Semi-automated 3-dimensional analysis of the normal foot and ankle using weight bearing CT – A report of normal values and bony relationships
Razi Zaidi, Dhrumin Sangoi, Nicholas Cullen, Shelain Patel, Matthew Welck, Karan Malhotra
Abstract
BACKGROUND: Foot and ankle deformities have translational and rotational components in multiple planes, at multiple levels. Semi-automatic segmentation is a relatively new technology, which when used with weight-bearing CT (WBCT), can build an accurate model of the foot and calculate the orientation and relationships of bones under physiological load. However, few papers report reference values using these techniques. We report normative values for key bony relationships based on semi-automated analysis of WBCT. METHODS: This was a single-centre, retrospective analysis of 100 feet without deformity from 55 adult patients undergoing WBCT as part of routine clinical activity (mean age 40.5 ± 17.3 years). Imaging was analysed using Bonelogic 2.1 (DISIOR, Finland). Semi-automatic segmentation was used to compute the various bony axes in 3-dimensional space. Selected coronal, axial and sagittal plane relationships were then calculated for bones of the hindfoot, midfoot and forefoot. RESULTS: Data is presented on axial and sagittal plane relationships between the metatarsals in the forefoot, and the metatarsals and cuneiforms in the midfoot. In the hindfoot, the calcaneal pitch, talar-first-metatarsal angles, talonavicular coverage angles and Saltzman angles are reported. Coronal plane axes and their relationships are reported at multiple levels from hindfoot to forefoot. Results are presented as mean values with standard deviations and 95% confidence intervals. CONCLUSIONS: We present an observational analysis of the normal values from non-deformed feet. We highlight the major relationships in the axial, sagittal and coronal planes as obtained by semi-automated analysis of WBCT. This data may serve as a reference for future research. LEVEL OF EVIDENCE: Basic science study.