Gross, histological and histomorphometric features of the navicular bone and related structures in the horse.
Authors: Wright, Kidd, Thorp
Journal: Equine veterinary journal
Summary
Wright, Kidd and Thorp examined navicular bones and surrounding tissues from 38 horses with clinical navicular disease (ND) alongside age-matched and immature control groups to characterise the pathological changes associated with this chronic condition. Histological and histomorphometric analysis revealed that whilst some features such as mid-ridge synovial fossae appeared across all groups, horses with ND exhibited distinctive gross lesions including full-thickness palmar fibrocartilage defects, palmar cortex erosion, medullary lysis, and characteristic flexor digitorum profundus tendon (FDPT) surface fibrillation with core lesions and adhesions to the bone. Microscopic examination demonstrated that fibrocartilage thinning was accompanied by reduced cell density and chondrocyte clustering, whilst bone remodelling manifested as increased trabecular volume, decreased medullary area, and elevated osteoid content—changes the authors likened to osteoarthritic pathology in articular cartilage. The FDPT showed consistent degeneration including surface fibrillation, tag formation and necrotic foci, with medullary pseudocysts and mineralised foci appearing specific to diseased horses. For practitioners, these findings underscore that navicular disease involves progressive structural breakdown across multiple tissues rather than isolated bone pathology, suggesting that effective management strategies must address both the fibrocartilage surface integrity and the underlying bone remodelling, whilst the characteristic FDPT changes highlight the mechanical interdependence between tendon and skeletal structures in this region.
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Practical Takeaways
- •Navicular disease involves progressive degenerative changes extending throughout the bone structure, not just palmar surface damage, requiring comprehensive diagnostic imaging and assessment.
- •The involvement of flexor tendon degeneration, fibrillation and adhesions alongside bone changes means management must address soft tissue healing alongside any farriery or joint interventions.
- •Early detection of palmar fibrocartilage partial thickness loss and distal border fragmentation may help identify navicular disease before full thickness defects develop, supporting earlier intervention strategies.
Key Findings
- •Full thickness palmar fibrocartilage defects, palmar cortex erosion, and FDPT adhesions were pathognomonic for clinical navicular disease, not seen in control horses.
- •Histomorphometric analysis revealed decreased medullary area but increased trabecular bone volume in navicular disease horses, indicating bone remodelling throughout the bone from medial to lateral margins.
- •Palmar fibrocartilage changes in navicular disease were characterized by thinning, loss, fibrillation and reduced cell density, similar to osteoarthritic changes in hyaline cartilage.
- •Age-related differences in immature horses included smaller subchondral area and greater osteoid volume compared to mature controls, suggesting developmental factors in navicular bone.