CMC Arthritis defined as The carpometacarpal joint of the thumb is a common site of osteoarthritis. Carpometacarpal osteoarthritis is a degenerative condition of the hand that causes pain, stiffness and weakness. It is the second most common site of degenerative disease in the hand after arthritis of the distal interphalangeal joints.
You may not think much about your thumb—after all, it’s a digit and not even a finger—but it plays an important role in your everyday life. You use your thumb to grasp and pinch objects, open jars, play the guitar, dress yourself, operate tools, and perform countless other tasks.
And even if you do appreciate your thumb, you might not be aware of how the first carpometacarpal or “CMC” joint helps it do its job. The CMC joint is located where the thumb (metacarpal) bone meets the wrist (carpal) bone.
As this joint becomes worn, often due to age, it can lead to a painful condition called thumb arthritis (also known as CMC arthritis or basal joint arthritis). Arthritis refers to inflammation in a joint, causing the pain, stiffness, and swelling that makes it so difficult to perform even simple tasks. Thumb arthritis is the second most common type of arthritis in the hand.
Xuan Luo, MD, a Yale Medicine hand, shoulder, and elbow surgeon, draws from evolutionary history when he explains thumb arthritis to patients. “If you look at certain ancestors of ours, not all of them had opposable thumbs [meaning they can be placed opposite the fingers, which is what allows us to grasp objects]. This is a relatively new evolutionary invention,” Dr. Luo says. “And like any new feature on your car or computer, it’s not always tested well and tends to wear out first. As we get older, that CMC joint in particular often wears out, causing pain at the base of the thumb.”
Treatment for thumb arthritis starts conservatively with the patient wearing a soft brace. If that doesn’t work, injections at the base of the palm may work. And if there still isn’t relief, surgery is an option.
Joints are connections between two or more bones. A normal joint is made of two smooth, cartilage-covered bone surfaces that fit well together and glide when the body moves. But if the smooth surface wears out—often, just from the wear and tear that comes with age—then the bone surfaces no longer fit together and arthritis can develop.
There are many different types of arthritis, but the kind that most often affects the thumb is osteoarthritis, the most common form of arthritis. With osteoarthritis, the cartilage inside your joints starts to break down, causing changes in the bone that typically start slowly and worsen over time.
An injury to the thumb raises the likelihood that you will develop thumb arthritis. Other conditions, including lupus and rheumatoid arthritis, might also cause deterioration of the basal joint.
Thumb arthritis typically occurs after age 40. It is more common in women, but it can affect men, too. There is a genetic predisposition that makes people more likely to develop thumb arthritis.
“Thumb arthritis is unbelievably common, and if we look at the X-rays of people in their 50s, 60s, and 70s, 30 to 50 percent of that population can have it,” Dr. Luo says. “But not everyone will have symptoms that are severe enough to require any treatment.”
Pain in the thumb is the most common symptom of thumb arthritis. You might feel pain when you are pinching or gripping objects, Dr. Luo says. “You may also notice a little bump at the base of your thumb,” he adds, explaining that this would be a bone spur, or a projection that develops along joints as a result of inflammation, including osteoarthritis.
Other symptoms may include the following:
To make a diagnosis of thumb arthritis, your doctor will start by gathering your medical history, discussing symptoms, prior injuries, and what activities cause you pain.
For the physical examination, your doctor will hold the basal joint while rocking your thumb back and forth, Dr. Luo says. If that causes pain or a grinding sound, it means the bones are rubbing directly against each other and likely have thumb arthritis. An X-ray can confirm the diagnosis.
What is basal joint arthritis?
Basal joint arthritis is the result of the wearing away of cartilage in the joint at the base of the thumb. That’s why it is also known as thumb arthritis. The basal joint allows your thumb to move around so you can perform small motor tasks. Without plenty of cushioning cartilage, the joints become rough and grind over each other when you move, causing more joint damage. According to the Mayo Clinic, thumb arthritis is the most common form of osteoarthritis (wear and tear arthritis) of the hand. It can also be caused by injury to the thumb.
Usually, the first sign of arthritis in the thumb is pain, tenderness, and stiffness. You’re most likely to feel it at the base of your thumb as you try to grip, pinch, or clasp something between the thumb and index fingers. You might also feel a pain when you try to apply mild force, such as when you twist a key in a lock, turn a door handle, or snap your fingers. You might be left with a lingering ache. A high level of pain doesn’t always mean your arthritis is more severe.
Over time, pain and inflammation can rob your hand of strength and restrict your range of motion. These restrictions become especially obvious when you try to pinch something or clasp an object tightly. You might find it increasingly difficult to open jars, hold a drink, or use buttons, zippers, and snaps. For those with a severe case of arthritis in the thumb, small motor tasks that were once a matter of routine become too painful to attempt, or almost impossible to accomplish without assistance.
The thumb may appear swollen, especially at its base, and you may develop a bony bump. Overall, the base of the thumb can take on an enlarged appearance. One alarming sign of thumb arthritis is improper alignment of the joint as it shifts from its normal positioning. This may affect the joint above the base as well, creating a bent-back appearance (hyperextension). In particularly severe cases, the thumb cannot get out of the palm of the hand.
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