• Ryan O'Shea, Jyoti Panwar, William Chu Kwan, Jennifer Stimec, Mark W Camp, and Martin Gargan.
• Kaiser Permanente, San Diego, California.
• J Bone Joint Surg Am. 2019 Dec 4; 101 (23): 2101-2110.

BackgroundThe surgical anatomy of upper-extremity peripheral nerves in adults has been well described as "safe zones" or specific distances from osseous landmarks. In pediatrics, relationships between nerves and osseous landmarks remain ambiguous. The goal of our study was to develop a model to accurately predict the location of the radial and axillary nerves in children to avoid iatrogenic injury when approaching the humerus in this population.MethodsWe conducted a retrospective review of 116 magnetic resonance imaging (MRI) scans of entire humeri of skeletally immature patients; 53 of these studies met our inclusion criteria. Two independent observers reviewed all scans. Arm length was measured as the distance between the lateral aspect of the acromion and the lateral epicondyle. We then calculated the distances (defined as the percentage of arm length) between the radial nerve and distal osseous landmarks (the medial epicondyle, transepicondylar line, and lateral epicondyle) as well between the axillary nerve and the most lateral aspect of the acromion.ResultsThe axillary nerve was identified at a distance equaling 18.6% (95% confidence interval [CI], ±0.62%) of arm length inferior to the lateral edge of the acromion. The radial nerve crossed (1) the medial cortex of the posterior part of the humerus at a distance equaling 63.19% (95% CI: ±0.942%) of arm length proximal to the medial epicondyle, (2) the middle of the posterior part of the humerus at a distance equaling 53.9% (95% CI: ±1.08%) of arm length proximal to the transepicondylar line, (3) the lateral cortex of the posterior part of the humerus at a distance equaling 45% (95% CI: ±0.99%) of arm length proximal to the lateral epicondyle, and (4) from the posterior to the anterior compartment at a distance equaling 35.3% (95% CI: ±0.92%) of arm length proximal to the lateral epicondyle. A strong linear relationship between these distances and arm length was observed, with an intraclass correlation coefficient of >0.9 across all measurements.ConclusionsThe positions of the radial and axillary nerves maintain linear relationships with arm lengths in growing children. The locations of these nerves in relation to palpable osseous landmarks are predictable.Clinical RelevanceKnowing the locations of upper-extremity peripheral nerves as a proportion of arm length in skeletally immature patients may help to avoid iatrogenic injuries during surgical approaches to the humerus.

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