Neurovascular anatomy of the adult female medial arm in relationship to potential sites for insertion of the etonogestrel contraceptive implant

Abstract

ObjectiveAnatomic assessment of the medial upper arm to identify potential sites for insertion of the etonogestrel (ENG) implant. Study designForty female cadaveric arms were dissected. Two rows of 1×2-cm dissection windows were created in the inner arm overlying the triceps approximately 2–3 and 4–5 cm posterior to the bicipital sulcus (sulcus). The primary window was 8–10 cm proximal to the medial epicondyle and approximately 2–3 cm posterior to the sulcus. Neurovascular structures within each window were identified. The entire medial upper arm was dissected to visualize underlying structures. ResultsMean age (± SD) of cadavers at death was 72.0±11.0 years. Arm measurements at the primary window were circumference 28.2±4.8 cm [range: 21–41], skin thickness 0.6±0.2 mm [0.3–1.0] and subcutaneous tissue thickness: 12.3±4.9 mm [4.7–21]. The basilic vein and the medial brachial cutaneous, ulnar and medial antebrachial cutaneous nerves were located in 40%, 58%, 40% and 18% of the primary windows, respectively. No major neurovascular structures were located 3–5 cm posterior to the sulcus. More neurovascular structures were identified overlying the biceps than triceps. Elbow flexion with the hand underneath the head displaced the ulnar nerve anteriorly towards the sulcus. ConclusionAs no major neurovascular structures were identified overlying the triceps 8–10 cm proximal to the medial epicondyle and 3–5 cm posterior to the sulcus, ENG implant insertion at this location may minimize risk of injury associated with improper deep insertion. Elbow flexion deflects the ulnar nerve away from this area and may further decrease risk of injury secondary to inadvertent deep insertion. ImplicationsAlthough a limited cadaver study, this anatomic assessment provides rationale for insertion of the ENG implant overlying the triceps 8–10 cm proximal to the medial epicondyle and 3–5 cm posterior to the sulcus. This area is theoretically safer for insertion of the ENG implant than areas of the inner arm where major neurovascular structures are commonly located.