A randomised trial of all-polyethylene and metal-backed tibial components in unicompartmental arthroplasty of the knee

Abstract

This randomised trial evaluated the outcome of a single design of unicompartmental arthroplasty of the knee (UKA) with either a cemented all-polyethylene or a metal-backed modular tibial component. A total of 63 knees in 45 patients (17 male, 28 female) were included, 27 in the all-polyethylene group and 36 in the metal-backed group. The mean age was 57.9 years (39.6 to 76.9). At a mean follow-up of 6.4 years (5 to 9.9), 11 all-polyethylene components (41%) were revised (at a mean of 5.8 years; 1.4 to 8.0) post-operatively and two metal-backed components were revised (at one and five years). One revision in both groups was for unexplained pain, one in the metal-backed group was for progression of osteoarthritis. The others in the all-polyethylene group were for aseptic loosening. The survivorship at seven years calculated by the Kaplan-Meier method for the all-polyethylene group was 56.5% (95% CI 31.9 to 75.2, number at risk 7) and for the metal-backed group was 93.8% (95% CI 77.3 to 98.4, number at risk 16) This difference was statistically significant (p < 0.001). At the most recent follow-up, significantly better mean Western Ontario and McMaster Universities Arthritis Index Scores were found in the all-polyethylene group (13.4 vs 23.0, p = 0.03) but there was no difference in the mean Knee injury and Osteoarthritis Outcome scores (68.8; 41.4 to 99.0 vs 62.6; 24.0 to 100.0), p = 0.36). There were no significant differences for range of movement (p = 0.36) or satisfaction (p = 0.23). This randomised study demonstrates that all-polyethylene components in this design of fixed bearing UKA had unsatisfactory results with significantly higher rates of failure before ten years compared with the metal-back components.

Use of All-polyethylene Tibial Components in Unicompartmental Knee Arthroplasty Increases the Risk of Early Failure

“…These findings support previous studies indicating that the use of the all-poly tibial component designs per se may be a risk factor for early failure, 19,20,23,24 and the notion that there is a high failure rate following all-poly tibial components in UKA (►Table 5). [18][19][20]34 On the other hand, the most common mode of failure in this study was early medial tibial collapse; this is in accordance with a previous study. 20 However, this result is not consistent with another study, which reported on the cause of UKA failure for a different type of tibial component design.…”

“…Although one previous study reported an excellent 5-year survivorship rate of 95%, 16 other studies reported high early failure rates of 9 to 41% within 5 years of all-poly tibial component UKA. [17][18][19] In addition, numerous studies have reported that all-poly tibial component UKAs increase proximal medial tibial strain, resulting in cancellous bone damage at the microscopic level and adaptive bone remodeling around the proximal tibia. In contrast, metal-backed tibial component UKAs decrease proximal tibial strain.…”

“…[20][21][22][23][24][25][26][27] Moreover, the majority of previous studies on all-poly tibial component UKAs used case series designs and assessed single all-poly tibial components, and few previous comparative study had assessed all-poly and metal-backed tibial component UKAs. 19,28 Therefore, at present, data supporting the use of all-poly tibial components during UKA, otherwise known as all-poly tibial components in TKA, are insufficient.…”

Metal-Backed Tibial Components Do Not Reduce Risk of Early Aseptic Loosening in Unicompartmental Knee Arthroplasty: A Systematic Review and Meta-Analysis

“…According these criteria, only nine comparative studies [18][19][20][21][22][23][24][25][26] were found to be eligible, and since only two randomized comparative studies (RCTs) were found in our search, 21,22 we included also case-control and cohort studies, whether prospective or retrospective, that reported comparative clinical outcomes of AP and MB UKAs.…”

Finite-Element Analysis of Stress on the Proximal Tibia After Unicompartmental Knee Arthroplasty

“…3,4 These failures come from a variety of factors including misjudgment of patient selection, postoperative malalignment, and poor implant design with inadequate thickness and without metal backing. In recent years, with UKA indication strictly controlled and with improvement of implant design including metal backing, 5,6 there have been many reports of successful outcomes. 1,2 The reasons for mechanical failure of UKA have been reported to be the following: 1) technical failure such as varus positioning of the implant and overcorrection of the postoperative leg alignment, 2) design and material of the element, 3) errors in the selection of patients such as severe varus deformity, involvement of patello-femoral joint, pan-arthritis such as rheumatoid arthritis and chondro-carcinosis, ligament insufficiency, severe obesity, high activity, osteoporosis and others.…”