For the last few decades there have been several successful reports of TEA of both semi-constrained and non-linked prosthesis: pain relief, improvement of range of motion, functional improvement, and good survival rate of the components. However, other reports also showed that TEA had higher complication rates and lower survival rate than knee and hip joint replacement. To solve this problem some in vitro kinematic studies about TEA have been done and reported. But in vivo research has not been reported yet in the TEA, and it must be done for an essential solution. The aim of this study is to analyze in vivo motion of TEA components using two- to three- (2D/3D) registration technique.

Six patients, six elbows were included in this study, having been treated with K-Elbow because of rheumatoid arthritis. The mean age at the operation was 47.2 years The mean duration between the operation and the fluoroscopic surveillance was 56.7 months.

Under fluoroscopic examination in the sagittal plane, each patient was asked to bend his or her elbow from full extension to full flexion. Successive elbow motions were recorded as serial digital X-ray images using a digital image intensifier system. In vivo 3D poses of the humeral and the ulnar components were estimated using a 2D/3D registration technique, which uses CAD models to reproduce spatial postures of the humeral and the ulnar components from calibrated single view fluoroscopic images. The algorithm utilizes a feature-based approach to minimize distances between lines drawn from a contour found in the 2D image to the X-ray source and a surface CAD model with iterative computations. The amount of extension/flexion, varus/ valgus, and internal/external rotation angles of the ulnar component for the humeral component were evaluated quantitatively using Euler’s method.

Results: The minimum flexion angle between the components was 33.6°± 18.5. Four of the six elbows exhibited inimum flexions of > 30° and the other two elbows exhibited < 30°. One elbow exhibited excessive flexion contracture > 50°. The maximum flexion angle was 126.7° ± 5.5. Only one elbow demonstrated flexion angle < 120° and all the others > 120°. The arc of range of motion was 93.0°±19.4.

Concerning the valgus/varus angles between the components, there was a variation among patients. And from 30 to 120° flexion, there was a tendency to incline valgus with the increase of flexion. The mean valgus angle through flexion was −0.1°± 4.3 and the magnitude of displacement of valgus angle was 9.5° ± 4.0. In a similar way, there was a variation among patients about the rotation between the components. And from 30 to 120° flexion, there was a tendency to incline external rotation with the increase of flexion. The mean internal rotation through flexion was −1.0° ± 4.3 and the magnitude of displacement of internal rotation was 8.1°± 3.3.

Recently mobile-bearing total knee arthroplasty (TKA) has become more popular. However, the advantages of mobile bearing (MB) PS TKA still remain unclear especially from a kinematic point of view. The objective of this study was to investigate the difference and advantage in kinematics of mobile baring PS TKA compared with fixed bearing (FB) PS TKA. Femorotibial nearest positions for 20 subjects (20 knees), 10 knees implanted with NexGen Legacy flex with mobile bearing PS TKA, and 10 knees implanted with NexGen Legacy flex with fixed bearing PS TKA were analyzed using the sagittal plane fluoroscopic images. All the knees were implanted by a single surgeon. All the subjects performed weight bearing deep knee bending motion. The average range of motion between femoral component and tibial component was 119±18 in MB and 122±10 in FB. The axial rotation of the femoral component was 11.8±6.2 in MB and 11.8±4.9 in FB. There was no significant difference both in range of motion and axial rotation between BM and FB. The kinematic pathway pattern was externally rotated due to a lateral pivot pattern in both MB and FB. In four subjects, more than 12°axial rotation was observed in knees implanted with FB TKA which allows only 12°axial rotation.

The data in this study demonstrates that there was no significant difference in kinematics of weight bearing deep knee bending motion. The advantage of MB is allowance of axial rotation which restricted until 12 °in FB NexGen Legacy flex PS TKA.

The objective of this study was to evaluate the kinematics of a high-flexion, posterior-stabilized total knee arthroplasty (TKA) in weight-bearing, deep knee bending motion. Fifteen patients implanted with the Legacy Posterior Stabilized Flex (8; mobile bearing and 7; fixed bearing), 18 patients with Scorpio NRG, and 8 patients with PFC sigma RP-F were examined during a deep knee bending motion using fluoroscopy. Femorotibial motion was determined using a 2-dimensional to 3-dimensional registration technique, which used computer-assisted design models to reproduce the position of metallic implants from single-view fluoroscopic images. The average flex-ion ranges of motion between the metallic implants were 120° with Legacy Flex, 125° with NRG and 121° with RP-F. The average rotation of the femoral component was 11° external rotation (ER) with Legacy Flex, 12° with NRG and 11° with RP-F. The mean kinematic pathways were early rollback, lateral pivot with ER, and bicondylar rollback with Legacy Flex, medial pivot with ER and bicondylar rollback with NRG and central pivot with ER and bicondylar rollback with RP-F. The in vivo kinematics was different due to the prosthesis designs to obtain weight-bearing deep knee bending motion.