A comparison of total hip resurfacing and total hip arthroplasty - patients and outcomes.

A comparison of pertinent preoperative and postoperative data relative to total hip resurfacing versus total hip arthroplasty (THA) would assist in evaluating current perceptions in outcome. We compared 50 consecutive metal-metal resurfacing replacements in 50 patients with 44 consecutive conventional total hip arthroplasties in 35 patients, who were implanted during the same time period, by the same surgeon, and followed prospectively for 2 to 4 years. The patients undergoing hip resurfacing were 62% male, 9 years younger, and 3.2 inches taller, with a lower mean body mass index and American Society of Anesthesiologists (ASA) grade than patients undergoing total hip arthroplasty. Preoperatively, patients undergoing resurfacing had a lower Harris hip score (46 vs 52 points), more pain, higher UCLA (University of California at Los Angeles) activity scores (4.2 vs 3.6), and better range of motion. Surgical time for resurfacing was 18% longer, but there was less total blood loss and fewer transfusions. Postoperatively, there was no difference in Harris hip score (97 vs 96). Patients undergoing resurfacing had higher function, Short Form-12 physical activity scores, and UCLA activity scores, but also a higher incidence of slight or mild pain. There were no differences in postoperative range of motion or dislocation (one each). The preoperative characteristics and general health status of the average patient undergoing resurfacing are more favorable than that of the average patient undergoing conventional total hip arthroplasty. Caution should be applied in attributing differences in outcomes directly to the arthroplasty technology.

Activity sampling in the assessment of patients with total joint arthroplasty.

Quantitative assessment of patient activity is important in evaluating the outcomes of joint prostheses, and such methods are gaining popularity. The single greatest impediment to quantitative activity assessment is patient compliance. How many days of sampling are necessary to provide reliable and accurate estimates of walking activity? The current study analyzes how well sampling for 4 consecutive days of activity compares to assessing activity for 7 or more days with the same pedometer in 131 patients with either a total hip or total knee prosthesis. The mean steps per day obtained throughout the full-length sampling (7-123 days) was strongly correlated to the one obtained from the random consecutive 4-day sample (r2 = 0.94, P < .001) with only 5 outliers. The 4-day activity assessment gave an underestimation of 4.7% (P = .5). The number of outliers increased with fewer days of sampling. Monitoring activity for 4 consecutive days yields a quantitative assessment that is within 5% of a sampling of 7 or more days.

The effects of lower-extremity total joint replacement for arthritis on obesity.

Total hip or knee replacement patients who are overweight or obese often consider their disabling joint disease a cause for their increased weight. This prospective study investigated weight change in 100 patients after successful total joint replacement to determine whether surgical treatment of hip or knee arthritis leads to weight reduction. Postoperatively, both hip and knee replacement patients gained weight, with no difference in weight gain between hip and knee replacement patients. Younger hip patients gained a significant amount of weight. Patients a with normal body mass index and obese patients did not lose weight, while overweight patients gained a significant amount of weight after surgery. These findings demonstrate successful treatment of lower-extremity arthritis does not lead to weight loss, and obesity should be treated as an independent disease that is not the result of inactivity from arthritis.

Short-term in vivo wear of cross-linked polyethylene.

BACKGROUND: Cross-linked polyethylene was developed to reduce volumetric wear in prosthetic joints. Hip simulator studies have shown promising results with regard to wear reduction. This study evaluated the short-term in vivo wear of a moderately cross-linked polyethylene. METHODS: Linear head penetration, as an assessment of in vivo polyethylene wear, was measured in two groups of patients after total hip replacement. Twenty-four hips received a conventional polyethylene insert and thirty-four, a cross-linked polyethylene liner; both inserts were manufactured by the same company. Linear and volumetric wear rates were measured on radiographs with use of a validated computer-assisted technique and were adjusted for patient-related factors. Patient activity was assessed by a computerized two-dimensional accelerometer worn on the ankle. RESULTS: Patients with a conventional polyethylene insert showed a mean linear wear rate of 0.13 mm per year and a mean volumetric wear rate of 87.6 mm(3) per year. The group with a cross-linked polyethylene liner showed a mean linear wear rate of 0.02 mm per year and a mean volumetric wear rate of 17.0 mm(3) per year. Wear in the group with cross-linked polyethylene was 81% lower than that in the group with conventional polyethylene (p < 0.00001). Accounting for differences in patient activity, the adjusted wear rates per million cycles for a patient weight of 70 kg were 53 mm(3) per million cycles for conventional polyethylene and 15 mm(3) per million cycles for cross-linked polyethylene, a 72% reduction (p = 0.0002). No factor, other than the type of polyethylene, was found to influence the difference in wear rates between the two groups. CONCLUSIONS: The results of this study are promising. The in vivo wear reduction with this cross-linked polyethylene is consistent with the predictions of hip simulator studies.

The biomechanical results of total hip resurfacing arthroplasty.

BACKGROUND: With the advent of more wear-resistant bearings, there is renewed interest in resurfacing total hip arthroplasty. However, there is a paucity of information on the biomechanical results of this type of arthroplasty compared with those of contemporary total hip arthroplasty. METHODS: Using standardized radiographs, we measured and compared the biomechanical parameters that affect the hip joint reactive forces in fifty hips that had a metal-metal surface replacement with those parameters in forty hips that had a contemporary cementless total hip replacement performed during the same time-period by the same surgeon. RESULTS: On the average, the arthritic hips that were treated with metal-metal surface replacement had had a more valgus preoperative neck-shaft angle and less horizontal femoral offset than the normal, contralateral hips (p = 0.0003). After both the metal-metal surface replacements and the cementless total hip replacements, the hip center of rotation was medialized by approximately 6 mm. Both procedures were associated with an average increase in limb length of approximately 3 or 4 mm. After the metal-metal surface replacements, the horizontal femoral offset was essentially equal to the preoperative value, but both values averaged about 8 mm less than those on the normal, contralateral side (p < 0.00001). In the hips with a conventional total hip replacement, the horizontal femoral offset increased an average of 9.5 mm compared with the preoperative value and was an average of 5 mm more than that for the normal, contralateral hip (p = 0.001). CONCLUSIONS: The biomechanical results of total hip resurfacing depend on the preoperative anatomy of the proximal part of the femur. Limb lengthening of 1 cm can be achieved, but horizontal femoral offset is essentially unchanged by hip resurfacing. Horizontal femoral offset can be increased reliably with a contemporary total hip replacement. Arthritic hips of limbs that are more than 1 cm shorter than the contralateral limb or that have a comparatively low horizontal femoral offset may be better served by a contemporary total hip replacement. These biomechanical limitations should be considered in the selection of hips for resurfacing. LEVEL OF EVIDENCE: Therapeutic study, Level III-1 (case-control study). See Instructions to Authors for a complete description of levels of evidence.

The effect of total knee arthroplasty design on extensor mechanism function.

The effect of total knee arthroplasty design on extensor mechanism function was evaluated prospectively in a consecutive, single-surgeon series. Group 1 knees (n = 83) were implanted with a prosthesis that has a multiradius femoral component, and group 2 knees (n = 101) were implanted with a femoral prosthesis that has a single flexion-extension axis. Group 2 knees gained flexion more rapidly: At 6 weeks, the average flexion for was 94.5 degrees for group 1 and 107.1 degrees for group 2 (P<.001). Significantly more patients with group 2 knees were able to arise from a 16-inch (low) chair without using their arms starting at 6 weeks, and a difference was maintained through 2 years (90% vs 73%; P=.003). Patients with group 2 knees had significantly less anterior knee pain when rising from a seated position starting at 6 weeks, and a difference was maintained through 2 years (1% vs 22%; P=.001).