In vitro evaluation of metacarpophalangeal joint loading during simulated walk.

The research aims to determine the loading pattern in the equine metacarpophalangeal (MCP) joint during a simulated walk to gain insights into how biomechanical factors contribute to joint trauma and osteoarthritis (OA). The study reveals a heavier medial loading in the MCP joint, which aligns with areas associated with the initiation of cartilage degeneration in OA.

Objectives

• The main goal of the study was to simulate and evaluate the loading pattern of the metacarpophalangeal (MCP) joint, found in the limbs of horses, during a walkthrough. The results can provide insights into how mechanical stress might contribute to joint trauma and the development of osteoarthritis (OA).

Methods

• Eight cadaveric limbs from mature Dutch Warmblood horses were used for the experiment.
• The limbs were loaded into a pneumatic loading device, and the MCP joint was positioned in six different ways (labelled A1 through A6).
• To measure the pressure distribution on the cartilage surface, pressure-sensitive films were placed intra-articularly at seven sites (S1-S7) on the proximal phalanx, which is the bone in the hoof of a horse.
• The pressure-sensitive films were then analyzed through scanning and densitometry to record the results.

Results

• The research shows that pressures recorded after mid-stance (positions A4, A5, and A6) were significantly higher than those before (positions A1, A2, and A3). This shows a biphasic loading pattern during the walk at all sites, except for one site halfway along the sagittal groove (S7).
• At the S7 site, there was a linear increase in pressure as the stance phase of the stride progressed in most horses.
• Medially (positions S4, S5, S6), the pressure was significantly higher than laterally (positions S1, S2, S3), indicating heavier loading on the inner side of the joint.

Conclusions

• The study found that the heavier medial loading aligns with the area where articular cartilage degeneration usually begins in the process of OA in the equine MCP joint.
• The disparity between the loading of the central groove and other parts of the joint might lead to substantial stress differences at the end of the stance phase. This could potentially be related to the development of stress fractures in the first phalanx and the distal third metacarpal bone.