Tendinosis

Populations and Risk Factors

• Repetitive occupations: Keyboard workers, assembly line workers, mechanics, carpenters, musicians — cumulative microtrauma exceeds the tendon's repair capacity; occupational tendinopathy accounts for the majority of cases in clinical practice
• Age: Incidence increases significantly after age 35 as tendon collagen cross-linking decreases, water content drops, and the ratio of Type III to Type I collagen increases — older tendons are stiffer, less elastic, and less able to self-repair; most tendon conditions presenting beyond 6–8 weeks of symptom duration are tendinosis rather than tendinitis
• Athletic overuse: Runners (Achilles, patellar), swimmers (rotator cuff), tennis/racquet sports (lateral epicondyle), basketball/volleyball (patellar) — sports with high repetitive loading volumes; the "weekend warrior" pattern (high-intensity activity without adequate progressive conditioning) is particularly high-risk
• Sex prevalence: Achilles tendinopathy is more common in men (related to greater peak loading forces and absolute tendon loads); rotator cuff tendinopathy is approximately equal between sexes
• Biomechanical factors: Poor flexibility, muscle strength imbalances, abnormal joint mechanics (e.g., overpronation contributing to Achilles and posterior tibial tendinopathy), inadequate recovery time between loading sessions
• Medications: Fluoroquinolone antibiotics (ciprofloxacin, levofloxacin) increase tendon rupture risk 3–4 times, particularly the Achilles tendon — the mechanism involves direct toxicity to tenocytes and inhibition of collagen synthesis; corticosteroid injections provide short-term pain relief but accelerate tendon degeneration with repeated use by inhibiting collagen repair and reducing tendon tensile strength; statins may contribute through mitochondrial dysfunction in tenocytes
• Systemic conditions: Diabetes (glycation of collagen reduces tendon elasticity and impairs healing), hypothyroidism, chronic kidney disease — all impair tendon healing capacity
• Watershed zones of hypovascularity: The Achilles tendon (2–6 cm above calcaneal insertion), supraspinatus tendon (near the greater tuberosity), and posterior tibial tendon (behind the medial malleolus) have zones of relative hypovascularity where blood supply is reduced — these zones are predisposed to degeneration because the limited blood supply cannot support adequate repair

Causes and Pathophysiology

• Chronic repetitive mechanical overload (primary mechanism): Tendons transmit muscle force to bone. Each loading cycle produces microscopic collagen fiber disruption at the point of greatest mechanical stress — typically the teno-osseous junction or zones of relative hypovascularity. When the cumulative rate of microtrauma exceeds the rate of repair, the tendon enters a degenerative cascade. Unlike tendinitis (which is a reversible inflammatory response to acute overload), tendinosis represents a failed healing response where the repair mechanisms have been overwhelmed and the tendon tissue progressively deteriorates.
• Angiofibroblastic degeneration (histological hallmark): The defining histological feature of tendinosis is angiofibroblastic hyperplasia — disordered proliferation of fibroblasts that produce mechanically inferior matrix. Under microscopy, tendinosis tissue shows: (1) loss of the normal parallel alignment of collagen fibers — fibers become disorganized, wavy, and irregularly spaced; (2) replacement of mature Type I collagen (thick, strong, highly cross-linked) with immature Type III collagen (thin, weak, loosely organized); (3) increased mucoid ground substance — the normally firm tendon matrix becomes soft and gelatinous; (4) tenocyte apoptosis in some regions and hyperproliferation in others — producing an inconsistent, mechanically compromised tissue architecture; (5) critically, inflammatory cells (neutrophils, lymphocytes) are ABSENT — this is what distinguishes tendinosis from tendinitis at the tissue level.
• Neovascularization and neonerves (pain mechanism): In degenerative tendon tissue, new blood vessels (neovascularization) grow into the previously avascular degenerative zone. These new vessels are accompanied by unmyelinated sensory nerve fibers (neonerves) containing substance P and calcitonin gene-related peptide (CGRP). The neonerves are believed to be a primary source of the chronic pain in tendinosis — they sensitize the tendon to mechanical loading, producing pain with activity. This mechanism explains why tendinosis pain does not respond to anti-inflammatory treatment (there is no inflammation) but does respond to treatments that address the degenerative tissue directly (eccentric loading, friction massage). Some treatment approaches (sclerotherapy, high-volume injection) specifically target the neovessels to disrupt the pain-producing neonerve network.
• Failed healing vs. inflammation (the critical distinction from tendinitis): Understanding this distinction determines treatment selection:
• Tendinitis (acute/reactive): True inflammatory response — inflammatory cells present; tendon is swollen, warm, painful; responds to anti-inflammatory treatment (NSAIDs, ice, rest); reversible with load reduction; presents within the first 6–8 weeks of symptom onset
• Tendinosis (degenerative): Failed healing response — no inflammatory cells; tendon is thickened but not warm; does NOT respond to anti-inflammatory treatment; requires tissue remodeling through controlled mechanical stress (eccentric loading, friction); presents after 6–8 weeks of persistent symptoms; anti-inflammatory treatment may actually impair the limited repair activity
• Clinical implication: Most tendon conditions that a massage therapist sees have been present for weeks to months — these are tendinosis, not tendinitis, regardless of what the patient has been told. Treatment must be directed at stimulating fibroblast activity and collagen remodeling, not at reducing an inflammation that is not present.
• Eccentric loading rationale (primary intervention): Eccentric contractions (muscle lengthening under load) produce the specific type of mechanical stress that most effectively stimulates tendon repair: (1) Eccentric loading produces greater tensile force within the tendon than concentric loading, maximizing the mechanical stimulus to tenocytes; (2) The controlled tensile stress activates mechanoreceptors on tenocyte cell membranes, stimulating production of Type I collagen; (3) The direction of the tensile stress guides the orientation of newly synthesized collagen fibers along functional stress lines (Wolff's law for connective tissue); (4) Progressive eccentric loading increases the tendon's load-bearing capacity over time, breaking the cycle of degeneration. The Alfredson heavy-load eccentric protocol (3 sets of 15 repetitions, twice daily, for 12 weeks) is the gold-standard rehabilitation for Achilles and patellar tendinosis.

Signs and Symptoms

Tendinitis vs. Tendinosis

General Findings

• Pain peaks during and after repetitive activity — may recede after "warming up" (increased blood flow temporarily improves the ischemic zone), then returns with intensity post-activity
• No visible redness, warmth, or swelling (no active inflammation) — the absence of inflammatory signs despite persistent tendon pain is the clinical clue to tendinosis
• Tendon feels thickened, dull, or soft on palpation (vs. hard, shiny healthy tendon) — the degenerated tissue has lost its normal firm, taut quality
• Gritty, grinding crepitus when the tendon moves through a restricted sheath — the roughened, degenerated tendon surface creates friction
• Pain at the musculotendinous junction or teno-osseous insertion — the site of maximum mechanical stress and degeneration
• Pain with resisted isometric contraction (RROM) — confirms contractile tissue involvement; "strong and painful" (strength maintained, pain present)
• The "warm-up phenomenon" — pain at the start of activity that decreases with continued movement as blood flow increases, then returns after activity cessation; this is characteristic of tendinosis and helps distinguish it from acute tendinitis (which worsens steadily with activity)

Assessment Profile

Subjective Presentation

• Chief complaint: Persistent tendon pain that has not resolved with rest, ice, or anti-inflammatory medication — "my Achilles has been sore for months and nothing helps" or "my elbow pain started six months ago and it's just not getting better"; the chronicity and failure of anti-inflammatory management are key subjective clues
• Pain quality: Deep, aching pain at the tendon site; may be sharp during heavy loading; described as "stiff" and "tight" in the morning that loosens with movement; not throbbing (which would suggest acute inflammation)
• Onset: Gradual — develops insidiously over weeks to months with repetitive overuse; no acute traumatic moment; the patient often reports that it "started as mild soreness after activity that kept getting worse" despite rest periods
• Aggravating factors: Repetitive loading of the affected tendon (running for Achilles, gripping for lateral epicondyle, overhead reaching for rotator cuff); the specific activity that produces the highest eccentric demand on the tendon is the most provocative; morning stiffness (the tendon stiffens during the period of inactivity overnight)
• Easing factors: The warm-up phenomenon — initial movement reduces stiffness and pain temporarily; relative rest (reducing the provocative activity without complete immobilization); eccentric loading programs (the patient may report improvement with structured eccentric exercise before identifying the program specifically)
• Red flags: Sudden severe pain with a "pop" or "snap" during activity → suspect tendon rupture; refer for orthopedic consultation; fluoroquinolone use (current or recent) with tendon pain → increased rupture risk; refer for medical review and activity modification; rapid progressive weakness of the tendon's action → possible partial tear evolving toward complete rupture

Observation

• Local inspection: Tendon may be visibly thickened compared to the contralateral side (nodular thickening in Achilles, fullness over the lateral epicondyle); no redness or visible swelling (absence of inflammatory signs); no acute deformity; in chronic Achilles tendinosis, the tendon may lose its sharp posterior contour and appear fusiform (spindle-shaped)
• Posture: Postural compensation varies by tendon location — rotator cuff tendinosis: protracted shoulder and reduced arm swing; Achilles tendinosis: compensatory external rotation during push-off to offload the painful tendon
• Gait: Achilles tendinosis: toe-off is shortened or absent on the affected side; may push off the lateral foot to offload the medial Achilles; patellar tendinosis: reduced knee flexion during stance phase; stairs may produce visible difficulty

Palpation

• Tone: Hypertonic muscle belly proximal to the degenerative tendon — the muscle compensates for the pain-inhibited tendon by increasing its resting contraction; trigger points commonly develop in the muscle belly from chronic overload; antagonist muscles may also develop compensatory hypertonia from altered joint mechanics
• Tenderness: Tenderness directly over the degenerated tendon — localizes to the zone of maximal degeneration (often the watershed zone of hypovascularity); the tenderness is reproducible and consistent in location from session to session; the tendon feels thick, soft, or nodular compared to the contralateral healthy tendon; no warmth (distinguishing from tendinitis)
• Temperature: Normal — the absence of warmth despite tenderness is the key finding distinguishing tendinosis from tendinitis; compare bilaterally; any warmth present suggests superimposed acute reactive inflammation (which can occur during flares of activity on a background of tendinosis)
• Tissue quality: The degenerative tendon has lost its normal firm, taut, "twang" quality — it feels thickened, dull, or soft, described as having a "boggy" or "mushy" texture compared to healthy tendon; gritty crepitus may be felt during passive tendon excursion; the surrounding muscle-tendon complex has reduced fascial glide; in sheathed tendons (de Quervain's area, flexor tendons), adhesions between the tendon and its sheath produce restricted and painful gliding

Motion Assessment

• AROM: Pain during the specific movement that loads the affected tendon — plantarflexion for Achilles, wrist extension/grip for lateral epicondyle, shoulder abduction for supraspinatus; ROM is typically near-normal or only mildly restricted; the warm-up phenomenon may be observed: initial movement is stiff and painful but improves with repetition, then worsens with continued loading
• PROM / end-feel: Mild pain at end-range when the tendon is placed on maximum stretch — stretching increases tension on the degenerative fibers; end-feel is typically muscle stretch (elastic) with early pain; no capsular restriction (tendinosis is a tendon condition, not a joint condition); passive tendon excursion may produce palpable crepitus in sheathed tendons
• Resisted testing: "Strong and painful" — the hallmark RROM finding for tendinopathy; the tendon produces pain when loaded (confirming contractile tissue involvement) but strength is maintained (the tendon is degenerated but structurally intact); this distinguishes tendinosis from partial tear (weak and painful) and complete rupture (weak and pain-free); the specific resisted test depends on the tendon: resisted plantarflexion (Achilles), resisted wrist extension (lateral epicondyle), resisted shoulder abduction (supraspinatus)

Special Test Cluster

Tendinosis vs. tendinitis clinical checklist: (1) Duration >6–8 weeks; (2) No warmth, redness, or swelling; (3) Failed response to anti-inflammatory treatment; (4) Pain improves with warm-up; (5) Tendon feels thickened and soft, not swollen and taut. If 3 or more features are present, the working diagnosis is tendinosis and treatment should target tissue remodeling, not inflammation.

Differential Assessment