Pathology of the distal phalanx in equine laminitis: more than just skin deep

The etiopathogenesis of laminitis is complex and involves multiple tissue types. It may be initiated by biomechanical, traumatic, inflammatory, vascular, toxic, and metabolic factors. Although histopathologic changes occurring within the lamellae of experimental models of laminitis are well described and reported, histopathologic changes occurring in the distal phalanx are not, even though gross and radiographic evidence of disease are often apparent and bony lesions could be considered a significant source of pain. Recent scientific evidence indicates that the microenvironment of bone is an important modulator of inflammatory processes that can both influence, and be influenced by components of other organ systems, including the immune, nervous, gastrointestinal, and integumentary systems. This article describes various laminitis-associated histopathological changes in the distal phalanx, introduces concepts of osteoimmunology with regards to equine laminitis, and provides a rationale for histopathological examination of the distal phalanx, as well as the soft tissue structures of the lamellae and corium in laminitis cases.