How Tendon Tendinosis Develops
Tendon tendinosis occurs through a degenerative process caused by repetitive mechanical loading that overwhelms the tendon's ability to repair itself, resulting in collagen disorientation and fiber separation—not through inflammation as commonly misunderstood. 1
Primary Mechanism: Degenerative Overuse
The fundamental pathophysiology involves repetitive microtrauma from cumulative mechanical stress that exceeds the tendon's reparative capacity 1. When tendons are subjected to intensive repetitive activity (often eccentric in nature), the following cascade occurs:
- Microtrauma accumulation: Repetitive loading causes cumulative microtrauma that weakens collagen cross-linking, damages the non-collagenous matrix, and disrupts vascular elements 2
- Failed repair response: The tendon cells (tenocytes) lose their basal reparative ability when the repetitive microtraumatic processes overwhelm their capacity to repair fiber damage 2
- Structural breakdown: This results in degeneration of the normally highly arranged collagen fiber structure, with visible collagen disorientation and fiber separation on histology 1
Contributing Factors
Vascular Insufficiency
Tendons are relatively hypovascular proximal to their insertion points, which predisposes them to hypoxic degeneration 1. The mechanism involves:
- Decreased blood flow combined with increased activity leads to local tissue hypoxia 2
- Impaired nutrition and energy metabolism result from this vascular insufficiency 2
- A sedentary lifestyle contributes to poor basal circulation, making occasional high-intensity activity particularly damaging 2
Age-Related Changes
Age plays a consistent role in tendon degeneration, though the exact mechanisms remain incompletely understood 3, 4
Common Clinical Pitfall
The critical error is mislabeling tendinosis as "tendonitis" 1, 5. By the time most patients present to primary care, any acute inflammation has subsided and been replaced by chronic degenerative changes 1. This misdiagnosis leads to:
- Overreliance on anti-inflammatory medications that provide only short-term pain relief 5
- Failure to address the underlying degenerative process 5
- Underestimation of the condition's chronicity by athletes and coaches 6
Histopathologic Reality
In over 1000 spontaneously ruptured tendons analyzed, degenerative changes were found in the vast majority, with specific inflammatory or systemic diseases accounting for less than 2% of cases 2. The histology shows:
- Collagen disorientation and fiber separation (versus the densely arranged collagen fibers of normal tendon) 1, 5
- Degenerative lesions consistent with tendinosis rather than inflammatory infiltrates 3
- Evidence that spontaneous rupture represents the clinical end-state of a degenerative process 2
Typical Presentation Pattern
The natural history follows a predictable course 1:
- Insidious onset of load-related localized pain coinciding with increased or new activity 5
- Early-stage pain during activity that may subside after warm-up 1
- Progressive intensification with pain eventually present at rest in later stages 1
- Most (but not all) patients report engaging in new activity or increasing intensity before symptom onset 1