Age, Sex, and Location Impact Osteochondritis Dissecans Lesion Depth and Their Relation to the Physis in Skeletally Immature Knees.

PURPOSE: To characterize the size of medial and lateral femoral condyle osteochondritis dissecans (OCD) lesions and their relation to the physis in skeletally immature patients. METHODS: Skeletally immature patients from 2008 to 2023 with medial or lateral femoral condyle OCD lesions on magnetic resonance imaging were included. At the center of each OCD lesion, 2 reviewers independently measured on coronal and sagittal cuts: (1) lesion depth, (2) shortest distance from subchondral bone to open physis, and (3) shortest distance from cartilage to open physis. Intraclass correlation coefficients for inter-rater reliability and a mixed effects regression model were used to determine repeatability and between-group differences. RESULTS: A total of 123 surgically treated knees from 101 patients were included. Among 82 medial lesions, mean lesion depth from the subchondral bone was 7.51 mm [range 4.10-12.8], mean distance from subchondral bone-to-physis was 27.6 mm [19.1-36.8], and mean distance from cartilage-to-physis was 30.3 mm [21.9-38.1]. Subchondral bone-to-physis distance was smaller in women versus men (P = .026) and in patients under 13 versus over 13 (P = .006). For the 41 lateral OCD lesions, mean depth was 7.97 mm [3.78-12.5], subchondral bone-to-physis was 21.4 mm [14.8-26.5], and cartilage-to-physis distance was 24.4 mm [19.0-28.7]. Subchondral bone-to-physis distance did not substantially differ between men and women (P = .560); however, subchondral bone-to-physis distance was smaller in those under versus over age 13 (P = .027). The mean distance between the OCD lesion base and the physis (safe zone) was 20.0 mm [12.0-28.3] for medial lesions and 13.4 mm [5.33-17.5] for lateral lesions. CONCLUSIONS: OCD lesion characteristics in skeletally immature knees vary by age, sex, and location with younger patients (<13), female patients, and lateral lesions being closer to the physis than their counterparts. In our cohort, a drill or screw length of 16 mm would allow complete lesion penetration while leaving a minimum 3 mm safe zone. LEVEL OF EVIDENCE: Level IV, retrospective case series.