Underlying Pathology in Chronic Achilles Tendinopathy
Chronic Achilles tendinopathy is fundamentally a degenerative condition, not an inflammatory one, characterized by failed healing response with collagen disorganization, increased glycosaminoglycans, and neovascularization—not by the presence of inflammatory cells. 1
Core Pathological Features
The underlying pathology involves a degenerative process that should be labeled as "tendinosus" or "tendinopathy" rather than the commonly misused term "tendonitis," which incorrectly implies inflammation. 1 This distinction is critical because it fundamentally changes treatment approach—anti-inflammatory strategies alone are insufficient for a degenerative condition.
Histological Characteristics
The microscopic examination of chronic Achilles tendinopathy reveals specific degenerative changes:
- Absence of inflammatory cells despite the presence of pain and dysfunction 2, 3
- Increased tenocyte numbers and elevated concentration of glycosaminoglycans in the ground substance 2
- Collagen fiber disorganization and fragmentation representing failed structural integrity 2
- Neovascularization with abnormal blood vessel formation 2
- Increased interfibrillar glycosaminoglycans with altered collagen fiber structure and arrangement 3
Failed Healing Response Model
The pathological process follows a continuum of three stages representing progressive degeneration 2:
- Reactive tendinopathy - initial response to overload
- Tendon disrepair - failed healing attempts
- Degenerative tendinopathy - end-stage structural breakdown
Vascular Considerations
Tendons are relatively hypovascular proximal to the tendon insertion, which predisposes them to hypoxic tendon degeneration. 1 This hypovascularity has been implicated in the etiology of tendinopathies and explains why healing is often prolonged or incomplete.
Clinical Implications of the Pathology
Understanding that this is a degenerative rather than inflammatory condition explains why:
- NSAIDs provide only acute pain relief but do not alter long-term outcomes 4
- Corticosteroid injections may actually worsen the condition by reducing tendon tensile strength 4
- Eccentric strengthening exercises work by stimulating collagen production and guiding proper alignment of newly formed collagen fibers 4
- Recovery typically requires 3-6 months as the tendon undergoes structural remodeling 1
Common Pitfall to Avoid
The most critical error is mislabeling chronic Achilles tendinopathy as "tendonitis" and treating it primarily with anti-inflammatory medications. 1 While NSAIDs may provide short-term pain relief, they do not address the underlying degenerative pathology and cannot reverse the structural changes. Treatment must focus on mechanical loading strategies (eccentric exercises) that promote proper collagen remodeling rather than simply suppressing non-existent inflammation.