DO WE NEED A HIGH-FLEX TOTAL KNEE PROSTHESIS TO IMPROVE RANGE OF KNEE MOTION?

Abstract

The high-flex total knee arthroplasty system was introduced to enhance knee flexion and to facilitate tibiofemoral articulation at high-flexion by the design modification of an increased thickness of the posterior wall of the femoral component by 2 mm compared with the standard total knee prosthesis. However, several clinical studies on the effectiveness of designs intended to provided high flexion following total knee arthroplasty have produced conflicting results. We performed a prospective, randomized study to compare the ranges of motion of the high-flex and standard total knee replacements in patients who were managed with simultaneous bilateral total knee arthroplasty.

This study comprised of three independent groups of patients.

1. The first group: Fifty patients (mean age, 68 years old) received a standard NexGen LPS prosthesis in one knee and a NexGen LPS-Flex prosthesis in the contralateral knee. Two patients were men, and 48 were women. At a mean of 2.1 years postoperatively, the patients were assessed clinically and radiographically with use of the knee-rating systems of the KS and HSS.

2. The second group: Fifty-four patients (mean age 69.7 years) received a NexGen CR prosthesis in one knee and a NexGen CR-Flex prosthesis in the contralateral knee. Five patients were men, and 49 were women. The minimum follow-up was 3 years (mean, 3.1 years). At each follow-up, the WOMAC score and range of knee motion were evaluated and patients were assessed clinically and radiographically with use of the knee-rating systems of the KS and HSS.

3. The third group: Two hundred and fifty patients (mean age, 71.6 years) received a NexGen CR-Flex knee prosthesis in one knee and a NexGen LPS-Flex knee prosthesis in the contrallateral knee. Ten patients were men and 240 were women. At each follow-up (mean follow-up, 2.3 years) the patients were assessed clinically and radiographically with use of the knee-rating systems of the KS and HSS.

4. The first group: The mean postoperative HSS knee score was 90 points for the knees treated with the NexGen LPS prosthesis and 89.4 points for those treated with the NexGen LPS-Flex prosthesis. At the time of the final follow-up, the knees with the NexGen LPS prosthesis had a mean range of motion of 135.8° (range, 105° to 150°) and those with a NexGen LPS-Flex prosthesis had a mean range of motion of 138.6° (range, 105° to 150°). No knee had aseptic loosening, revision, or osteolysis.

5. The second group: The mean postoperative KS and HSS knee scores were 93.7 and 89 points, respectively in the knees with a NexGen CR prosthesis and those were 93.9 and 90 points, respectively in the knees with a NexGen CR-Flex prosthesis. The mean postoperative WOMAC score was 22 points. Postoperatively, the mean non-weight and weight bearing ranges of motion were 131° (range, 90° to 150°) and 115° (range, 75° to 145°), respectively in the knee with a NexGen CR prosthesis and those were 133° (range, 90° to 150°) and 118 (range, 75° to 145°), in the knees with a NexGen CR-Flex prosthesis. Patients satisfaction and radiographic results were similar in both groups. No knee had aseptic loosening, revision, or osteolysis.

6. The third group: The mean postoperative KS and HSS knee scores were 95 and 90 points, respectively in the knees with a NexGen CR-Flex prosthesis and those were 95 and 91 points, respectively in the knees with a NexGen LPS-Flex prosthesis. Postoperatively, the mean non-weight and weight bearing ranges of motion were 133° (range, 90° to 145°) and 118° (range, 75° to 135°), respectively in the knees with a NexGen CR-Flex prosthesis and those were 135° (range, 85° to 140°) and 122° (range, 70° to 135°), respectively in the knees with a NexGen LPS-Flex prosthesis. No knee had aseptic loosening, revision, or osteolysis.

After a minimum follow-up of two years, we found no significant differences among the first, second and the third groups with regard to range of knee motion, or clinical and radiographic results.