A Screw Length of 14 mm Is Sufficient to Avoid the Physis During Juvenile Osteochondritis Dissecans Lesion Repair but This Can Vary Based on Age and Region of the Distal Femur

Abstract

Purpose

To determine the safest screw length that will avoid penetrating the femoral physis for surgical fixation of juvenile osteochondritis dissecans lesions and to compare the safe screw lengths for different regions in the condyles.

Methods

After institutional review board approval, we retrospectively reviewed T1-weighted magnetic resonance images of pediatric patients. Longitudinal axis reference lines were made on the femur. Lines were then placed at 45° anterior and posterior to this axis to simulate screw start points. From these points, we measured the shortest distance from the articular surface to the physis, noting the shortest distances. These measurements simulated screw lengths in the anterior, posterior, and central regions on both the medial and lateral condyle. Statistical analysis was performed to determine the 95% confidence interval for all measurements. Analysis of variance was performed to compare different regions.

Results

A total of 97 knee magnetic resonance images from patients aged 6 to 17 years were reviewed. The safe screw lengths among all samples were 14.1 mm, 20.9 mm, 18.2 mm, 14.4 mm, 17.5 mm, and 14.1 mm for the anteromedial, central medial, posteromedial, anterolateral, central lateral, and posterolateral regions, respectively. There was a difference in simulated screw lengths among all 6 groups (P < .001). There was a moderate correlation between increasing age of the patient and increasing screw length (r = .397, P < .001).

Conclusions

While a screw length of 14 mm appears to be safe in all ages and regions of the distal femur, safe screw length varies based on age and location of the lesion. The posteromedial region has a safe length of 18 mm.

Clinical Relevance

Surgeons must respect the physis when repairing knee osteochondritis dissecans lesions in pediatric patients. Fluoroscopic confirmation should be used to confirm safe screw lengths, and surgeons should use caution when using screws longer than 14 mm (or 18 mm posteromedially), particularly in younger patients.