Abstract
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.
Highlights
The medial and lateral collateral ligaments of the distal interphalangeal (DIP) joint arise from the middle phalanx and insert on fossae close to the articular margin of the distal phalanx 1
There was contrast media in the DIP joint on 64.3% (9/14; 95% confidence interval (CI): 35%, 87%) of injections and, after attempted injection of both the lateral and medial collateral ligaments, contrast media was present in the DIP joint of all the legs
The contrast media was within the distal portion of the collateral ligament and/or periligamentous in 7/14 (50%; 95% CI: 27%, 73%) of injections (Figure 3)
Summary
The medial and lateral collateral ligaments of the DIP joint arise from the middle phalanx and insert on fossae close to the articular margin of the distal phalanx 1. The increased use of standing MRI for the diagnosis of foot lameness without radiographic abnormalities has increased the frequency of this diagnosis significantly because of its greater ability to identify soft tissue pathology inside the hoof capsule in those cases even when there are no palpable abnormalities and collateral ligament desmopathy represents the second most common soft tissue injury in the forefoot. The MRI diagnosis of collateral ligament desmopathy is, still challenging because the angulation of the ligament in standing horses makes it susceptible to a magic angle artefact 8-10. Appreciation of this artefact has improved our diagnostic accuracy of this condition, especially with the use of additional sequences such as T2-weighted fast spin echo sequences with a long echo time (TE) to distinguish injury from artefact 11. In human medicine use of fat-suppressed T2-weighted images has been described recently to reduce the magic angle effect in peroneal tendons 12
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