[Does the NexGen LPS flex mobile knee prosthesis offer advantages compared to the NexGen LPS?--a comparison of clinical and radiological results].

Under experimental conditions, mobile bearing knee prostheses have several advantages. The optimized congruence of the tibio-femoral joint surface allows a knee flexion of more than 120 degrees without creating instability or increase of wear. The aim of this study is to compare the results of a prospective randomized study after implantation of the mobile bearing knee prosthesis NexGen LPS Flex with the results of the fixed bearing knee prosthesis NexGen LPS. Sixty patients underwent a total knee replacement (30 patients with NexGen LPS Flex mobile, 30 patients with NexGen LPS) via a mid vastus approach. All implants were cemented (Palacos) including the patella resurfacing. We evaluated the Hospital for Special Surgery Score (HSS) and different radiological parameters (maximal flexion, positioning of the implants, leg axis) preoperatively as well as 3 months and 3 years (34.6 +/- 7.3 months) postoperatively. After 3 months the NexGen LPS Flex group showed better results in the scores for pain, range of motion (122.5 degrees vs. 107.33 degrees ) as well as the overall HSS (87.21 vs. 82.68 points) compared to the NexGen LPS group. Three years postoperatively there were no differences in all scores between the two groups. The theoretical advantages of the mobile bearing knee prostheses were reflected in the clinical results only partly and temporarily. Probably the results of long-term follow-ups will show characteristic advantages or disadvantages of mobile bearing knee prostheses.