Abstract
Introduction
In vitro studies showed that the anti-oxidative properties of vitamin E stabilize free radicals while retaining the mechanical strength of UHMWPE. The purpose was to evaluate vitamin E diffused polyethylene (VEPE) wear and stability of femoral components using RSA. Patient reported outcome measures (PROMs) were evaluated to determine the clinical outcome at 5 years.
Methods
48 patients (52 hips), with osteoarthritis, participated in a 5 year RSA study. Each patient received a VEPE liner, a porous titanium coated shell, and an uncemented stem with a 32mm head. Tantalum beads were inserted into the VEPE and the femur to measure head wear and stem stability using RSA. RSA and PROM follow-up was obtained postoperatively, 6 months, 1, 2, 3, and 5 years after surgery. The Wilcoxon signed-ranks test determined if changes in penetration or migration were significant (p≤0.05).
Results
47 hips were followed at 3 years, and 35 at 5 years. The median± standard error (SE) superior head penetration into the polyethylene was 0.05±0.01mm at 3 years and 0.06±0.01 mm at 5 years. There was no difference after 2 years. The median± SE distal stem migration was 0.06±0.21mm at 3 years, and 0.06±0.29mm at 5 years with no significant differences over time. All PROMs improved significantly from the preoperative to all other intervals (p<0.001 for all).
Discussion
The VEPE liners show low head penetration at 5 years. The early head penetration, probably due to creep, is lower relative to that reported for non-VEPE measured by RSA. While most stems were stable, the high standard error results from one stem that migrated substantially by 6 months (9.4mm), which has since stabilized. This study documents the longest-term evaluation of in vivo wear performance of vitamin E stabilized UHMWPE. The low wear and the stability of the femoral stem shows promise for long-term survivorship.
