Thumb Base Osteoarthritis (CMC Joint)

Overview

The carpometacarpal (CMC) joint sits at the base of the thumb, where the long thumb bone meets a small wrist bone. It is a saddle-shaped joint that lets the thumb swing across the palm and pinch against the fingers — movements we rely on hundreds of times a day. Because it is so mobile and so heavily used, it is one of the most common places in the hand for osteoarthritis to develop.

Osteoarthritis is the gradual wearing of the smooth cartilage that lines a joint. At the thumb base this causes a deep ache at the bottom of the thumb, pain with pinching (turning keys, opening jars, writing, texting), and weakness of grip. Over time the joint may become enlarged or develop a bump, and the thumb can start to sit in a slightly collapsed position.

It is most common in women over 50, and often runs in families. Symptoms tend to fluctuate: flares of several weeks are followed by quieter periods. Osteoarthritis is a long-term condition and the aim of treatment is to manage pain, protect the joint and keep the hand working well, rather than to reverse the changes. Many people maintain good function for years with the right strategies.

Causes and risk factors

• Age over 50, and female sex
• Family history of hand osteoarthritis
• Previous thumb injury or fracture
• Naturally loose thumb ligaments
• Years of repetitive pinching and gripping in work or hobbies
• Being overweight, which is linked to osteoarthritis in many joints

How we may be able to help

We assess the thumb to confirm the joint as the source of pain and to distinguish it from De Quervain's tenosynovitis or a wrist problem, which can feel similar. Where needed, we can arrange an online private GP consultation for an X-ray to grade the arthritis, or for a specialist opinion if pain remains limiting despite treatment. We do not provide splinting or hand therapy; we will advise you if a thumb support is likely to help.

Physiotherapy is centred on a targeted exercise programme that strengthens the small muscles stabilising the thumb base — evidence suggests this can reduce pain and improve pinch strength — along with joint protection advice: how to grip, open jars and use tools in ways that take load off the joint. Gentle joint mobilisation and soft tissue techniques for the thumb and forearm muscles may ease stiffness and pain.

Therapeutic ultrasound over the joint may provide pain relief during a flare, and interferential therapy can be used for the same purpose. Kinesiology taping around the thumb base is used by some people for extra support during busy periods. Where appropriate, your GP may discuss medication or other options; we can arrange that conversation.

What you can do at home

• Use larger, padded grips on pens, tools and cutlery to reduce pinch force
• Open jars with a rubber grip or jar opener and lean your body weight in rather than twisting with the thumb
• Spread load across the whole hand — carry bags on the forearm rather than hooked on the fingers
• Keep the thumb moving with gentle daily exercises your therapist shows you
• Use warmth (a warm bowl of water or a heat pack) for stiffness, and ice briefly for a painful flare
• Pace activities during a flare: shorter bursts with breaks rather than long sessions