Background: Traditional radiographic measurements of distal phalanx (Pd) displacement are not considered useful for diagnosis and monitoring of acute laminitis.
Objectives: Compare the radiographic distance between inner hoof wall and Pd (“lamellar lucent zone”; LLZ) for healthy horses vs acute laminitis. Animals: Lateromedial forelimb radiographs from healthy (University and client-owned) and acutely laminitic (client-owned, hospitalized) mixed-breed horses were analyzed retrospectively.
Methods: Acute laminitis was defined by ≥ 2 clinical signs (acute multi-limb lameness; increased digital pulse amplitude; persistently warm hooves) for ≤ 3 days, without radiographic evidence of palmar rotation (≥ 3°), remodeling, or obvious distal displacement of the Pd. Radiographic measurements (Figure 1A) were compared blindly between 18 acute laminitis cases (14 sepsis-related, 4 hyperinsulinemia-associated) and 32 healthy control horses using a mixed-effects linear regression model and receiver-operator characteristic (ROC) curves.
Results: Marginal mean [95% confidence interval] LLZ (mm) was increased in acute laminitis compared to control in the proximal (8.8 [8.4-9.2] vs 7.3 [6.9-7.7]), middle (8.9 [8.5-9.3] vs 6.9 [6.5-7.2]), and distal (9.2 [8.6-9.7] vs 7.5 [7-8]) dorsal lamellar regions (P< 0.001) (Figure 1B). With a cutoff of >7.5 mm middle LLZ was 87% sensitive and 91% specific for identification of acute laminitis (ROC area-under-the-curve [AUC]=0.96). The ratio of LLZ:Pd palmar cortex length was 95% sensitive and 95% specific for acute laminitis with a cutoff >11% (AUC=0.99) (Figure 1C).Conclusions and clinical importance: Radiographic measurements of LLZ are potentially useful for diagnosis of acute laminitis; their utility can be further improved using the ratio to Pd cortex length.
