Is There a Benefit to Highly Crosslinked Polyethylene in Posterior-stabilized Total Knee Arthroplasty? A Randomized Trial

Background Polyethylene wear and osteolysis remain a concern with the use of modular, fixed-bearing total knee arthroplasty (TKA). A variety of highly crosslinked polyethylenes (XLPs) have been introduced to address this problem, but there are few data on the results and complications of this polyethylene in posterior-stabilized knee prostheses.

Questions/purposes In a randomized prospective study design comparing standard polyethylene (SP) tibial inserts with XLP inserts, we asked the following questions: (1) Are there any differences in the clinical results (as measured by the classic Knee Society scoring system) and radiographic results (as measured by an evaluation for radiolucencies and osteolysis) between these groups? (2) What is the frequency of reoperation in these two groups? (3) Are there any specific complications related to XLP liners?

Methods These are preliminary data from a single surgeon of a planned interim analysis of a prospective randomized study of one modular posterior-stabilized TKA. One hundred ninety-two patients (236 knees) were randomized to receive a SP compression-molded liner or a XLP (6.5 CGy electron beam-irradiated and remelted) polyethylene liner. There was no difference in the number of knees who were lost or refused followup (14 knees [13%] with XLP and 21 knees [17%] with SP). Patients were evaluated clinically using the original Knee Society scores, Lower Extremity Activity Score (LEAS), presence of knee effusion, and by standard radiographs for radiolucent lines and osteolytic lesions. This analysis was performed at a mean followup of 4.5 years (range, 2-8 years).

Results There were no clinical differences between 99 knees with SP and 94 knees with XLP in original Knee Society total score (SP mean 95, SD 5; XLP mean 94, SD 7 [p = 0.16]); change in total score (SP mean 41, 95% confidence interval [CI], 39-41; XLP mean 43, 95% CI, 39-48 [p = 0.56]); knee function score (SP mean 64 [SD 25]; XLP mean 64 [SD 24] p = 0.98; change in function score (SP mean 22, 95% CI, 17-27; XLP mean 21, 95% CI, 17-27 [p = 0.79]); LEAS score (both SP and XLP 9 [SD 2]; p = 0.88); and change in LEAS (both SP and XLP mean 1, 95% CI, 1-2 [p = 0.0.38]). There were no differences, with the numbers available, in the presence of effusion (two of 94 XLP and five of 99 SP) with 2 years minimum followup. There were no differences in the frequency of radiolucent lines (13 knees with SP and 15 with XLP) or of osteolysis (two knees with SP and none with XLP). There was no difference in frequency of reoperation between the two groups (three infections in 110 knees allocated to the XLP group and five (two infections, one femoral loosening, one instability, one fracture plating) in 122 knees allocated to the standard group. There were no complications related to the XLP liner.

Conclusions In this interim analysis, with the numbers available, there were no complications, but no advantages, related to the use of this XLP tibial liner. Additional enrollment has continued, and longer followup of these patients will be necessary to determine whether long-term wear characteristics differ between the groups.

Level of Evidence Level I, therapeutic study.