LAUSR

Purpose: During percutaneous pinning of the pediatric distal femur, iatrogenic vascular damage in the medial thigh is a frequent concern. The proximity of a proximal-medial pin to these vessels has never been studied in children. This study describes a radiologic vascular safe zone that is easily visualized during surgery (wherein the superficial femoral vessels are safely posterior). Methods: Patients ≤16 years old with magnetic resonance imaging of one or both femora between 2005 and 2020 were retrospectively reviewed. The “at-risk level” (ARL) was defined as the distal-most axial image with a femoral vessel anterior to the posterior condylar axis. A standardized retrograde lateral-to-medial pin was templated. A correlation matrix and least squares regression identified age and physeal width (PW) as ideal independent variables. A vascular safe zone above the medial femoral condyle (MFC) was modeled as a multiple of PW (i.e. x*PW) and needed to satisfy 3 age-dependent criteria: (1) at the ARL, the pin is medial to the vessels, (2) the pin exits the medial thigh before the ARL, and (3) the chosen “vascular safe zone” (x*PW) is always distal to the ARL. Results: Forty-three patients averaging 7.1±3.9 (0.3-16) years old were included. Intra-Class correlation coefficients were excellent (0.92-0.98). All measurements strongly correlated with age (r=0.76-0.92, P<0.001) and PW (r=0.82-0.93, P<0.001). All patients satisfied criteria 1. Criteria 2 was satisfied in all patients ≥6 years old, 86% of children 4-5, and only 18% of children ≤3. In children >3 years old, the largest safe zone that satisfied criteria 3 was 2×PW. On average, the ARL was 2.5×PW (99% CI 2.3-2.7) above the MFC. The average ARL in children ≥6 years old was significantly higher than 2×PW (162 mm vs. 120 mm, P<0.001). Conclusion: During passage of a distal femur pin into the medial thigh, children ≥6 years old have a vascular safe zone that extends 2×PW proximal to the MFC. Surgeons should be cautious with medial pin placement in children 4-5 years old and, if possible, avoid this technique in children ≤3. Level of Evidence: IV.