Effects of analgesia of the digital flexor tendon sheath on pain originating in the sole, distal interphalangeal joint or navicular bursa of horses

Summary Reasons for performing study: Specific analgesic techniques are required in diagnosis of lameness to isolate the exact origin of pain to the many structures of the foot that may be involved. Objective: To determine if analgesia of the digital flexor tendon sheath (DFTS) results in anaesthesia of other portions of the foot, such as the sole, distal interphalangeal joint (DIPJ), or navicular bursa (NB). Methods: Lameness caused by pain in the dorsal margin or heel region of the sole of the foot was induced in 18 horses by: using set-screws to create solar pressure (Trial 1: n = 5); or administering endotoxin intrasynovially into the DIPJ (Trial 2: n = 6) and NB (Trial 3: n = 7). The gait of each horse was evaluated by examining videotape recorded before and after creation of lameness and after administration of mepivacaine hydrochloride into the DFTS. Results: Median lameness scores in Trial 1 at 10 min post injection of the DFTS were not significantly different from those before administration of local anaesthetic solution into the DFTS (P>0.05), but median lameness scores were reduced significantly at 20 min (P<0.05). In Trials 2 and 3, median lameness scores were not significantly different at observations made at 10 and 20 min post injection of the DFTS. Conclusions: Analgesia of the DFTS has little effect on lameness caused by pain originating in the sole, DIPJ or NB. Potential relevance: Improvement of lameness in horses after intrasynovial analgesia of the DFTS is probably caused by attenuation of pain within the structures contained in the DFTS.