The Healthy Wrist Joint Capsule
A sealed capsule keeps synovial fluid where it belongs.
- ~1 mL: Synovial fluid volume (normal wrist joint)
- 2: Capsule layers (fibrous + synovial)
- Dorsal wrist: Most common site (scapholunate joint)
- ~1 in 10: Population affected (lifetime prevalence)
Capsule structure
Fibrous outer layer, synovial inner lining.
Synovial fluid role
Lubricates cartilage, nourishes the joint.
Pressure balance
Intact capsule holds fluid at steady pressure.
Capsule Weak Point and Fluid Herniation
A thin spot in the capsule wall starts to bulge.
- Repetitive strain: Common trigger (wrist flexion/extension)
- 3:1: Female predominance (vs males)
- 20–40: Peak age range (years)
- Scapholunate ligament: Herniation origin (70% of cases)
Weak point formation
Collagen thinning creates a herniation site.
One-way valve
A narrow stalk lets fluid out but not back.
Early symptoms
A small bump appears, often painless.
Mucinous Cyst Formation
Thick gel-like fluid slowly fills the sac.
- 0.5–3 cm: Typical cyst size (diameter)
- Mucinous: Fluid type (high viscosity gel)
- Hyaluronic acid: Main component (and glucosamine)
- Fluctuates: Growth pattern (with joint activity)
Fluid composition
Rich in hyaluronic acid, thick and gel-like.
Sac expansion
The sac stretches as fluid keeps arriving.
Stalk connection
The stalk stays open, feeding the cyst.
Needle Aspiration Procedure
A needle drains the thick fluid from the cyst.
- 18–20 G: Needle gauge (wide bore for viscosity)
- ~10 min: Procedure time (outpatient setting)
- 1–5 mL: Fluid withdrawn (typical volume)
- High: Immediate relief (symptom reduction)
Needle placement
Needle enters the sac under sterile technique.
Fluid withdrawal
Viscous fluid is slowly drawn out.
Sac deflation
The cyst visibly collapses after drainage.
Recurrence Risk After Aspiration
The stalk can refill the sac within months.
- ~50–70%: Recurrence rate (aspiration alone)
- ~5–15%: Surgical excision rate (lower recurrence)
- 3–6 mo: Typical recurrence window (post-aspiration)
- Reduces risk: Stalk removal benefit (if excised)
Why recurrence happens
The stalk is rarely fully closed off.
Refill process
Fluid slowly re-accumulates in the sac.
Reducing recurrence
Surgical excision removes the stalk itself.