Mechanical nociceptive thresholds of the foot do not change following anaesthesia of the digital flexor tendon sheath in horses

Background The selectivity of diagnostic analgesia of the digital flexor tendon sheath (DFTS) in horses remains debated. This study aimed to determine whether intrasynovial administration of 2% lidocaine into the DFTS increases the mechanical nociceptive threshold (MNT) of the dorsal lamellar stratum, sole, coronary band and heel bulbs, with correct placement confirmed by contrast tenography. Methods Six healthy horses with no clinical or radiographic distal limb abnormalities were used. Forelimbs were randomly assigned, with one limb receiving 2% lidocaine and the contralateral limb receiving lactated Ringer's solution via the palmar pastern approach to the DFTS; both solutions were mixed with radiographic contrast to confirm accurate placement. MNT was measured in 10‐foot regions using a portable pressure dynamometer before and at predefined time points up to 4 hours after DFTS injection. Data were compared using Friedman and Wilcoxon tests ( p < 0.05). Results No significant differences in MNT were observed over time or between groups. MNT values rarely exceeded 1‐kg force, and medians in both groups showed only minor fluctuations, remaining close to 0.5‐kg force across the evaluated foot regions. Conclusion Under the conditions of this study, contrast‐confirmed intrasynovial administration of 2% lidocaine into the DFTS did not produce detectable desensitisation of the evaluated foot regions in clinically normal horses.