Vascular perfusion of the dorsal and palmar condyles of the equine third metacarpal bone

Reasons for performing study: Palmar osteochondral disease (POD) is an overload arthrosis that commonly affects fetlock joints of racing Thoroughbreds (TB) but the aetiopathogenesis of the disease has not been well defined. Objectives: The aim of this study was to compare India ink perfusion in the dorsal and palmar condyles of the third metacarpal bone (McIII) in both passively flexed and maximally extended fetlock joints from paired equine cadaver limbs. Study design: Descriptive cadaver study comparing perfusion of condyles of McIII in paired cadaver limbs in flexion (control group) and maximal extension (intervention group). Methods: Pairs of forelimbs were acquired from 5 TB horses subjected to euthanasia for reasons unrelated to lameness. Limb pairs were perfused intra-arterially with India ink and then randomly assigned to passive flexion or maximal extension of the fetlock joint. Limbs were sectioned sagittally in 3mm sections through the fetlock and 12 sections per limb processed using a modified tissue-clearing technique. Sections were subsequently digitally imaged and bone perfusion evaluated with image analysis software. Results: Greater perfusion of the dorsal condyle than of palmar condyle was observed in 78% of sections from limbs in passive flexion and 92% of maximally extended sections. Perfusion to the palmar aspect of the condyle was significantly decreased (P<0.0001) when the limbs were placed in maximal extension compared to passive flexion. Conclusions: The palmar condyle of McIII had less perfusion than the dorsal condyle when the fetlock joint was in passive flexion and this difference was exacerbated by maximal extension. Based on the anatomical location of POD lesions, perfusion differences between the dorsal and palmar condyles of McIII may be associated with development of these lesions.