Scapula

Function

Its shape and landmarks

The shoulder blade lies on the back of the shoulder¹. It is a flat, triangular bone with a raised ridge across its back surface¹. It sits on the back of the rib cage, in the upper thoracic (chest) region².

The bone has three borders: the superior (top), medial (inner) and lateral (outer) borders¹. The medial border ends in a superior angle at the top and an inferior angle at the bottom¹. The inferior angle is the bone’s lowest point¹. Several powerful muscles that move the shoulder and arm attach there¹.

The ridge is called the spine of the scapula, and it runs across the upper part of the back surface¹. At its outer end it flattens into the acromion, the bony tip of the shoulder¹. The coracoid process is a hook-like point that juts forward from the top of the bone¹. Muscles from the front of the chest and arm attach to it¹.

Three hollows for muscle

The shoulder blade has three hollows, called fossae¹:

Hollow	Where it sits	Width
Supraspinous fossa	Above the spine, on the back	Narrow1
Infraspinous fossa	Below the spine, on the back	Broad1
Subscapular fossa	On the front, facing the rib cage	Broad1

All three give large surfaces for muscles that cross the shoulder and act on the humerus¹.

The shoulder socket

The glenoid cavity is a shallow dip at the upper outer corner of the shoulder blade¹. It meets the humerus to form the glenohumeral joint, the main shoulder joint¹. The head of the humerus, a large, smooth, rounded surface, fits against it as a ball and socket^1,7. Small bumps just above and below the socket, the supraglenoid and infraglenoid tubercles, anchor muscles of the arm¹.

A bone held in place by muscle

The shoulder blade has muscle on both its front and back surfaces, so it does not form a joint with the ribs¹. Together with the clavicle it makes up the pectoral girdle¹. This girdle attaches the arm to the sternum (breastbone)¹.

The shoulder blade has muscle on both its front and back surfaces, so it does not form a joint with the ribs.

The acromioclavicular joint, where the collarbone meets the top of the shoulder blade, passes forces from the arm to the clavicle¹. The ligaments around this joint are fairly weak¹. Its main support is the strong coracoclavicular ligament, which ties the coracoid process to the underside of the clavicle¹.

Six muscles position the girdle¹:

• On the front of the chest: the subclavius, pectoralis minor and serratus anterior¹.
• On the back: the trapezius, rhomboid major and rhomboid minor¹.

By holding the girdle steady, these muscles give other muscles a firm base from which to move the arm¹. When the rhomboids contract, the shoulder blade moves toward the spine¹. This can pull the shoulder and arm backward¹.

How it moves as the arm rises

One narrative review states that the shoulder blade turns upward and tilts backward on the rib cage as the arm is raised overhead³. It names upward rotation as the main movement³. Turning inward and outward varies more between people and between studies, the same review states³. It adds that shrugging and gliding forward and back actually come from the clavicle moving at the sternoclavicular joint, where the collarbone meets the breastbone³.

Two studies measured the bone’s motion directly, with pins or sensors fixed into the bone^8,9:

• In 8 healthy volunteers raising the arm in the shoulder blade’s plane, the bone turned upward about 50 degrees and tilted back about 30⁸.
• In the same 8 people, the shoulder joint moved on average 1.7 times as far as the shoulder blade⁸.
• In people without symptoms reaching freely, the shoulder joint rose 2.3 times as far as the blade turned upward⁹. When lowering the arm, it was 2.7 times⁹.
• In the same study, the ratio was greatest early in the lift, and upward rotation and backward tilt grew steadily to full height⁹.

Breakdown

How often it breaks

Fractures of the shoulder blade are fairly uncommon⁴. They make up under 1% of all fractures and about 3 to 5% of shoulder girdle fractures⁴. One anatomy chapter states that 17 muscles attach to the bone².

Two studies counted them^10,11:

• A 1995 study counted 338 fractures over 10 years in two Swedish counties¹⁰. That is an incidence (new cases per year) of 10 per 100,000 people¹⁰.
• In that Swedish study, 30% of the fractures involved the glenoid cavity¹⁰.
• Among all patients in the US National Trauma Data Bank from 2002 to 2012, 1.74% had a shoulder-blade fracture¹¹.

Who breaks it, and how

In the Swedish Fracture Register from 2011 to 2020, 3,930 adults had 3,973 shoulder-blade fractures⁴. Their average age was 58, and 64% were men⁴. The most common breaks were of the glenoid rim, the edge of the socket (32%), and the body of the bone (28%)⁴.

Sources describe these fractures differently^4,12. A 2006 review states that they typically follow high-energy trauma, and that about 90% of patients have other injuries too¹². In the Swedish register, 22% came from high-energy trauma and 21% came with at least one other fracture⁴. There, high-energy injury was most common in fractures of the neck of the socket and of the body⁴. Falls on level ground caused most fractures of the glenoid rim and inside the joint⁴.

When the shoulder blade moves differently

Scapular dyskinesis means abnormal control of the shoulder blade as it moves⁶. It is commonly linked with shoulder problems but also appears in people without symptoms⁶. Studies vary on whether it is a cause or a symptom⁶.

One review covered 34 studies of 2,365 people in both groups, another 12 studies of 1,401 athletes^5,6:

Group studied	Share with dyskinesis
People with shoulder symptoms	60%5
People without shoulder symptoms	48%5
Overhead athletes	61%6
Non-overhead athletes	33%6

The review of 34 studies concluded that many people with shoulder symptoms do not have dyskinesis⁵. It may be a normal finding in nearly half of people without symptoms⁵.

Two meta-analyses, which pool the results of earlier studies, looked at what happened next in athletes^13,14. Both pooled prospective studies, which follow people forward in time^13,14:

• In 419 athletes without symptoms, followed for 9 to 24 months, 35% of those with dyskinesis developed shoulder pain¹³. So did 25% of those without it, a 43% higher risk with dyskinesis¹³.
• In 923 athletes, 46% had dyskinesis, and it had no statistically significant link with later shoulder injury¹⁴.

A 2013 international consensus meeting on the scapula concluded that dyskinesis is present in a high share of most shoulder injuries¹⁵. It added that its exact role in causing or worsening shoulder problems is not clearly defined¹⁵.

Recovery

How bone answers load

A review of bone mechanics states that bone adapts its structure to the size, rate, frequency and spread of the strains it usually bears¹⁶. Too little loading may lead to bone loss, and too much to a stress reaction, an early bone stress injury before a crack forms¹⁶.

A meta-analysis of 10 articles on 761 males aged 10 to 26 looked at tennis¹⁷. Tennis raised bone mineral content in the dominant arm but had no significant effect on the other arm¹⁷.

How a broken bone heals

A review of fracture healing states that repair usually restores bone to its structure and function before the injury¹⁸. About 10% of fractures do not heal normally¹⁸.

In any broken bone, an anatomy textbook states, clotting blood first forms a fracture hematoma, then calluses of cartilage and bone steady the broken ends¹. Later, dead bone is cleared and the cartilage is replaced by trabecular (spongy) bone, then compact bone, the dense outer layer¹. Remodelling often leaves no outward sign of the break¹.

What studies found after shoulder-blade fractures

A systematic review of 35 papers covered 822 shoulder-blade fracture cases¹⁹. The great majority healed, and most people eventually returned to work¹⁹. Lasting pain was common, and shoulder motion and strength were lower than on the other side¹⁹. The most common complications were malunion (a broken bone that heals out of line), further surgery, and arthritis after the injury¹⁹. Nonunion, where a broken bone fails to join and heal, was exceptionally rare, with or without surgery¹⁹.

Other studies looked at how these fractures were managed^4,20:

• In the Swedish register, glenoid rim fractures and fractures inside the joint were operated on in over 30% of cases⁴. One year on, 4% of the whole group had died⁴.
• A meta-analysis of 26 studies covered 601 patients with fractures outside the joint²⁰. It found no significant overall benefit of surgery over non-surgical care, though differences between studies limited the evidence²⁰.
• A systematic review found ten reported sport-related fractures of the bone’s body²¹. Of these, 90% were managed without surgery, with no reported complications²¹. The average time back to sport was 2.5 months²¹.

Exercise and shoulder-blade movement

A systematic review of 20 clinical trials looked at exercise in people with scapular dyskinesis²². It found conflicting evidence, and concluded there is a lack of evidence that exercise changes shoulder-blade position and motion²². In people with subacromial impingement, pinching of tissue beneath the acromion, exercise reduced pain and disability²².

Connections

The upper arm bone and the rotator cuff

The shoulder blade joins the humerus at the glenohumeral joint and the clavicle at the acromioclavicular joint². The tendons of four muscles connect it to the humerus and form the rotator cuff around the shoulder joint¹. They are the subscapularis, supraspinatus, infraspinatus and teres minor¹. The infraspinatus fills much of the infraspinous fossa²³.

Muscles that start on it

Among the muscles that cross the shoulder and move the humerus, two are axial muscles, of the trunk: the pectoralis major and latissimus dorsi¹. The rest start on the shoulder blade¹. Examples include:

• The middle part of the deltoid, which starts from the acromion, and its back part, from the spine²⁴.
• The long head of the triceps, which starts from the infraglenoid tubercle²⁵.

The muscles that turn it

The trapezius steadies and moves the shoulder blade²⁶. It and the serratus anterior are considered the only muscles that turn the shoulder blade upward²⁷. The serratus anterior fans out from the upper eight or nine ribs²⁸. It attaches along the shoulder blade’s medial border and at both of its angles²⁸.

In 30 people, tiring the serratus anterior reduced backward tilt of the shoulder blade in the middle of the arm’s rise²⁹. It also increased inward rotation as the arm went up²⁹. Its upward rotation did not change²⁹.

Exercises studied

One study took 17 people with scapular downward rotation syndrome, a shoulder blade that sits turned downward at rest³⁰. It compared three shrugs with the arm 30 degrees out to the side³⁰. A “stabilization shrug” turned the shoulder blade upward significantly more than the other two³⁰. Related exercise page: shrug³⁰.

Sources

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Every source the library cites

Changes

• September 30, 2026 First published.