J Roberts, RMD Meek, Southern General Hospital, Glasgow
P Roberts, Royal Gwent Hospital, Newport
P Grigoris, Medical Engineering, School of Engineering, Design and Technology, University of Bradford
Corresponding author: RMD Meek, email: rmdmeek@doctors.org.uk
SMJ 2005 50(1): 10-12
Total hip replacement is a successful and common reconstructive procedure for patients with arthritis of the hip. Despite the excellent results in older patients, the outcome in the active patient younger than 55 years is generally poor as reported by various national arthroplasty registries. The Swedish Hip Registry reports conventional hip replacements performed in those over 65 years have survival rates in excess of 80% at 20 years but in patients less than 55years of age this figure is 33% by 16 years postoperatively.1 Approximately 10% of hip replacements are currently performed in patients under the age of 55, in whom there is a high risk of failure with a subsequent need for lengthy and difficult revision surgery. There are several reasons why hip arthroplasties fail. The principal cause is wear of the articulating surfaces. This results in the production of particulate debris which insights a localised inflammatory tissue reaction causing bone resorption and prosthetic loosening. The total amount of wear is related to the activity level of the patient and the duration the implant is in situ.
Recently there has been a marked increase in demand of metal on metal hip resurfacing. This is an alternative procedure to conventional total hip replacement with a low wear producing articulation. It has the advantages of preservation of proximal femoral bone stock at the time of surgery and avoidance of long-term stress shielding which can lead to bone resorption and implant loosening. Revision surgery, if required, should therefore be easier and more durable. In addition, the large diameter of the articulation, offers increased stability and range of movement for the active individual.2 The difference between a resurfacing and a standard total hip replacement can clearly be seen on the X- ray in fig 1.
The concept of hip resurfacing is not new. It has evolved directly from the original mould arthroplasty introduced by Smith Petersen in 1948.3 In the early 1950s, Sir John Charnley, the pioneer of conventional total hip replacement, experimented with hip resurfacing using Teflon, which was a material with poor wear characteristics.4,5 In the 1960s, Muller6 in Switzerland and Gerard7 in France developed metal-on-metal resurfacings. In the 1970s, cemented systems using a polyethylene acetabular component and a metal femoral cup were introduced by Paltrinieri and Trentani8 in Italy, Furuya9 and Tanaka10 in Japan, Freeman11 in England, Wagner12 in Germany, and Amstutz13 in the United States.
The results of hip resurfacing in the 1970s and 1980s were disappointing and the procedure was largely abandoned by the mid 1980s.14 The expectation that these prostheses would be easy to revise was not often fulfilled. The large diameter of the articulation combined with thin polyethylene cups or liners, led to accelerated wear and the production of large volumes of biologically active particulate debris leading to bone loss and implant loosening. However, as the implications of wear debris induced osteolysis were not fully appreciated at the time, failure was attributed to other factors primarily abascular necrosis of the femoral head. This mechanism of failure has not been confirmed by a number of retrieval studies.15,16
The high incidence of femoral neck fracture was also an issue. With the benefit of hindsight, neck fractures seen in the first generation of hip resurfacings were due to a combination of osteolysis of the femoral neck and the surgical technique advocated at the time. Notching of the femoral neck at the time of surgery, which is a potent cause of subsequent neck fracture was often a consequence of extreme valgus positioning of the implant which was recommended to reduce the tension and shear stresses across the head neck junction.17 Under sizing of the implants in order to minimise frictional torque also resulted in notching. Trochanteric osteotomy, which was commonly performed, could also compromise the femoral neck if it was too extensive.
The failure of previous generations of hip resurfacing was essentially a consequence of the use of inappropriate materials, poor implant design and inadequate instrumentation rather than an inherent problem with the procedure itself. The renaissance of metal-on-metal articulations for total hip arthroplasty began in 1988 when Bernard Weber in collaboration with Sulzer developed the MetasulTM bearing.18,19 The availability of a durable low wear bearing which could be used in a large diameter articulation enabled the introduction of a new generation of hip resurfacings in 1991. By the end of 2004, the majority of the main implant manufacturers had introduced metal-on-metal hip resurfacing systems. To date, only short to medium term results are available, but these results are much better compared to the earlier metal on polyethylene resurfacings. The complications commonly seen in the 1970s and 1980s, such as early implant loosening and femoral neck fracture now appear to be rare. 14,20,21
The results have been consistent with the National Institute for Clinical Excellence (NICE) medium term benchmarks. NICE recommends that the use of resurfacing implants should be considered in patients who are likely to outlive a conventional total hip replacement (principally individuals under the age of 65) taking into account activity levels of potential recipients. They should be performed by surgeons with specific training and in the context of ongoing collection of data on both the clinical effectiveness and cost effectiveness of this technology.22 The same guidelines have been adopted by the Health Technology Board for Scotland.23 The results of the Scottish hip arthroplasty registry for resurfacing are anticipated with great interest and a further review by NICE is due in 2005.
Concern has been raised about the biological effects of the elevated levels of metal ions and metal particles found in blood, periprosthetic tissues and lympho-reticular system in all patients with metal-on-metal bearings. The latency period for the development of haemopoetic or musculoskeletal malignancies is likely to be prolonged. However, to date, there is no evidence that patients with metal-on-metal bearings in situ are more likely to develop such malignancies when compared with the general population.24
Further work will be required to determine the prevalence of femoral neck fractures and avascular necrosis of the remaining femoral head and whether these complications are technique related, or whether they relate to biological problems of the femoral head inherent to the procedure itself. Long term observational studies and controlled trials will be required to determine if the potential advantages of hip resurfacing compared to conventional THR are realised. Whilst early results should be regarded with caution, the present generation of metal-on-metal hip resurfacings potentially offer the ultimate bone preservation and restoration of function in appropriately selected young patients. Resurfacing implants demand high manufacturing standards to produce consistently low wear bearings. The background research and better understanding of implant failure would suggest that hip resurfacing technology has now developed beyond that of an experimental procedure. Only long term results and experience with this technology in the wider orthopaedic community will give the answer as to whether the results will be durable, or if hip resurfacing will simply become a bone conserving intervention prior to conventional total hip replacement.
REFERENCES
1 Malchau H, Herberts P, Soderman P, Oden A. Prognosis of Total Hip Replacement. Update and Validation of Results from the Swedish National Arthroplasty Register 1979-1990. Acta Orthop Scand 1993; 64: 497-506.
2 Amstutz HC, Grigoris P, Dorey FJ. Evolution and future of surface replacement of the hip. J Orthop Sci 1998; 3: 169-86.
3 Smith-Petersen MN. Evolution of mould arthroplasty of the hip joint. J Bond Joint Surg 1948; 30-B: 59-75.
4 Charnley JC: Arthroplasty of the hip: A new operation. Lancet, 1:1129-1132, 1961.
5 Charnley JC. Tissue reactions to polytetrafluoroethylene (Letter). Lancet, 2:1379, 1963.
6 Muller ME. Lessons of 30 years of total hip arthroplasty. Clin Orthop.274:12- 21, 1992.
7 Gerard Y. Hip arthroplasty by matching cups. Clin Orthop. 134: 25-35,1978.
8 Furuya K, Tsuchiya M, Kawachi S. Socket-cup arthroplasty. Clin Orthop. 134: 41-44, 1978.
9 Tanaka S. Surface replacement of the hip joint. Clin Orthop. 134:75-79, 1978.
10 Trentani C, Vaccarino F. The Paltrinieri-Trentani hip joint resurface arthroplasty. Clin Orthop 134:36-40, 1978.
11 Freeman MAR, Swanson SAV, Cameron H et al. ICLH cemented double cup total replacement of the hip. J Bone Joint Surg. 60-B:137-138, 1978.
12 Wagner H. Surface replacement arthroplasty of the hip. Clin Orthop 134: 102-130, 1978.
13 Amstutz HC, Clarke IC, Cristie J et al. Total hip articular replacement by internal eccentric shells. Clin Orthop 1977; 128: 261-284.
14 Grigoris P, Roberts P, Panousis K, Bosch H. The evolution of hip resurfacing arthroplasty. Orthop Clin No Am, 2005 In Press.
15 Howie DW, Cornish BL, Vernon-Roberts B. The viability of the femoral head after resurfacing hip arthroplasty in humans. Clin Orthop 291: 171-184, 1993.
16 Campbell P, Mirra J, Amstutz HC. Viability of femoral heads treated with resurfacing arthroplasty. J Arthroplasty 15(1): 120-122, 2000.
17 Freeman MAR. Some anatomical and mechanical considerations relevant to the surface replacement of the femoral head. Clin Orthop 134: 19-24, 1978.
18 Weber BG. Experience with the Metasul total hip bearing system. Clin Orthop 329S: S69-77, 1996.
19 Amstutz HC, Grigoris P. Metal-on-metal bearings in hip arthroplasty. Clin Orthop 329S:S11-S34, 1996.
20 Amstutz HC, Beaule PE, Dorey FJ, Le Duff MJ, Campbell PA, Gruen TA. Metal-on-metal hybrid surface arthroplasty: two to six-year follow-up study. J Bone Joint Surg Am. 2004 Jan;86-A(1):28-39.
21 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.
22 Guidance on the use of metal on metal hip resurfacing. National Institutes for Clinical Effectiveness, NICE June 2002.
23 NICE Technology appraisal guidance No 44. Health Technology Board for Scotland, August 2002.
24 Visuri T, Pukkala E, Paavolainen P, Pulkkinen P, Riska EB. Cancer risk after metal on metal and polyethylene on metal total hip arthroplasty. Clin Orthop Aug;(329 suppl): S280-89, 1996.