A meta-analysis on the anatomical variability of the brachial plexus: Part II — Branching of the supraclavicular part

Introduction: The anatomy of the supraclavicular part of the brachial plexus is highly variable, therefore the aim of this study was to perform a systematic review and meta-analysis of the various origins of the long thoracic, dorsal scapular, suprascapular and subclavian nerves. Materials and methods: Major electronic databases were searched to identify all cadaveric studies investigating the morphology of the supraclavicular part of the brachial plexus. Data on the origins of these nerves were extracted and classified. A random effects meta-analysis was performed to state the pooled prevalence estimates. Results: A total of 26 studies, constituting a total of 1021 cases, were deemed eligible for inclusion into the meta-analysis. The usual origin of the long thoracic nerve from the C5, C6 and C7 roots was observed in 78.1% (95% CI 69.4–86.7%) of cases and 21.9% (95% CI 13.3–30.6%) had unusual origins. An accessory long thoracic nerve occurred in 0.3% (95% CI 0–0.7%) of cases. The overall prevalence of the dorsal scapular nerve arising from its usual origin the C5 root was found in 85.2% (95% CI 75.7–94.6%) of cases, while 14.8% (95% CI 5.4–24.3%) appeared abnormal. The suprascapular nerve emerged from its usual point on the superior trunk in 89.8% (95% CI 85.1–94.4%) of cases and in 10.2% (95% CI 5.6–14.9%) of cases had a variable origin. An accessory suprascapular nerve was present in 0.2% (95% CI 0–0.6%). Two possible sites of origin of the subclavian nerve were noted and the typical origin from the superior trunk was found in 98.3% (95% CI 96.3–100%) of cases and variable origin from the C5 root in 1.7% (95% CI 0–3.7%). All unusual origins of each nerve were much less common. Conclusions: The nerves emerging from the supraclavicular part of the brachial plexus express a wide spectrum of potential origins. Based on their various origins, a new classification system for all the nerves belonging to the supraclavicular part was proposed. Knowledge of these variations and their prevalence data is important to prevent iatrogenic injuries and to state useful landmarks for interventions in the axilla.