DOES HIGH-FLEXION DESIGN OF CRUCIATE RETAINING TOTAL KNEE PROSTHESIS INCREASE POSTOPERATIVE RANGE OF MOTION?

Abstract

The range of motion (ROM) after total knee arthroplasty (TKA) is one of the most important factors for patient satisfaction, especially in Asian countries. To enhance the knee flexion angle, “high-flexion” designs have been introduced in total knee prostheses. One of such design was a new design of femoral prosthesis, which increased the posterior cut on the bone by 2 mm and thickened the posterior condyle, allowing the posterior condylar radius to continue further. There were several reports on postoperative ROM of such “high-flexion” posterior-stabilized (PS) total knee prosthesis. However, there was no report on the postoperative ROM of “high-flexion” cruciate ligament retaining (CR) total knee prosthesis. The purpose of this study was to compare the ROM associated with standard and high-flexion posterior CR total knee prostheses.

One hundred and fifty-one consecutive patients (176 knees) had CR total knee prosthesis. 89 knees had standard CR TKA (NexGen CR, Zimmer, Warsaw, IL), and 87 knees had high-flexion CR knee prostheses (NexGen CR-Flex, Zimmer, Warsaw, IL). Differences in the age, diagnosis, preoperative Knee Society Score (KSS), and preoperative ROM of the knee between two groups were not significant. At one year postoperatively, the patients were assessed clinically and radiographically.

The mean postoperative KSS knee score was 96.2 points for the standard CR prosthesis group and 96.7 points for the high-flexion CR prosthesis group (p=0.464). The mean postoperative KSS function score was 83.4 points for the standard CR prosthesis group and 84.8 points for the high-flexion CR prosthesis group (p=0.446). The mean postoperative ROM was 110.8 degrees in the standard CR prosthesis group, and 114.0 degrees in high-flexion prosthesis group (p=0.236). No knee had aseptic loosening, revision, or osteolysis.

Previous report showed that “high-flexion” PS design did not increase postoperative ROM compared to standard design. However, there was no report on the postoperative ROM of “high-flexion” CR total knee prosthesis. We found no significant differences between the standard CR group and “high-flexion” CR group with regard to ROM or clinical and radiographic parameters. However, in the cases which achieved high flexion, “high-flexion” design, which chamfered posterior femoral edge, can reduce the possibility of deformation from posterior contacts under lord. Therefore, the results of the current study suggested that “high-flexion” CR design is not the design that increase ROM significantly, but might be the safe design even when the knee achieved deep flexion.