22u-D/1.1   Ulna, bowing

Traumatic bowing is a plastic deformity of the ulna. The cortical bone is subject to tensile forces on the convex side and compressive forces on the concave side. If this exceeds the elastic limit, but not the load to failure, deformity will occur without radiological evidence of fracture.

Bowing is more common in young children or in older children with vitamin D deficiency.

Note: In all cases of an isolated ulnar fracture, it is important to confirm the normal alignment of the radiocapitellar joint and specifically exclude a Monteggia lesion.

Note: Plastic deformity of a long bone is often underestimated. This can easily be overlooked in the ulna although it is a straight bone. Knowledge of the radiological anatomy and correct axis of the ulna is therefore important.