Thumb Base Arthritis (Rhizarthrosis)

1. What it is

Thumb base arthritis is osteoarthritis of the trapeziometacarpal (CMC) joint, located at the base of the thumb where it meets the wrist. This joint is also commonly referred to as the basal joint.

The CMC joint is a unique saddle-shaped joint that allows the thumb an extensive range of motion, enabling it to move up, down, across the palm, and pinch. Over time, the smooth cartilage that covers the ends of the bones (the trapezium and the first metacarpal) can wear away. This cartilage breakdown leads to bone rubbing against bone, causing joint degeneration, inflammation, and pain.

It is a very common, progressive condition that worsens over time without treatment. It severely impacts thumb function and overall hand strength, but there are multiple effective ways to manage it.

2. Causes and Risk Factors

Osteoarthritis is generally caused by "wear and tear," but several factors increase the likelihood of developing thumb base arthritis:

• Age: It is most common in individuals over 50 years old.
• Gender: Women are up to 10 times more likely to develop thumb base arthritis than men, particularly after menopause, suggesting a hormonal link to ligament laxity.
• Genetic predisposition: A family history of osteoarthritis increases your risk.
• Previous injury: A history of thumb trauma, such as a severe sprain or fracture, can alter joint mechanics and lead to post-traumatic arthritis years later.
• Repetitive use: Activities that heavily engage the thumb, such as certain occupational tasks, heavy manual labor, or repetitive gripping, can accelerate joint wear.
• Hypermobility: Loose ligaments around the joint can cause instability, leading to premature cartilage breakdown.
• Inflammatory arthritis: Conditions like rheumatoid arthritis can also destroy the basal joint.
• Idiopathic: In many cases, it develops without a clear identifiable cause.

3. Symptoms

Symptoms of rhizarthrosis tend to develop gradually and may include:

• Pain: Aching or sharp pain at the base of the thumb (at the CMC joint). The pain may be constant or intermittent.
• Worse with use: Pain heavily worsens with pinching, gripping, grasping, or twisting movements (e.g., opening jars, turning keys, or writing).
• Swelling and tenderness: The base of the thumb may feel tender to the touch and appear swollen.
• Loss of strength: A noticeable loss of pinch and grip strength.
• Morning stiffness: Symptoms are often worse in the morning upon waking or after a period of intense activity.
• Progressive deformity: As the joint deteriorates, the thumb may shift out of alignment, developing a "Z-shaped" or "swan-neck" appearance. A bony bump may become visible at the base.
• Reduced mobility: Decreased range of motion of the thumb, making it hard to stretch it away from the palm.
• Functional limitation: Increasing difficulty with fine motor tasks and daily activities.

4. Diagnosis

A hand specialist can usually diagnose thumb base arthritis through a physical exam and imaging:

• Clinical examination: The doctor will palpate the CMC joint for tenderness, swelling, and bony prominences.
• Grind test: The doctor holds the base of your thumb, applies axial compression, and rotates it. If this causes pain or a grinding sensation (crepitus), it is a positive sign for cartilage loss.
• Strength and mobility assessment: Measuring pinch strength and evaluating the thumb's range of motion.
• X-ray imaging: X-rays are the primary imaging modality used to confirm the diagnosis. They can reveal joint space narrowing, bone spurs (osteophytes), and bone cysts.
• Severity grading: X-ray findings are often used to grade the severity of the arthritis (commonly using the Eaton-Littler classification), which helps guide treatment decisions.
• MRI: Rarely needed, but an MRI may be ordered if the diagnosis is uncertain or to assess soft tissue structures like ligaments and tendons.

5. Medical Treatment

Treatment always begins with conservative (non-surgical) methods to manage pain and maintain function:

• Rest and activity modification: Avoiding or adapting repetitive thumb movements and forceful pinching.
• Thumb splint or brace: Wearing a custom or over-the-counter splint to immobilize and rest the CMC joint. This is highly effective in reducing pain, especially when worn at night or during heavy activities.
• NSAIDs: Non-steroidal anti-inflammatory drugs (like ibuprofen) to reduce pain and joint inflammation. Acetaminophen can also be used for pain relief.
• Ice application: Applying ice to the base of the thumb can help reduce acute swelling and pain.
• Corticosteroid injection: An injection of cortisone directly into the CMC joint can provide significant relief. About 50-70% of cases improve with this conservative approach. Multiple injections may be needed over time (typically limited to a maximum of 3).
• Physical therapy: Specific hand exercises to maintain thumb mobility and strengthen the muscles that stabilize the basal joint.

If conservative treatment fails to provide adequate relief after several months, surgical options are considered.

6. Surgical Treatment

Surgery is indicated for persistent pain that affects daily function, failure of conservative treatments, or significant joint deformity.

There are two main surgical options. Both have an 80-90% success rate for pain relief:

• Trapeziectomy (Removal of the trapezium): This is the most common procedure. The surgeon removes the arthritic trapezium bone entirely. This stops the painful bone-on-bone rubbing. Often, a piece of tendon is used to stabilize the thumb in the empty space. It is simple, highly effective, and definitive (arthritis cannot return). However, it may result in some loss of thumb length and pinch strength.
• Implant Arthroplasty (Joint Replacement): The arthritic joint surfaces are replaced with an artificial implant (similar to a mini hip replacement, made of metal, pyrocarbon, or silicone). This preserves thumb length and often provides a quicker return to strength. However, implants may wear out, dislocate, or fail over time, potentially requiring revision surgery.

These procedures are typically performed using a minimally invasive approach with a small incision, as a day surgery under local or regional anesthesia.

7. Recovery

Recovery after thumb base arthritis surgery requires time and rehabilitation:

• Immediate post-op: Pain and swelling are expected. Pain is managed with prescribed medications and NSAIDs.
• Immobilization: The thumb will be immobilized in a cast or rigid splint for 4 to 6 weeks to allow healing.
• Gradual mobilization: After 4-6 weeks, the splint is removed, and gentle, supervised movement begins.
• Physical therapy: Hand therapy is crucial to restore thumb strength, pinch grip, and mobility.
• Return to activity: Light activities can usually be resumed within 4 to 6 weeks. Return to normal, heavier activities takes about 8 to 12 weeks.
• Full recovery: Full recovery and return to all activities generally take 3 to 6 months. Regaining maximum pinch strength may take several months.

Possible temporary swelling or tenderness at the incision site is normal. Complications are rare but can include nerve injury, infection, stiffness, or implant failure (if an implant was used).

8. When to See a Doctor

You should consult a hand specialist if you experience:

• Persistent pain at the base of the thumb that lasts more than a few weeks.
• Pain that significantly affects daily activities (opening jars, turning keys, writing).
• Visible swelling or progressive deformity at the thumb base.
• Noticeable loss of pinch strength or overall grip strength.
• Symptoms that are not improving with rest and over-the-counter NSAIDs after 2-3 weeks.
• Progressive worsening of your symptoms over time.

Seek urgent medical care if you experience severe, sudden pain, signs of infection (redness, heat), or a sudden loss of thumb function. Book a consultation with Dr. Kilinc.

Frequently Asked Questions