Assessment of Elbow Deformity with an Ultrasonic Motion Analysis System via Its Rotation Axis: A Cadaver Study

Abstract

Background: Elbow deformities are frequently found in children following elbow trauma, and precise assessment of elbow deformity is difficult in current clinical practice, especially in the rotational component, even with computed tomographic (CT) images due to the presence of cartilage. Purpose: We are proposing a new method of assessing elbow deformity via the its rotational axis, calculated from data obtained by the motion analysis system, in order to provide orthopedic surgeons a better understanding of the elbow deformities before or during surgical corrections. Methods: Osteotomy was performed at the supracondylar region of humerus on a fresh-frozen cadaver, and the bone fragments were adjusted with a set of external skeletal fixator (ESF). Cycles of elbow flexion and extension were then performed passively, and the coordinates of the markers on both humerus and ulna were recorded by an ultrasonic motion analysis system. Mathematical algorithm was developed and the elbow rotation axis was determined by the normal vector of the best fitting plane calculated through random sample consensus (RANSAC) method. Five different elbow conditions in varus/valgus deformities as well as internal/ external rotations were created by adjusting the ESF, and three sets of data were collected for each condition. Results: The best fitting plane method was able to reduce the shifting of the marker positions from 11 mm to less than 4 mm, and the deformities calculated from each elbow rotation axis were found to be within 50 of the expected value.