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Hip resurfacing: Time for a second look
Newer implants with proper patient selection may make this a better procedure.
In terms of hip resurfacing versus total hip arthroplasty, the questions we have to address are: Is metal-on-metal the right choice for the patient; Is the resurfacing more conservative; What are the indications for resurfacing; and Is the large head metal-on-metal total hip better in most patients than a resurfacing?
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The clinical wear data that we have all seen basically shows that the alternative bearings fare much better than the traditional bearings and metal-on-metal and ceramic-on-ceramic really, in the clinical arena, tend to have the lowest rates of wear.
One big issue that has been debated over the last 15 to 20 years is the cancer risk related to metal ions. That question still must be answered. These patients must be monitored and watched, but at this time there is no real evidence that there is an increased risk of cancer. People have talked about metalosis and metal-on-metal, however the meta-analysis we performed of almost 500 hips, at 4 years follow-up showed only four loose stems and two loose cups. There were no cases of hypersensitivity, no cancers, no ion-related issues, and no revisions for unexplained pain. I think that puts the issue of hypersensitivity at rest, or at least tell us that if it occurs, it does so in less than 1% of patients.
Conservative operation?
Is this operation more conservative? Ian C. Clarke, PhD, said about 25 years ago that resurfacing arthroplasty is the ideal conservative procedure. However, in Harlan Amstutz, MD’s experience with the Tharies implant, in almost 600 hips with 10-year follow up, there was an unacceptably high failure rate, most of which was from acetabular loosening and a few femoral neck fractures. More recently Derek McMinn, MD’s results published in the Journal of Bone and Joint Surgery (Br.) in 2004, had almost 450 hips with a revision rate of less than 0.1% at an 8-year follow-up. He reported that one-third of his patients went back to heavy labor and two-thirds or more resumed leisure and sports. Therefore, I think we need to look at the old style and the new style of hip resurfacing and see if we have figured out patient selection, surgical technique, and if we have improved the implants to solve these problems. Because if we have solved these problems, we are much closer to a conservative procedure.
In a more recent report with contemporary metal-on-metal resurfacing, Amstutz reported on 600 hips. In this report, femoral neck fractures remained a problem although in less than 1%. He stated that notching, leaving cancellous bone uncovered, and a varus angulation are risk factors. Mont presented an interesting study 2 years ago that reported on 400 to 500 hips and noted an overall failure rate of 2%. However, in his first 50 resurfacings he had a 22% rate of femoral neck fracture, which is a very frightening number. I think we have gotten past that with surgical technique and indications, but the rate is still almost 2% in that series and is something that we still need to be cautious about if this is going to be a conservative operation.
Indications
As for the indications and contraindications, I think the bottom line is when you have a hammer not everything is a nail. Amstutz said that patients with avascular necrosis are OK; so are those with cystic defects, both genders and occasionally patients over 60 years old. To make an operation conservative, one must employ conservative indications. It is probably better to be a little more conservative where resurfacing is indicated in primary osteoarthritis (OA) patients and in male patients younger than 55 years old, who represent about 10% of hip cases. Paul F. Lachiewicz, MD, noted his indications were young males less than 50 years old, those with OA, a low body mass index (BMI), having less leg length discrepancy and perhaps a high horizontal offset that you cannot easily reconstruct with a regular total hip replacement. This represents somewhere around 5% of cases. Paul Beaule, MD, reported indications of patients less than 60 years old and a risk index of less than 3, which was defined as including femoral head cysts, the patient’s weight, any previous surgery, and UCLA score. If they are less than 3 than you can expect good results, but if they are greater than 3 they probably would benefit from a total hip.
Dislocation risk
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The dislocation risk of a large head, metal-on-metal total hip replacement is probably less than that of a metal-on-metal resurfacing simply because of the head-to-neck ratio. So, I am not sure that dislocation risk is a huge advantage.
A surface replacement obviously doesn’t reconstruct the hip any better than a large metal-on-metal hip replacement. It is purely whether or not it is more conservative. In our rookie year experience starting at the end of last year and running about 8 months, we have performed 32 resurfacings in 28 patients, representing 9% of our hip cases. The population was 82% male, with an average age of 45, but we have done some up into their late 50s. Their BMI was slight, although it does go up to 50, and we did revise one socket at 2 weeks for acetabular migration.
The bottom line is which procedure is more conservative? A resurfacing or metal-on-metal THA both can both have 62 mm cups and a 56 mm head, and identical metallurgy. One can be done through a minimally invasive approach perhaps and one cannot. The 3-month failure rate for THA is 0% in most publications and up to 22% in recent reports for resurfacing. Resurfacing may be more conservative, but there must be the voice of reason.
If we are going to be pro-resurfacing, we need to be just as conservative in our indications as we are expecting the operation to be. I think that means that in the United States we should be somewhere below 10% of THA. We need to have strict patient selection criteria. Hopefully we are encountering less femoral bone loss by performing this operation and we can allow the patient to have a better bearing surface and a lower rate of dislocation than traditional THA. Hip resurfacing may allow more activity and it certainly should be an easier femoral revision than some of the catastrophic femoral revisions we have seen in the past.
Hip resurfacing has a definite place in the armamentarium of the hip surgeon, but likely represents less than 10% of cases. Newer implants and learning from the lessons of our leaders such as McMinn and Amstutz will help us circumnavigate the pitfalls of the past.
For more information:
- Keith R. Berend, MD, can be reached at Joint Implant Surgeons, Inc., 7277 Smith’s Mill Road, Suite 200, New Albany, OH 43054: 614-221-4744; e-mail: BerendKR@joint-surgeons.com.
Reference:
- Berend KR. Hip resurfacing: Pro. Presented at the Tenth Annual Insall Scott Kelly Institute Sports Medicine and Total Hip & Knee Symposium. Sept. 14-16. New York.