Effects of 6 degree elevation of the heels on 3D kinematics of the distal portion of the forelimb in the walking horse

REASONS FOR PERFORMING STUDY: Understanding of the biomechanical effects of heel elevation remains incomplete because in vivo studies performed with skin markers do not measure the actual movements of the 3 digital joints. OBJECTIVE: To quantify the effects of 6 degree heel wedge on the 3-dimensional movements of the 4 distal segments of the forelimb in the walking horse. METHODS: Four healthy horses were used. Kinematics of the distal segments was measured invasively with a system based on ultrasonic triangulation. Three-dimensional rotations of the digital joints were calculated by use of a 'joint coordinate system' (JCS). Data obtained with heel wedges were compared to those obtained with standard shoes during the stance phase of the stride. RESULTS: Heel wedges significantly increased maximal flexion of the proximal (PIPJ) and distal (DIPJ) interphalangeal joints and maximal extension (mean +/- s.d. +0.8 +/- 0.3 degrees) of the metacarpophalangeal joint (MPJ). Extension of the PIPJ and DIPJ was decreased at heel-off. Few effects were observed in extrasagittal planes of movement. CONCLUSIONS: Heel wedges affect the sagittal plane kinematics of the 3 digital joints. POTENTIAL RELEVANCE: Controversial effects previously observed on the MPJ may be explained by the substantial involvement of the PIPJ, which was wrongly neglected in previous studies performed on the moving horse.