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

Abstract

Summary The objective of this study was to map topographically contact areas and pressure distributions on the proximal articular surface (PAS) of the proximal phalanx (PI) under various clinically relevant loading conditions. Left and right forelimbs of 13 mature horses were transected halfway down the radius and loaded in a position mimicking the weightbearing attitude close to the midstance phase. Five loads were used which corresponded with loads that can be expected in different gaits or during athletic performance (stance: 1800 N, walk: 3600 N, trot: 5400 N, gallop: 10,500 N and jumping: 12,000 N). Contact areas and pressure distributions at the PAS of PI were determined using a methylene blue dye staining technique and 2 pressure sensitive films (low pressure: range 2.5–10 MPa and medium pressure: range 10–50 MPa). The contact area of PI was positively correlated (r = 0.86; P<0.01) with the applied load. The contact area increased from 63% at 1800 N to 95% at 12,000 N and gradually shifted to include more of the edges of the articular surface, but especially the dorsal articular margin of PI. Pressure distribution patterns were similar under the different loading conditions. Pressure was less at the palmar margin and in the central depression and highest at the dorsal articular margin. With increasing load, the highest peak pressures were measured at sites of the dorsal articular margin that are not loaded in the standing or walking horse. The results of this study suggest that the frequent occurrence of osteochondral lesions at the dorsal articular margin of PI is caused by the combination of the intermittent character and the high absolute values of loads at this site as they occur during athletic performance.

Effect of loading on the organization of the collagen fibril network in juvenile equine articular cartilage

“…4,21 Different sites in a particular cartilage surface subjected to distinct loading patterns have different biochemical composition, [3][4][5] and the present study shows that there are also important differences in collagen structure between these sites: Irrespective of exercise group, there were significant differences in both parallelism and orientation of collagen fibrils between sites 1 and 2. PI was higher centrally (site 2) than peripherally (site 1), corresponding with marginal areas having a much larger transitional zone with more random fibril orientation than did central areas.…”

“…1), which is constantly loaded during standing and during locomotion at all velocities but with peak loads substantially lower than at site 1. 4 …”

“…1), which is exposed to dynamic, intermittent peak-type loading (likely to be encountered during gallop and jumping) but not loaded during standing or while the animal is moving slowly when walking or trotting. 4 Another plug was harvested from the mid-region of the medial joint surface (site 2, Fig. 1), which is constantly loaded during standing and during locomotion at all velocities but with peak loads substantially lower than at site 1.…”

“…2,3 Specifically much work has been done comparing two sites on the proximal articular surface of the proximal phalangeal bone of the metacarpophalangeal (MCP) joint, which are known to be subjected to strongly differing loading conditions and to feature large differences in the incidence and manifestations of osteochondral disease. [4][5][6] Much less is known about possible topographical variation in the ultrastructure of equine articular cartilage. Benninghoff 7 used plane-polarized light microscopy to show the spatial organization of collagen network as a complex of arcade-like structures passing throughout three zones of hyaline cartilage.…”

The potential role of training programmesin reducing injuries

“…In a more extensive study into the topographical heterogeneity of the same articular surface, in which 12 sites were sampled and proteoglycan content was determined as well, it was demonstrated that there was a distinct and consistent topographical variation for all parameters determined: water, DNA, glycosaminoglycans, collagen, hydroxylysylpyridinoline (HP) cross-links and degree of lysyl hydoxylation (Brama et al 2000a). The findings corresponded neatly with the load distribution in the joint as determined using pressure-sensitive films in an in vitro setting and applying loads occurring during activities such as standing, walking, trotting, cantering and jumping (Brama et al 2001), showing that in the mature individual there is normally a match between loading and tissue characteristics, i.e. between the resistance of the tissue and the demands placed upon it.…”