Risk of intra-articular injection with longitudinal ultrasound-guided injection of collateral ligaments of the equine distal interphalangeal joint.

Desmopathy of the collateral ligaments of the distal interphalangeal joint is a common cause of equine foot lameness and carries a poor prognosis with conservative management. Intralesional injections may improve healing, although accuracy of radiographically guided injections is significantly less than when guided by MRI, which requires special needles. Longitudinal ultrasound-guided injection of the distal collateral ligament has not been evaluated objectively. In this prospective, anatomic study, seven equine cadaver limbs (14 collateral ligaments) were injected with methylene blue dye and radiographic contrast medium using ultrasound to guide the needle longitudinally into the collateral ligaments until contacting bone. The insertion site of the needle proximal to the coronary band was measured on the limb and the needles left in place for radiography and CT to evaluate the needle angulation, location of the contrast medium, and whether the contrast entered the distal interphalangeal joint. The limbs were frozen and sectioned with a band saw to identify the location of the dye. Fifty percentage of injections were in or around the collateral ligaments. However, the percentage of "successful" injections, defined as in the collateral ligament but not in the joint, was only 36%. All legs had dye and contrast in the joint after both ligaments had been injected. There were no significant differences between the needle angle and entry site for "successful" and "unsuccessful" injections. Findings from this study indicates that the success rate is low for injecting the distal portions of the distal interphalangeal joint collateral ligaments using ultrasound guidance alone.