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.

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.