Elbow joint

Function

Three joints in one capsule

The elbow is a hinge joint formed by the humeroulnar joint¹. There, the pulley-shaped trochlea of the humerus (upper arm bone) sits in the trochlear notch of the ulna¹. The ulna is the forearm bone on the little-finger side, and the radius is the one on the thumb side. Two more joints sit with the hinge, inside the same joint capsule¹. The humeroradial joint lies between radius and humerus, and the proximal radioulnar joint between the upper ends of radius and ulna^1,6.

The radius has a disc-shaped head¹. A shallow dip on top of the head meets the capitellum, a rounded knob on the humerus¹. At the proximal radioulnar joint, the annular ligament holds the head against a notch on the ulna¹. This is a pivot joint: the radius rotates there when the forearm turns palm up or palm down¹.

The three joints work together to allow four movements⁶. They are flexion (bending), extension (straightening), pronation (turning the palm down) and supination (turning the palm up)⁶.

The back and top of the upper ulna form the olecranon, the bony tip of the elbow¹. The olecranon bursa lies at that tip, under the skin¹. A bursa is a small fluid-filled sac that cushions tissues where they rub.

What holds it steady

The capsule is thin at the front and back¹. At the sides, strong ligaments (tough bands of tissue that hold bones together at a joint) thicken it¹. They stop side-to-side movement and hyperextension (straightening a joint past its normal limit)¹. The main ligaments are these:

• On the inner side, the triangular ulnar collateral ligament runs from the medial epicondyle to the inner side of the upper ulna¹. The medial epicondyle is the inner bony bump at the elbow end of the upper arm bone.
• On the outer side, the radial collateral ligament runs from the lateral epicondyle, the outer bony bump¹.
• The radial collateral ligament blends into the annular ligament, a ring around the radial head¹.

What resists sideways bending

Valgus stress bends the forearm outward at the elbow, and varus stress bends it inward⁷. A preliminary study of four elbow specimens measured what resists each⁷. With the elbow straight, three parts shared the valgus resistance equally⁷. They were the collateral ligament on the inner side, the front of the capsule and the bony joint⁷. At 90 degrees of flexion, the inner-side ligament gave about 55% of it⁷.

In the same four specimens, the joint surfaces and the front of the capsule mainly resisted varus stress⁷. The ulnar collateral ligament page covers valgus restraint in detail.

How far it moves

In 352 healthy adults, the dominant arm reached a mean of 146 degrees of active flexion, 80 of pronation and 87 of supination⁸.

A study had 33 people with normal elbows do fifteen daily activities². Most fitted within an elbow flexion arc of 100 degrees, running from 30 up to 130². They also fitted within 100 degrees of forearm rotation, 50 degrees each of pronation and supination².

With the elbow straight and the palm facing forward, the forearm angles outward from the upper arm’s line by 5 to 15 degrees¹. This is the carrying angle¹.

The loads it carries

A review of elbow biomechanics notes that the upper limb is often called non-weightbearing⁹. Yet it states that forces across the elbow are very large when the joint straightens from a bent position⁹. The reason it gives is that the triceps has a small moment arm (a muscle’s leverage) and must generate high force⁹. It adds that the contact force between ulna and humerus may be as much as twenty times the load on the hand and wrist⁹.

In nine healthy men doing the push-up, peak force on the elbow along the forearm averaged 45% of body weight¹⁰. That was with the hands in the normal position, and it was significantly lower with the hands placed further apart or further up¹⁰.

Motion analysis of 26 highly skilled, healthy adult baseball pitchers calculated an elbow varus torque (a turning force) of 64 newton-metres¹¹. It came shortly before the arm reached its furthest outward rotation¹¹. A video and muscle-activity study of seven healthy adult baseball pitchers reported a varus torque of 120 newton-metres, resisting valgus stress¹². The ulnar collateral ligament page reports more on pitching.

Breakdown

Dislocation

A dislocation is when a bone is forced fully out of its normal place at a joint. Elbow dislocations are classed as simple, with no fracture, or complex, with a fracture¹³. Studies have counted how often it happens:

• A national sample of United States emergency departments from 2002 to 2006 gave an estimated rate of 5.21 dislocations in each 100,000 person-years³.
• In a study of United States emergency department data, people aged ten to nineteen had the highest rate, 6.87 per 100,000 person-years³.
• In United States emergency department data, 44.5% of dislocations in people aged ten or older happened in sports³.
• A later study of emergency department data, for 2014 to 2023 and without children under ten, estimated 3.58 per 100,000 person-years¹⁴.

Three elbow surgeons reviewed 62 online videos of elbow dislocations¹⁵. They judged that 92% happened at or near full extension¹⁵. Most showed a valgus moment (89%), a load along the arm (90%) and progressive supination (94%)¹⁵. The authors noted that this differs from earlier cadaver studies, in which elbows dislocated in flexion¹⁵. They suggested that some dislocations start with failure on the inner side under valgus force¹⁵.

Osteochondritis dissecans in young athletes

In osteochondritis dissecans, a segment of joint cartilage separates from the bone beneath it⁹. A review describes it as uncommon in the general population and typical of adolescent athletes who throw overhead or bear weight on their arms⁹. The most common site it names is the capitellum of the dominant elbow⁹.

A review states that the cause is still unclear⁹. It adds that repeated valgus forces, which compress the outer side of the joint, are thought to be the main trigger⁹.

One study screened the throwing elbow of 2,433 junior high and high school baseball players with ultrasound (a scan made with sound waves)⁴. Their mean age was 14.5 years⁴. It found osteochondritis dissecans of the capitellum in 82 elbows, or 3.4%⁴. The authors describe this figure as including latent cases⁴. Compared with players without a lesion, players with one:

• had begun playing baseball at an earlier age and had played competitively for longer⁴
• reported more present and more past elbow pain⁴
• did not differ in the position they played⁴

Stiffness after injury

A literature review names the most common causes of elbow stiffness¹⁶. They are trauma, including surgery for trauma, arthritis after trauma, and heterotopic ossification (bone forming in soft tissue, where bone does not normally grow)¹⁶. The review links the elbow’s tendency to stiffen to its closely fitting bones and its confined joint space¹⁶. It also names the tight collateral ligament complexes and the muscles lying close around the joint¹⁶.

Osteoarthritis

One study took X-rays of 318 randomly sampled residents of a Japanese town, aged over 50¹⁷. It left out anyone with a condition that could cause secondary elbow arthritis¹⁷. The X-rays showed primary elbow osteoarthritis (a long-term joint disease in which the cartilage lining the joint wears away) in 25.2%¹⁷. In 0.9%, it came with pain on movement or tenderness¹⁷.

Olecranon bursitis

In olecranon bursitis, also called student’s elbow, the bursa between the skin and the olecranon is inflamed¹. Israel Defense Forces records from 2005 to 2015 put it at 29 per 100,000 person-years in soldiers overall and 97 in combat duty¹⁸.

Recovery

After a dislocation

Three follow-up studies report how people fared years after an elbow dislocation^19,20,21. Two used the DASH, a questionnaire that scores disability of the arm, shoulder and hand.

• Of 110 adults reviewed a mean of 88 months after a simple dislocation, 56% reported leftover stiffness and 62% leftover pain¹⁹. Their function scores were generally good, with a mean DASH score of 6.7 points¹⁹.
• Seventy-one patients were followed for a mean of 19.3 years after a simple dislocation managed with brief splinting and early movement²⁰. They averaged 5.22 points on the DASH, and none had later surgery for instability²⁰.
• Of 52 patients re-examined an average of 24 years after an elbow dislocation, half had no remaining symptoms or signs²¹.

How motion returns after injury

In 25 people followed prospectively for a year after a traumatic elbow injury, range of motion kept improving up to one year⁵. At one year, 22 had a flexion-extension arc above 100 degrees⁵.

In 25 people followed prospectively for a year after a traumatic elbow injury, range of motion kept improving up to one year.

What studies of osteochondritis dissecans found

A retrospective study (one that looks back at past cases or records) covered young patients with early lesions of the capitellum²². It called the condition capitellar osteochondrosis and graded lesions in stages²². In it, 101 patients stopped using the elbow heavily for 6 months or more²². Among them, stage I lesions healed in 90.5% and stage II lesions in 52.9%²². Among 75 patients who did not stop, 22.7% healed²².

A 2016 review stated that the natural course of the condition in the capitellum was still undefined⁹. A review reports one follow-up of 31 patients, a mean of 23 years after osteochondritis dissecans of the elbow⁹. In it, 42% had pain or reduced range of motion, and one-third had degenerative changes on X-rays⁹.

Connections

The bones that form it

The humerus joins the radius and ulna at the elbow²³.

The muscles and tendons that cross it

The biceps brachii, on the front of the upper arm, flexes the forearm¹. The triceps brachii, on the back, extends it¹. The distal biceps tendon attaches to the radial tuberosity, a bump on the radius near the elbow²⁴. A systematic review describes the triceps as inserting through its tendon onto the tip of the olecranon²⁵.

A review of specimen studies lists three primary and four secondary constraints of the elbow¹³. Two of the secondary ones are tendons: the common flexor-pronator tendon and the common extensor tendon¹³. The common flexor tendon and common extensor tendon pages cover overuse of each.

The ligament and nerves beside it

The ulnar collateral ligament runs down the inner side of the joint¹. The ulnar collateral ligament tear page reports studies of its tears.

The ulnar nerve passes through the cubital tunnel on the inner side of the elbow²⁶. Above the elbow crease, the median nerve gives branches to the elbow joint²⁷.

Exercises that load it

In nine healthy men doing push-ups, valgus torque at the elbow rose significantly when the hands were placed further up¹⁰. In a dip, the exerciser lowers the body by bending the elbows and returns by straightening them²⁸. In 21 men and 4 women, the elbow moved through a mean range of about 93 degrees in the pull-up²⁹. Related exercise pages: push-up, dip, pull-up.

Sources

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Every source the library cites

Changes

• October 8, 2026 Revised to report sources added after their published corrections were read