Can we accurately measure multi-segment foot kinematics in ballet pointe shoes using marker-based methods?

Pointe shoes are unique to ballet allowing dancers to move on the tips of their toes. However, biomechanical demands of the foot and ankle en pointe may increase the risk of associated injury. Understanding foot and ankle mechanics in pointe shoes is therefore essential. Foot kinematics typically requires skin-mounted markers, yet accessing the skin via holes in pointe shoes is not feasible given their high cost and customisation requirement. The aim of our study was to evaluate the measurement error between skin-mounted and shoe-mounted markers when capturing foot and ankle kinematics with a multisegment foot model (MSFM) during en pointe movements. Twelve female ballet dancers (age: 16.66 ± 2.46yrs, mass: 55.33 ± 7.61 kg) participated in the study. A validated MSFM was used to measure foot and ankle kinematics in pointe shoes across two conditions: with markers (1) placed directly on the foot via holes in the pointe shoe; and (2) placed on the outside of the pointe shoe. An eight camera Vicon system, sampling at 250 Hz captured 3D kinematics of the dancers completing eight ballet movements (plié, tendu, rise, relevé, single leg relevé, hop en pointe, temps levé, pose). Root mean square differences (RMSD ± SD) of foot and ankle kinematics (from largest to smallest) were: tarsometatarsal flexion/extension (4.70°±3.47°), subtalar inversion/eversion 4.44°±2.46°), metatarsophalangeal flexion/extension (3.94°±2.35°), midtarsal flexion/extension (3.51°±2.64°), ankle dorsiflexion/plantarflexion (3.37°±2.50°), ankle inversion/eversion (1.75°±1.27°) and ankle internal/external rotation (1.23°±0.87°). A validated MSFM with markers placed on the external surface of a pointe shoe provides a relatively accurate method of capturing the kinematics of pointe work.