Why does thumb arthritis cause pain & deformity?

Thumb pain can make simple daily tasks like gripping a cup or buttoning a shirt surprisingly hard. If you’ve noticed swelling, unusual bending of your thumb joints, or difficulty moving your thumb, you might be wondering what’s happening. This article explains what scientists uncovered about thumb arthritis, also called rhizarthrosis, and how it affects your muscles.

Here’s what you’ll learn:

• What happens to your joints with thumb arthritis?
• How your thumb muscles change with arthritis.
• Why thumb deformities occur and what the study discovered.

In this article:

• What is Rhizarthrosis?
• What Happens to Your Thumb in Arthritis?
• How Your Thumb Muscles Change & Cause Deformity
• Frequently Asked Questions
• Final Thoughts
• Disclaimer

What is Rhizarthrosis?

Rhizarthrosis is another name for thumb arthritis, especially when it affects the base of your thumb where it connects to your wrist. This joint is called the carpometacarpal joint. It can wear down over time, which means the cartilage—the cushiony surface between your bones—breaks apart. Without that cushion, the bones can rub against each other, causing pain.

You might notice swelling, stiffness, or changes in how your thumb looks. Some people lose their grip strength, and their thumb may start bending in unusual ways.

What Happens to Your Thumb in Arthritis?

The study mentioned that advanced thumb arthritis does specific things to your thumb:

• The base of your thumb joint can move out of place, causing “subluxation,” which is a partial dislocation.
• Your thumb may twist inward toward your palm. Doctors call this an adduction deformity.
• The joint near your thumbnail can bend backwards into what’s called hyperextension, where it moves beyond the normal range.

All of these changes make using your thumb much harder.

How Your Thumb Muscles Change & Cause Deformity

Let’s look closer at what the study found. It explored what happens to the muscles in your thumb with arthritis:

• The M. abductor pollicis brevis, or a muscle that lifts your thumb away from the palm, works differently because the direction it pulls in actually changes. Imagine trying to pull on a door handle in a strange direction—it doesn’t work the same.
• The flexor pollicis brevis, a muscle that gives you strength to bend your thumb, becomes smaller with arthritis—about 50% smaller, according to the study.
• Electromyography (a fancy test that tracks how muscles are working) showed that some thumb muscles lose their ability to fire correctly. They don’t contract the way they’re supposed to, which makes your thumb weaker.

Here is where it gets interesting. These problems in your muscles create an imbalance. Scientists compare it to a system of ropes where one rope pulls too tightly while others loosen. Without balance, your thumb becomes stuck in what’s called a “Z-deformity.” This means your thumb bends in odd ways and becomes harder to straighten.

Frequently Asked Questions

Final Thoughts

Your thumb plays a huge role in daily life—so understanding how arthritis affects it can help you take healthy next steps. If these symptoms sound familiar, don’t hesitate to visit your doctor or physical therapist. Strengthening exercises and treatment, like supportive splints, might be a helpful option.

At this site, we make medical science simple and easy to understand, especially for those facing thumb pain and rhizarthrosis. Every article is based on trusted published research. Be sure to browse our other blogs to find more information that you can put into action!

Disclaimer

This article is for educational purposes only. It is not intended to be medical advice. For any health concerns, please consult a qualified healthcare professional.

Study Source

Schoneberger, M.; Koebke, J. (1989). Rhizarthrosis and thenar muscles. A clinico-anatomic study.