INTRODUCTION: Many orthopaedic device companies now offer a high flexion (HF) choice within their knee Arthroplasty portfolios. Early published results are mixed between standard (STD) and HF knee devices despite claims of increased flexion with the HF offerings. The purpose of this randomized, controlled, simultaneous, bilateral study was to compare two coronally conforming rotating platform devices to determine if flexion differences were attributed to implant design.

METHODS: Ninety-three subjects underwent simultaneous bilateral TKA across 8 centers. The HF device was randomly assigned to one side and the contralateral leg received the STD device. Average age was 61 years, 99% were diagnosed with osteoarthritis, 66% were females, average BMI was 32 and range of motion was measured by subjective expectations versus satisfaction.

RESULTS: The HF design had statistically better single leg active flexion (SLAF) 12 months after surgery compared to the STD. Consistent with Gupta et. al, in a subgroup with pre-op flexion < 120 degrees in both knees, the HF device was statistically superior in passive flexion, ROM, and SLAF by between 1.8 and 4.5 degrees at 6 months, 12 months, and longitudinally over all postoperative intervals using raw degrees, improvement from pre-op, and adjusting for potentially confounding variables. 57% of subjects preferred their HF knee 6 months postoperatively, although there was no difference in preference at 12 months.

DISCUSSION: The simultaneous bilateral design of this study necessitates that subjects act as their own control eliminating most confounding variables. Gains in postoperative flexion, although small, were superior in the HF TKA group and were greater in those subjects with less than 120 degrees of preoperative flexion, suggesting the ideal candidate for a HF TKA is one with lesser preoperative flexion.