Flexor tenosynovitis is inflammation of the synovial sheath and tendons in the fingers, usually caused by infection or inflammatory conditions. Diagnosis depends on Kanavel’s four signs. Infectious cases are often caused by trauma, while noninfectious cases can be caused by various conditions. Treatment involves medical therapy and, in severe cases, surgery.
Flexor tenosynovitis (FT), also called flexor tendon synovitis or flexor synovitis, refers to inflammation of the synovial sheath and tendons in the joints of the fingers. It is usually caused by an infection, but acute and chronic inflammatory pathophysiological states, such as arthritis and diabetes, can also cause this condition. Diagnosis of infectious or septic FT depends on the four signs of Kanavel, which include finger positioned in slight flexion, swelling, tenderness along the flexor tendon sheath, and pain elicited when the affected finger is passively extended. This inflammation can quickly destroy the functional ability of a person’s fingers, so it is considered one of the orthopedic emergencies. Proper treatment must be started immediately.
Penetrating trauma is usually the primary cause of infectious flexor synovitis. Other causes include bite wounds and hematogenous or blood-borne spread of bacteria from other infected sites in the body. Trauma disrupts the normal anatomy and physiology of the hand, allowing native skin flora, such as staphylococcus and streptococcus, to invade subcutaneous tissues. Most cases of infectious flexor synovitis are due to Staphylococcus aureus, but there are many others.
Noninfectious flexor synovitis can occur secondary to amyloidosis, crystal deposition, sarcoidosis, psoriatic arthritis, rheumatoid arthritis, diabetes mellitus, and systemic lupus erythematosus. Studies show that when flexor tenosynovitis is diagnosed with magnetic resonance imaging (MRI), it strongly predicts early rheumatoid arthritis. People who have diabetes are also at a higher risk of having multiple fingers affected by flexor synovitis.
A tendon sheath has both an inner layer, called the visceral layer, and an outer layer, called the parietal layer. The visceral layer is very close to the flexor tendon, and the space between these layers, called the synovial space, contains synovial fluid. Based on this anatomical organization, a tendon sheath infection is called a closed space infection. When pus builds up in the flexor tendon sheath, pressure builds and leads to decreased blood flow to the area or ischemia. With the onset of tendon ischemia, the risk of necrosis and rupture is high and can lead to loss of flexor function.
Noninfectious flexor synovitis occurs when there is an overgrowth of certain substances, such as amyloid or crystals, within the joint space. These substances act on nearby tendons, causing swelling and pain. With repetitive microtrauma or overload syndrome, the tendon tissues are unable to adapt to the chronic injury, leading to inflammation, proliferation and maturation.
A person with infectious flexor tenosynovitis often complains of symptoms of pain, redness, and fever, and physical findings include Kanavel’s four signs. Kanavel’s signs may not be present if the patient is in an early stage of the disease, has recently taken antibiotics, is chronically infected, or is immunocompromised. A person with noninfectious flexor synovitis often has swelling of the knuckles as an initial symptom and complains of limited motion and pain.
Treatment of this condition involves medical therapy, including intravenous antibiotics, elevation of the affected area, and rehabilitation with range of motion (ROM) exercises. People who are immunocompromised, have diabetes, or have flagrant pus in the tendons should have surgery. Surgical management includes an incision over the affected area, drainage of pus, irrigation, immobilization and elevation, as well as concurrent antibiotic therapy.
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