Desmitis of the palmar or plantar ligaments of the proximal interphalangeal joint: A descriptive case series.

Background: Limited reports in the literature are available regarding desmitis of the palmar/plantar ligaments of the proximal interphalangeal joint (PL-PIPJ); the clinical significance of such injuries is unknown.

Objectives: To describe the ability to differentiate the PL-PIPJ on low-field magnetic resonance (MR) examination. To describe the injury characteristics of the PL-PIPJ on MR examination and the correlation with clinical features and lameness.

Study design: Retrospective case series.

Methods: Data and MR images of 29 horses were collected from the databases of three institutions. Horses were included when desmitis of the PL-PIPJ was present, specifically the axial palmar/plantar ligament, the abaxial palmar/plantar ligament, the proximal enthesis of the distal digital annular ligament, and the distal enthesis of the proximal digital annular ligament. The clinical features and lameness scores were noted for all cases. The MR examinations were reviewed. Ligaments were graded for visibility and degree of pathology by a board-certified diagnostic imaging specialist.

Results: Differentiation between the different ligaments is not always reliably possible, especially as the abaxial palmar/plantar ligament was only distinctly visible in 4 out of 80 ligaments (5%, 95% confidence interval (CI): 1%-12%). Desmitis of the PL-PIPJ was the main MR finding in 13 out of 29 (45%, CI: 26%-64%) clinical cases. Periligamentous oedema was evident in 53 of the 71 (74%, CI: 63%-84%) abaxially located ligaments with desmitis. Enthesophyte formation was present in 34 out of 102 ligaments with desmitis (33%, CI: 24%-43%).

Main limitations: Retrospective nature of the study, lack of control.

Conclusions: Pathology to the PL-PIPJ can be a primary cause of lameness in horses and these structures should therefore be critically evaluated on MR examination. Differentiation between the abaxially located structures can be challenging. Periligamentous oedema is often present in cases of desmitis of the abaxially located ligaments; its presence should prompt closer assessment.