The role of the digital cushion in the biomechanics of the equine foot

The digital cushion (DC) is a convoluted wedge shaped structure located in the palmar portion of the equine foot. The composition of the DC is reported to be a combination of fibrous connective tissue, adipose tissue, and fibrocartilage. Most farriers and veterinarians agree that the DC plays a role in energy dissipation in the equine foot.; Several hypotheses in regard to the biomechanical function of the DC have been offered. This study examined the gross anatomy, histology, displacement under vertical and non-vertical loads on solid and non-deformable surfaces, and the material properties of the DC in an attempt to determine the role of the DC in the biomechanics of the equine foot.; The gross anatomy assessment revealed that the DC is composed of various regions with distinct structural organization. The histological evaluation found that the DC is primarily made up of collagen and proteoglycans with lesser amounts of elastin and adipose tissue.; The displacement of the DC was evaluated in vitro by loading equine cadaver front limbs on both a solid and deformable surface. The results showed no significant difference (p < .05) in the distance that the DC displaced when loaded on the two surfaces. The average displacement was 0.591 cm and occurred primarily in a distal and caudal direction. Directional patterns of displacement were present and were related to the direction of the applied load on the limb.; Material properties testing of the DC discovered a unique stress-strain curve. The stress-strain curve for the DC had a series of micro-fractures prior to reaching the yield stress. The average values for the material properties was much less than the same values for other biological tissue.; The results of this study indicate that the DC may play a relatively passive yet important role in the biomechanics of the equine foot by providing flexibility to the caudal half of the foot thereby allowing the displacement of the hoof capsule and axial skeletal core to occur without encountering large resistances or danger of traumatic tearing of the DC.