Fixation of high-flexion total knee prostheses: five-year follow-up results of a four-arm randomized controlled clinical and roentgen stereophotogrammetric analysis study.

BACKGROUND: High-flexion total knee arthroplasty was introduced to meet the demands of daily activity requiring increased knee flexion. However, concerns have been raised regarding the fixation of high-flexion total knee arthroplasty components and increased rates of loosening have been reported. To date, migration, and thus fixation, of high-flexion total knee arthroplasty components has not been analyzed and the preferential bearing type (mobile or fixed) is unknown.

METHODS: Of eighty-six consecutive eligible patients, seventy-four patients (seventy-eight knees) scheduled for total knee arthroplasty were randomized to one of four Legacy Posterior Stabilized (LPS) total knee prosthesis designs: (1) LPS-Flex mobile, (2) LPS-Flex fixed, (3) LPS mobile, and (4) LPS fixed. The primary outcome was component migration measured with use of Roentgen stereophotogrammetric analysis, and secondary outcomes were postoperative knee flexion and extension and Knee Society Score. Patients were evaluated postoperatively at six, twelve, twenty-six, and fifty-two weeks and annually thereafter. At the five-year follow-up, eight patients had died and two patients were lost to follow-up. Seventy-seven tibial and forty-two femoral components were suitable for migration measurements.

RESULTS: The overall five-year migration of the seventy-seven tibial components was not significantly different among the four total knee prosthesis designs (compared with the LPS fixed design, the range of overall mean differences for the other three designs was 0.02 to 0.25 mm) and migration was comparable at the two and five-year follow-up. Migration stabilized in all but three components (two LPS-Flex mobile and one LPS fixed); one of these components has already been revised and was aseptically loose. The overall five-year migration of the forty-two femoral components was comparable among the four designs (compared with the LPS fixed design, the range of overall mean differences for the other three designs was 0.01 to 0.18 mm) and was similar at two and five years postoperatively. One femoral component (LPS-Flex mobile) migrated excessively. In patients who had a mean postoperative flexion of ≥ 125° or a maximum flexion of ≥ 135° during the one to five-year follow-up period, migration of high-flexion components was comparable with that of conventional components and indicative of appropriate fixation. Postoperative flexion, extension, Knee Society Score, and Knee Society Score function were comparable during the five-year follow-up period and at the two and five-year follow-up.

CONCLUSIONS: The LPS-Flex total knee prosthesis with either a mobile or a fixed bearing had migration comparable that of with its conventional counterpart and is expected to have similar (excellent) long-term survival in these patients.

LEVEL OF EVIDENCE: Therapeutic Level I. See Instructions for Authors for a complete description of levels of evidence.