New Jersey low contact stress knee replacement system. Ten-year evaluation of meniscal bearings

A metal-backed, interchangeable, meniscal bearing knee replacement system has been designed to combine low constraint forces with low contact stresses (LCS) to allow nearly normal joint articulation and loading as well as long-term wear resistance of the implants. System components allow unicompartmental, bicompartmental, tricompartmental, and revision knee arthroplasties. In this prospective comparison study, the early series of cases used methyl methacrylate for prosthesis-to-bone fixation, whereas the more recent series of knee replacements used sintered-bead porous coating to allow tissue ingrowth stabilization of all implants. Overall results in the first 149 cemented cases with 2- to 10-year follow-up (mean 7.6 years) were good to excellent in 85.2 per cent, fair in 3.4 per cent, and poor in 11.4 per cent using a strict knee scoring scale. Fair and poor results were seen predominantly in multiply operated and implant revision cases. The best cemented results were noted in primary cases, 95.1 per cent of which had good to excellent results. Overall results in the first 208 cementless cases with 2- to 7-year follow-up (mean 4.4 years) were good to excellent in 91.8 per cent, fair in 2.4 per cent, and poor in 5.8 per cent. Fair and poor results were also seen predominantly in multiply operated and implant revision cases. The best cementless results were noted in primary cases, 98.2 per cent of which had good to excellent results. Of 140 meniscal bearing implants in the entire series, one dislocation occurred (0.7 per cent) which required open bearing replacement. Of 217 rotating platform bearing implants in the entire series, 7 dislocations occurred (3.2 per cent), which required open bearing replacement or revision of components for malposition. These dislocations were seen predominantly in revision cases involving insufficient flexion stability; 6 of the 7 cases were revisions. This study demonstrates the efficacy of mobile bearing elements for use in knee replacement arthroplasty. It is essential that flexion and extension gaps be controlled to maintain contact pressure on such bearings to avoid problems of subluxation or dislocation.