Distal border fragments and shape of the navicular bone: radiological evaluation in lame horses and horses free from lameness.
Authors: Biggi, Dyson
Journal: Equine veterinary journal
Summary
# Editorial Summary: Distal Border Fragments and Navicular Bone Shape Biggi and Dyson's 2012 radiological study addressed a significant gap in equine orthopaedic knowledge by objectively characterising navicular bone morphology in 55 sound horses and 377 forelimb-lame horses confirmed via palmar nerve blocks, with measurements of palmar cortex thickness, proximal and distal extensions, and systematic grading of radiological abnormalities. Distal border fragments appeared in only 3.6% of sound horses but in 8.7% of lame horses generally, rising to 24.1% among horses with a confirmed primary navicular diagnosis—a substantially higher prevalence suggesting clinical significance. Beyond fragment presence, lame horses demonstrated measurably thicker palmar cortices and larger proximal extensions compared with sound horses, though notably the distal extension was smaller, indicating redistribution rather than uniform hypertrophy of the palmar aspect. Fragment detection correlated significantly with worse overall navicular bone grades, radiolucent areas at the distal border angles, and increased numbers and sizes of synovial invaginations, suggesting fragments may represent degenerative markers rather than incidental findings. For practitioners interpreting radiographs, these objective data support the diagnostic value of distal border fragments and morphological changes as indicators of navicular pathology, making systematic assessment of palmar cortex shape and bone contour potentially as important as searching for classical features like bone cysts or resorption.
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Practical Takeaways
- •Distal border fragments on radiographs are not diagnostic of lameness alone (present in 3.6% of sound horses), but their presence warrants careful evaluation of other navicular bone changes
- •Increased palmar cortex thickness on radiographs is a consistent finding in lame horses and may help differentiate sound from lame horses with navicular involvement
- •Objective measurement and grading of navicular bone shape changes alongside fragment assessment provides better diagnostic accuracy for navicular pathology than fragment presence alone
Key Findings
- •Distal border fragments were present in 3.6% of sound horses, 8.7% of lame horses, and 24.1% of horses with primary navicular pathology
- •Palmar cortex thickness of the navicular bone was significantly greater in lame compared with sound horses
- •Strong association between distal border fragments and overall navicular bone grade, radiolucent areas at distal border angles, and synovial invaginations
- •All measurements were larger in lame horses except distal extension of the palmar cortex