Relative forefoot abduction and its relationship to foot length in vitro

Background. The human foot is often modelled as a rigid body in gait analys is. A more realistic model separates this segment into a forefoot and rearf oot. However: no three-dimensional data has been published on dynamic relat ive ab-adduction between these segments, and how this impacts changes in fo ot shape. Objective. The purpose was to quantify three-dimensionally forefoot ab-addu ction relative to the rearfoot in vitro, and to determine how forefoot ab-a dduction affects foot length. Methods. Video data were collected from reflective marker triads affixed to the ends of Steinmann pins drilled into the tibia, calcaneus, cuboid, and the first and fifth metatarsal bones. Medial and lateral foot length and fo refoot ab-adduction relative to the rearfoot were calculated under two axia l tibial loads (200 N, 600 N) and two input motions (dorsi-plantarflexion, internal-external tibial rotation). Results. It was found that patterns of change for each variable were depend ent on the degree of rigidity of the foot. Relative forefoot ab-adduction v alues ranged from 4.4 degrees of adduction to 1.7 degrees of abduction. Med ial foot length values changed +/- 0.8 mm (+/- 0.5%) and lateral foot lengt h values changed +/- 0.5 mm (+/- 0.3%). Medial foot length was correlated p ositively with relative forefoot abduction, and external tibial rotation wa s correlated positively with relative forefoot adduction.