• Ena Nielsen, Lindsay M Andras, and David L Skaggs.
• Children's Hospital Los Angeles, Los Angeles, CA.
• J Pediatr Orthop. 2018 May 1; 38 (5): e292-e295.

BackgroundIn adults, a relative "safe zone" for lateral approaches to the elbow has been well described in efforts to reduce iatrogenic injury, typically a minimum of 6 cm proximal to the lateral epicondyle. To avoid iatrogenic injury to the radial nerve intraoperatively, we investigated the distance of the nerve from the distal humeral physis in children.MethodsAll patients who had axial and coronal T1-weighted magnetic resonance imagings of the humerus and elbow between 2005 and 2015 were eligible. Patients were excluded if there was any pathology causing significant alteration to the normal anatomy of the distal humerus or surrounding soft tissue. The axial cut in which the radial nerve was positioned along a line passing through the center of the humerus in the transverse plane was identified, and the location of the nerve was marked. This axial cut was cross-referenced with the corresponding coronal view. The distance along the lateral edge of the humerus in a straight line from the marked location of the radial nerve to the distal humeral physis was measured.ResultsIn total, 21 magnetic resonance imagings of 20 patients met the inclusion criteria. The mean distance of the radial nerve proximally from the distal humeral physis was as follows by age group: below 1-year old=1.7 cm (range, 1.2 to 2.5 cm); 1 to 2-years old=2.8 cm (range, 1.8 to 3.2 cm); 4 to 5-years old=5.3 cm (range, 5.1 to 5.5 cm); 6-years old and above=7.3 cm (range, 6.0 to 9.2 cm). For below 6-years old, when age was multiplied by 1 cm to define a predicted safe zone all radial nerves were found proximal to this. All patients 6 years and above had measurements that fell into the adult range of >6 cm, whereas no patients below 6-years old had measurements in this range.ConclusionsThe distance of the radial nerve proximally from the distal humeral physis can be safely approximated for children below 6 years of age by multiplying patient age in years by 1 cm. By the age of 6 the distance of the radial nerve falls within the adult range (>6 cm).Level Of EvidenceLevel III.

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