Kinematic analysis of the instant centers of rotation of the equine metacarpophalangeal joint.

This study conducts a scientific examination of the movement and details of the metacarpophalangeal joint in horses. The researchers used both manual and computer-aided techniques to investigate how this joint rotates and they discovered that the joint surfaces slide on each other, causing compression at certain points.

Study Design and Methodology

• The researchers performed a kinematic analysis on 21 metacarpophalangeal joints from 11 horses, investigating the immediate centers of rotation.
• The team used both manual and computerized techniques to locate the instant center of rotation by using photocopies of composite tracings derived from a series of radiographs.
• The instant centers of rotation analysis focused on the proximal phalanx positioning about the distal portion of the third metacarpal bone and the sesamoids about the distal portion of the third metacarpal bone.

Findings and Results

• The researchers found that the instant centers of rotation for the proximal phalanx and the sesamoids were consistently located on or near specific areas such as the eminence for attachment of the collateral ligaments and the dorsal articular margin of the distal portion of the third metacarpal bone respectively.
• However, they noted that variations in the radiographic projection, resulting from the rotation of the joint during its extension, inhibited the precision of the analysis. This limitation prevented them from identifying a single instant center of rotation or an instant center of rotation pathway for the articulation of the proximal phalanx or the proximal sesamoids with the distal portion of the third metacarpal bone.
• The velocity vectors, determined from the instant centers of rotation, indicated that the joint surfaces slide on each other during movement. This sliding motion caused a compression at the dorsal articular margins at the maximal extension, limiting further extension.
• At this degree of extension, the study found that proximal sesamoids only articulated with the proximal sesamoid-metacarpal articular surface of the distal portion of the third metacarpal bone.