Shoulder Pain

Story

Connected to · 2

regulates · 2

Knee Pain
Joint cartilage has no nerves and no blood vessels, so cartilage itself does not hurt; shoulder pain more often comes from tendons, bursae and the joint capsule. Rotator cuff–related shoulder pain and jumper's knee (patellar tendinopathy) follow the same path of degeneration after overload: under the microscope there is disorganized collagen and repair that cannot keep up, not a crowd of inflammatory cells.
Low Back Pain
Modern care for acute soft-tissue injuries has replaced complete rest with appropriate loading: long bed rest or keeping an arm in a sling both weaken the muscles that should stabilize the joint and stiffen the tissues that should glide, so recovery ends up slower.

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Why the shoulder is mobile but unstable

EVIDENCEREVIEW 1

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The top of the upper-arm bone sits like a golf ball on a shallow dish: it can point in any direction, but on its own it is not stable at all.

The shoulder trades that shallow socket for the largest range of motion in the body, and its stability depends almost entirely on the four small muscles of the rotator cuff holding the ball in place moment by moment. The knee and hip sit in deep sockets and are stable by design; the shoulder takes the opposite route. Most shoulder pain comes back to this trade of stability for movement: either the joint cannot stay in place, or the tendons that keep it steady wear out.

One kind of shoulder pain is not about the shoulder: pain in the left shoulder or arm together with chest tightness, breathlessness, or a cold sweat may be a heart problem. Call emergency services right away.

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Educational content, not medical advice — consult a clinician.

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Shoulder Pain

Story

Connected to · 2

regulates · 2

Knee Pain
Joint cartilage has no nerves and no blood vessels, so cartilage itself does not hurt; shoulder pain more often comes from tendons, bursae and the joint capsule. Rotator cuff–related shoulder pain and jumper's knee (patellar tendinopathy) follow the same path of degeneration after overload: under the microscope there is disorganized collagen and repair that cannot keep up, not a crowd of inflammatory cells.
Low Back Pain
Modern care for acute soft-tissue injuries has replaced complete rest with appropriate loading: long bed rest or keeping an arm in a sling both weaken the muscles that should stabilize the joint and stiffen the tissues that should glide, so recovery ends up slower.

Read full story

Stop 1/6

Why the shoulder is mobile but unstable

EVIDENCEREVIEW 1

READ THE ORIGINAL

The top of the upper-arm bone sits like a golf ball on a shallow dish: it can point in any direction, but on its own it is not stable at all.

The shoulder trades that shallow socket for the largest range of motion in the body, and its stability depends almost entirely on the four small muscles of the rotator cuff holding the ball in place moment by moment. The knee and hip sit in deep sockets and are stable by design; the shoulder takes the opposite route. Most shoulder pain comes back to this trade of stability for movement: either the joint cannot stay in place, or the tendons that keep it steady wear out.

One kind of shoulder pain is not about the shoulder: pain in the left shoulder or arm together with chest tightness, breathlessness, or a cold sweat may be a heart problem. Call emergency services right away.

Watch this step as a mechanism animationOpen mechanism

Educational content, not medical advice — consult a clinician.