Bones of the Upper Limb: Humerus

The humerus consists of three main regions: the proximal head, the shaft, and the distal condyles. The head articulates with the scapula's glenoid cavity to form the shoulder joint. The shaft contains the deltoid tuberosity for muscle attachment. The distal end features the trochlea and capitulum, which articulate with forearm bones to form the elbow joint.

The greater and lesser tubercles are prominent projections lateral to the humeral head that anchor the rotator cuff muscles. These muscles stably attach the humerus to the scapula, providing shoulder stability. Between the tubercles lies the bicipital groove, which allows the bicep tendon to pass through and assist in arm flexion.

The surgical neck is a clinically significant narrowed region where the humeral shaft joins the proximal end, located just below the tubercles. It is a common fracture site due to its structural weakness. Understanding its location is important for diagnosing and treating upper limb injuries.

The humerus has three fossae that position forearm bones during elbow movement. The coronoid fossa receives the ulna's coronoid process when flexed. The radial fossa accommodates the radius head during flexion. The olecranon fossa receives the ulna's olecranon process when the forearm is fully extended.

The radial groove is a posterior depression on the humeral shaft that provides passage for the radial nerve. This nerve controls motor and sensory responses of arm muscles during elbow extension. Damage to this groove or nerve can impair arm movement and sensation.

The ulnar nerve crosses the elbow joint near the humerus. When struck, the nerve gets rubbed against the bone, producing the characteristic tingling sensation commonly called hitting the funny bone. This demonstrates the anatomical relationship between nerves and bone structures.

The humerus undergoes structural changes throughout life as part of changes in the appendicular skeleton with age. These modifications affect bone density, strength, and susceptibility to fractures. Understanding age-related changes helps explain why older individuals are more prone to humeral fractures.