High-resolution MR imaging of talar osteochondral lesions with new classification.

PURPOSE: Retrospective review of high-resolution MR imaging features of talar dome osteochondral lesions and development of new classification system based on these features.
MATERIAL AND METHODS: Over the past 7 years, 70 osteochondral lesions of the talar dome from 70 patients (49 males, 21 females, mean age 42 years, range 15-62 years) underwent high-resolution MR imaging with a microscopy coil at 1.5 T. Sixty-one (87%) of 70 lesions were located on the medial central aspect and ten (13%) lesions were located on the lateral central aspect of the talar dome. Features evaluated included cartilage fracture, osteochondral junction separation, subchondral bone collapse, bone:bone separation, and marrow change. Based on these findings, a new five-part grading system was developed. Signal-to-noise characteristics of microscopy coil imaging at 1.5 T were compared to dedicated ankle coil imaging at 3 T.
RESULTS: Microscopy coil imaging at 1.5 T yielded 20% better signal-to-noise characteristics than ankle coil imaging at 3 T. High-resolution MR revealed that osteochondral junction separation, due to focal collapse of the subchondral bone, was a common feature, being present in 28 (45%) of 61 medial central osteochondral lesions. Reparative cartilage hypertrophy and bone:bone separation in the absence of cartilage fracture were also common findings. Complete osteochondral separation was uncommon. A new five-part grading system incorporating features revealed by high-resolution MR imaging was developed.
CONCLUSIONS: High-resolution MRI reveals clinically pertinent features of talar osteochondral lesions, which should help comprehension of symptomatology and enhance clinical decision-making. These features were incorporated in a new MR-based grading system. Whenever possible, symptomatic talar osteochondral lesions should be assessed by high-resolution MR imaging.