Basal joint arthritis is the breakdown of cartilage in the joint at the base of your thumb, where the thumb’s metacarpal bone meets a small wrist bone called the trapezium. This joint, known as the carpometacarpal (CMC) joint, is what gives your thumb its wide range of motion, letting you pinch, grip, and rotate in ways your other fingers can’t. When the cartilage cushioning that joint wears away, bone grinds against bone, causing pain, swelling, and progressive loss of function.
It’s one of the most common sites for osteoarthritis in the hand, and it disproportionately affects women. By age 70, roughly 24% of women and 20% of men show radiographic signs of thumb base osteoarthritis, though many more women seek treatment. The condition tends to worsen over time, but a combination of splinting, activity modification, and sometimes surgery can keep most people functional.
Why the Thumb Base Is Vulnerable
The CMC joint is built for mobility, not stability. Unlike your finger joints, which mostly bend and straighten, the CMC joint allows the thumb to move in multiple directions: forward, backward, across the palm, and in a circular motion. That freedom of movement comes at a cost. The joint absorbs enormous force during everyday tasks. Something as simple as pinching a key between your thumb and index finger can multiply the load on the CMC joint to several times the force you actually apply at the fingertip.
Over decades of use, the cartilage lining the joint surfaces gradually thins. Once enough cartilage is lost, the bones begin to remodel. Small bone spurs (osteophytes) develop, the joint space narrows, and the base of the thumb may start to look visibly enlarged or bony. In advanced cases, the arthritis spreads to neighboring wrist joints, a pattern sometimes called pantrapezial arthritis.
Who Gets It
Age and sex are the two strongest risk factors. At age 50, radiographic prevalence is about 7.3% in women compared to 5.8% in men. By 80, those numbers climb to 39% and 33%, respectively. But the gap in who actually seeks treatment is much wider. A large Swedish registry study found that 5% of women over 70 sought care for thumb base arthritis, compared to just 1.8% of men. That threefold difference suggests that beyond the structural disease visible on X-rays, other factors (possibly hormonal changes, differences in ligament laxity, or differences in hand use patterns) make the condition more symptomatic in women.
Repetitive pinching and gripping activities, previous thumb injuries, and joint hypermobility also increase risk. People whose work or hobbies involve sustained thumb pressure, like sewing, gardening, or using hand tools, may develop symptoms earlier.
What It Feels Like
Pain at the base of the thumb is usually the first sign. It shows up when you grasp, pinch, or twist something: turning a key, opening a jar, snapping a button closed. Early on, the pain fades with rest. Over time, it can become constant and start interfering with sleep.
Other common symptoms include:
- Swelling and tenderness at the fleshy mound where your thumb meets your wrist
- Weakened grip and pinch strength, making it harder to hold objects or open containers
- Reduced range of motion, particularly when trying to spread the thumb away from the hand
- A visible bump at the thumb base as the joint enlarges from bone spur formation
Many people first notice the problem during a specific activity and gradually realize their thumb has been getting weaker and stiffer over months or years.
How It’s Diagnosed
A doctor can often identify basal joint arthritis with a physical exam. One common test involves applying pressure along the thumb’s axis while gently rotating the joint. If this reproduces your pain or produces a grinding sensation, it strongly suggests CMC arthritis. This maneuver has about 64% sensitivity (meaning it catches most cases) and 100% specificity (meaning if it’s positive, it’s almost certainly arthritis and not something else).
X-rays confirm the diagnosis and help determine severity. Doctors use a four-stage classification system to describe how far the arthritis has progressed:
- Stage I: The joint space actually looks slightly widened, a sign of early ligament looseness before real cartilage loss begins.
- Stage II: Mild narrowing of the joint space with small bone spurs (under 2mm) and early bone hardening.
- Stage III: Significant joint narrowing with larger bone spurs (over 2mm) and more pronounced bone changes.
- Stage IV: Arthritis has spread beyond the CMC joint into the surrounding wrist bones.
The stage doesn’t always match how much pain you’re in. Some people with advanced X-ray findings have manageable discomfort, while others with milder structural changes experience significant limitations.
Nonsurgical Treatment
Most people start with conservative measures, and many never need surgery. The core strategy is reducing the load on the joint while maintaining as much thumb function as possible.
Splinting
A thumb splint (sometimes called a thumb spica orthosis) immobilizes the CMC joint to reduce pain and inflammation. The typical approach starts with full-time wear for two to three weeks, removing the splint only for bathing and gentle exercises. After that initial period, you transition to wearing it mainly during activities that provoke pain. Some people wear a splint long-term for heavy tasks like cooking or yard work and go without it the rest of the day.
Activity Modification and Adaptive Tools
Small changes to how you use your hands can dramatically reduce thumb stress. The general principle is to shift force away from your thumb and onto larger, stronger joints whenever possible. Carry a shoulder bag instead of a clutch purse. Use your palm or fingers to push open heavy doors rather than your thumb.
A range of adaptive tools can help with specific daily tasks. In the kitchen, electric can openers, jar-seal breakers, and utensils with large-diameter handles let you grip with your fingers instead of relying on thumb pressure. For writing, thicker pens, pen grips, and gel or felt-tip pens reduce the force needed. Lever-style door handles require far less effort than round doorknobs. Magnetic jewelry clasps, ergonomic garden tools, easy-grip nail clippers, and keyless car starters all target activities that would otherwise stress the thumb joint.
These aren’t just comfort measures. Consistently protecting the joint during daily activities can slow progression and help you avoid or delay surgery.
Injections and Medication
Over-the-counter anti-inflammatory medications can help manage flares. When those aren’t enough, a corticosteroid injection directly into the CMC joint can provide relief lasting weeks to months. The injection won’t reverse cartilage damage, but it can reduce inflammation enough to get you through a difficult period or confirm that the CMC joint is truly the source of your pain.
When Surgery Becomes an Option
Surgery is generally considered when conservative treatment no longer controls pain and the arthritis significantly limits what you can do with your hand. The most established procedure is trapeziectomy, in which the damaged trapezium bone is removed entirely. In many cases, the surgeon also reconstructs the ligaments using a nearby tendon to stabilize the thumb in its new position. This combination is sometimes called ligament reconstruction tendon interposition, or LRTI.
Recovery is gradual. You’ll typically wear a cast or splint for several weeks after surgery, then work with a hand therapist to rebuild strength and range of motion. Full recovery can take three to six months, and grip strength continues to improve for up to a year. Most people report significant pain relief and improved function, though the thumb may be slightly shorter and pinch strength may not fully return to pre-arthritis levels.
Joint replacement implants for the thumb CMC joint also exist, but they have a less consistent long-term track record than trapeziectomy. They remain an option in specific situations, and techniques continue to evolve.
Living With Basal Joint Arthritis
This condition is progressive, but “progressive” doesn’t mean you’re on an inevitable path to disability. Many people manage well for years or even decades with a combination of splinting during flare-ups, joint protection habits, and targeted exercises to maintain thumb strength and flexibility. The earlier you adopt protective strategies, the longer you’re likely to preserve function. If you start noticing pain at the thumb base when gripping or pinching, getting an evaluation early gives you more options and a longer runway before the arthritis limits your daily life.