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Surface replacement 2008: Back to the future
The American renewed interest in the clinical use of metal-on-metal hip surface replacement as a solution for problems of noninflammatory arthritis has gained considerable attention. Currently, both the Birmingham Hip Resurfacing (Smith & Nephew) and the Cormet Hip Resurfacing (Corin/Stryker) systems have received FDA clearance, with a number of other surface replacement designs in the regulatory pipeline. The success of these devices in Europe and Australia, particularly among younger, active patients, further contributes to this increased demand. These systems are hybrid in their fixation application and benefit from a large metal-on-metal articulation that increases hip stability and preserves femoral bone. We acknowledge that the surgical technique is different and consequently more challenging than a primary hip replacement. There is a small risk of neck fracture and compromise of the femoral head blood circulation. Other concerns relate to wear and ion production from the metal-metal bearing, including the potential for a local immune reaction and cell toxicity.In keeping with the above, FDA clearances have required the establishment of training programs to overcome the intricacies of the procedure and address the surgeon learning curve. This is in addition to the establishment of post-approval studies extending to 10 years postoperative.
In this first part of a two-part Round Table discussion, we bring together experienced orthopedic surgeons whose collective background is intended to provide reader insight into the pros and cons of hip resurfacing arthroplasty.
A. Seth Greenwald, DPhil (Oxon)
Moderator
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A. Seth Greenwald, DPhil
(Oxon)
Robert L. Barrack, MD
Bernard N. Stulberg, MD
Michael A. Mont, MD
Michael L. Swank, MD
Thomas P. Schmalzried, MDA. Seth Greenwald, DPhil (Oxon): What do you believe are the time-honored stated advantages of hip resurfacing arthroplasty?
Robert L. Barrack, MD: There are numerous stated advantages of hip resurfacing arthroplasty, some of which are well established and some of which are theoretical. One undisputed advantage is that you do maintain more of the patient’s own bone, which may be an advantage for future revisions. Another is that there is less stress shielding or bone loss over time due to the absence of a stem in the femoral canal. This is actually the only hip arthroplasty that has shown evidence of increased bone density over time due to the substantially different loading pattern. Additionally, the low incidence of dislocations after the perioperative period is a benefit compared to a conventional total hip replacement (THR), although this may not be a significant advantage over large head, metal-on-metal, modular THR.
The theoretical advantages include improved proprioception and the ability to return to a higher activity level. Although numerous studies have shown higher activity levels are achieved following hip resurfacing compared to traditional THR, these studies are prone to selection bias, although there is at least one prospective randomized study that did conclude that hip resurfacing patients achieved a higher activity level at work and in recreation.
Michael A. Mont, MD: Obviously, hip resurfacing arthroplasty preserves femoral bone. The purported other advantages of hip resurfacing include: fewer dislocations; more range of motion; more normal gait; leaving options open for revision and an easier revision; the use of a device for special circumstances, such as extra-articular deformities of the proximal femur; and the ability to retain the hardware of the proximal femur.
Some of these purported advantages are debatable. In almost every study, the dislocation rate is lower with resurfacing; however, this might be matched by large-femoral-head standard hip replacements. Some studies, such as those by Vail and colleagues and our group, find increased range of motion with resurfacing, although this can also be considered debatable and might be matched with large femoral heads.
There are three studies that show better gait mechanics in patients with resurfacing, but a recent study by Shimmin did not corroborate this. Again, more work is necessary to analyze whether this is the effect of patient selector simply the large femoral head. Two recent studies, by Amstutz and colleagues and Mont and colleagues, have shown fairly straightforward conversion of resurfacing to a standard hip replacement.
Finally, another possible advantage is highlighted in a recent study by McGrath and colleagues, which showed that resurfacing could be used in very difficult hip arthroplasties where there are extra-articular deformities that would otherwise require an ancillary osteotomy, or there was retained hardware which would be very difficult to remove to perform a standard hip arthroplasty.
Thomas P. Schmalzried, MD: An advantage of hip resurfacing is conservation of femoral bone with more physiological loading that minimizes stress shielding and bone mass is maintained over time. Also, the absence of an intramedullary device provides more options for subsequent hip surgery or other surgery on that femur.
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Greenwald: Based on previously experienced clinical complications with metal-on-plastic designs, including component loosening, wear, avascular necrosis, femoral neck fracture, and uncorrected leg length discrepancy, how are these problems now overcome?
Mont: Component loosening on the acetabular side should be similar, as most acetabular cups utilize bony ingrowth and have been time-tested for at least 10 years.
On the femoral side, there is a rare incidence of component loosening with a cemented design and this experience is over 10 years old as well. Additionally there has been recent interest by a number of companies in cementless designs, but that will need to be evaluated in the mid- and long-term to see if they are efficacious and whether there are any negative stress-shielding effects.
The problem of femoral neck fracture can be overcome in large part by careful attention to: patient selection, avoiding osteopenic, small women; operative technique, avoiding notching; and paying attention to appropriate positioning. The emphasis on surgeon education for this technique is paramount.
Finally, this device is inappropriate for most patients with 2 cm or greater leg length discrepancies, as the nonmodularity cannot address these differences.
Schmalzried: The low wear rate of currently available bearings has dramatically reduced loosening of resurfacing components. Accumulating data from single-surgeon series, multi-surgeon series, as well as national joint registries, all indicate that the risk of femoral neck fracture is predominantly a function of patient selection. As is the case with the general population, the risk of femoral neck fracture is higher with increasing age, in female patients and those who are small-boned. The risk of femoral neck fracture is low in the opposite demographic.
Resurfacing will always be limited in regard to adjusting limb length. Fortunately, the majority of patients with end-stage hip arthritis do not have a functionally significant limb length difference. Avascular necrosis from the surgical dislocation is uncommon and can be minimized by respecting the soft tissues of the proximal femur.
Bernard N. Stulberg, MD: My experience has been primarily with the Cormet Hip Resurfacing system. Current hip resurfacing designs, such as Cormet, have addressed device-related issues that affect wear and fixation. They have done this through significant attention to improved coatings for the acetabular component with titanium plasma spray coating and HA and improved cementing techniques for fixation of the femoral component.
Other improvements relate to automated manufacturing techniques to enable better bearing surfaces and optimal clearances that can promote fluid-film lubrication and therefore decrease wear. Attention to patient selection and technical implantation issues are approaches used to decrease the complications of necrosis, loosening and femoral neck fracture that are less likely related to the implant designs.
Modern instrumentation systems, such as those available with the Cormet system, are important to allow for predictable techniques for implantation. Proper implantation of these devices is critical if the surgeon is to avoid both short-and-long term complications of this procedure
Greenwald: The FDA designates surface replacement systems as Class III significant-risk devices, for which there is a need to demonstrate safety and effectiveness. In addition to laboratory and clinical evaluation, surgeon training is required as well as long-term post-approval follow-up studies. Are these latter requirements justified?
Barrack: I believe that the requirement for surgeon training is prudent and justified. This is a more difficult hip arthroplasty procedure. It is more similar to a moderately complex revision procedure than a primary procedure, and there is also less room for error in achieving component alignment and fixation.
There is also a substantial learning curve, and a high complication rate is not warranted based on the excellent results of modern THR. Because of this, I believe both surgeon training and postmarket follow-up studies are warranted.
Schmalzried: Surgeon training may be the most important element for success with resurfacing. It has already been demonstrated that short-term failures are predominantly a function of patient selection and surgical technique. There is no need for later-adopting surgeons to repeat the learning curve. It is hard to argue against the value of long-term studies for any total joint arthroplasty procedure.
Stulberg: Yes. The Cormet device was the first device to be approved in the United States based upon the experience of American surgeons. We have recently published data that suggest that there were higher rates of femoral neck fracture and femoral loosening in the initial study group. If patient selection and technical implantation issues are addressed, these femoral complication rates were substantially decreased, as was seen with those patients implanted later in the study.
There clearly will be some variation in a surgeon’s ability to perform this procedure predictably, and a definite learning curve is present. Results will improve with increased use of the procedure and device.
I am currently associated with the Stryker training program for the Cormet Hip System. This program believes strongly that surgeons benefit from training as to the critical components of the technique, the importance of proper patient selection, and the appropriate indications for using this procedure. This program establishes four levels of interactive training, including hands-on cadaveric practice and the ability to mentor surgeons new to hip resurfacing.
Long-term follow-up studies to track survivorship and clinical outcomes will be critically important for us to be able to judge the applicability of this procedure in the armamentarium of the hip surgeon. As clinicians, we want to see these results, and it is important that we and the FDA look for such studies.
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Greenwald: What surgical approaches, inclusive of trochanteric osteotomy, optimize femoral head blood supply while achieving construct stability?
Barrack: Laboratory studies indicate that the posterior approach is associated with at least a transient interruption of blood supply compared to anterior-based approaches. These findings, however, do not correlate with the clinical results since the vast majority of hip resurfacings have been performed through the posterior approach, particularly by the group in Birmingham. Their clinical results indicate an extremely low incidence of avascular necrosis despite some studies that show decreased perioperative blood flow.
Mont: Some authors have described the anterolateral approach as optimizing femoral head blood supply. For example, Forrest and colleagues in 2006 showed that this approach with CAT scanning demonstrated adequate blood supply. In a comparison study, Kahn and colleagues in 2007 compared the blood flow to the femoral head with both anterolateral and posterolateral approaches measuring the antibiotic cefuroxime (Ceftin, GlaxoSmithKline) concentration in bone samples. In 20 operations, they found the concentration to be significantly higher with the anterolateral approach when compared to the posterolateral approach.
In a 2007 study by Stefan and colleagues, 12 patients had oxygen concentration measured at the head and neck junction. They found that there were higher values for the anterolateral approach than for the posterior approach. They postulated that an anterolateral approach would lead to less disruption of the blood supply and possibly a decreased incidence of femoral neck fractures.
I believe these are all theoretical studies. Recently, a longer-term follow-up study by Revell and colleagues compared the results of anterolateral and posterior approaches and showed similar results for resurfacing with either approach. Therefore, it is probable that with any of these approaches the blood supply effects may not have a clinical significance.
Michael L. Swank, MD: Of the four basic approaches to the hip – direct anterior employing the Hana table, trochanteric osteotomy, direct lateral and posterior – the direct anterior and trochanteric osteotomy theoretically interfere least with the blood supply to the anterior superior femoral head by preserving the retinacular vessels. In spite of this theoretical advantage, no clinical data has demonstrated these approaches to be more advantageous than the posterior approach, at least during the first 10 years of implantation. All approaches may achieve adequate construct stability.
A note from the editor:
Look for Part 2 of this Round Table discussion in the January issue of Orthopedics Today.
For more information:
- Robert L. Barrack, MD, can be reached at Washington University School of Medicine, 660 S. Euclid Ave., Campus Box 8233, Department of Orthopedic Surgery, St. Louis, MO 63110; 314-727-2562; e-mail: barrackr@wustl.edu. He receives royalties for certain total hip products, none of which are resurfacing implants.
- A. Seth Greenwald, DPhil (Oxon), director, Orthopaedic Research Laboratories, can be reached at 2310 Superior Ave. East, Cleveland, OH 44114; 216-523-7004; e-mail: seth@orl-inc.com.
- Michael A. Mont, MD, can be reached at Rubin Institute for Advanced Orthopedics, 2401 West Belvedere Ave., 5th Floor, Sinai Hospital of Baltimore, Baltimore, MD 21215; 410-601-8500; e-mail: Mmont@lifebridgehealth.org. He is a consultant for Stryker Orthopaedics and Wright Medical and receives research or institutional support from Biomet, BrainLab, DePuy, Finsbury, Smith & Nephew and Salient Surgical Technologies.
- Thomas P. Schmalzried, MD, medical director, Joint Replacement Institute, can be reached at 2200 W. Third St., Los Angeles, CA 90057, 213-484-7600; e-mail: schmalzried@earthlink.net He has indicated he has a consulting and research relationship with DePuy, a Johnson & Johnson company, and Stryker Corp.
- Bernard N. Stulberg, MD, can be reached at Cleveland Clinic Center for Joint Reconstruction, 1730 W 25th St., Cleveland, OH 44113; 216-363-3300; e-mail: bstulberg.ccjr@sbcglobal.net. He is a consultant for Aesculap.
- Michael L. Swank, MD, can be reached at 8250 Kenwood Road, Suite 100, Cincinnati, OH 45236; 513-221-5500; e-mail: mswank2789@aol.com. He is a consultant for Smith & Nephew.