Using Biotensegrity to Explain the Mechanically‐Induced Lesions in Navicular Disease

Abstract

Degenerative joint disease (DJD), the most common disease affecting humans and animals, has long been believed to result from failure of the joints from ‘wear and tear’ in which damage exceeds repair. However, models that depict the body as a machine do not adequately explain the functional musculoskeletal anatomy, in particular the role of fascia, nor do they explain why the lesions of DJD do not always correlate with pain and dysfunction. In contrast a body structured through tensegrity (integrity by tension; biotensegrity) has a seamless integration of structure and function from the molecular, cellular, tissue and organ levels to the whole body, and better explains how life evolved by adapting to different environments. Joints structured through tensegrity have more functional flexibility as tensegrity allows mechanical forces to be transmitted and dispersed throughout the surrounding connective tissues and counteracted by muscular contractions rather than being transmitted as compression across a joint space, which is the case in machine models. The purpose of this study was to use biotensegrity to explain the pathogenesis of tissue damage in navicular disease, a devastating form of DJD in horses. The structure of the navicular apparatus indicates it is an enthesis organ that functions through tensegrity to dissipate forces away from the osteotendinous junction between the deep digital flexor tendon and the distal phalanx. Functional analyses of 3D models reconstructed from CT scans of a horse's forelimb were used to predict where mechanical forces were most impacting the navicular enthesis organ. These models show that pronounced dorsiflexion of the foot, a posture commonly observed in horses with navicular disease, increased the mechanical forces on the deep digital flexor tendon, navicular bone, impar and collateral sesamoidean ligaments, which are all sites of tissue damage in navicular disease. Histochemical staining with Masson's trichrome and picrosirius red, confirmed evidence of mechanical stress in the target tissues as stretched collagen was prominent in the tendon, navicular bone and fibrocartilage, and the impar and collateral sesamoidean ligaments and correlated with the sites of tissue damage. The identification of widespread mechanical damage in the soft tissues of the navicular enthesis organ in affected horses confirms its function as a tensegrity structure and emphasizes the relevance of biotensegrity models in understanding the pathogenesis of DJD.Support or Funding InformationLSU SVM Charles V. Cusimano Equine Health Studies ProgramThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.