Osteopathology in the Equine Distal Phalanx Associated With the Development and Progression of Laminitis

Abstract

Although the equine distal phalanx and hoof lamellae are biomechanically and physiologically integrated, bony changes in the distal phalanx are poorly described in laminitis. The aims of this study were (1) to establish a laminitis grading scheme that can be applied to the wide spectrum of lesions seen in naturally occurring cases and (2) to measure and describe changes in the distal phalanx associated with laminitis using micro-computed tomography (micro-CT) and histology. Thirty-six laminitic and normal feet from 15 performance and nonperformance horses were evaluated. A laminitis grading scheme based on radiographic, gross, histopathologic, and temporal parameters was developed. Laminitis severity grades generated by this scheme correlated well with clinical severity and coincided with decreased distal phalanx bone volume and density as measured by micro-CT. Laminitic hoof wall changes included progressive ventral rotation and distal displacement of the distal phalanx with increased thickness of the stratum internumcorium tissues with lamellar wedge formation. Histologically, there was epidermal lamellar necrosis with basement membrane separation and dysplastic regeneration, including acanthosis and hyperkeratosis, corresponding to the lamellar wedge. The changes detected by micro-CT corresponded to microscopic findings in the bone, including osteoclastic osteolysis of trabecular and osteonal bone with medullary inflammation and fibrosis. Bone changes were identified in horses with mild/early stages of laminitis as well as severe/chronic stages. The authors conclude that distal phalangeal pathology is a quantifiable and significant component of laminitis pathology and may have important implications for early detection or therapeutic intervention of equine laminitis.Keywords horse, laminitis, distal phalanx, pathology, diagnostic imaging, micro-computed tomography, x-ray microtomography, osteolysis, osteopathologyThe structural integrity of the highly specialized and complex elements composing the equine foot-including the epidermal and dermal lamellae, bone, tendons, ligaments, and other connective tissues-is essential for suspension of the distal phalanx (DP) within the hoof capsule. The interface between the equine DP and inner hoof wall is unique in that the dorsal cortex of the DP is highly porous relative to the solar cortex or to the cortices of other bones in the appendicular skeleton.39 These porosities correspond to perforating vascular channels that extend from the medullary spaces of the DP to supply the overlying lamellar tissues. 30,39 Thus, the unique interface of this specialized musculoskeletal unit provides a direct microanatomic integration between bone and epidermal/dermal lamellar tissues.Laminitis is a disease affecting the epidermal and dermal lamellae of the inner hoof wall, which often progresses to a chronic phase. The chronic phase of laminitis is characterized by inadequate tissue healing and aberrant regenerative responses that result in lamellar hyperplasia and dysplasia,...

Pain management for laminitis in the horse

“…In contrast, the insidious clinical onset of endocrinopathic laminitis may be, in part, explained by the relative lack of lamellar inflammation (at least early) in this form of the disease (Visser and Pollitt 2011). There is a component of ongoing inflammation within both the lamellae and adjacent distal phalanx in chronic laminitis regardless of the inciting cause (Engiles et al 2015). Lamellar ischaemia may be an important initiator of supporting limb laminitis and may contribute to the progression of other forms of laminitis Gardner et al 2017).…”

“…There is a component of ongoing inflammation within both the lamellae and adjacent distal phalanx in chronic laminitis regardless of the inciting cause (Engiles et al . ). Lamellar ischaemia may be an important initiator of supporting limb laminitis and may contribute to the progression of other forms of laminitis (van Eps et al .…”

“…In many of these cases, there is also marked osteolysis and inflammation of the bone that may also itself contribute to pain (Engiles et al . ). Interestingly, the refractory neuropathic pain of complex regional pain syndrome in human patients is responsive to therapy aimed at inhibiting similar osteoclastic bone resorption using bisphosphonates (Wang et al .…”

“…) and it follows that the bone pathology of laminitis, marked by osteolysis/remodelling, oedema and inflammation (Engiles et al . ), may directly contribute to pain, particularly in chronic cases. Changes in pressure both within the lamellar/solear soft‐tissue ‘compartments’ as well as within the distal phalanx have been suggested as potential sources of pain in laminitis (Collins et al .…”

No Bones About It

“…Similarly, understanding laminitis in horses, an age-old disease with several etiologies, has been greatly enhanced by Engiles et al, 6 who used micro-computed tomography (CT) and histology to measure and describe changes in the distal phalanx of affected horses. Karikoski et al 9 provide a detailed correlation of endocrinopathic laminitis with clinical, macroscopic, and microscopic findings.…”