Comparison of A Mobile-Bearing Total Knee System With A Fixed-Bearing Total Knee System In Cemented Total Knee Arthroplasty

Comparison of A Mobile-Bearing Total Knee System With A Fixed-Bearing Total Knee System In Cemented Total Knee Arthroplasty

A Prospective, Randomized, Controlled Study Comparing A Mobile-Bearing Total Knee System With A Fixed-Bearing Total Knee System In Cemented Total Knee Arthroplasty

Pain, weakness, instability, and progressive dysfunction are the hallmarks of arthritis of the knee. Total knee replacement may frequently be the only therapeutic intervention to provide adequate improvement in pain and function. Both fixed bearing and mobile bearing knees have a long track record of clinical success. Mobile bearing designs have theoretical advantages of decreased contact stresses on the tibial tray, decreased polyethylene wear, and improved range of motion relative to fixed bearing designs. These theoretical advantages may become especially important in the young patient who requires a knee arthroplasty. This study will attempt to see if there is a clinical difference in outcome between mobile bearing and fixed bearing knee arthroplasties in patients who require total knee replacement.

This prospective, randomized, single-blinded clinical trial compared a mobile-bearing total knee system with two types of fixed-bearing total knee systems in patients undergoing cemented total knee arthroplasty. The devices to be used are FDA approved: the Sigma Knee System (mobile-bearing), the Sigma, Pressfit Condylar posterior cruciate substituting (fixed-bearing) system with a metal backed tibial tray, and the Sigma press-fit condylar posterior cruciate substituting system (fixed bearing) with an all polyethylene tibial tray. The surgical procedures were performed by 4 experienced orthopedic surgeons with a subspecialty interest in total knee arthroplasty. A midline skin incision and medial parapatellar arthrotomy were used to expose the knee. The distal femoral resection was performed with an intramedullary alignment guide, and the proximal tibial resection was performed with an extramedullary alignment guide. Knees with fixed deformities had a surgical release of the contracted tissues on the medial or lateral side, as appropriate, to obtain symmetric balance of the total knee replacement in both flexion and extension. The flexion and extension gaps and the medial and lateral soft-tissue structures were balanced in accordance with standard techniques. Patients began progressive weight-bearing on the first postoperative day, and active knee range of motion was initiated with 24 hours after surgery. Patients were typically discharged on the fourth or fifth postoperative day after obtaining the ability to walk with a walker, to ascend several stairs, and to flex the knee 290 degrees. Patients were asked to return for examination and radiographs at 3 months, 1 year, 2 years, and 5 years after surgery.

Sigma Pressfit Condylar Posterior Cruciate Substituting System with a metal back tibial tray (fixed-bearing knee with the metal backed tray)

Sigma Pressfit Condylar Posterior Cruciate Substituting System with a metal back tibial tray (fixed-bearing knee with the metal backed tray)

Sigma Pressfit Condylar Posterior Cruciate Substituting System (fixed bearing with an all polyethylene tray)

The range of knee motion was measured clinically with use of a goniometer. Measurements were performed by physician assistants in the Department of Orthopedic Surgery who were blinded to the type of implant used. The subject was positioned supine on the examination table, and maximum active flexion was measured.

The Knee Society Function Score considers only walking distance and stair climbing, with deductions for walking aids. The maximum function score, which is 100, is obtained by a patient who can walk an unlimited distance and go up and down stairs normally. The minimum function score is 0.

The Knee Society Pain Score includes walking and climbing stairs. The maximum score per knee is 50 indicating no pain, and 0 indicates severe pain. Therefore the total score (for both knees) could range from 0 to 100.

The stair-climbing portion of the Knee Society clinical rating system assigns a maximum score of 50 points for patients able to ascend and descend stairs in a normal fashion, 40 points for patients needing a rail to descend, 30 points for patients using a rail in both directions, 15 points for patients able to ascend but not descend at all, and 0 points for patients unable ascend or descend. Because stair ascent and descent put substantial demands on the patellofemoral joint, we used that portion of the Knee Society clinical rating system as a proxy for patellofemoral function in this study.

Inclusion Criteria: Patients undergoing unilateral primary knee surgery for degenerative joint disease (DJD). Exclusion Criteria: Severe deformity greater than or equal to 20 degrees varus, valgus malalignment Osteomyelitis, septicemia, or other active infections that may spread to other areas of the body The presence of infections, highly communicable diseases, e.g., AIDS, active tuberculosis, venereal disease, hepatitis Significant neurological or musculoskeletal disorders or disease that may adversely affect normal gait or weight bearing Metastatic disease Any congenital, developmental, or other bone disease or previous knee surgery that may, in the surgeon's judgement, interfere with total knee prosthesis survival or success, e.g., Paget's disease, Charcot's disease secondary to diabetes, severe osteoporosis, previous high tibial osteotomy, etc. Presence of previous prosthetic knee replacement device (any type) Arthrodesis of the affected knee Patients not requiring patella resurfacing.

Kalisvaart MM, Pagnano MW, Trousdale RT, Stuart MJ, Hanssen AD. Randomized clinical trial of rotating-platform and fixed-bearing total knee arthroplasty: no clinically detectable differences at five years. J Bone Joint Surg Am. 2012 Mar 21;94(6):481-9. doi: 10.2106/JBJS.K.00315.