Hip Resurfacing Arthroplasty

James P. Waddell, M.D., FRCSC
Toronto, ON

The first successful hip arthroplasty to be widely used was a surface replacement known as cup or mould arthroplasty. In this procedure, a single shell was placed between a shaped femoral head and a prepared acetabulum and movement was used to try and develop fibrocartilage on the two bony surfaces. This operation was supplanted by stemmed total hip replacement using a polyethylene cup and a stainless steel or cobalt-chrome stem - both components being held in position by methylmethacrylate. This total hip replacement was reliable and the results were reproducible.

Over time, conventional total hip replacement was recognized as having a number of problems including wear of the polyethylene component, loosening of the femoral and acetabular components with accompanying attritional bone loss. In addition, activity reduction was recommended for patients and dislocation remained a persistent problem. Resurfacing arthroplasty was a very attractive option for the young active patient. Large head size made dislocation virtually impossible and because of the increased stability and decreased potential for wear, activity reduction for the patient would not be necessary.

In the early 1980s resurfacing utilizing a polyethylene acetabular component and a metal femoral component was introduced. There was a very high failure rate because of decreased polyethylene thickness (secondary to increased head size) which led to accelerated polyethylene wear. In addition, head avascularity as a consequence of the surgical procedure, led to loosening of the femoral component or fracture of the femoral neck.

The metal-on-metal hip prosthesis (which eliminated polyethylene) has been adapted to resurfacing. It is hoped that by going to a metal-on-metal articulation, the problems associated with excessive wear and acetabular loosening could be eliminated.

Unfortunately, a number of problems both theoretical and practical are becoming evident with the use of current metal-on-metal resurfacing prostheses.

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Fig 1b Fig 1b

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Fig 1c.

Figure 1 (a), (b), (c): Femoral neck fracture 18 months after femoral head resurfacing the commonest cause of early failure following this operation.

There is a theoretical problem with regard to the metal ions2,4,6 which are produced by the metal-on-metal articulation. The release of metal ions leads to a substantial increase in blood and urine metal ion levels. The number of ions liberated appear to be directly related to the size of the bearing surface; thus resurfacing arthroplasty could be expected to have substantially more ion release than a conventional metal-on-metal hip with a 28 millimetre articulation.

Practical problems relate to the outcome after resurfacing. Although Daniel et al5 have reported excellent mid-term results in patients under 55 years of age, other reports have not been as promising. Silva et al7 reported that resurfacing cannot deal with shortening of the limb greater than one centimetre, nor can it address problems with abnormal femoral offset. Amstutz et al1 reported on 400 hips followed for three and a half years with a survival rate of only 94%. The Australian Hip Registry (October 2004) reported that resurfacing arthroplasty has a revision rate twice as high as conventional hip replacement in the first year after surgery. Cutts et al3, reporting at the British Hip Society Meeting in 2003, reported on 60 patients with 65 hips followed for as long as six years. Of the 65 hips, 13 required revision, 12 for mechanical failure.

These discordant reports, some documenting excellent mid-term results and others documenting high revision rates both early and mid-term are hard to reconcile. An early revision rate twice that of conventional hips might be acceptable if the final result was 95% survivorship at 10-15 years with no wear and no loosening. The fact that survivorship at three and half years is 94% in one study and 80% at six years in another study, raises serious concerns about the long-term outcome of this procedure. Of equal concern is the unknown effect of long-term exposure to elevated metal ion levels in young adults. Although this is only a theoretical concern and may not be relevant to every metal-on-metal bearing, it should give one pause considering that a surgical procedure done to relieve hip pain might have a long lasting, harmful effect on the systemic health of the recipient of the prosthesis.

There is no question that resurfacing arthroplasty has many attributes - the most significant being low wear rates, excellent stability and no activity reduction for the patient. Deficiencies (as I see them at present) are the unknown effects of metal ions which will be produced over a long period of time in the young patient and minimal deformity correction with the operation. The most significant problem, however, remains the relatively short-term nature of the reported results. I would urge caution in the use of this technology until independent studies, prospective and controlled, corroborate the findings which the designers have reported. In addition, registry data should be carefully assessed to determine the true revision rate and complication rate relating to this procedure.

References

  1. Amstutz H.C., Beaule P.E., Dorey F.J., Le Duff M.J., Campbell P.A., Gruen T.A.: Metal-on-metal hybrid surface arthroplasty: Two to six-year follow-up study. J Bone and Joint Surg, 86-A, No. 1, January 2004, 28-39.
  2. Clarke M.T., Lee P.T.H., Arora A., Villar R.N.: Levels of metal ions after small- and large-diameter metal-on-metal hip arthroplasty: J Bone and Joint Surg, 85-B, No. 6 August 2003, 913-917.
  3. Cutts S., Datta A., Ayoub K., Rhaman H., Lawrence T.: Early failure modalities in hip resurfacing. J Bone and Joint Surg (BR) 200;86-B: SUPP 1, 80.
  4. Daley B., Doherty A.T., Fairman B., Case C.P.: Wear debris from hip or knee replacements causes chromosomal damage in human cells in tissue culture. J Bone and Joint Surg, 86-B, No. 4, May 2004, 598-606.
  5. Daniel J., Pynsent P.B., McMinn D.J.W.: Metal-on-metal resurfacing of the hip in patients under the age of 55 years with osteoarthritis. J Bone and Joint Surg, 86-B, No 2, March 2004, 177-184.
  6. Lee P.T.H., Clarke M.T., Arora A., Villar R.N.: Serum cobalt and chromium ion levels after small and large diameter metal-on-metal hip arthroplasty. J Bone and Joint Surg (BR) 200;86-B: SUPP 1, 79.
  7. Silva M., Lee K.H., Heisel C., Dela Rosa M.A., Schmalzried T.P.: The biomechanical results of total hip resurfacing arthroplasty. J Bone and Joint Surg, 86-A, No. 1, January 2004, 40-46.

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