Your elbow is three joints inside one capsule, which is why it behaves so strangely after injury.
One joint is a hinge, one is a pivot that lets you turn your palm up and down, and one couples them together. Injure any of the three and all three stop working properly… and the tight single capsule wrapped around all of them is why the elbow stiffens faster than any other joint in the arm.
The three joints
Ulnohumeral — the hinge. The humerus sits in a deep notch on the ulna. Bending and straightening only; extremely stable. Break the tip of that notch and you have an olecranon fracture.
Radiocapitellar — the radial head spinning against a knob on the humerus. This is where forearm rotation happens at the elbow end, and where a fall onto the outstretched hand usually breaks something: the radial head fracture.
Proximal radioulnar — the radius pivoting against the ulna, held by a ring ligament. Paired with the same joint at the wrist, this is what turns your palm up and down.
Palm-up and palm-down needs two joints, one at each end of the forearm. A problem at either end costs you the whole movement.
Which is exactly why, after a forearm fracture, rotation is the number that predicts how the arm actually works.
Why it stiffens so fast
Three reasons, stacked.
One capsule surrounds all three joints. Any bleeding inside it distends and then scars the whole thing, not one compartment.
The brachialis muscle lies directly across the front of the joint. It bleeds readily and is unusually prone to forming bone within the muscle after trauma, which mechanically blocks straightening.
And the resting position of comfort — about 70 to 90 degrees of bend — is a terrible position to be stuck in. An elbow held comfortably for three weeks is an elbow that will not straighten.
Hence the theme running through every elbow article here: move early, don’t protect. See elbow dislocation and elbow release for stiffness.
The three bony points, and what attaches to each
- Lateral epicondyle (outer) — the wrist and finger extensors anchor here. Overload it and you have tennis elbow
- Medial epicondyle (inner) — the wrist and finger flexors anchor here. Overload it and you have golfer’s elbow or climber’s elbow
- Olecranon (the point) — the triceps attaches here, with a bursa over it. Hence triceps tendinopathy and olecranon bursitis
Three bony points, three tendon problems. Ask someone to put one fingertip on the sore spot and the diagnosis is mostly done.
The nerve that runs over it
The ulnar nerve passes in a groove behind the inner bony point — the “funny bone”. It is superficial, it stretches every time you bend the elbow, and it has nowhere to hide.
That’s why sleeping with bent elbows, leaning on a desk, or a long phone call produces tingling in the ring and little fingers: cubital tunnel syndrome.
The range you actually need
A full elbow goes from 0 to about 145 degrees, with 80 degrees of rotation each way.
But most daily tasks need only 30 to 130 degrees of bend and 50 degrees of rotation each way. That functional arc is what rehab aims at first, and it’s why someone missing the last 10 degrees of straightening often notices very little.
Three joints, one capsule, one comfortable position that ruins you. Every elbow rehab rule follows from those facts.
Every article on this site is written using the Closing Window Method: name the window your condition runs on, find where you are in it, and act while it’s still open.