To better understand nursemaid's elbow, it helps to understand the anatomy of the elbow joint.

The elbow consists of three bones:

• Humerus: the large, long bone in the upper arm
• Radius: one of the long bones in the forearm
• Ulna: one of the long bones in the forearm

These three bones are bonded together by strong bands, called ligaments. The ligaments, muscles and tendons keep the bones of the elbow together during movement.

The annular ligament is a band of fibers that surround the radial head at the elbow. This ligament is weak in young children, which allows it to be easily injured.

Anatomy of the elbow:

• Bones of the arm
• Area of weakness in nursemaid's elbow