midshaft

Midshaft refers to the middle portion of a shaft-like structure. In anatomy, it most often describes the central segment of a long bone, known as the diaphysis, which runs between the proximal and distal ends. The midshaft is typically thick-walled and composed mainly of compact bone, with a central medullary (marrow) cavity in many bones. The outer surface is covered by the periosteum, while the inner surface is lined by the endosteum. The region is relatively rigid and designed to withstand bending and torsional loads, while allowing some flexibility for growth and stress distribution. The nutrient artery usually enters through a small foramen in the diaphysis, supplying the inner bone.

Clinically, a midshaft fracture refers to a break that occurs in this central region, away from the ends of the bone. Midshaft fractures are common in weight-bearing or trauma-prone bones such as the tibia, femur, radius, and ulna. Treatment varies by fracture pattern and patient factors, ranging from immobilization in a cast to surgical fixation with intramedullary nails or plates. Healing involves inflammatory and reparative phases with callus formation and remodeling.

The term midshaft can also apply to non-biological shafts or stem-like structures, where it denotes the central portion. See also diaphysis, metaphysis, epiphysis, fracture.