Basal thumb arthritis is a common and often debilitating form of osteoarthritis that targets the base of the thumb. This condition makes everyday hand movements painful and difficult, significantly impacting daily activities. Osteoarthritis is characterized by the breakdown of joint cartilage, and the thumb’s basal joint is one of the most frequently involved sites in the hand.
The Anatomy of Basal Thumb Arthritis
Basal thumb arthritis affects the carpometacarpal (CMC) joint, sometimes called the trapeziometacarpal joint, which connects the thumb to the wrist. This joint is formed by the first metacarpal bone of the thumb and a small wrist bone called the trapezium. The CMC joint is uniquely shaped like a saddle, allowing the thumb a wide range of motion, including the ability to rotate and oppose the fingers.
This mobility makes the joint inherently less stable and more vulnerable to mechanical stress over time. In a healthy joint, hyaline cartilage covers the ends of the trapezium and metacarpal bones, providing a smooth, cushioned surface for movement. Basal thumb arthritis occurs when this cartilage gradually wears away, becoming rough and thin.
When the protective cartilage is gone, the bones begin to rub directly against each other, causing friction, inflammation, and joint damage. This bone-on-bone contact results in joint space narrowing and, in advanced stages, the formation of bony outgrowths called osteophytes, or bone spurs. The resulting instability and friction within this joint cause the patient’s pain and loss of function.
Identifying Symptoms and Diagnosis
The most prominent symptom is pain localized at the base of the thumb, often radiating into the wrist. This discomfort is aggravated by activities requiring pinch, grip, or twisting movements, such as turning a key or opening a jar. As the condition progresses, a dull ache may become constant, even during periods of rest.
Patients commonly report stiffness or tenderness, especially in the morning or after prolonged periods of inactivity. A gritty sensation or an audible grinding noise, known as crepitus, may be felt when moving the thumb due to the roughened joint surfaces. The base of the thumb may also appear visibly enlarged or develop a bony bump due to joint inflammation and bone spurs.
Diagnosis begins with a physical examination, where the physician assesses the range of motion and tenderness of the hand and thumb. A common provocative test is the “grind test,” where the doctor applies axial pressure to the thumb metacarpal while rotating it. The test is positive if it reproduces the patient’s pain or a grinding sound. The diagnosis is confirmed with X-rays, which visualize joint space narrowing, bone spurs, and any potential joint subluxation, or partial dislocation.
Primary Causes and Risk Factors
Basal thumb arthritis is overwhelmingly a form of osteoarthritis, meaning the primary cause is mechanical wear and tear on the joint over decades. The cumulative effect of repetitive motions and high forces placed on the joint during gripping and pinching gradually degrades the cartilage.
Age is a major risk factor, with the condition becoming significantly more common after the age of 40. Radiographic evidence of the disease is found in a large percentage of the population over 50. Gender is another risk factor, as the condition affects women far more frequently than men, particularly after menopause.
There is also a genetic component to basal thumb arthritis, suggesting that a predisposition for osteoarthritis or conditions affecting joint stability can be inherited. Prior trauma to the joint, such as fractures or sprains, can accelerate the degenerative process, leading to secondary arthritis years later. Certain occupations or activities that require repetitive, forceful gripping may also increase the risk.
Comprehensive Treatment Options
Initial treatment focuses on conservative methods aimed at reducing pain and maintaining function. Activity modification is recommended, which involves finding alternative ways to perform tasks that require painful gripping or twisting motions. Wearing a supportive splint or brace is a common first-line treatment, as it limits the movement of the joint to allow it to rest.
Medication management involves oral or topical non-steroidal anti-inflammatory drugs (NSAIDs) to decrease pain and inflammation. For more pronounced symptoms, a corticosteroid injection may be delivered directly into the joint. These injections can provide substantial relief for several months, though their effect is temporary and they may become less effective if repeated too frequently.
Physical or occupational therapy is an important part of conservative care. Hand therapists teach exercises to improve joint stability, strengthen surrounding muscles, and optimize hand mechanics. These specialists also help patients find and use adaptive equipment to reduce stress on the joint during daily tasks. If conservative measures fail to provide adequate pain relief and function is severely limited, surgical options are considered.
Surgical intervention for advanced cases aims to eliminate painful bone-on-bone contact and restore mobility. The most common procedure is a trapeziectomy, which involves removing the trapezium bone. This removal is often combined with ligament reconstruction and tendon interposition (LRTI) to stabilize the thumb and fill the void with a piece of tendon. Other options include joint fusion (arthrodesis), which permanently joins the bones to eliminate movement and pain, or joint replacement, where the arthritic joint surfaces are replaced with a prosthetic.