Contact areas and pressure distribution on the proximal articular surface of the proximal phalanx under sagittal plane loading.

This study analyses the contact areas and pressure distribution on the upper part of a specific horse bone under various load conditions normally observed while the horse performs different gaits or activities. It shows that the bone’s contact area expands and shifts, especially under increased pressure, which might explain the frequent occurrence of joint and cartilage injuries at certain parts of the bone during athletic activity.

Study Objective and Methodology

• The research aimed to topographically map the contact areas and pressure distributions on the Proximal Articular Surface (PAS) of the Proximal Phalanx (PI), a bone found in horse’s forelimbs, under different relevant loading conditions usually faced during various gaits or athletic performances.
• The researchers used 13 mature horse forelimbs, cut halfway down the radius, and placed it in a position that resembles a weightbearing position near the midstance phase.
• Five different load conditions were tested, each corresponding to those encountered during different gaits or athletic activities: stance (1800N), walk (3600N), trot (5400N), gallop (10500N), and jump (12000N) were used.
• The contact areas and pressure distributions were explored by using a methylene blue dye staining technique and two pressure-sensitive films with both low (2.5-10 MPa) and medium (10-50 MPa) pressure range.

Results and Findings

• The PAS of PI’s contact area demonstrated a positive correlation (r = 0.86; P<0.01) with the level of load applied. The contact area expanded from 63% at 1800N to 95% at 12000N and started to shift to incorporate more of the articular surface's edges, particularly the dorsal articular margin of PI.
• The pressure distribution patterns were similar across the different loading conditions. Pressure was lowest at the palmar margin and central depression and highest on the dorsal articular margin.
• As the load increased, the highest peak pressures were seen at the dorsal articular margin areas, which do not bear load in a horse standing or walking.

Implications of Results

• The study suggests that the frequent instances of osteochondral injuries (damages to bones and cartilages) on the Proximal Phalanx’s dorsal articular margin are likely due to the high absolute load values and its intermittent character during athletic performance.
• The findings give valuable insights into the equine bone’s response to varying loads, which can be useful in understanding bone injuries and developing relevant preventive strategies in horse performance and veterinary practice.