Tendonitis vs Bursitis: What Actually Differs

The difference is anatomical, not a matter of degree. Tendonitis is inflammation of a tendon — the NIH defines it as a flexible band of fibrous tissue connecting muscle to bone. Bursitis is inflammation of a bursa, a small fluid-filled sac that cushions between a bone and the muscles, tendons or skin moving over it. Same joint, different tissue.

Two structures with different jobs

A tendon transmits force. It is a cable, and it fails from repeated pulling. A bursa reduces friction. It is a cushion, and it fails from being squeezed — StatPearls names prolonged pressure as the most common cause of bursitis, the bursa crushed between a hard surface and a bony prominence. That difference in mechanism is what makes kneeling produce one and throwing produce the other.

The exam finding that separates them

This is the useful one, and it is something a clinician tests in seconds. StatPearls notes that many patients with bursitis have pain with active motion but not with passive motion — when the examiner moves the limb for you, the surrounding muscles are not squeezing the inflamed sac, so it stops hurting. An irritated tendon is loaded either way and tends to complain in both. Add location: bursitis is tender over the sac, often right under the skin at the elbow or kneecap; tendonitis is tender along the tendon itself.

	Tendonitis	Bursitis
Tissue involved	Tendon, muscle to bone	Fluid-filled cushioning sac
Typical cause	Repetitive pulling load, sudden overload	Prolonged pressure, repetitive motion, infection
Passive movement	Usually still painful	Often painless
Visible swelling	Modest	Can be marked where the sac is superficial
Infection risk	Not a feature	Real, and sometimes the main problem

Where the shoulder blurs the line

Ask which one you have in the shoulder and the honest answer is often “both”. The subacromial bursa sits directly between the rotator cuff tendons and the acromion — the AAOS describes it as the sac that lets those tendons glide, and covers shoulder bursitis and rotator cuff tendinitis on a single page rather than as rival diagnoses. The steroid injection used for the condition goes into that bursa, treating the space rather than picking a side. See shoulder tendonitis symptoms and shoulder bursitis symptoms for the two readings of the same shoulder.

The bursa that swells and does not hurt

One presentation belongs to bursitis alone: StatPearls notes chronic bursitis is often painless, because the sac has had time to expand and accommodate the extra fluid, leaving significant swelling and thickening without much pain. A visibly puffy elbow or kneecap that does not hurt is a recognized picture, and it has no tendon equivalent.

When to be seen

Either one warrants evaluation if pain lasts beyond a few days, limits the joint, or comes with obvious swelling. Move faster when redness, warmth or fever join in — that combination suggests an infected bursa rather than either simple inflammation. Full symptom lists are in tendonitis symptoms and bursitis symptoms.

This content is informational and does not replace a medical consultation, diagnosis, or treatment.