Surgeon’s meeting Roy Crowninshield illustrated the fact that the advantages of large heads are routinely only borne out if the acetabular component is abducted to 45° or less.  As the opening angle of the acetabular component increases, so the advantage of a large head articulation decreases.  A large head, therefore, allows for a greater range of impingement free and dislocation free movement but risks increased wear unless component position is optimised.

The early outcome of the Birmingham hip resurfacing in our practice has been very satisfactory and has allowed patients an excellent return of function. Our experience of hip resurfacing suggests that the large heads do allow for a more physiological early rehabilitation.  These patients rehabilitate more quickly as inpatients and are discharged, on average, 3 days earlier.  They have better outcomes at 6 weeks, 3 months and 6 months although there little difference from young control patients with uncemented hip replacements by 1 year.

With large head metal on metal hip resurfacing, the dislocation risk has been decreased but has to some extent been replaced by a significant fracture risk.  In our experience there is a learning curve to hip resurfacing that requires over 30 cases before the risk of mal-alignment is decreased.  Nevertheless complication rates are low and the early outcome of this intervention is excellent.

As our understanding of new hip articulations and their wear properties improves, and with modern manufacturing processes, it is clear that we are now capable of taking advantage of the mechanical properties of large femoral heads, of metal on metal technology and of resurfacing implants. This has been borne out by our early outcomes of hip resurfacing.

Glyn-Jones S, Gill HS, McLardy-Smith P, Murray DW. Roentgen stereophotogrammetric analysis of the Birmingham hip resurfacing arthroplasty. A two-year study. J Bone Joint Surg Br. 2004 Mar;86(2):157-8.

Daniel J, Pynsent PB, McMinn DJ.Metal-on-metal resurfacing of the hip in patients under the age of 55 years with osteoarthritis. J Bone Joint Surg Br. 2004 Mar;86(2):177-84.

Silva M, Lee KH, Heisel C, Dela Rosa MA, Schmalzried TP. The biomechanical results of total hip resurfacing arthroplasty. J Bone Joint Surg Am. 2004 Jan;86-A(1):40-6.

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