Radiographic Imaging and Finite Element Modeling Methods for Analysis of the Basilar Thumb Joint

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Abstract

Laxity of the stabilizing ligaments, specifically the anterior oblique ligament (AOL) and the dorsoradial ligament (DRL), is believed to play a major role in the development of osteoarthritis (OA) of the basilar thumb joint. Increased laxity of the stabilizing ligaments is believed to contribute to cartilage degeneration through dorsal translation of the metacarpal, increased shear stresses, and a shift in contact to areas of weaker cartilage. Stress radiographs during functional tasks, such as key pinch, can be used to help assess joint instability. Eleven cadaveric specimens were rigged to simulate key pinch, and a mobile C-arm was used to take a series of radiographic images with the joint capsule intact, opened, and after transection of the AOL. Images were taken from the anteroposterior (AP) view up to 60⁰ toward the ulnar aspect of the arm to determine which angle allowed the best assessment of subluxation. The AP view showed the maximum amount of subluxation in a majority of the specimens. Subluxation significantly correlated with radiographic grades of OA but did not correlate with visual/arthroscopic grades of OA. Transection of the AOL did not have a significant effect on subluxation. Three-dimensional modeling techniques, such as finite element modeling, can be used to measure in vivo contact mechanics without disrupting the joint capsule and other supportive soft tissues. Models could have future clinical diagnostic and research applications, but they must first be validated against experimental data. Three specimens underwent MRI scanning in “relaxed” and “pinch” configurations to create finite element models for intact and open joint capsule simulations of key pinch. Model results were compared to experimental data collected by electronic sensors. Only measurements for contact force met validation criteria, and contact area was overestimated in every specimen. Contact measurements were not significantly affected by opening the joint capsule, but all four contact measures trended upward after opening the joint capsule. This supports the need for continued refinement of validation experimental methods and the benefits of computational modeling for future studies of contact mechanics.

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