CMC Joint Injection (Thumb Arthritis)

About this injection

The carpometacarpal (CMC) joint — the joint at the base of the thumb — is one of the most commonly affected joints in osteoarthritis, particularly in women over 50. This saddle-shaped joint allows the thumb its wide range of movement, and when it becomes arthritic, even simple daily tasks such as pinching, gripping, and opening jars become painful.

Corticosteroid injection into the CMC joint delivers targeted anti-inflammatory relief directly to the affected joint, often providing weeks to months of meaningful pain relief. It is a safe and effective non-surgical treatment that can delay or avoid the need for surgical intervention.

Dr Hasham performs CMC joint injection using careful anatomical landmark technique. The joint is small, so precise placement is important — Dr Hasham's clinical experience ensures accurate and effective injection.

Conditions treated

• ✓Carpometacarpal (CMC) joint osteoarthritis — the primary indication
• ✓Thumb base pain on pinching, gripping, and fine motor tasks
• ✓Post-traumatic thumb base arthritis
• ✓Rhizarthrosis — degenerative change at the CMC joint

Symptoms

• —Pain at the base of the thumb, particularly on pinching and gripping
• —Swelling and tenderness at the base of the thumb
• —Weakness of grip and pinch strength
• —Crepitus (grinding) at the thumb base on movement
• —Difficulty with fine tasks — buttons, keys, opening jars, writing
• —Pain that worsens with use and eases with rest

Assessment & diagnosis

The grind test (axial compression and rotation of the thumb metacarpal) reproduces pain and crepitus in CMC OA. Maximum tenderness is at the anatomical snuffbox and CMC joint line. X-rays confirm the degree of joint space narrowing and osteophyte formation.

Treatment options

What happens on the day

1. Clinical assessment and grind test to confirm CMC OA
2. Thumb positioned with wrist in slight flexion and thumb adducted
3. CMC joint line identified by palpation at the base of the thumb metacarpal
4. Skin cleaned with antiseptic
5. Small gauge needle (23–25G) inserted into the joint space
6. Gentle aspiration — if resistance felt, needle repositioned
7. Corticosteroid and local anaesthetic injected
8. Needle withdrawn, small dressing applied
9. Patient advised to rest thumb and given written aftercare

Injection technique

The CMC joint is accessed from the dorsoradial aspect of the thumb base, with the thumb in a relaxed adducted position. A small-gauge needle is inserted along the joint line between the trapezium and the base of the first metacarpal. Methylprednisolone 20mg or triamcinolone 20mg in 0.5–1ml local anaesthetic is used. The joint volume is small, so only a small injection volume is required.

Risks & side effects

• —Post-injection flare — temporary increase in pain for 24–48 hours
• —Skin depigmentation and fat atrophy — may occur with repeated superficial injections
• —Tendon injury — rare with careful technique
• —Infection — very rare with sterile technique
• —Temporary blood glucose elevation in diabetic patients

Aftercare

• ✓Rest the thumb for 24–48 hours — avoid pinching and gripping
• ✓A thumb spica splint for 1–2 weeks can improve the response
• ✓Effect builds over 48–72 hours
• ✓Return to normal activities gradually
• ✓Consider hand therapy to strengthen thenar muscles and reduce long-term progression

Frequently asked questions