🥶 Hydrodilatation (Distension Arthrography) Simulator

Contracted Fibrotic Capsule in Adhesive Capsulitis

Chronic inflammation shrinks and stiffens the joint capsule.

• ~15 mL: Normal capsule volume (healthy glenohumeral joint)
• <5–10 mL: Frozen shoulder volume (contracted capsule space)
• 2–5%: Prevalence (of general population)
• 40–60: Peak age range (years old)

Capsular fibrosis

Collagen thickens and adhesions bind capsule to humeral head.

Loss of range of motion

External rotation and abduction become sharply limited.

Rationale for hydrodilatation

Fluid pressure mechanically stretches and tears adhesions.

Frozen shoulder can persist one to three years untreated.

Needle Placement Into the Glenohumeral Joint

Imaging confirms accurate intra-articular needle position.

• Fluoroscopy / US: Guidance modality (real-time imaging)
• 20–22G: Needle gauge (spinal needle)
• Posterior: Approach (common entry route)
• Arthrogram: Placement check (contrast confirmation)

Posterior approach

Needle enters below the scapular spine landmark.

Contrast confirmation

Iodinated contrast outlines the joint capsule shape.

Patient positioning

Seated or prone position stabilizes the shoulder.

Correct placement avoids injury to the axillary nerve.

Saline Injection Gradually Distends the Capsule

Slow saline infusion begins expanding the joint space.

• Saline + LA + steroid: Typical injectate (combined solution)
• 1–2 mL/min: Initial injection rate (slow controlled infusion)
• ~10 mL: Early volume tolerated (before resistance felt)
• Pressure / ache: Patient sensation (commonly reported)

Progressive filling

Saline fills the shrunken capsular recess first.

Pressure monitoring

Injection resistance signals rising intracapsular pressure.

Local anesthetic effect

Lidocaine numbs discomfort during ongoing distension.

Injection stops if patient pain becomes intolerable.

Capsular Stretching and Adhesion Micro-Rupture

Rising pressure stretches capsule fibers until they tear.

• up to 250 mmHg: Peak intracapsular pressure (during active distension)
• Audible / felt pop: Rupture sensation (capsular release event)
• ~20–30 mL: Volume at rupture (typical threshold)
• Type I collagen: Adhesion type torn (fibrotic bands)

Capsular tear mechanics

Pressure exceeds adhesion tensile strength and fibers snap.

Pain-pressure relief cycle

Each rupture briefly drops intracapsular pressure.

Multiple rupture events

Repeated stretching frees multiple adhesion sites.

A sudden pressure drop often signals successful rupture.

Increased Joint Volume Improves Range of Motion

Expanded capsule allows greater passive shoulder movement.

• 30–40 mL: Post-procedure volume (markedly increased capacity)
• +30–50°: Range of motion gain (external rotation improvement)
• Days–weeks: Symptom relief onset (after procedure)
• 70–90%: Reported success rate (clinical improvement)

Volume expansion outcome

Capsule capacity approaches near-normal joint volume.

Physical therapy follow-up

Stretching exercises maintain gained mobility afterward.

Durability of effect

Benefits often persist for many months.

Hydrodilatation with physiotherapy gives the best long-term results.