Ultrasonography Appearance of the Equine Proximal Palmar Metacarpal Region After Local Anesthetic Infiltration

Suspensory ligament (SL) disease is a common source of lameness in the horse. Once injury of the proximal SL is suspected, based on the clinical examination and response to analgesia, diagnostic imaging of the region is often performed. The aim was to describe the presence of ultrasonographic artifacts in the palmar metacarpal area after 20 minutes and at 24 hours after infiltration of local anesthetic solution using the lateral approach. In the present study, SL and other proximal palmar metacarpal structures were ultrasonographically evaluated before and after perineural injection of mepivacaine 2% in eight forelimbs of four horses. The limbs were divided into two groups: group 1: needle not filled with anesthetic (right forelimbs); group 2: needle filled with anesthetic (left forelimbs). The ultrasonographic examination of the palmar metacarpal structures was performed after 20 minutes and at 24 hours after injection to evaluate qualitative postinjection changes and to perform measures. In the present study, there were no significant differences in the SL and other palmar metacarpal structures between baseline measurement and pattern and postinjection measurements. No changes in echogenicity or fiber pattern of the tendons and ligaments were found. Alterations consistent with gas echoes were detected in one limb in group 1 at 20 minutes after injection, whereas no gas patterns were visualized at 24 hours. Gas or fluid artifacts, due to local anesthetic infiltration, may be present. This suggests that diagnostic ultrasonography of the origin of the SL should be interpreted with caution if performed within 24 hours after diagnostic analgesia.