Humerusschaft

Humerusschaft, or humerus shaft, is the long central portion of the humerus, the upper arm bone. It extends from the region just below the proximal end near the tubercles to the distal metaphysis that transitions into the distal humerus near the elbow. The shaft forms the principal body of the bone, connecting the shoulder region with the elbow joint.

Anatomy and surfaces: The diaphysis is predominantly cortical bone surrounding a medullary cavity that contains bone marrow in adulthood. The outer surface is covered by the periosteum and the inner surface by the endosteum. The anterolateral surface bears the deltoid tuberosity, where the deltoid muscle attaches. The posterior aspect contains the radial groove, or spiral groove, through which the radial nerve and profunda brachii vessels run. The nutrient foramen typically opens on the anteromedial surface. The shaft is roughly cylindrical in its midportion and becomes broader distally toward the metaphysis.

Clinical significance: The humerus shaft is a common site of fractures, often resulting from direct trauma or falls. Midshaft fractures may put the radial nerve at risk due to its proximity in the spiral groove, with possible nerve palsy as a complication. Treatment considerations include restoration of alignment and healing, with radiographic monitoring for proper union and to prevent complications such as malunion or nonunion.