Semi-automated Segmentation and Distance Mapping of Weight Bearing CT Data to Estimate Select Midfoot Joint Volumes

Background: Injury to the Lisfranc complex can prove difficult to diagnose, particularly injuries that are purely ligamentous. Missed Lisfranc injuries can cause long-lasting consequences including accelerated midfoot arthritis and collapse. Previous studies have investigated the volume and area of the space between the medial cuneiform and the second metatarsal, but the Lisfranc complex involves additional joints whose articulations have yet to be described. The objective of this study was to define volumes of each individual Lisfranc joint under physiological load to establish healthy baselines for clinical reference. Methods: Forty-three volunteers (54 feet) receiving a weightbearing computed tomography (CT) scan were included in this study. This cohort included 11 bilateral and 32 unilateral feet in patients that were scanned because of the presence of a contralateral ankle injury. The images were segmented using a semiautomated segmentation method. Opposing articular spaces in the Lisfranc joint of the midfoot were manually selected, and interarticular distance mapping was then performed to characterize the joint space width. Interarticular volume was then estimated using an area-weighted volume measurement. Results: All articulating surfaces within the tarsometatarsal region of the Lisfranc complex had a coefficient of variance below 30%, with the least variable region corresponding to the medial cuneiform–intermediate cuneiform articulating space (19.4%) and the most variable tarsometatarsal region corresponding to the medial cuneiform–second metatarsal (28.1%). Bilateral volunteers (n = 11) had nonsignificant contralateral differences in every articulating space within the Lisfranc complex except for the first metatarsal–medial cuneiform joint where we identified an average contralateral difference of 3.61 mm 3 , P = .03. Conclusion: We present our data on using a semiautomatic algorithm to estimate volume of midfoot joints from weightbearing CT scan in a cohort of noninjured control subjects. Further studies determining if this algorithm may have clinical utility to help identify subtle Lisfranc instability are needed.