PURPOSE OF THE STUDY: Mobile-bearing total knee arthroplasty has become increasingly popular over the last few years since this option presents several theoretical advantages compared with the fixed-bearing models. The clinical advantage remains to be demonstrated. We therefore conducted a prospective randomized trial to ascertain the potential benefits. MATERIAL AND METHODS: This study included patients treated by three senior orthopedic surgeons. Each group included 52 prostheses in 52 patients in the fixed-bearing group and 50 patients in the mobile-bearing group. The per- and postoperative protocols were the same for both groups. Implants were cemented in all cases and patellae were resurfaced. The SF-12, the Knee Society Score (KSS), the Hospital of Special Surgery score (HSS) and pain and joint motion were noted before and after surgery. RESULTS: Among the 104 prostheses implanted, 100 were reviewed at mean follow-up of 36 months (range 24-41). One patient in the fixed-bearing group died six months after surgery from an unrelated cause. Three patients were lost to follow-up: one in the fixed-bearing group and two in the mobile-bearing group. There was no difference between groups for the SF-12, KSS, HSS, pain and joint motion measured postoperatively. Postoperative femorotibial alignment was one degree varus on average in the fixed-bearing group and zero degree in the mobile-bearing group. At last follow-up, there were no radiological signs of prosthesis loosening. One patient in the fixed-bearing group developed a deep venous thrombosis, complicated by pulmonary embolism. Two of the mobile-bearing prostheses were revised, one for patellar fracture caused by a bicycle accident and one for prosthesis infection in a patient with endocarditis 1.5 years after implantation. DISCUSSION: The clinical results were similar for the two groups in terms of function, pain, general status and complications. The outcome at 36 months was considered excellent or good in 90% of the fixed-bearing group and 88% in the mobile-bearing group. This study did not reveal any difference between the two groups regarding maximal flexion and anterior knee pain, two parameters which would theoretically show short-term improvement with the mobile bearing. Mid- and long-term follow will be required to confirm these findings and to determine the survival of these two types of implants.