Overview
Tendinitis (also spelled tendonitis) is inflammation of a tendon, the thick fibrous cord attaching muscle to bone. Common sites include the Achilles tendon, patellar tendon (knee), rotator cuff (shoulder), elbow (tennis elbow, golfer's elbow), and wrist. Modern understanding recognises that most chronic tendon problems involve degeneration rather than pure inflammation, better called tendinopathy.
How common is it?
Tendinopathy is one of the most common musculoskeletal conditions, accounting for up to 30% of all musculoskeletal consultations. Achilles tendinopathy affects about 2 per 1,000 adults each year.
Causes and risk factors
Tendinopathy develops when the rate of tendon loading exceeds the tendon's capacity to recover and remodel. This causes cumulative microdamage and disorganised collagen.
Common risk factors
- Sudden increase in training volume or intensity
- Repetitive loading beyond tendon recovery capacity
- Biomechanical factors: foot pronation, poor technique
- Age (tendon vascularity and elasticity decline)
- Fluoroquinolone antibiotics (direct tendon toxicity — Achilles tendon rupture risk)
- Corticosteroid injections (repeated injections weaken tendon)
- Diabetes (increases tendon stiffness)
- Sedentary to active transition
Symptoms
- Pain at and around the affected tendon, typically worse with activity
- Pain after prolonged rest ('warming-up pain') that improves with movement
- In acute tendinitis: redness, swelling, and warmth
- In chronic tendinopathy: diffuse tenderness along the tendon, thickening
- Weakness in the affected muscle-tendon unit
- Crepitus (creaking sensation) on movement in some cases
When to see a doctor
See a doctor for sudden severe pain at a tendon site after a snap or pop during exercise (possible tendon rupture). Also seek assessment if tendon pain has not improved after 6 weeks of self-management.
Diagnosis
Clinical diagnosis. Ultrasound shows tendon thickening, altered echo-texture, and neovascularisation. MRI for detailed assessment and pre-surgical planning. X-ray for tendon calcification.
Treatments
Progressive loading (tendon rehabilitation)
The most evidence-based treatment. Isometric exercises reduce pain acutely. Heavy slow resistance exercise (e.g. Alfredson protocol for Achilles: heel drops on a step) rebuilds tendon structure over 12 weeks. Load must be progressive and individualised.
Relative rest and activity modification
Reduce but do not eliminate loading. Complete rest allows further degeneration. Identify and reduce the provocative activity while maintaining overall fitness.
Corticosteroid injection
Provides short-term pain relief but evidence suggests long-term outcomes are WORSE than physiotherapy. Should not be repeated and should not be the primary treatment strategy.
Shockwave therapy
Extracorporeal shockwave therapy (ESWT) stimulates tendon healing. Evidence supports its use in calcific tendinopathy, chronic Achilles, and patellar tendinopathy that has not responded to loading programmes.
Self-care and lifestyle
- Increase training load gradually (10% per week maximum)
- Warm up properly before sport and cool down after
- Avoid anti-inflammatory ice as the first-line response — it can impair healing signals
- Wear appropriate footwear for the activity
Prevention
Gradual training progression, adequate recovery between sessions, appropriate footwear, and correction of biomechanical factors reduce tendinopathy risk. Avoid fluoroquinolones in active sportspeople when alternatives are available.