Three-dimensional kinematics of the proximal interphalangeal joint: effects of raising the heels or the toe.

This study focuses on understanding how the proximal interphalangeal joint (PIPJ), a joint in large mammals like horses, moves during loading, specifically when heel and toe wedges are used.

Introduction

• The proximal interphalangeal joint (PIPJ) in horses has traditionally been considered as a low-motion joint, maintaining a nearly constant angle during limb loading.
• However, recent studies have shown that the joint experiences a surprisingly wide range of motion in real-life scenarios.
• The purpose of this study was to measure the movements of the PIPJ in vitro during limb loading and after the use of heel and toe wedges.

Methodology

• The team studied joint movements in terms of three possible rotations: flexion/extension, collateromotion, and axial rotation.
• Limb loading was tested at a neutral position (500-6000 N) and after heel and toe wedges of 6 degrees and 12 degrees were added.
• The researchers used a joint coordinate system, specifically described for use in horses, to calculate the three components of rotation.

Results

• When the hoof was in a neutral position, low-amplitude flexion movements of 7.9 degrees were observed, but came without the associated collateromotion or axial rotation.
• The flexion of the joint increased exponentially with load, suggesting that heavy loads during the midstance phase are necessary to evoke significant flexion.
• When the heels were raised, the joint flexed earlier and had an increased total amplitude.
• In contrast, raising the toe resulted in an extension at 500 N, beyond which the amount of flexion decreased.
• The results indicate that the amount of flexion/extension experienced during in vitro loading is significantly less than indicated by in vivo studies based on skin markers.

Implications

• Raising the toe or heel does affect the behaviour of the PIPJ, but it does not induce movement outside the sagittal plane.
• The study indicates that when hoof wedges are used in clinical practices for purposes other than affecting PIPJ motion, their biomechanical effects on this joint should be taken into consideration.