Talonavicular joint coverage and bone morphology between different foot types.

This study explored three dimensional (3D) talonavicular joint (TNJ) coverage/orientation and bone morphology to reveal parameters that could classify and identify predispositions to cavus and planus feet. 3D models of 65 feet from 40 subjects were generated from computed tomography images classified as pes cavus, neutrally aligned, or asymptomatic/symptomatic pes planus. We calculated the talar and navicular overlap (TNJ coverage). We also measured orientation of the navicular, morphological parameters of the talus and navicular, and angular position of the talar head to body. Pes cavus showed significantly less talonavicular coverage (58 ± 2% talus and 86 ± 2% navicular) compared to asymptomatic pes planus (63 ± 2% and 95 ± 2%) and neutrally aligned feet (98 ± 2% navicular), and significantly more navicular dorsiflexion and adduction relative to the talus (p < 0.0083). The talar head in cavus feet was inverted relative to the body compared to planus feet (p < 0.0083). For symptomatic pes planus, significant abduction was measured for the navicular relative to the talus and the talar head was plantar flexed relative to the body (p < 0.0083). The talar head in planus feet was everted relative to the body compared to neutrally aligned feet. Both intrinsic (bone morphology) and extrinsic (bone position) differences exist in groups of feet described as cavus and planus.