Topographical anatomy of the posterior elbow region during fetal development.

We studied the topography of the elbow region with special regard to the ulnar nerve during fetal life. Plastinated 600 microns thick sections through the right and left arms of ten fetuses with a crown-rump length (CRL) of 105 to 360 mm and of a newborn infant were investigated. The ulnar groove does not appear on the dorsal side of the medial humeral epicondyle earlier than at a crown-rump length of 130 mm. It provides the entrance into a formerly described fibro-osseous tunnel called the cubital tunnel. Its floor is formed by the posterior bundle of the ulnar collateral ligament, which bulges medially on flexion of the elbow joint. Up to 270 mm CRL it is composed of rather loosely arranged connective tissue fibres. Later on, its fibres are densely packed and show a parallel orientation. The ulnar nerve is pushed medially but remains behind the medial epicondyle. None of the specimens showed displacement to the anterior site of the elbow joint. An aponeurotic arch bridging the humerus and ulna and covering the ulnar nerve medially could not be identified. The findings in the newborn infant did not reveal any significant differences compared to the fetal specimens.