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Ultrasound · Hand

First Carpometacarpal (CMC) Joint Injection (Thumb Base / Basal Joint)

handcmcthumb basebasal jointarthritis

Treats

  • Thumb basal joint (1st CMC) arthritis or synovitis

Contraindications

  • Active local skin infection at entry site (absolute)
  • Suspected septic joint (absolute — aspirate first)
  • Known allergy to local anesthetic, steroid, or antiseptic prep
  • Therapeutic anticoagulation — review case-by-case
  • Uncontrolled diabetes (relative)

Pre-procedure checklist

  • Confirm patient identity (two identifiers)
  • Confirm procedure, side, and site — mark with patient awake
  • Review allergies and anticoagulation
  • Confirm informed consent
  • Pre-scan: identify the trapezium-1st metacarpal joint between APL and EPL tendons; Doppler-screen for radial artery
  • Time-out immediately before needle entry

Positioning

  • Hand on table; thumb in relaxed/neutral position with radial aspect up; slight wrist ulnar deviation to open the anatomical snuffbox; small towel under wrist
Positioning

Probe

  • High-frequency linear probe (15+ MHz hockey-stick if available)
Probe

Landmarking — find the view

  • Slide distal to the radial styloid and identify the trapezium → 1st metacarpal base joint, between the APL/EPB tendons (volar border) and the EPL tendon (dorsal border).
  • Center the joint cleft and Doppler the radial artery (lies just deep/dorsal in the snuffbox).

The correct ultrasound view

  • Two cortical bones (trapezium and 1st MC base) with thin anechoic joint line; APL/EPL on either side
The correct ultrasound view

Needle corridor

  • Dorsal in-plane approach distal-to-proximal along the joint plane, between APL and EPL tendons
Needle corridor

Avoid

  • Radial artery (deep in the snuffbox — Doppler before entry)
  • Dorsal sensory branches of the radial nerve
  • Intratendinous APL or EPL placement

Steps

  1. 1Advance in-plane into the joint cleft; inject up to 1 mL slowly.
  2. 2STOP IMMEDIATELY if the patient reports electric, shooting, or paresthetic sensations into the thumb.

Tips

  • Tiny joint — total injectate ≤ 1 mL. Don't waste space with too much local first.
  • Limit to ≤ 3 injections per joint per year.
  • If color Doppler shows the radial artery in the planned path, abandon and re-plan.

Resident pearls

  • Identify the 1st CMC joint by sliding distal to the radial styloid; avoid the radial artery in the snuffbox.
  • The target is the 'joint gap' — confirm flow with capsular distension.
  • Limited volume — pre-mix steroid and a tiny lidocaine aliquot in the same syringe.

Supplies

  • 3 mL Syringe
  • 27G 0.5-1" Needle
  • 18G Drawing Needle
  • 1% Lidocaine (0.3-0.5 mL)
  • Dexamethasone 4 mg (PREFERRED — non-particulate, non-particulate; lower risk of skin and fat atrophy at this superficial joint) OR triamcinolone 10-20 mg
  • Alcohol Swabs (vial tops)
  • Betadine/Chloraprep
  • Sterile Gloves
  • Sterile 4x4 Gauze Pads
  • Sterile Towels & Drapes
  • Adhesive Bandage (Band-Aid)
  • Washcloth/Towel (gel cleanup)
  • Needle Disposal Safety Cap
  • Sterile probe cover & gel

Post-procedure

  • Apply a clean dressing; remove after 24 hours.
  • Local anesthetic relief for 1-4 hours; steroid begins 24-72 hours.
  • Steroid 'flare' in 2–10% — manage with ice and acetaminophen.
  • Rest the thumb 24-48 hours; thumb spica splint optional for comfort.
  • Return immediately for: spreading redness, swelling, fever, disproportionate pain, OR thumb/finger color change or coolness (concern for vascular compromise).
  • Diabetics: expect 50-100 mg/dL glucose rise for 3-5 days.
  • Maximum 3 injections per year.