Abstract
Introduction
Large variations in knee kinematics existed after conventional TKA. Different design of TKA showed different intra-operative kinematics with navigation system.
Purpose
The purpose of this study was to compare the kinematics of the three different types of prosthesis in navigation-based in vivo simulation.
(Material and Method) Studies were carried out on 15 osteoarthritis Knees using the CT-free navigation system (Kolibri Knee, Brain LAB). Fourteen patients were female and one patient was male with mean age of 72 years. Five knees were implanted with the CR knee, 5 knees were implanted with the PS knee and 5 knees were implanted with PS mobile knee by navigated measured resection technique (PFC-sigma knee system, DePuy, Warsaw, IN). Intra-operative knee kinematics during passive range of motion from full extension to 130 degrees of knee flexion was measured after implantation while patella reduced and tourniquet released. While supporting the foot with one hand, the surgeon used his opposite hand to gently lift the thigh, flexing the hip and knee. Three types of prosthesis were compared for following factors: Presence of condylar lift-off (the gap difference greater than 1mm between medial gap and lateral gap) and anterior-posterior (AP) displacement of the center of femur relative to the tibia.
Results
Lateral condylar lift-off was found in patients with the PS implant between 120° and 130° of flexion. Remaining two types of implant did not show the condyar lift-off (Fig. 1). The pattern of AP displacement showed the same manner in three implants. Femur moved anterior side form extension to 50∼55° of flexion, after that, femur moved posterior side to full flexion. The mean maximum anterior movement and angle in CR implant was 14mm @ 55°, PS implant was 17mm ï¼ 50° and PS-mobile implant was 17mm @ 55°. The mean maximum posterior movement @ 130°, CR implant was −10.5mm, PS implant was −8.3mm and PS-mobile implant was −6.9mm. There was no significant difference among three groups.
Discussion
In CR implant, the function of PCL could influence to prevent the condyar lift-off. In PS-mobile implant, the mechanism of rotation platform might have contributed to prevent the condylar lift-off. The paradoxical anterior slide of the femoral condyles during mid flexion was observed in all types of implant. We could not find any difference in AP displacement of these 3 types of prosthesis.
