Dr. Amstutz (center) has performed more than 1,100 metal-on-metal hip resurfacings.


Published 8/1/2007
Annie Hayashi

Hip resurfacing: A boon for Boomers or too risky?

Although some orthopaedic surgeons say hip resurfacing is a viable alternative procedure for some patients, others raise serious concerns about the surgical learning curve, the incidence of femoral neck fractures, and metal ions toxicity.

With aging “baby boomers” looking for ways to maintain their active lifestyles, hip resurfacing has been getting a lot of media attention. Proponents of the procedure see it as the ideal alternative to a total hip arthroplasty (THA) for younger patients, while its detractors express a broad range of concerns—from the technical difficulty of the procedure to toxicity from metal-on-metal ions.

Unlike THA, which requires the removal of the top of the femur and insertion of a stem into the bone shaft, hip resurfacing puts a metal “cap” over a reshaped femoral head, thus saving both the head and neck and eliminating the need to enter the intramedullary canal. Proponents point to these benefits, as well as to the greater stability and decreased risk of dislocation due to the larger femoral head size, as reasons for surgeons and patients to choose resurfacing rather than replacement.

Critics caution, however, that the procedure is far more difficult to perform than THA, that few patients meet the criteria for the surgery, and that an increased risk of femoral neck fracture and an unknown potential for metal-on-metal ion toxicity exist.

Not a panacea
Hip resurfacing is certainly not a panacea, according to James C. Kudrna, MD, PhD, but it is a good alternative to THA in the “younger patient population that has end-stage hip disease that requires some form of arthroplasty.”

Dr. Kudrna has been performing hip resurfacing procedures since the late 1970s, and has seen the procedure change significantly since its inception. Cemented polyethylene acetabular and cemented metal femoral components have been replaced by cementless metal, porous-coated acetabular components, and a cemented stemmed metal femoral component.

The field continues to evolve as manufacturers, particularly in the United States, introduce new products and the surgical technique improves, according to its proponents.

“Hip resurfacing is a conservative procedure,” says Harlan C. Amstutz, MD, who has performed more than 1,100 metal-on-metal hip resurfacings. “It preserves the bone. During preparation, only the pathologic bone is removed, normalizing the anatomy and biomechanics. Unlike the first generation of hip resurfacing arthroplasty, today no more bone is removed from the acetabulum than with a THA.

“You don’t have to worry about creating a leg length discrepancy as you do with a THA,” he continues. “One of the most important advantages of hip resurfacing is the ease of revision. The sockets are likely to be durable for 20 or more years—possibly forever—so that if revision is necessary, it is much like performing a primary THA.”

Both doctors agree on what they believe are the many benefits of hip resurfacing: preservation of bone stock on the femoral side, little to no limb length discrepancy, and the patient’s ability to resume a very active lifestyle.

Paul F. Lachiewicz, MD, also agrees that hip resurfacing is a “conservative” procedure on the femoral side, with less bone removal than conventional THA. But he points to a retrospective, case-control study that compared the volume of acetabular bone removed during resurfacing with the Birmingham Hip Resurfacing system (BHR) and that removed during a hybrid THA. The study found that a larger amount of acetabular bone (mean: 5.4 mm) was removed with hip resurfacing. Dr. Lachiewicz concludes, “Resurfacing was less bone-conserving for the acetabulum than hybrid THA.”

The study is valid, agrees Dr. Kudrna, but he doesn’t believe that acetabular bone loss will be a long-term issue. He thinks that component manufacturers will soon be offering more incremental sizes, which will help conserve acetabular bone and reduce the difference between the amount of bone removed in a regular hybrid hip procedure and the amount removed for hip resurfacing.

Patient selection is key to success
Patient selection is important to the success of the procedure, says Dr. Kudrna. “Hip resurfacing has a narrow focus. I think that primary osteoarthritis, secondary osteoarthritis due to trauma, and perhaps a mild slipped capital femoral epiphysis with secondary osteoarthritis are reasonable indications. I don’t perform hip resurfacing on people with osteonecrosis; I do not think that is a good indication.”

Dr. Amstutz does take cases with risk factors—patients with osteonecrosis and cystic defects. His patients include both men and women, some of whom are older than age 60. He stresses the importance of optimal bone preparation and cementing technique for the femoral component. His recently published study in the Journal of Arthroplasty shows how improving surgical techniques enables patients with risk factors to become candidates for hip resurfacing.1 He admits, however, that the “best patients are males with osteoarthritis and those who have more normal bone stock with a large head/neck ratio. Male patients have larger hips with more surface area to get fixation.”

Dr. Kudrna restricts hip resurfacing arthroplasty to younger patients—those younger than age 55 years. He performs the procedure on both men and women, although 80 percent of his patients are men.

The patient selection criteria for hip resurfacing are so selective, counters Dr. Lachiewicz, that the procedure is not that useful. “In my opinion,” he says, “metal-on-metal hip resurfacing is truly indicated for only a limited number of patients. The proponents of the procedure have suggested that young men—younger than age 50 years old—with osteoarthritis and a body mass index of less than 35 are good candidates.2,3,4

“In addition, a biomechanical study recommended there should not be a leg length discrepancy greater than 1 cm and the hip should have a ‘high’ horizontal femoral offset,”5 he points out. In his own practice data, only 6 percent of patients fit these criteria.

With such a small patient population, Dr. Lachiewicz believes it would be difficult for any surgeon to develop “a large surgical experience of resurfacing for the proper indications.”

Dr. Amstutz (center) has performed more than 1,100 metal-on-metal hip resurfacings.
James C. Kudrna, MD, PhD
Paul F. Lachiewicz, MD

The ideal hip resurfacing candidate for Dr. Kudrna meets all of these same conditions as outlined by Dr. Lachiewicz. However, Dr. Kudrna will not do the procedure on patients who are taller than 6'6'' to 6'8'', particularly if they have hypermobile joints. He also lists anatomic abnormalities of the femoral head and neck, a very small femoral head (which excludes many female patients), Legg-Calve-Perthes disease, slipped capital femoral epiphysis, or severe osteopenia as other contraindications. About 10 percent of his surgical cases are hip resurfacings.

Technically challenging with a long “learning curve”
All three agree on one aspect of hip resurfacing—the “learning curve.” Even the two proponents (Drs. Kudrna and Amstutz) admit that hip resurfacing is technically more difficult than THA and should not be performed by all orthopaedic surgeons.

“Exposure is more difficult because you have to work around the hip to get to the socket,” explains Dr. Amstutz. “The second issue has to do with pin placement, so the femoral component is placed in an optimal position. From my perspective, pin placement is an art and is dependent on the patient’s anatomy and pathology. More emphasis is needed on the technique of preparing the bone and optimizing the cementation of the femoral component.”

When the BHR was released, he recalls, several U.S. surgeons flew to England for a one-day training session on using the device. One day of training is not adequate, according to Dr. Amstutz, who would like to see more extensive “hands-on” cadaver training and mentoring of inexperienced surgeons by those who are skilled in the procedure.

Although reluctant to specify the number of procedures needed to reach a level of minimum proficiency, Dr. Amstutz believes that a surgeon should not get the experience at the expense of his or her patients. That is one reason he promotes mentoring.

“It’s not an operation that every orthopaedic surgeon should be doing,” says Dr. Kudrna. “My practice is restricted to surgery of the hip and has been throughout my career. I don’t know that hip resurfacing is a procedure that a surgeon in general orthopaedics who does 30 THAs a year should be doing.” He estimates that about 30 percent to 40 percent of orthopaedic surgeons who do THAs would have enough volume to do hip resurfacing.

Dr. Lachiewicz is also concerned about the technical difficulty of this procedure and its impact on patients. In one study, he notes, the author reports that femoral neck fractures occurred in 22 percent of his first 50 resurfacing procedures.6 “If the so-called ‘learning curve’ for an experienced hip surgeon is 50 to 100 resurfacing procedures, how can this procedure be ‘mastered’ by community surgeons who perform fewer than 10 or 15 THAs a year?” he asks. He advocates that hip resurfacing be done by a “select group of experienced surgeons and specific hands-on learning centers be established.”

Dr. Kudrna agrees that the occurrence rate of femoral neck factures could be cause for concern. He supports experienced surgeons working with those who are interested in the procedure, not simply to show them how it’s done, but to take them through the entire learning process. “We’re not just talking about ‘saw-bones’ work, but cadaver work,” he says.

Computer-based navigation techniques are currently being developed that will facilitate reproducible pin insertion. Dr. Kudrna believes this technology will improve the quality of femoral component placement and enable more orthopaedic surgeons to perform this procedure.

The range of motion question
Proponents of hip resurfacing arthroplasty have claimed that it provides a greater range of motion and a lower rate of dislocation than conventional THA. Study results, however, are mixed. A three-dimensional computer simulation study, for example, showed that resurfacing resulted in less flexion and extension and reduced hip motion with simulated dislocation activities than hip replacement.7 But, a retrospective study that compared 53 patients who had hip resurfacing (54 hips) with 51 patients who received hybrid THAs (54 hips) did show higher activity scores for the group with resurfaced hips.8

What is truly important, according to Dr. Kudrna, is functional range of motion. “It’s one thing to do a computer simulation and say this thing is going to impinge here and here, but how many people are going to flex their hips to 130 degrees? When you look at range of motion from a functional standpoint, there is very little difference between a hybrid THA and hip resurfacing. The real advantage of resurfacing is stability. That’s the big issue.”

Aging femoral heads and fractures
The issue of decreased bone mineral density (BMD) in the aging femoral neck is one Dr. Lachiewicz believes has been largely ignored by the proponents of hip resurfacing. According to one study, 18 percent of men and 25 percent of women lose BMD in the femoral neck between the ages of 30 and 70 years.9 As a result, he believes the chances of a femoral neck fracture will be greater in resurfaced hips over the long term.

Dr. Kudrna concurs that those changes do occur, but he points to several studies in which increases in bone density in specific “Gruen zones” of the femoral head have been reported following hip resurfacing.10 Finite element analysis work currently being done shows that increased stress concentration in the medial aspect of the femoral neck leads to improved bone density. As a result, he does not think that resurfacing will increase the incidence of femoral neck fractures.

Metal-on-metal articulation
The issue of metal-on-metal articulation raises the most concern among opponents of hip resurfacing. Dr. Lachiewicz, for example, is concerned that increased levels of chromium and cobalt in the blood and urine of patients may not be related to activity levels.11,12,13 Although the clinical significance is not yet known, two studies report that lymphocytic perivascular aggregates were found in patients who required reoperation.14,15 He is also concerned about reports of hypersensitive reactions to metal-protein complexes, which may be linked to osteolysis.

Dr. Kudrna believes that the issue of metal ions could become negligible. “We now have data showing that as you improve the clearance of the bearing, you actually improve wear. We’ve also noted that as you go to larger metal bearings, the wear rates actually decrease. For example, with a 36-mm hip ball, cobalt and chromium levels are about 1 part per billion; the levels drop to ½ part per billion with a 45-mm bearing. That’s now equivalent to what you see in a metal-on-polyethelene hip.”

Though Drs. Kudrna, Amstutz, and Lachiewicz have different views about various aspects of hip resurfacing, they agree on three specific issues:

  1. Patient selection is very important. The patient criteria for this procedure are quite specific.
  2. Hip resurfacing is a difficult procedure to perform and has a longer learning curve than many other orthopaedic procedures. Experienced surgeons should act as “mentors” with those who want to learn the procedure. This learning process should include work with cadavers.
  3. More prospective studies of hip resurfacing need to be done. Until they are, the issue will remain open and the discussions will continue.

Annie Hayashi is the senior science writer for AAOS Now. She can be reached at hayashi@aaos.org. References for the studies cited in this article can be found online at www.aaos.org/now


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