Validation of 9-Grid Scheme for Localizing Osteochondral Lesions of the Talus

A 9-grid scheme has been integrated into the foot and ankle literature to help clinicians and researchers localize osteochondral lesions of the talus (OLTs). We hypothesized that fellowship-trained orthopedic foot and ankle surgeons would have a high rate of intra/inter-observer reliability when localizing OLTs, therefore validating the scheme.

We queried our institution's foot and ankle radiographic database for magnetic resonance images with OLTs. Each MRI was reviewed by the senior author, and 2 key images (widest OLT diameter) from each tangential view were copied and combined onto one slide. Fifty consecutive deidentified images of ankles were then sent to 4 practicing fellowship-trained foot and ankle surgeons. Each was asked to identify which zone the OLT was localized within. A radiologist's report served as the control. Statistical analyses were performed using Cohen and Fleiss kappa tests.

The reviewers demonstrated majority consensus on 45/50 images with substantial agreement for zones 4 and 6. The interobserver reliability was moderate with a κ = 0.55. The mean intraobserver reliability was substantial, with a κ = 0.79. A musculoskeletal radiologist determined there were 3 lesions in zone 7, 18 lesions in zone 4, and 29 lesions in zone 6.

This study is the first to critically evaluate the 9-grid scheme and its reliability among orthopedic foot and ankle surgeons. Our study found that the 9-grid scheme is an accurate method of localization for OLTs with high intra- and moderate interobserver reliability between surgeons.

Level IV, retrospective diagnostic study.