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

Abstract

Retrospective review of high-resolution MR imaging features of talar dome osteochondral lesions and development of new classification system based on these features. Over the past 7years, 70 osteochondral lesions of the talar dome from 70 patients (49 males, 21 females, mean age 42years, range 15-62years) underwent high-resolution MR imaging with a microscopy coil at 1.5T. 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 1.5T were compared to dedicated ankle coil imaging at 3T. Microscopy coil imaging at 1.5T yielded 20% better signal-to-noise characteristics than ankle coil imaging at 3T. 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. 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.