Basal thumb arthritis, also known as carpometacarpal (CMC) joint arthritis, is a degenerative condition affecting the joint at the base of the thumb where the first metacarpal bone meets the trapezium bone of the wrist. This joint is crucial for the thumb’s wide range of motion and its ability to pinch and grip. Medical professionals use a staging system to classify the progression of this condition, which guides the appropriate treatment plan. Stage 4 represents the most advanced classification of basal thumb arthritis, indicating extensive damage to the joint structure.
Anatomical Markers of Stage 4 Arthritis
The diagnosis of Stage 4 arthritis is based on specific radiographic findings, typically using the Eaton-Littler classification system. This stage signifies that the degenerative process has extended beyond the primary CMC joint. The defining feature is the involvement of the adjacent scaphotrapeziotrapezoidal (STT) joint, resulting in pantrapezial arthritis. This means that arthritic changes, including cartilage loss and bone erosion, are present in multiple joints surrounding the trapezium bone.
The CMC joint itself displays severe deterioration. This includes marked joint space narrowing, often resulting in bone-on-bone contact where the bones grind directly against each other. Large osteophytes, or bone spurs, are often present and typically measure greater than two millimeters. The advanced destruction is accompanied by significant subluxation, or partial dislocation, of the thumb metacarpal base on the trapezium.
Functional Impairment and Pain Severity
The structural collapse of the joint at Stage 4 corresponds to a profound deterioration in hand function. Pain becomes markedly more severe and often transitions from being activity-related to a constant, aching sensation, even when the hand is at rest or during the night. The destruction of the cartilage lining causes grinding, or crepitus, which is often felt during thumb movement.
The ability to perform strong pinch and grip maneuvers is dramatically compromised due to instability and pain at the joint base. Simple daily tasks, such as turning a doorknob, opening a jar, or using a key, become extremely difficult or impossible. A visible sign of this advanced stage can be the development of a “zigzag” or “Z” deformity. This occurs when the CMC joint collapses inward and the joint closer to the fingertip (metacarpophalangeal joint) hyperextends to compensate.
Surgical and Non-Surgical Treatment Options
For Stage 4 basal thumb arthritis, the goal of treatment shifts toward effective, long-term pain relief and restoration of function, often requiring surgical intervention. Conservative, non-surgical approaches, such as splinting, anti-inflammatory medications (NSAIDs), and corticosteroid injections, typically offer only limited or temporary relief. These non-operative methods are usually exhausted first but cannot reverse the extensive joint damage.
Since the joint is extensively destroyed and the adjacent STT joint is also involved, surgery is typically the recommended pathway. The most common surgical procedure is a trapeziectomy, which involves the complete removal of the damaged trapezium bone. This creates a space that relieves the bone-on-bone pain.
Combined Procedures
Trapeziectomy is often combined with a procedure called ligament reconstruction and tendon interposition (LRTI) or suspensionplasty. In this combined approach, a tendon is harvested from the wrist and used to create a sling or cushion in the void left by the removed trapezium, preventing the metacarpal from collapsing into the wrist bones.
Joint Replacement and Fusion
Joint replacement, or arthroplasty, is another option where the damaged joint is replaced with an artificial implant. While this aims to maintain joint length and motion, the long-term failure rates of implants can be a concern. A third surgical approach is arthrodesis, or joint fusion, which locks the bones together to eliminate movement and pain. Fusion is generally reserved for younger patients or those with high manual demands who prioritize stability and strength over range of motion.