IN VIVO MOTION ANALYSIS OF TOTAL ELBOW ARTHROPLASTY

Abstract

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.