A 4D ULTRASOUND SYSTEM TO DETECT JOINT LAXITY IN BASAL THUMB OSTEOARTHRITIS

Hypermobility, or joint laxity, has been hypothesized to be a risk factor for thumb osteoarthritis (OA) [1]. Previous studies assessing thumb biomechanics in thumb OA patients have utilized various imaging modalities including radiography, magnetic resonance imaging, computed tomography imaging, and ultrasound. However, these imaging techniques provide limited information on joint laxity during motion. However, four-dimensional ultrasound (4DUS) can detect joint laxity by visualizing the thumb's stabilizing ligaments during motion. Hence, this work utilizes a novel 4DUS imaging system to characterize the degree of joint laxity associated with varying stages of thumb OA progression. A 4DUS system consisting of a motorized semi-submerged transducer assembly was developed (Figure 1). A high frequency transducer was automatically translated 1-2 centimeters laterally back and forth along the location of the thumb joint. Five healthy volunteers and five thumb osteoarthritis patients were recruited to validate the system's capability to resolve the thumb's dorsoradial ligament during motion. 4D images of thumb abduction were collected from each participant. The images were reviewed by an MSK radiologist to confirm the anatomy of interest. The images were then exported into 3D Slicer, and the dorsoradial ligament was segmented from each 3D volume of the 4D images (Figure 2). Each 4D image contained 10 3D volumes, and the length of the dorsoradial ligament in each volume was calculated along the midline of the ligament. These measurements were repeated multiple times over the course of two weeks to test for intra-rater reliability. Intraclass correlation coefficients were calculated to determine intra-rater reliability and reproducibility. The segmentations of the dorsoradial ligament from the 4DUS scans indicate a change in ligament length throughout thumb abduction in the healthy volunteers and patients. With an intraclass correlation coefficient greater than 0.9, the ligament length measurements indicate excellent repeatability. In this preliminary study, a novel 4DUS system for the assessment of ligament behaviour during thumb motion was developed, and its reliability and reproducibility were tested. This system will be used in a cohort of thumb OA patients to evaluate a) the patterns of ligament laxity associated with various stages of disease progression and b) whether there are sex-differences in ligament laxity. This imaging system will provide a deeper understanding of the morphological changes to the thumb's stabilizing ligaments that influence the onset and progression of thumb OA. This novel 4DUS system may allow clinicians to detect patients’ predisposition to thumb OA and allow for the development of joint protection techniques to target patients with increased joint laxity. For any figures or tables, please contact the authors directly.