Detection of degenerative joint disease of the distal interphalangeal joint in thoracic limbs characterized by joint space narrowing using standing low-field MRI in 25 equine patients

OBJECTIVE: To report low-field standing MRI findings and, when available, postmortem findings of 25 thoracic limbs with degenerative joint disease of the distal interphalangeal joint (DIPJ) characterized by narrowing of the joint space suggestive of cartilage loss.

METHODS: Medical records from September 2015 to July 2022 were reviewed for clinical history, signalment, MRI, and postmortem findings. The study retrospectively analyzed cases in which lameness was linked to DIPJ joint space narrowing using a partially nested comparative design. Width was measured at 4 DIPJ sites, as well as a ratio to the proximal interphalangeal joint. Affected limbs were compared to contralateral and randomly selected control limbs. Statistically significant differences in measurements were found between affected and control groups. In the affected group, subjective DIPJ narrowing, synovial effusion, heterogeneous dorsal recess material, periarticular osteophytosis, and STIR hyperintense signal within the foot were graded.

RESULTS: Standing low-field MRI identified DIPJ degenerative joint disease with joint space narrowing and cartilage loss. A dorsomedial DIPJ width measurement of < 3 mm suggests cartilage damage. Narrowing of the DIPJ may occur without marked effusion, periarticular osteophytosis, or adjacent bone STIR hyperintensity.

CONCLUSIONS: Measurements of the joint space on standing low-field MRI can be supportive for the identification of cartilage loss in the DIPJ, which may occur without other concomitant findings.

CLINICAL RELEVANCE: Low-field standing MRI is valuable for assessing DIPJ narrowing. Prognosis appears to be poor for cartilage loss, as 22 of 25 horses did not return to performance.