Tenosynovitis vs Tendonitis: Key Differences
Tenosynovitis involves inflammation of the tendon sheath (the synovial covering around the tendon), while tendonitis refers to inflammation or degeneration of the tendon itself—though true inflammation in tendonitis is rarely found on pathologic examination, making "tendinopathy" a more accurate term.
Anatomical and Pathological Distinctions
Tenosynovitis
- Location: Affects the synovial sheath surrounding the tendon
- Pathology: True inflammatory process with exudation, thickening, and potential stenosis of the tendon sheath 1
- Clinical presentation: Often presents with visible swelling along the tendon course, crepitus (crackling sensation), and pain with tendon gliding 2
- Common examples: De Quervain disease (stenosing tenosynovitis of the first dorsal compartment), trigger finger, flexor tenosynovitis 1, 3
Tendonitis/Tendinopathy
- Location: Affects the tendon substance itself
- Pathology: Despite the name "tendonitis," actual inflammatory cells are rarely seen on pathologic examination 4. Instead, there is tendon degeneration with collagen fiber disruption, hypoxic changes, and microscopic structural breakdown 5, 6
- Clinical presentation: Localized pain at the tendon or its insertion point, pain with resisted contraction, and pain with passive stretching 5, 2
- Common examples: Achilles tendinopathy, rotator cuff tendinopathy, lateral epicondylitis 5
Diagnostic Approach
Both conditions share a symptomatic triad: pain on palpation, pain with passive tendon tension, and pain with resisted muscular contraction 2. However, key differentiators include:
- Tenosynovitis: Look for swelling along the tendon sheath, crepitus with movement, and triggering or catching sensations
- Tendinopathy: Look for point tenderness at the tendon insertion or mid-substance, without sheath swelling
Imaging Considerations
When clinical examination is unclear, imaging can distinguish between these conditions:
- Ultrasound: Can diagnose both conditions effectively. Shows tendon sheath effusion and thickening in tenosynovitis, versus tendon substance changes (thickening, hypoechogenicity) in tendinopathy 7
- MRI: More sensitive for tenosynovitis, especially when IV contrast is used, which enhances the inflamed synovial sheath 7. MRI also detects tendon substance pathology but may miss some tendon sheath effusions that ultrasound detects 8
Clinical Implications
The distinction matters because:
- Tenosynovitis may respond better to corticosteroid injection into the tendon sheath (as in De Quervain disease or trigger finger) 9
- Tendinopathy requires caution with corticosteroid injection directly into tendon substance due to risk of tendon weakening or rupture 5
- Tenosynovitis may require surgical release of the tendon sheath if conservative treatment fails 3
- Tendinopathy benefits more from eccentric strengthening exercises and load management 5
Common Pitfall
The terms are often used interchangeably in clinical practice, but this is imprecise. Many conditions labeled as "tendonitis" are actually tendinopathy (degenerative) or tenosynovitis (sheath inflammation). Accurate diagnosis guides appropriate treatment—sheath injection for tenosynovitis versus eccentric exercises and load modification for tendinopathy 5, 4.
In inflammatory arthritis like rheumatoid arthritis, tenosynovitis is particularly important to identify as it predicts erosive progression and may be more conspicuous with contrast-enhanced MRI 1, 8.