Radiographic enthesopathy signals hidden cartilage damage in horses’ DIP joint

Distal interphalangeal joint capsule enthesopathy of the middle phalanx and articular cartilage loss

Monika A. Samol, Myra F. Barrett, David D. Frisbie

Background
The distal interphalangeal joint (DIPJ) is a frequent source of lameness in horses, but significant pathology such as cartilage damage often cannot be identified radiographically. Joint capsule enthesopathy of the middle phalanx (P2) is visible on radiographs and may serve as a marker of underlying DIPJ pathology. This study aimed to determine the frequency of DIPJ articular cartilage abnormalities associated with capsule enthesopathy and to evaluate correlations with other soft tissue and osseous lesions.

Methods
This retrospective case series reviewed medical records from 2013 to 2024 at a single referral center. Horses were included if DIPJ capsule enthesopathy was confirmed on both radiographs and high-field MRI. Radiographs and MRI studies were graded for enthesopathy severity, articular cartilage loss, proliferative synovitis, effusion, osteophytes, and collateral ligament (CL) abnormalities. Correlations between these findings and clinical lameness were analyzed using Spearman’s rank correlation.

Results
The study included 18 horses (21 limbs). Radiographic capsule enthesopathy grades correlated well with MRI grades (r = 0.63, p = 0.002). Articular cartilage lesions were present in 95% of cases, most commonly moderate to marked in severity. Proliferative synovitis (91%) and periarticular osteophytes (95%) were also common. CL abnormalities were present in 52% of limbs and correlated moderately with MRI-based enthesopathy grades (r = 0.53, p = 0.01). However, the severity of capsule enthesopathy did not correlate with the degree of cartilage loss or with lameness grade. Interestingly, increasing enthesopathy severity was negatively correlated with joint effusion volume, suggesting chronic progression of joint disease.

Limitations
The study was retrospective, with a small sample size from a single referral center and no histopathological confirmation. The absence of low-field MRI cases limits applicability in more common clinical settings.

Conclusions
DIPJ capsule enthesopathy visible on radiographs strongly suggests underlying cartilage loss and associated joint pathology. Radiographs can therefore be a reliable screening tool when advanced imaging is unavailable. High-field MRI remains superior for characterizing cartilage and soft tissue damage. Recognition of radiographic enthesopathy should guide case management, prognosis, and potential surgical decision-making in horses with lameness.

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