Radiographic evaluations of distal navicular border fragments and forefeet conformation in the horse

Radiographic examination has good sensitivity in revealing fragments located at the distal border of the navicular bone (DSBF) in the dorsoproximal-palmarodistal oblique (DPr-PaDiO) view with a proximo-distal angle between 55° and 65° (1). DSBF is a common finding in lame horses as well as in radiographic screenings (2). Aim of the study was to evaluate the correlation between presence of DSBF and navicular and forefeet conformation. The radiographs of 120 horses (Italian Saddlebred and Angloariabian, aged 3-15 years), obtained during pre-purchase or for diagnostic purposes, were used. Feet were classified in 3 groups: 1. lame feet with DSBF, 2. lameness-free feet with DSBF, 3. feet from sound horses without DSBF. Location of the lameness at the foot was confirmed by diagnostic anesthesia in lame horses. The averages of 3 consecutive measurements of 3 ratios and 1 angle were statistically compared among the 3 groups: 1. distal navicular border length / navicular maximal width ratio (Y/Z), 2. height of sole at the toe / height of the heels ratio (E/D), 3. length of the toe / length of the foot ratio (C/B), 4. angle of the dorsal hoof wall to the ground (F). In feet with DSBF, Y/Z, E/D and C/B ratios were higher if compared with feet without fragment (P<0.05). In feet with fragment, feet without lameness showed higher E/D ratio than feet with lameness (P<0.05). Although the difference was not statistically significant, Y/Z and C/B ratios were also higher in lame feet if compared with non lame feet. Even if not statistically significant, F angle was smaller in feet with both fragment and lameness and in feet without fragment if compared with feet with fragment without lameness. DSBF seem to be more present in navicular bones with more “rectangular” rather “trapezoidal” shape in the DPr-PaDiO 60° oblique view (high Y/Z ratio) and in feet with long toe-low heel conformation (high E/D and C/B ratios). This correlation between conformation of the foot, navicular shape and presence of DSBF suggests an important role of mechanical forces in the occurrence of DSBF in horses's foot and highlight the importance of early foot trimming and managment. 1) Claerhoudt S. et al. "Association between navicular bone fragmentation and shape in Belgian Warmblood horses", Vet. Comp. Orthop. Traumatol., 24(2)132-136(2011); 2) Verwilghen D. et al. "Prevalence of radiographic findings in candidate sires (2001-2008)", Res. Vet. Science, 87,319-328(2009).