Basal thumb arthritis is a common degenerative joint condition, a form of osteoarthritis, that affects the base of the thumb. It is particularly prevalent among older adults, often developing in people aged 40 to 50, and is significantly more common in women, especially following menopause. The progressive wear and tear causes pain, weakness, and stiffness, severely limiting the hand’s function. Because the thumb is responsible for approximately 40% of overall hand function, this arthritis can be quite disabling, interfering with many basic daily activities.
The CarpoMetacarpal Joint and Disease Process
Basal thumb arthritis specifically involves the first carpometacarpal (CMC) joint, which connects the first metacarpal bone of the thumb to a small wrist bone called the trapezium. The CMC joint is uniquely structured as a saddle joint, featuring two opposing curves that allow the thumb an extensive range of motion, including rotation and opposition.
This remarkable mobility comes at the cost of stability, making the joint inherently susceptible to degeneration. The joint is primarily stabilized by a network of ligaments, with the anterior oblique ligament preventing the metacarpal bone from sliding out of place. Arthritis begins when the smooth articular cartilage covering the ends of the bones starts to wear away, becoming thin and rough.
The breakdown of this cartilage leads to bone-on-bone friction and an inflammatory response within the joint. Over time, the loss of cartilage and the weakening of stabilizing ligaments can cause the first metacarpal to shift or subluxate out of its proper position. This misalignment increases mechanical stress and can stimulate the growth of small bony projections, known as osteophytes or bone spurs, further damaging the joint structure.
Recognizing Common Symptoms
The most frequent complaint is a dull, aching pain localized at the base of the thumb, near the wrist. This pain is aggravated by activities that require forceful use of the thumb, such as gripping, pinching, or twisting. Simple daily tasks become painful, including turning a key, opening jar lids, or writing.
As the condition progresses, patients often notice a loss of strength when trying to grasp or pinch objects. Swelling, tenderness, and stiffness at the base of the thumb are also common findings. In advanced stages, the joint may appear enlarged or form a visible bony prominence near the wrist as the metacarpal shifts position, sometimes resulting in a zig-zag deformity.
A gritty sensation or grinding noise, medically termed crepitus, can be felt or heard when moving the thumb. Symptoms may fluctuate, with periods of greater discomfort followed by relative rest, but the underlying degenerative process continues.
Confirming the Diagnosis and Staging Severity
A healthcare provider typically diagnoses basal thumb arthritis through a detailed history and physical examination. During the examination, the provider looks for tenderness when pressing directly on the CMC joint and may perform provocative maneuvers. The “grind test” is a specific maneuver where the provider compresses and rotates the thumb metacarpal to check for pain, crepitus, or instability, which strongly suggests arthritis.
X-rays are necessary to confirm the diagnosis and visualize the extent of the joint damage. These images clearly show signs of osteoarthritis, such as joint space narrowing, bone spurs, and joint subluxation. Clinicians use staging systems to classify the severity of the arthritis based on these radiographic findings, which guides the treatment plan.
The most widely used classification system is the Eaton-Littler classification, which separates the condition into four progressive stages. These stages range from Stage I, showing slight joint space widening, to Stages III and IV, which indicate marked joint narrowing, larger osteophytes, and significant subluxation.
Comprehensive Management Options
Treatment for basal thumb arthritis begins with conservative, non-surgical approaches, which are often successful in relieving symptoms. Initial management focuses on reducing pain and inflammation through activity modification, avoiding forceful pinching or gripping, and using nonsteroidal anti-inflammatory drugs (NSAIDs). Resting the joint with a supportive splint or orthosis is a mainstay of conservative care, as it helps stabilize the CMC joint and reduce stress.
Hand therapy, which includes targeted exercises to strengthen the muscles around the thumb and improve joint stability, is a highly effective non-operative strategy. If these measures do not provide adequate relief, a corticosteroid injection directly into the CMC joint can reduce inflammation and provide pain relief for several months. The effectiveness of injections may diminish over time, and they are reserved for more severe symptoms.
When conservative treatments fail to control pain and functional limitations, surgical options become necessary, particularly in advanced stages. A common surgical procedure is a trapeziectomy, where the damaged trapezium bone is removed completely. This may be combined with a ligament reconstruction and tendon interposition (LRTI), using a tendon to fill the space and stabilize the joint. Other options include joint fusion (arthrodesis), which eliminates movement and pain but sacrifices flexibility, and joint replacement, which uses an implant to recreate the joint articulation. The choice of procedure depends on the disease stage, the patient’s age, and functional demands, aiming to provide long-term pain relief and restore hand function.