Normal three-dimensional behaviour of the metacarpophalangeal joint and the effect of uneven foot bearing.

This research study examined the small rotational movements in a horse’s metacarpophalangeal joint (MPJ) and the effect on those movements when the foot is placed unevenly. The findings indicated that minor rotations do occur in the MPJ and that these movements are influenced substantially by uneven bearing of the foot, suggesting a potential area of focus for understanding MPJ injuries and corrective measures in horses.

Methodology

• The research involved experimental setup with four isolated forelimbs of a horse, where trihedrons (three-dimensional figure formed by four triangles) were used to support kinematic markers defining a local frame.
• The limbs were then loaded in a press, and the lateral or medial aspects, which are the sides of the foot, were alternately raised using a 12-degree wedge.
• Use of the Joint Coordinate System enabled simultaneous and continuous computation of the three angles of rotation of the joint.

Results

• During neutral loading, the researchers found that extension of the MPJ was associated with lateral axial rotation of the proximal phalanx, the bone between the MPJ and the first digit.
• Adding a lateral wedge caused medial rotation and abduction or movement away from the centreline of the proximal phalanx. Conversely, use of a medial wedge resulted in the opposite effect.
• The quantitative results validated observations from earlier semi-quantitative studies, confirming the combination of axial rotation (rotation along the axis) and expansion of the space in the joint on the side opposite to the raised part of the foot.

Significance of Results

• Despite the high congruence, or alignment, of the joint, the study demonstrated significant influence of uneven bearing of the foot on the three-dimensional behavior of the MPJ.
• Although the amplitude of these movements was small, their biomechanical effects could have implications in understanding MPJ injuries and rationalising exercise management and corrective shoeing in the lame horse.