Elbow

What it is

Three articulations sharing a single joint capsule:

• Humeroulnar — the hinge proper, between the trochlea of the humerus and the trochlear notch of the ulna. This is a genuinely deep, interlocking fit.
• Humeroradial — between the capitulum of the humerus and the head of the radius
• Proximal radioulnar — between the head of the radius and the ulna, held by the annular ligament

Unlike the shoulder, the elbow has real bony stability. The olecranon of the ulna hooks into a fossa on the back of the humerus, which is what stops the joint extending past straight.

The carrying angle — the slight outward angle of the forearm when the arm hangs straight with the palm forward — comes from the shape of the trochlea. It varies between people and is on average larger in women.

What it does

Flexes and extends, at the hinge. Separately, it permits pronation and supination, the radius rotating around the ulna at the proximal radioulnar joint and again at the wrist end.

Those are two different mechanisms sharing a capsule, which is why you can turn your palm over with your elbow held still.

What loads it

Pressing, pulling, carrying, and every resisted elbow movement.

What is commonly got wrong about it

"Tennis elbow" and "golfer's elbow" as inflammation. Both are named with an "-itis" implying inflammation, and tissue studies have generally found degenerative rather than inflammatory change. Both are now more often called tendinopathies. Neither is usually caused by the sport it is named after.

That hyperextension means damage. Some people extend past straight, which is normal variation in joint laxity rather than a fault.

That elbow pain is a training problem to be worked around. Persistent elbow pain warrants assessment; this site does not give rehabilitation advice.