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Three Joints, One Capsule, and One Comfortable Position That Ruins You.
Your elbow is three joints inside one capsule, where three bones meet: the humerus (upper arm) and the ulna and radius (forearm). One joint is a hinge for bending and straightening, one is a pivot that turns your palm up and down, and one couples them together. A healthy elbow moves from straight to about 145 degrees of bend. Daily life needs roughly 30 to 130.
That single shared capsule is why the elbow behaves so strangely after injury. Injure any of the three and all three stop working properly… and the tight capsule wrapped around all of them is why the elbow stiffens faster than any other joint in the arm.
So when someone says “radial head”, “lateral epicondyle” or “olecranon” and you nod along, this is the page that makes those words mean something.
It matters more than it sounds. Most elbow injuries go wrong the same way: the arm goes into a sling at a comfortable bend, it feels better, and three weeks later it won’t straighten. The anatomy below is why your therapist keeps telling you to move it.
What are the three joints of the elbow?
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. The wrist end of that partnership is covered in wrist anatomy.
What bones make up the elbow?
- Humerus. The upper arm bone flares out at the bottom into two rounded surfaces: the capitellum on the outside (meets the radius) and the trochlea on the inside (meets the ulna). Just above them sit the two bony bumps you can feel, the epicondyles. In children, the thin bone just above the joint is the classic break: the supracondylar fracture.
- Ulna. The forearm bone on the little finger side. Its top end is the olecranon, the point of your elbow, the bit you lean on. At the front it has a small lip, the coronoid, that stops the ulna sliding backward.
- Radius. The forearm bone on the thumb side. Its top is a disc-shaped radial head that spins in place when you turn your palm over.
What ligaments hold the elbow together?
- Medial (ulnar) collateral ligament, on the inner side. It resists the arm bending outward, which is the exact force in a throw. Overload it and you get thrower’s elbow. In growing kids the growth plate on that side gives first: little league elbow.
- Lateral collateral ligament, on the outer side. It stops the elbow rotating out of joint, and it’s the ligament that matters most after an elbow dislocation.
- Annular ligament. The ring that holds the radial head against the ulna. In toddlers it’s loose enough that a yank on the hand can slip the radial head partly out of it: pulled elbow.
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.
- 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 front of the elbow has no bony point you can feel, but two big tendons cross it. The brachialis, the main elbow bender, runs straight across the joint, and it’s the muscle climbers strain in climber’s elbow. The biceps tendon dives into the radius, which is why the biceps turns your palm up as well as bending the elbow. A sudden pop at the front of the elbow lifting something heavy is a distal biceps rupture, and that one runs on a short clock, weeks not months.
Not sure which of these it is? Elbow pain by location sorts it by where it hurts.
The nerves that run past 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.
- Median nerve crosses the front of the elbow and passes through the pronator muscle. Squeezed there, it gives forearm ache and thumb-side tingling that looks like carpal tunnel: pronator teres syndrome.
- Radial nerve wraps around the outer side and dives into the forearm muscles just below the elbow. Irritated there, it aches a few finger-widths below where tennis elbow hurts: radial tunnel syndrome.
The full map of which nerve feeds which finger is in the hand nerve map.
Why does the elbow get stiff 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, within whatever your surgeon allows. If stiffness has already set in, see elbow release for stiffness. Wear-and-tear stiffness with locking is a different story: elbow osteoarthritis.
The window: after an elbow injury the window for getting movement back is OPEN in the first weeks, when every degree is cheap. It’s CLOSING through the first 3 months, which is when most of the movement you’ll get by exercise alone comes back. After about 6 months, exercise and splinting gain far less, and the conversation starts to include surgery. Don’t spend the cheap weeks resting it at 90 degrees.
How much elbow movement do 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.
- Straightening matters for reaching, carrying a bag at your side, and pushing up from a chair.
- Bending to around 130 degrees is what gets your hand to your mouth, face and hair. Lose that and eating and grooming get awkward fast.
- Palm up is needed to receive change, carry a tray, or turn a key. Palm down is typing, pouring and the mouse.
Quick self-check. Stand with both arms by your sides, palms forward, and compare how straight each elbow goes. Then touch each shoulder with the hand on the same side. Then tuck both elbows into your sides, bent to a right angle, and turn the palms up to the ceiling and down to the floor. Any difference side to side is worth writing down.
Early movement basics, once your surgeon or doctor says the elbow can move: bend and straighten 10 times, then, with the elbow tucked into your side, turn the palm up and down 10 times. Hold each end position for 5 seconds. Three times a day. Slow and smooth beats forced.
What a hand therapist does for an elbow
- Measures it. Degrees of straightening, bending and rotation, every visit, so progress is a number and not a feeling.
- Splints it when needed. A hinged elbow brace protects healing ligaments while still letting the joint move. For stiffness, static progressive splints hold a gentle stretch for long periods, which a few reps a day can’t match.
- Loads the tendons properly for tennis and golfer’s elbow, with a progression rather than rest.
- Watches the nerves. Ulnar nerve tingling after an elbow injury or surgery is common and needs positioning advice early.
More on that in what a hand therapist does.
Get it checked today if
- After a fall, the elbow looks deformed, or you can’t bend, straighten or turn it at all. Go to the ER. See elbow dislocation and radial head fracture.
- The elbow is hot, red and swollen and you have a fever or feel unwell. An infected bursa or joint needs treating the same day. See olecranon bursitis.
- You felt a pop at the front of the elbow lifting something, followed by bruising in the elbow crease or forearm. See a surgeon within days, not weeks. More in distal biceps rupture.
Get it checked if
- Your ring and little fingers are numb or tingling, or the hand is getting weak or clumsy. See cubital tunnel syndrome.
- The elbow locks or catches partway through a movement. See elbow osteoarthritis.
Three joints, one capsule, one comfortable position that ruins you. Every elbow rehab rule follows from those facts.
Written by Nigel Chua, hand occupational therapist in practice since 2005. Thousands of hands, wrists and elbows assessed and treated. My credentials are here. This article explains; it doesn’t examine. An elbow that still won’t straighten a few weeks after an injury deserves a look now, while the window is still open.
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.