Tenosynovitis is inflammation of the synovial sheath, the thin, fluid-filled lining that surrounds certain tendons in your body. This sheath normally allows the tendon to glide smoothly during movement. When it becomes inflamed and thickened, that gliding is compromised, leading to pain, swelling, and restricted motion. It most commonly affects the hands, wrists, and feet, though it can occur anywhere a tendon passes through a sheath.
How the Tendon Sheath Works
Tendons connect muscle to bone, and some of them pass through tight tunnels or around bony curves where friction would otherwise cause damage. These tendons are wrapped in a synovial sheath that produces a small amount of lubricating fluid, similar to the fluid inside joints. This system lets the tendon slide back and forth with very little resistance every time you bend a finger, rotate your wrist, or flex your foot.
When the sheath or the tendon itself becomes irritated, the lining swells and thickens. The space inside the sheath narrows, creating friction where there was once smooth movement. In some cases, the tendon can swell enough to catch or lock as it tries to pass through, which is exactly what happens in trigger finger.
Common Types
Tenosynovitis is an umbrella term. The specific name depends on which tendon is affected.
- De Quervain’s tenosynovitis involves the tendons on the thumb side of the wrist. It causes pain when you grip, twist, or make a fist. A classic test involves tucking your thumb into your fist and bending your wrist toward your pinky finger. Sharp pain along the wrist confirms the diagnosis.
- Trigger finger (stenosing tenosynovitis) affects the flexor tendons in the fingers. The tendon thickens until it can no longer pass smoothly through its pulley, causing the finger to catch, click, or lock in a bent position. The thumb and ring finger are the most frequently affected digits.
- Flexor tenosynovitis of the foot involves the tendon that bends the big toe. It occurs most often in runners and can cause pain at the back of the ankle or under the ball of the foot near the big toe.
- Peroneal tenosynovitis affects the tendons along the outer ankle and is common in people who repeatedly roll or twist their ankle during activity.
What Causes It
The most common cause is repetitive motion. Any activity that forces a tendon to glide back and forth thousands of times, whether typing, assembly line work, knitting, or playing an instrument, can irritate the sheath over time. Sports that load the wrist or ankle repeatedly carry the same risk.
Infection is a more serious cause. Bacteria, most commonly Staphylococcus aureus, can enter the tendon sheath through a cut, puncture wound, or animal bite. Infectious tenosynovitis in the hand is a surgical emergency because pus trapped inside the sheath can destroy the tendon within days.
Systemic inflammatory conditions also play a role. Rheumatoid arthritis, gout, and other forms of inflammatory arthritis can trigger tenosynovitis even without repetitive use. In gout, microscopic crystals deposit inside the sheath and provoke intense inflammation. Sometimes two causes overlap: one published case found both gout crystals and a bacterial infection in the same tendon sheath at the same time.
Symptoms to Recognize
The hallmark symptoms are pain along the tendon, swelling over the affected area, and stiffness that limits movement. Pain typically worsens with use and improves with rest. The area may feel warm or look red, especially if infection is involved.
In stenosing forms like trigger finger, you may feel a clicking or catching sensation when you bend and straighten the affected digit. In more advanced cases, the finger locks in a bent position and you have to manually straighten it with the other hand.
Signs of Infection
Infectious tenosynovitis in the hand has four classic warning signs, known as Kanavel signs: the finger is held in a slightly bent resting position, the entire finger is swollen in a sausage-like shape, there is tenderness along the full length of the tendon sheath, and straightening the finger passively causes severe pain (particularly at the base). If you notice these signs after a wound to the hand, seek emergency care. Delayed treatment risks permanent damage to the tendon.
How It’s Diagnosed
Most tenosynovitis is diagnosed through a physical exam. Your doctor will press along the tendon, check for swelling, and move the joint to reproduce your pain. For de Quervain’s, the Finkelstein test (bending the wrist with the thumb tucked) is the standard bedside check.
Ultrasound is the most common imaging tool when the diagnosis is unclear or the doctor needs to assess severity. It can detect thickening of the tendon sheath and fluid buildup around the tendon, though its accuracy varies. Studies report sensitivity ranging from 45% to 100% for sheath thickening and 29% to 100% for fluid, depending on the operator and the specific location being examined. MRI provides a more detailed picture when ultrasound results are inconclusive or when surgery is being planned.
Non-Surgical Treatment
Initial treatment focuses on reducing inflammation and giving the tendon time to recover. That typically means resting the affected area, wearing a splint or orthosis to limit movement, and using anti-inflammatory medications. For de Quervain’s, a thumb spica splint that immobilizes the wrist and thumb is standard first-line care.
Corticosteroid injections are the most effective non-surgical option for persistent cases. For de Quervain’s tenosynovitis, about 52% of people get sufficient relief from a single injection. When a second injection is added, the success rate rises to roughly 73%. The interval between injections varies widely, averaging about six months, though some people need a second shot as early as four weeks and others go years before needing another.
Exercise and Rehabilitation
Physical or occupational therapy plays an important supporting role. A typical program starts with gentle, pain-free range of motion exercises during the first couple of weeks. Once pain settles, isometric exercises (where you engage the muscle without actually moving the joint) are introduced because they load the tendon without creating the friction that comes with gliding. For de Quervain’s, isometric thumb extension exercises performed over four to six weeks have shown improvements in pain and function. Over time, eccentric exercises, where you slowly lower a load rather than lift it, may be added as part of a progressive program. About 84% of patients treated for de Quervain’s in occupational therapy receive some form of exercise prescription.
When Surgery Is Needed
Surgery becomes an option when splinting, injections, and therapy fail to provide lasting relief. The procedure, called a tendon sheath release, involves cutting open the constricting tissue to give the tendon more room to glide. For trigger finger, the surgeon releases the A1 pulley at the base of the finger. For de Quervain’s, the retinaculum over the first wrist compartment is opened.
Recovery after surgical release takes 6 to 12 weeks for full healing. If your work doesn’t require hand use, you may return within a few days. Jobs involving repetitive hand motions, gripping, or lifting require a longer absence, and your surgeon will help you decide the timeline based on what your role demands.
What Happens if It’s Left Untreated
Ongoing inflammation causes the sheath and tendon to progressively thicken, making the problem harder to treat over time. In stenosing tenosynovitis, a finger that occasionally catches can eventually lock permanently. Chronic thickening also compromises the tendon’s blood supply and structural integrity, raising the risk of long-term stiffness. Infectious tenosynovitis poses the most acute danger: untreated infection can destroy the tendon and spread to surrounding tissues, potentially threatening the entire hand’s function within 48 hours.