Surface Arthroplasty of the Hip: Does it Have a Role in the 21st Century?

Paul E. Beaul, M.D., FRCSC
Assistant Clinical Professor
David Geffen School of Medicine at UCLA
Joint Replacement Institute at Orthopaedic Hospital
Los Angeles, CA

Introduction
In recent years, there has been resurgence of interest in metal-on-metal surface arthroplasty of the hip1 as an alternative to total hip replacement for the young and active adult2. Concomitantly, ceramic-on-ceramic bearings and new polyethylenes are being introduced as promising technology to improve the longevity of standard total hip replacements. Although these technologies are being embraced3,4by many, the 10-year survivorship of ceramic-on-ceramic total hips is relatively low at 79-85%5,6, and the new polyethylenes have only two-year data7.

Similarly, the renewed interest in the clinically proven low wear of the metal-on-metal bearing8,9combined with the capacity of inserting a thin wall cementless acetabular component10, has fostered the reintroduction of surface arthroplasty of the hip. As in other forms of conservative hip surgery. i.e. pelvic osteotomies11 and surgical dislocation with head-neck contouring 12,13, patient selection will help minimize complications14 and the need for early reoperation. Currently there are two applications for hip resurfacing: 1) hemi-resurfacing in the early stages of osteonecrosis and 2) full surface arthroplasty in presence of advanced arthritis. Both will be discussed in terms of indications and results.

Hemiresurfacing Arthroplasty for Osteonecrosis

Hemi-resurfacing arthroplasty has been in clinical use for over 20 years15. The success of this conservative hip procedure relies on the minimal involvement of the acetabular cartilage once collapse of the head has occurred in Ficat Stage III and IV osteonecrosis. Beaul and associates16 showed a longer duration of preoperative symptoms was associated with more severe acetabular cartilage damage and hips that had been converted to total hip replacement had a longer duration of symptoms than the ones that were still functioning (17 versus 12 months, respectively). When assessing the clinical results of hemi-resurfacing arthroplasty there has been a tendency to compare its clinical outcome to that of total hip replacement. However because this technique relies to some extent on the quality of the acetabular cartilage and its failure results in a total hip replacement, a comparison to other conservative procedures such as free-vascularized fibular graft17 or proximal femoral osteotomies18,19would be more useful to the clinician15. Several centres20-22using different hemi-resurfacing designs have reported comparable survivorship (i.e. 80% at five years and 60% at 10 years) and pain relief for osteonecrosis of the hip with Ficat Stage III and IV disease. However, the pain relief is not as predictable as that following total hip replacement23.

The age of the patient at presentation should be considered carefully; the younger the patient, the more strongly hemi-resurfacing should be considered since it is very likely that he or she will require another operative procedure in their lifetime. Grading of the acetabular cartilage is important at the time of the operative procedure and if significant damage is identified (exposure and/or erosion of subchondral bone) especially in an older patient, a total hip replacement or a metal-on-metal surface arthroplasty should be considered24. Ideal candidates are patients less than 40 years old with Ficat Stage III and early stage IV (Figure 1) or in some cases of Ficat Stage II disease with Kerboull angles > 200 degrees15. Because the quality of the cartilage is directly related to the duration of symptoms and ultimately dictates the outcome of this procedure, early intervention is recommended. Over the last two years we have used the even sized femoral components of the Conserve Plus (Wright Medical Technology, Arlington, TN) as a hemi-resurfacing in order to permit the later conversion to a full hip resurfacing by implanting the acetabular component

beaule figure 1a.jpg beaule figure 1b.jpg
Figure 1a: Preoperative Anteroposterior Radiograph (Outlet View) of a 36 year-old male with Ficat Stage III osteonecrosis of the femoral head. Figure 1b: Postoperative Radiograph post hemiresurfacing arthroplasty using the Conserve Plus Femoral Component.

 

Metal-on-metal Surface Arthroplasty of the Hip

There have been two recent publications on the short-term results of hybrid metal-on-metal surface arthroplasty with a 94% to 99.8% survivorship at four years25,26. In both series, patients returned to very high activity level with a mean patient age for both series of 48 years old. Amstutz and associates25 identified several variables putting patient at risk for early failure: femoral head cysts, patient height and previous hip surgery. In contrast, Daniel and associates26 emphasized metallurgy and manufacturing of the metal-on-metal bearing as the main determinants for a well-functioning surface arthroplasty. Hot isostatic pressing and solution annealing of the components were reported to be unfavorable to the wear properties27. Based on that assumption, a group of 186 hips were excluded from their study26 due to a sub-optimal manufacturing process of the implant which reportedly lead to a high incidence of osteolysis and associated component loosening. Unfortunately, no radiographic evaluation was provided in their review making the improvement in the manufacturing of the components difficult to confirm. In addition, Nevelos and associates28 recent analysis of metal-on-metal bearings tested in hip simulators found no influence of the manufacturing process on the wear properties with the main determinants for optimal wear performance being relatively low radial clearances and a high carbon content.

As with the introduction of cementless designs in total hip replacements29, metal-on-metal bearings are not the only answer to the success of surface arthroplasty of the hip. A Surface Arthroplasty Risk Index (SARI)14 was developed and based on a six point scoring system (Table 1) with a score >3 representing a 12 fold increase risk in early failure or adverse radiological changes. In addition, when Amstutz and associates25 reported on the overall experience in the first 400 hybrid metal-on-metal SA, a SARI >3 had a survivorship of 89% at four years versus 97% with a score < 3.

Another factor identified was femoral component orientation to which little attention was given with only Freeman favoring a valgus orientation30,31. In a recent review of the relationship between femoral component orientation and clinical outcome, Beaul and associates32 noted that implants placed at angle of 130 degrees or less had a six-fold increase in the risk for premature failure. A varus placement of the femoral component in relation to the femoral neck resulted in an increase in the tensile stresses above the yield value in the resurfaced femoral head near the junction of the prosthesis increasing the risk of fatigue failure of the underlying bone.

beaule figure 2a.jpg beaule figure 2b.jpg

Figure 2a: Preoperative Radiograph of a 34 year-old male with a post-traumatic arthritis of the left hip.

Figure 2b: Postoperative Radiograph with Conserve Plus Total Resurfacing done through a surgical dislocation approach.


One must also consider the underlying diagnosis when evaluating a patient for surface arthroplasty (Figure 2). In cases of dysplasia, acetabular deficiencies combined with the inability of inserting screws through the acetabular component may make initial implant stability unpredictable. This deformity in combination with a significant leg length discrepancy or valgus femoral neck could compromise the functional results of surface arthroplasty, and in those situations a stem type total hip replacement may provide a superior functional outcome33. Finally, the presence of a metal-on-metal bearing leads to an increase in metal ion release9,34. Consequently, because the information on the systemic distribution of metal ions and their interaction with living cells is limited, patients with compromised renal function and a history of metal sensitivity are probably not good candidates for a metal-on-metal bearing9,35.

Conclusion
Surface arthroplasty of the hip has always been appealing because of its conservative nature and stability. Although early clinical results are encouraging, we must not forget the predictable outcome of standard stem-type hip replacements. By careful patient selection and visiting centres with a significant experience with surface arthroplasty, we can minimize short-term failures and offer patients a return to normal activity levels.


Table 1: The Surface Arthroplasty Risk Index (SARI)14

  POINTS
Femoral Head Cyst >1cm 2
Patient Weight < 82kg 2
Previous Hip Surgery 1
UCLA Activity level >6 1
MAXIMUM SCORE
6



References
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