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CMC Joint Arthritis
(Thumb Base Arthritis) 

CMC Joint Arthritis (Thumb Base Arthritis)

Pain at the base of the thumb is one of the most common reasons patients see a hand surgeon in London. This condition is known as CMC joint arthritis, thumb base arthritis, basal joint arthritis, or trapeziometacarpal arthritis. It develops when the cartilage in the joint connecting the thumb to the wrist wears down, causing pain, weakness and reduced grip strength.

What Is CMC Joint Arthritis?

The carpometacarpal (CMC) joint sits at the base of the thumb, where the trapezium bone in the wrist meets the first metacarpal bone. This joint allows the thumb to pinch, grip and rotate, which places load on it during everyday tasks such as turning a key, opening a jar or holding a pen.

When the cartilage that cushions this joint breaks down, bone can rub against bone. The result is CMC joint arthritis, known as basal thumb arthritis or trapeziometacarpal (TMC) arthritis. It is a form of osteoarthritis and one of the most frequent causes of thumb pain in adults over 40.

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Other Names for This Condition

  • Thumb base arthritis

  • Basal joint arthritis

  • Trapeziometacarpal (TMC) arthritis

  • First CMC joint osteoarthritis

Symptoms of Thumb Base Arthritis

  • Pain at the base of the thumb, worse with pinching or gripping

  • Swelling or a bony prominence at the joint

  • Reduced grip and pinch strength

  • Stiffness after rest, easing with movement

  • A grinding or grating sensation (crepitus) when moving the thumb

  • Difficulty with tasks such as opening jars, turning keys or writing

Causes and Risk Factors

CMC joint arthritis develops as cartilage wears down over time. Factors that raise the risk include:

  • Age, since cartilage wear increases with age

  • Sex, as the condition affects women more than men

  • A history of thumb or wrist injury

  • Joint hypermobility or ligament laxity

  • Repetitive gripping or pinching through work or hobbies

  • A family history of osteoarthritis

How Thumb Base Arthritis Is Diagnosed

Diagnosis starts with a clinical examination of the thumb and CMC joint, including the grind test, where gentle compression and rotation of the joint reproduces the pain. X-rays confirm the diagnosis and show the extent of joint space narrowing, bone spurs and joint subluxation. Staging (Eaton-Littler stages I to IV) helps guide treatment choice.

Non-Surgical Treatment Options

Many patients begin with non-surgical treatment in the early stages of the condition.

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Splinting and Activity Modification​

A thumb spica splint rests the joint and reduces pain during flare-ups. Adjusting how tasks are performed, using larger grips on tools or jar openers, can reduce load on the joint.

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Steroid Injections​

A corticosteroid injection into the CMC joint can settle pain and inflammation for weeks or months. Injections work best for mild to moderate arthritis and can be repeated a limited number of times.

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Hand Therapy​

Hand therapy includes exercises to maintain thumb movement, strengthen supporting muscles and teach joint protection techniques for daily activities.

When Surgery Is Considered

Surgery becomes an option when pain continues despite splinting, injections and therapy, or when arthritis limits hand function and quality of life. The right procedure depends on the stage of arthritis, activity level and patient goals, and is agreed after a detailed discussion in clinic.

Surgical Treatment Options for CMC Arthritis

Trapeziectomy (with or without LRTI)

Trapeziectomy removes the trapezium bone, the source of the bone-on-bone contact causing pain. The procedure can be combined with ligament reconstruction and tendon interposition (LRTI), using a strip of tendon to support the space left behind. Trapeziectomy is the established surgical treatment for advanced CMC joint arthritis and offers a marked reduction in pain with preserved thumb movement.

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CMC Joint Replacement (Thumb Arthroplasty)

CMC joint replacement, or thumb base arthroplasty, replaces the damaged joint surfaces with an implant, in a similar way to hip or knee replacement. Modern implants aim to preserve joint height and thumb strength, with a faster return to function compared with trapeziectomy for some patients. Implant options include pyrocarbon and suture-suspension designs, and suitability depends on bone quality, joint stability and assessment in clinic.

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Joint Fusion (Arthrodesis)

Fusion locks the CMC joint in a fixed, pain-free position. It suits patients with high physical demands, such as manual work, who need stability over movement, though it comes at the cost of some thumb flexibility.

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