Scintigraphic evaluation of 99mTc-methylene diphosphonate uptake in the navicular area of horses with lameness isolated to the foot by anesthesia of the palmar digital nerves.
Authors: Keegan, Wilson, Lattimer, Twardock, Ellersieck
Journal: American journal of veterinary research
Summary
# Editorial Summary Navicular syndrome remains a challenging diagnosis in equine practice, requiring multiple diagnostic approaches to confirm bone involvement when clinical signs point to palmar foot pain. Keegan and colleagues used nuclear scintigraphy with 99mTc-methylene diphosphonate to compare radiopharmaceutical uptake patterns in the navicular bone of seven lame horses with confirmed palmar foot pain (isolated via palmar digital nerve blocks) against seven sound control horses, acquiring soft tissue images at 7–12 minutes post-injection and bone-phase images at 30 minutes through to four hours. Affected horses demonstrated significantly elevated navicular-to-distal phalangeal density ratios (1.77 versus 0.97 in controls; P = 0.003) and higher subjective uptake scores on both palmar views alone and palmar-lateral view combinations (1.85–1.99 versus 0.51–0.62; P < 0.01), indicating substantially increased bone metabolic activity in the navicular region. Critically, imaging at one hour post-injection provided equivalent diagnostic discrimination to later timepoints, and palmar projections proved more sensitive than lateral views for detecting navicular uptake. For practitioners managing suspected navicular cases, this work establishes scintigraphy as a reliable ancillary diagnostic tool when palmar digital nerve anesthesia has successfully isolated lameness to the foot, with the practical advantage that diagnostic-quality images can be acquired within an hour rather than requiring prolonged imaging protocols.
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Practical Takeaways
- •99mTc-MDP scintigraphy is a useful diagnostic tool for confirming navicular bone involvement in horses with palmar foot pain; consider imaging at 1 hour post-injection rather than waiting longer
- •Always obtain palmar view images as they are more diagnostic than lateral views alone for navicular area evaluation
- •This imaging modality helps differentiate navicular syndrome from other causes of forelimb lameness after palmar digital nerve blocks isolate pain to the foot
Key Findings
- •Affected horses showed significantly higher navicular-to-distal phalangeal density ratios (1.77 vs 0.97, P=0.003) on scintigraphy compared to controls
- •Palmar view bone-phase images were more sensitive than lateral views at detecting navicular area uptake
- •Images obtained at 1 hour post-injection were equally effective as those at 2-4 hours for differentiating affected from control horses
- •Mean subjective scores for affected horses were significantly higher on palmar-only views (1.85, P<0.01) and combined palmar-lateral views (1.99, P<0.01) versus controls (0.51, 0.62)