The suspensory apparatus of the coffin bone - Part 2: Clinical relevance of the suspensory apparatus and its fan-shaped reinforcement in chronic equine laminitis with coffin bone or hoof capsule rotation.
Acute laminitis is a serious equine disease resulting in degenerative changes of the suspensory apparatus of the coffin bone, ranging from severe disturbance to complete destruction. Metabolic/endocrinologic laminitis is a progressive disease of domestication, as a consequence of continuous overfeeding and limited exercise, and of longevity. Traumatic laminitis is the result of inadequate hoof protection on hard surfaces and/or excessive exercise. Chronic laminitis is the condition that develops subsequently to any kind of laminitis, if not healed completely. While part 1 of our study focused on the suspensory apparatus, particularly on its fan-shaped re-enforcement at the tip of the coffin bone, the aim of the second part of the study is to describe the ruptures within the suspensory apparatus in chronic laminitis and to suggest therapeutic measures. The present study was based on twenty hooves that were classified as laminitic according to adspectory examination or preliminary report. The hooves were analysed macroscopically via plastinated thin sections or microscopically via conventional histological methods. Chronic laminitis becomes manifest either in mild or severe coffin bone rotation on the one hand, or in hoof capsule rotation on the other hand. Hoof capsule rotation resembles coffin bone rotation in mild cases. Coffin bone rotation is characterised by a dorsally broken toe axis in varying degree. Additionally, a prominent scar horn shield (tubulolamellary wedge) is developed between horn capsule and coffin bone in the toe region. Hoof capsule rotation becomes also manifest in different degrees and appears similar to coffin bone rotation in the initial moderate cases while the severe cases display a distinct bend of the hoof wall. Proximal to the bend the hoof wall displays physiological growth direction but distal to the bend the hoof wall growth is disturbed resulting in the disfigured "lump" hoof characteristic for laminitis. Removal of the superficial layers of the cornified lump exposes its composition of horn masses of the ectopic White Line. In chronic laminitis, predilection sites for ruptures within the suspensory apparatus were detected at the following locations: the initial anchorage at the coffin bone and the terminal anchorage within the hoof capsule, as well as the intermediate anchorage both at the basal membrane of the interlamellary bond and at the epithelial microstructure of the epidermis within the area of the stick-slip effect. The fan-shaped re-enforcement at the tip of the coffin bone was totally ruptured in severe coffin bone rotation and grossly overexpanded in severe hoof capsule rotation. The orthopedic measures should concentrate on the dorsal, middle and palmar/plantar aspects of the hoof in coffin bone rotation. In severe hoof capsule rotation, the therapy focuses on resection of the pathologic horn mosses ('lump') produced by the White Line.