Correlating Increased Mechanical Forces with Tissue Lesions in Equine Navicular Disease

Abstract

Navicular disease is a common form of chronic lameness in horses that currently can only be managed but not effectively treated. The navicular apparatus is a functional enthesis organ very similar to the human Achilles, and is highly adapted to dissipate forces away from the osteotendinous junction between the deep digital flexor tendon and the distal phalanx. Force analyses using 3D models constructed from CT scans of a horse's forelimb indicate that an exaggerated dorsiflexion of the foot, a posture commonly observed in horses with navicular disease, puts the deep digital flexor tendon under greater tension. With this in mind, tissue lesions in the navicular enthesis organ in horses euthanized for navicular disease were correlated with the force analysis. Areas of tension in the deep flexor tendon and underlying adipose tissue were identified by differential histological staining of stretched versus relaxed collagen using Masson's trichrome and picrosirius red. These areas correlated with tendon lesions documented by MRI and were in line with compressive lesions in the navicular bone. The dorsiflexed position of the foot was also found to increase forces on the impar and suspensory ligaments in which enthesial loss and disruption of collagen fibers and deposits of cartilage and bone was documented. These findings confirm the primary mechanical pathogenesis of navicular disease and indicate that rehabilitative therapy focused on decreasing dorsiflexion of the foot by reducing overloading of the forelimb is likely to be an effective treatment for many cases of navicular disease.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.