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

Background: Significant distal interphalangeal joint (DIPJ) pathology, particularly affecting soft tissue and articular cartilage, is often not identifiable on radiographs but can be accompanied by joint capsule enthesopathy on the middle phalanx (P2), which can be readily identified.

Objectives: To explore frequency and correlations between DIPJ capsule enthesopathy identified on magnetic resonance imaging (MRI) and radiographs and DIPJ articular cartilage abnormalities and other concurrent soft tissue or osseous pathology within the foot found on MRI.

Study design: Retrospective descriptive case series.

Methods: Cases identified with DIPJ capsule enthesopathy on MRI and radiographs were retrospectively reviewed. Abnormalities were graded using a 4-point scale. Descriptive statistics and Spearman's rank correlations were used to analyse the relationship between the presence and grade of DIPJ capsule enthesopathy, lameness, and DIPJ intra-articular and collateral ligament abnormalities seen on MRI.

Results: MRI and radiographic studies of 21 feet with DIPJ capsule enthesopathy were analysed. DIPJ articular cartilage lesions were identified in 20/21 limbs (95%). There was no significant correlation between the degree of DIPJ capsule enthesopathy and the severity of articular cartilage lesions. DIPJ proliferative synovitis and osteophytes were present in the majority of limbs (91% and 95%), respectively. DIPJ collateral ligaments were abnormal in 52% of the limbs. With MRI-based assessment, DIPJ capsule enthesopathy grade was moderately positively correlated with DIPJ collateral ligaments' findings severity (r = 0.53, p = 0.01).

Main limitations: Retrospective character, no histopathology, studied cases limited to one referral centre, low case numbers and statistical power.

Conclusions: The presence of DIPJ capsule enthesopathy on radiographs is a reliable finding to rule in DIPJ damage and support further case management, particularly in cases where advanced imaging is unavailable or desired.