All-polyethylene vs. metal-backed tibial component in total knee arthroplasty—a randomized RSA study comparing early fixation of horizontally and completely cemented tibial components: Part 1. Horizontally cemented components: AP better fixated than MB

Background Controversy still exists as to whether to mount the tibial bearing on a metal baseplate or not. Furthermore, the tibial component can be either horizontally or completely cemented. We evaluated metal backing versus all-polyethylene using horizontal cementing technique.

Patients and methods We randomized 40 patients with knee arthrosis (40 knees) to 2 groups: cemented total knee arthroplasty (AGC, Biomet) using either all-polyethylene (AP) or metal-backed (MB) tibial compo-nents (n = 20 for each group). All tibial implants had a total thickness of 8 mm. We used proximal cement-ing, including only the horizontal part of the tibia with avoidance of the stem-bone interface.

Results The positioning of the implants, as judged by the HKA angle, showed an average neutral alignment in both groups. Preoperatively and after 2 years, there was no statistically significant difference between the HSS scores in both groups (p = 0.6 and 0.4). After 2 years, the metal-backed components had rotated more around the longitudinal axis, median 0.5° vs. 0.2° (internal or exter-nal rotation, p = 0.002), and showed increased maximum total point motion, median 1.0 vs. 0.4 mm (maximum migration or MTPM, p = 0.003).

Interpretation Our study indicates that better fixation can be obtained with the all-polyethylene design if proximally cemented thin components are used.