Trapeziometacarpal osteoarthritis

Trapeziometacarpal osteoarthritis, also known as osteoarthritis at the base of the thumb or as rhizarthrosis, is a reparitive joint disease affecting the first carpometacarpal joint (CMC1). This joint is formed by the trapezium bone of the wrist and the first metacarpal bone of the thumb. Because of its relative instability, this joint is a frequent site for osteoarthritis. Carpometacarpal osteoarthritis (CMC OA) of the thumb occurs when the cushioning cartilage of the joint surfaces wears away, resulting in damage of the joint. Trapeziometacarpal osteoarthritis, also known as osteoarthritis at the base of the thumb or as rhizarthrosis, is a reparitive joint disease affecting the first carpometacarpal joint (CMC1). This joint is formed by the trapezium bone of the wrist and the first metacarpal bone of the thumb. Because of its relative instability, this joint is a frequent site for osteoarthritis. Carpometacarpal osteoarthritis (CMC OA) of the thumb occurs when the cushioning cartilage of the joint surfaces wears away, resulting in damage of the joint. The main complaint of patients is pain. Pain at the base of the thumb occurs when moving the thumb and might eventually persist at rest. Other symptoms include stiffness, swelling and loss of strength of the thumb. Treatment options include conservative and surgical therapies. The primary and most common symptom in patients with CMC OA of the thumb is pain. Pain at the base of the thumb is mainly experienced when moving the thumb or when applying pressure with the thumb. However, in advanced stages of CMC OA, pain might persist at rest. Another prominent symptom is loss of strength of the thumb. Patients struggle to grab or hold an object due to weakening of the thumb. For example, tying a knot or holding a saucepan becomes increasingly difficult. If patients present themselves with similar symptoms, physicians should also consider De Quervain syndrome, rheumatoid arthritis or flexor carpi radialis and flexor pollicis longus tendinopathy as a possible cause. Typical signs of CMC OA can be observed from the outside of the hand. For example, the area near the base of the thumb can be swollen and could appear inflamed. Advanced stages of CMC OA can eventually lead to deformity of the thumb. This deformity, also called a ‘zigzag’ deformity, is characterized by a deviation of the thenar eminence towards the middle of the hand, whilst the thumb phalanges overextend. Also a grinding sound, known as crepitus, can be heard when the CMC1 joint is moved. CMC OA of the thumb is a degenerative joint disease. Although the exact cause remains unclear, there is a general consensus among researchers about some of the mechanisms leading to CMC OA of the thumb. It is believed that laxity of the ligaments surrounding the CMC1 joint is the main cause of CMC OA. Especially laxity of the most significant ligament, the palmar beak ligament, will lead to joint instability. This instability causes misalignment of the joint bones, which will then rub against each other. As a consequence, the cushioning cartilage, which covers the surfaces of the joint bones, wears down. The synovial membranes get irritated and synovitis occurs. Eventually, the bare surfaces of the joint bones are exposed to each other. The gap between the joint bones decreases, as there is hardly any cartilage left. In reaction of this process the joint bones thicken at the surface, resulting in subchondral sclerosis. Also bony outgrowths, called osteophytes, are formed at the joint margins. In advanced stages of CMC OA, misalignment of the joint bones causes the tendons attached to thumb to force the base of the thumb into radial deviation and extension and the thumb phalanges in hyperextension. As a consequence the ‘zigzag’ deformity becomes visible.