tendonitis
Meaning of tendonitis: Tissue from painful tendons usually shows disorganized collagen rather than inflammatory cells, which is why tendinopathy has largely replaced the name.
Definition of tendonitis
Tendonitis is pain, swelling and tenderness of a tendon, the tough cord anchoring muscle to bone, usually where the tendon meets bone or passes over it. It follows repeated loading rather than a single injury, and it hurts most when the attached muscle contracts against resistance. Shoulder, elbow, wrist, knee and heel tendons are the sites involved most often.
Is the tendon actually inflamed?
Often far less than the name implies. A tendon overloaded once, sharply, does mount genuine inflammation, with inflammatory cells arriving in the tissue around it. Tissue taken from tendons that have hurt for months usually shows something else: collagen fibers disorganized instead of running in parallel, extra water and ground substance between them, new blood vessels and nerve fibers growing in, and very few inflammatory cells. That degenerative picture is called tendinosis. Because most persistent cases look this way, tendinopathy has become the preferred umbrella word, covering both the inflamed and the degenerate states without claiming to know which is present.
How does it differ from nearby problems?
| Problem | Structure affected | Characteristic feature |
|---|---|---|
| Tendonitis | The tendon itself | Pain on resisted contraction of the muscle |
| Bursitis | Fluid sac cushioning the tendon | Tenderness over the sac, pain at rest |
| Tenosynovitis | Sheath the tendon slides through | Creaking or catching on movement |
| Partial tear | Fibers of the tendon | Sudden onset, weakness as well as pain |
These occur together frequently, since a swollen tendon rubs on its sheath and irritates the sac beside it, so the labels describe which structure dominates rather than marking separate diseases.
Which tendons are usually involved?
- Rotator cuff at the shoulder, painful on reaching overhead
- Outer elbow, called tennis elbow, from repeated gripping and wrist extension
- Inner elbow, called golfer's elbow, from repeated wrist flexion
- Thumb side of the wrist, where tendons pass under a tight band
- Patellar tendon below the kneecap, from jumping and landing
- Achilles tendon at the heel, from running and sudden increases in load
The common thread is load applied repeatedly and increased faster than the tissue adapts to it. Tendon adapts slowly, having a modest blood supply and an unhurried rate of collagen turnover, so the interval between doing more and feeling it is measured in weeks.
Also known as
Used in a sentence
The shoulder pain was attributed to tendonitis of the rotator cuff.
Good to know
Tendonitis and tendinitis name the same condition, and tissue from long-standing cases typically shows disorganized collagen with few inflammatory cells, which is why the broader term tendinopathy is often preferred.
Word origin
Where “tendonitis” comes from
From the Latin tendo, tendinis, a tendon, from tendere, to stretch, with the Greek suffix -itis for inflammation.