✋ Wrist Extensor Tendinopathy (Intersection Syndrome) Simulator

The Dorsal Extensor Crossing Point

Two extensor compartments cross about 4cm above the wrist.

• ~4 cm: Crossing distance (above wrist joint line)
• 2: Compartment 1 tendons (APL and EPB)
• 2: Compartment 2 tendons (ECRL and ECRB)
• ~60°: Crossing angle (oblique intersection)

Two compartments, one crossing

First compartment holds APL and EPB tendons.

Second compartment holds ECRL and ECRB tendons.

They cross obliquely on the forearm surface.

Smooth gliding mechanics

Synovial sheaths let tendons slide with low friction.

Normal wrist extension causes no irritation here.

Healthy crossing tolerates thousands of glide cycles daily.

Repetitive Wrist Extension Begins

Repeated extension motion irritates the crossing point.

• Rowing/paddling: Typical trigger (or heavy typing)
• 1–2 wk: Onset window (of repetitive load)
• ~20%: Early inflammation (crossing-point marker)
• High volume: Risk factor (plus poor rest)

Where the irritation starts

Friction concentrates exactly where tendons cross.

Repetition without recovery raises local shear stress.

Early warning signs

Mild ache appears with wrist extension.

No visible swelling yet at this stage.

Reducing volume now can fully prevent progression.

Friction Inflammation of the Sheaths

Tendon sheaths at the intersection become inflamed.

• ~48%: Inflammation level (at crossing point)
• 5/10: Pain score (with extension)
• ~4 mm: Swelling onset (localized thickening)
• Peritendinitis: Condition also called (crepitans)

Inflammatory cascade

Repeated friction triggers local inflammatory response.

Sheath fluid and tissue thicken around tendons.

Symptoms sharpen

Pain now appears during daily wrist use.

Tenderness localizes to the crossing point.

Early rest and bracing limit further sheath damage.

Crepitus Develops at the Crossing

Crackling is now heard and felt with wrist motion.

• ~7/10: Crepitus intensity (palpable and audible)
• "Wet leather": Classic sign (creak description)
• ~66%: Inflammation level (sustained without rest)
• Moderate: Function impact (grip and extension limited)

What causes the crackle

Roughened, thickened tendon surfaces rub together.

Each glide cycle now produces audible friction.

A diagnostic clue

Crepitus at this exact spot is a hallmark sign.

Clinicians can often feel it by palpation alone.

Crepitus rarely reverses without a real rest period.

Swelling and Pain Limit Wrist Use

Visible swelling at the crossing now limits motion.

• ~9 mm: Swelling (visible dorsal bulge)
• 8/10: Pain score (with extension)
• ~85%: Inflammation level (chronic, unrested state)
• 2–6 wk: Typical recovery (rest plus splinting)

Visible swelling forms

Fluid and thickened tissue bulge above the wrist.

Skin over the crossing may feel warm.

Recovery pathway

Rest days steadily reduce inflammation and swelling.

Splinting and activity modification speed healing.

Consistent rest is the single strongest recovery lever.