Osteochondral lesions of the talus: localization and morphologic data from 424 patients using a novel anatomical grid scheme.

BACKGROUND The primary aim of this study was to evaluate the true incidence of osteochondral lesions on the talar dome by location and by morphologic characteristics on MRI. Because no universally accepted localization system for talar dome osteochondral lesions currently exists, we established a novel, nine-zone anatomical grid system on the talar dome for an accurate depiction of lesion location. METHODS We assigned nine zones to the talar dome articular surface in an equal 3 x 3 grid configuration. Zone 1 was the most anterior and medial, zone 3 was anterior and lateral, zone 7 was most posterior and medial, and zone 9 was the most posterior and lateral. The grid was designed with all nine zones being equal in surface area. Two observers reviewed MRI examinations of 428 ankles in 424 patients (211 males and 213 females; mean age 43 years; age range 6 to 85 years) with reported osteochondral talar lesions. We recorded the frequency of involvement and size of lesion for each zone. Statistical analyses were performed using ANOVA and Scheffe tests. RESULTS Four hundred and twenty-eight lesions were identified on MRI. The medial talar dome was more frequently involved (n = 269, 62%) than the lateral talar dome (n = 143, 34%). In the AP direction, the mid talar dome (equator) was much more frequently involved (n = 345, 80%) than the anterior (n = 25, 6%) or posterior (n = 58, 14%) thirds of the talar dome. Zone 4 (medial and mid) was most frequently involved (n = 227, 53%), and zone 6 (lateral and mid) was second most frequently involved (n=110, 26%). Lesions in the medial third of the talar dome were significantly larger in surface area involvement and deeper than those at the lateral talar dome. CONCLUSIONS Our established nine-grid scheme is a useful tool for localizing and characterizing osteochondral talar lesions, which are most frequently located in zone 4 at the medial talar dome, and second most in zone 6 at the lateral talar dome near its equator. Medial talar dome lesions are not only more common but are larger in surface area and in depth than lateral lesions. Posteromedial and anterolateral lesions rarely were found.