Humerus

Function

Where the bone sits

Among the bones of the upper limb, the humerus is the largest, and it forms the skeleton of the upper arm^1,2. Above, it meets the scapula (shoulder blade) at the glenohumeral joint, the main shoulder joint¹. Below, it meets the radius and ulna, the two forearm bones, at the elbow¹.

The upper end: a ball and two bumps

The head of the humerus is a large, smooth, rounded surface that faces inward^1,2. It sits against the glenoid cavity (the shoulder socket) of the shoulder blade, and the two form a ball-and-socket joint^1,2.

Two tubercles (bony bumps) sit beside the head: the greater tubercle on the outer side and the smaller lesser tubercle at the front². Both are anchor points for muscles that work across the shoulder². The anatomical neck is the rim around the smooth head, marking it off from the two tubercles^1,2. Just below the tubercles, the surgical neck is where the wide upper end narrows into the shaft^1,2. Between the tubercles runs the bicipital groove, which carries a tendon of the biceps brachii².

The shaft and its groove

The shaft of the humerus is shaped like a cylinder¹. It has the deltoid tuberosity on its outer side and the radial groove, also called the spiral groove, on its back¹. The deltoid tuberosity is a rough, V-shaped patch halfway down the shaft where the deltoid (the rounded muscle that caps the shoulder) attaches². The radial groove runs along the back and outer side of the middle third of the bone⁶. The radial nerve and the profunda brachii artery (the deep artery of the upper arm) run in it⁶.

The lower end: the elbow surfaces

Toward the elbow, the bone flattens and has two epicondyles (bony bumps where muscles attach) and a ridge above the outer one². These are anchor points for muscles that move the forearm, wrist and hand². The medial epicondyle (the inner bony bump) is the larger of the two². The strong gripping muscles of the front of the forearm start there². The weaker muscles of the back of the forearm start from the lateral epicondyle, the bump on the outer side².

The lower end has two joint surfaces². The trochlea is shaped like a pulley and meets the ulna². The capitulum is a small knob just outside it that meets the radius².

Where it grows in length

The growth plate (the layer of cartilage where a bone grows longer) at the top of the humerus supplies about 80% of its length growth⁷. A systematic review gives up to 80% and says the plate typically closes between 16 and 20 years of age⁸.

How throwing and lifting load it

A review of arm stress fractures (small cracks in a bone from repeated loading) describes lifts like the bench press and overhead press⁹. In these, the deltoid and rotator cuff (four muscles that steady the shoulder joint) counter the pull of the pectoralis major, the large chest muscle⁹. This balance moves some stress off the humerus, which the review calls stress shielding⁹.

Breakdown

Breaks at the upper end

Breaks of the upper humerus are common, and older people have them most³. Osteoporosis is a disease in which bones become thin and weak. Among fractures linked to it in older people, these breaks rank third, after the wrist and the hip¹⁰.

One study counted upper-humerus fractures in a Finnish town from 2006 to 2010¹⁰. It found 678 people with these breaks, and 73% of them were women¹⁰. The breaks became more common with age¹⁰. Of 692 breaks, 62% were two-part fractures (the bone split into two main pieces), and 78% were managed in a sling without surgery¹⁰.

Group in the Finnish study	New upper-humerus fractures per 100,000 people a year
Everyone	8210
Women	11410
Men	4710

Breaks of the shaft

Breaks of the shaft make up 1% to 3% of fractures overall, and happen in both young and older people¹¹.

Nerves close to the bone

The radial nerve runs in the groove on the back of the shaft⁶. Two systematic reviews counted radial nerve palsy with shaft fractures^4,12:

• One found radial nerve palsy in 11.8% of shaft fractures, or 532 of 4,517⁴.
• An updated review of studies from 1964 to 2017 put it at 12.3%, or 890 of 7,262¹².

Stress fractures in sport and lifting

The review of stress fractures in the arm describes Little League shoulder as one type⁹. It calls it a twisting stress fracture through the upper growth plate of the humerus⁹. It reports it in roughly 5% of Little League players aged 9 to 12⁹. A systematic review of 23 studies covered 266 young athletes with Little League shoulder, with an average age of 12.8⁸. Widening of the upper growth plate of the throwing arm was reported in 99% of them⁸.

Frequent weightlifting rarely leads to humeral stress fractures, the review reports, and the bench press is the lift most often involved⁹. It describes muscle fatigue as weakening stress shielding and raising the bending load on the bone⁹.

Recovery

How a broken bone mends

An anatomy textbook describes how a broken bone heals in stages²:

• First, a blood clot called a fracture hematoma forms².
• Next, calluses (new tissue that bridges the break as it heals) of cartilage and bone form².
• Later, spongy bone (light bone made of a honeycomb of thin struts) replaces the cartilage in the callus².
• Remodelling can then remove the outward signs of the break².

A review of fracture healing reports that repair usually restores bone’s structure and function, but about 10% of fractures do not heal normally¹³.

A Cochrane review (a systematic review done to the Cochrane Collaboration’s published standards) calls upper-humerus breaks a serious injury, frequent in older people³. Getting back the use of the arm can take several months³. Some loss of movement and some pain are common long-term problems³.

What studies of surgery found

The same review looked at randomised trials in upper-humerus fractures³. Its 47 trials were mostly in women, mainly aged 60 or over, and 10 trials of 717 people looked at displaced breaks³. It found high-certainty evidence that surgery gave no clinically important gain in shoulder function at one and two years over non-surgical care³. It also found low-certainty evidence of a higher risk of further surgery after surgical care³.

Two reviews compared surgery with non-surgical care for breaks of the shaft^11,14:

• One pooled 12 studies of 1,406 adults. It found fewer nonunions (broken bones that fail to join and heal) after surgery, but more deep infections¹¹.
• A meta-analysis (a study that pools the results of several earlier studies) of 17 studies reported trends that favoured surgery over splint or brace care¹⁴. The trends were toward faster return of arm function and fewer nonunions and repeat procedures¹⁴.

For radial nerve palsy with shaft fractures, one systematic review found that 70.7% of nerves recovered on their own in people managed without surgery⁴. An updated review of palsy with humeral fractures found recovery on its own in 77.2% managed without surgery¹². It found recovery in 89.8% of those who had surgical exploration and fracture repair within 3 weeks of injury¹².

For Little League shoulder managed without surgery, the review of arm stress fractures reports that symptoms fully cleared within two to eight months⁹. Of those imaged again, 84.6% showed healing⁹. In the systematic review, 94% returned to sport and 92.5% to their pre-injury level, while 18.7% had symptoms come back⁸.

How the bone builds up with use

A review of bone strength reports that bone adapts to the loads it usually bears, shaping its structure to their size, rate and frequency¹⁵. An anatomy textbook adds that bone changes its structure as mechanical stress rises or falls, so its size and weight suit its activity². Without stress, bone loses mineral and collagen (a strong, rope-like protein), and so loses strength². The review of bone strength likewise says strain below a minimum effective level leads to bone loss¹⁵.

Comparing the two arms of 103 professional baseball players with arm differences in 94 controls, throwing loaded the shaft heavily and nearly doubled its strength⁵.

In professional baseball players, the upper humerus of the throwing arm differed from the other arm in these ways¹⁶:

Measure in the throwing arm	How much more than the other arm
Bone mass of the upper humerus	28%16
Cross-sectional area at the surgical neck	12%16
Thickness of the cortex (dense outer layer) at the surgical neck	31%16
Estimated resistance to twisting at the surgical neck	57%16

When the gains are made and how long they last

In 90 male throwing athletes and 51 controls, the gap between arms at mid-humerus was larger in each more mature group¹⁷. In professional baseball players, the extra bone mass and cortex thickness built in youth faded after throwing stopped⁵. Yet about half the extra bone size and a third of the extra strength lasted for life⁵. Players who kept throwing as they aged kept more of the strength, because their marrow cavity (the hollow centre of the bone) widened less⁵.

One study looked at 105 female national-level tennis and squash players¹⁸. The playing arm’s bone benefit was about twice as large in those who started at or before their first period¹⁸. In 64 female tennis and squash players, the playing arm’s shaft had about 19% more bone mineral in early starters and 9% in later starters¹⁹. This came from a larger outer cortex, while cortex density matched the other arm¹⁹.

A meta-analysis covered 761 males aged 10 to 26²⁰. In it, tennis raised bone mineral in the playing arm but not in the other arm²⁰.

A twist in throwers’ arms

A systematic review of 14 studies covered 1,152 overhead throwing athletes²¹. Each study that measured bone shape found more backward twist (retroversion) in the throwing arm, by average differences of 9.6 to 25.8 degrees²¹. These studies also found less internal rotation, meaning less inward turning, in that arm²¹.

A review of 32 baseball studies found humeral torsion (twist along the bone) did not differ between players with and without shoulder or elbow injuries²².

Connections

Muscles and tendons attached to it

Apart from the pectoralis major and latissimus dorsi, the muscles that cross the shoulder and move the humerus start on the shoulder blade².

Structure	Where it meets the humerus
Deltoid	Deltoid tuberosity, on the outer side2,23,24
Pectoralis major	Outer lip of the bicipital groove25
Latissimus dorsi	Floor of the bicipital groove26,27
Rotator cuff tendons	Connect the shoulder blade to the humerus2
Triceps brachii	Its lateral and medial heads start on the humerus28
Long head of the biceps tendon	Runs in the bicipital groove2,29
Superficial back-of-forearm muscles	Start on the humerus2
Common extensor tendon	Shared by several of these muscles, starting on the lateral epicondyle30

The shoulder blade and the upper arm

The scapula joins the humerus at the glenohumeral joint³¹. The upper arm has two compartments around the humerus⁶:

• The front holds three muscles: the biceps brachii, brachialis and coracobrachialis⁶. Brachialis bends the elbow from under the biceps; coracobrachialis is a small muscle at the front of the arm. The front also holds the brachial artery, the main artery of the upper arm⁶. Three nerves run there too: the musculocutaneous, median and ulnar nerves⁶. The musculocutaneous nerve works the front muscles; the ulnar nerve runs past the inner elbow to the little finger.
• The back holds the three heads of the triceps and the radial nerve⁶.

Sources

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Every source the library cites

Changes

• September 30, 2026 First published.