Rhizarthrosis of the Thumb: Symptoms, Causes, Diagnosis, and Treatment

What is Rhizarthrosis of the thumb?

Rhizarthrosis, also known as thumb carpometacarpal (CMC) joint osteoarthritis, is a common degenerative joint disease affecting the base of the thumb, specifically where the first metacarpal bone meets the trapezium bone. This condition leads to pain, stiffness, and functional limitations, significantly impacting daily activities requiring thumb use.

Understanding the Thumb's CMC Joint

The thumb's carpometacarpal (CMC) joint, sometimes referred to as the basal joint, is a saddle-shaped synovial joint located at the base of the thumb. It is formed by the articulation of the first metacarpal bone of the thumb and the trapezium bone of the wrist (one of the carpal bones).

• Anatomy of the CMC Joint: This unique saddle shape allows for a wide range of motion, including flexion, extension, abduction, adduction, and most notably, opposition – the ability to bring the thumb across the palm to touch the tips of other fingers. This complex movement is crucial for fine motor skills and gripping. The joint surfaces are covered with articular cartilage, a smooth, slippery tissue that allows bones to glide effortlessly against each other and acts as a shock absorber. A network of ligaments surrounds the joint, providing stability.
• Role of the CMC Joint in Thumb Function: The CMC joint is fundamental to the thumb's dexterity and its role in nearly all hand functions. From pinching and gripping to writing, opening jars, and using tools, the health of this joint directly dictates our ability to interact with our environment effectively. Its mobility makes the human thumb incredibly versatile but also renders it susceptible to degenerative changes due to repetitive stress and load.

What is Rhizarthrosis?

Rhizarthrosis is a specific form of osteoarthritis that targets the thumb's carpometacarpal (CMC) joint. It is a progressive condition characterized by the gradual breakdown of the articular cartilage within the joint.

• Definition and Alternative Names: While "rhizarthrosis" is the medical term, it is commonly referred to as thumb CMC osteoarthritis or basal joint arthritis of the thumb. Regardless of the name, the underlying pathology is the same: degenerative changes leading to joint dysfunction.
• Pathophysiology: The disease process begins with the erosion of the smooth articular cartilage. As the cartilage wears away, the bones begin to rub directly against each other, leading to friction, inflammation, and pain. In response to the increased stress, the body may attempt to repair the joint by forming new bone, often resulting in the development of osteophytes (bone spurs) around the joint margins. These spurs can further limit movement and cause pain. Over time, the joint space narrows, the joint may become unstable, and the bones themselves can undergo changes, potentially leading to subluxation (partial dislocation) or deformity.

Causes and Risk Factors

Rhizarthrosis is a multifactorial condition, meaning several factors contribute to its development.

• Age: This is the primary risk factor. The incidence of rhizarthrosis significantly increases with age, typically affecting individuals over 40-50 years old. The cumulative wear and tear on the joint over decades contribute to cartilage degradation.
• Gender: Women are significantly more prone to developing rhizarthrosis than men, particularly after menopause. Hormonal factors, such as decreased estrogen levels, are believed to play a role in cartilage health and ligamentous laxity.
• Genetics: A family history of osteoarthritis, particularly in the hands, increases an individual's risk, suggesting a genetic predisposition.
• Repetitive Stress/Overuse: Occupations or hobbies involving repetitive, forceful gripping, pinching, or twisting movements of the thumb can accelerate the wear and tear on the CMC joint. Examples include certain manual labor jobs, knitting, gardening, or even excessive smartphone use.
• Previous Injury: A history of trauma to the thumb or wrist, such as fractures, dislocations, or sprains involving the CMC joint, can predispose an individual to developing post-traumatic arthritis in that joint.
• Ligamentous Laxity: Individuals with naturally hypermobile joints or generalized ligamentous laxity may have less stable CMC joints, leading to increased stress and premature cartilage degeneration.

Common Symptoms

The symptoms of rhizarthrosis typically develop gradually and worsen over time, significantly impacting hand function.

• Pain: This is the hallmark symptom, usually felt at the base of the thumb, near the wrist. The pain is often described as a deep, aching sensation that worsens with activities requiring thumb motion, such as gripping, pinching, twisting, or lifting objects. It may subside with rest.
• Stiffness: The joint may feel stiff, especially in the morning or after periods of inactivity. This stiffness often improves with gentle movement but can return with prolonged use.
• Swelling: Localized swelling around the base of the thumb is common, indicating inflammation within the joint.
• Loss of Strength: As the condition progresses, individuals may experience a noticeable decrease in grip strength and pinch strength, making it difficult to perform tasks like opening jars, turning keys, or holding small objects.
• Decreased Range of Motion: The ability to move the thumb through its full range of motion, particularly opposition (bringing the thumb across the palm), becomes limited and painful.
• Grinding Sensation (Crepitus): A grinding, popping, or crunching sensation may be felt or heard when moving the thumb's CMC joint, indicative of bone-on-bone friction due to cartilage loss.
• Deformity: In advanced stages, the joint may appear enlarged or "squared off" at the base of the thumb due to bone spurs and joint subluxation. This is sometimes referred to as the "shoulder sign" due to the outward prominence.

Diagnosis

Diagnosing rhizarthrosis typically involves a combination of a thorough clinical examination and diagnostic imaging.

• Clinical Examination: A healthcare professional, such as an orthopedic surgeon, hand specialist, physical therapist, or kinesiologist, will assess the thumb's range of motion, observe any swelling or deformity, and palpate the joint for tenderness. Specific provocative tests, such as the Grind Test, are often performed. In this test, the examiner compresses and rotates the thumb metacarpal bone into the trapezium. Pain and crepitus during this maneuver are strong indicators of CMC arthritis. The clinician will also assess pinch and grip strength.
• Imaging:
  • X-rays: Plain X-rays are the primary imaging modality used to confirm the diagnosis and assess the severity of the arthritis. X-ray findings characteristic of rhizarthrosis include:
    • Joint space narrowing: Indicating cartilage loss.
    • Osteophytes: Bone spurs around the joint margins.
    • Subchondral sclerosis: Increased bone density beneath the cartilage.
    • Subchondral cysts: Fluid-filled sacs within the bone.
    • Joint subluxation: Partial dislocation of the joint.
  • Other imaging, such as MRI, is generally not necessary for diagnosis but may be used in complex cases or to rule out other conditions.

Management and Treatment Approaches

The primary goals of rhizarthrosis management are to reduce pain, improve function, and slow the progression of the disease. Treatment strategies range from conservative (non-surgical) measures to surgical interventions for more severe or refractory cases.

Conservative Management (Non-Surgical)

Most cases of rhizarthrosis are initially managed with conservative approaches.

• Activity Modification: Identifying and avoiding activities that aggravate the joint is crucial. This might involve changing gripping techniques, using adaptive tools, or taking frequent breaks during repetitive tasks.
• Splinting/Bracing: Wearing a thumb splint or brace (e.g., a custom-molded orthosis or an off-the-shelf soft brace) can help immobilize or support the CMC joint, reduce pain, and provide rest. This is often recommended during painful flare-ups or for specific activities.
• Pain Management:
  • Over-the-counter medications: Non-steroidal anti-inflammatory drugs (NSAIDs) like ibuprofen or naproxen can help reduce pain and inflammation. Topical NSAIDs may also be beneficial.
  • Ice/Heat: Applying ice packs can reduce swelling and pain during acute flare-ups, while heat can help soothe stiffness.
• Physical and Occupational Therapy: A cornerstone of conservative management, therapy focuses on:
  • Joint protection strategies: Educating patients on ergonomic principles and ways to reduce stress on the thumb joint during daily activities.
  • Strengthening exercises: Targeting the muscles around the thumb and forearm (e.g., thenar muscles, wrist extensors) to improve stability and support the joint.
  • Range of motion exercises: Gentle exercises to maintain or improve thumb mobility without exacerbating pain.
  • Modalities: Therapeutic modalities like ultrasound, paraffin wax baths, or TENS (Transcutaneous Electrical Nerve Stimulation) may be used to reduce pain and inflammation.
• Injections:
  • Corticosteroid injections: Injections of corticosteroids directly into the CMC joint can provide significant, though often temporary, relief from pain and inflammation. They are typically used for acute flare-ups.
  • Hyaluronic acid injections: While less commonly used for the CMC joint compared to larger joints like the knee, some evidence suggests they may provide lubrication and shock absorption.

Surgical Interventions

Surgery is typically considered when conservative treatments fail to provide adequate pain relief or functional improvement, or when the joint deformity significantly impairs function.

• Trapeziectomy: This is the most common surgical procedure for advanced rhizarthrosis. It involves the removal of the trapezium bone, which eliminates the bone-on-bone friction. Often, a tendon interposition arthroplasty is performed concurrently, where a portion of a wrist tendon is used to fill the space left by the removed bone, creating a cushion.
• Arthrodesis (Joint Fusion): This involves permanently fusing the first metacarpal to the trapezium, eliminating all movement at the joint. While it provides excellent pain relief and stability, it sacrifices the thumb's mobility, making it less common for the CMC joint compared to other finger joints.
• Arthroplasty (Joint Replacement): In some cases, joint replacement with an artificial implant may be considered, similar to hip or knee replacements. However, these are less common for the thumb CMC joint due to the small size and complex mechanics.

Prognosis and Living with Rhizarthrosis

Rhizarthrosis is a chronic, progressive condition, but its symptoms are often manageable. With appropriate treatment, most individuals can maintain significant functional independence and a good quality of life.

Early diagnosis and adherence to a comprehensive management plan, including activity modification, therapeutic exercises, and potentially splinting, are key to slowing disease progression and minimizing pain. While there is currently no cure for osteoarthritis, ongoing research continues to explore new treatments to preserve joint health and restore function. Living with rhizarthrosis often involves adapting daily routines and consistently applying strategies learned from healthcare professionals to protect the thumb and reduce symptoms.