Flexor Tendon Sheath Infections

Infections around the tendons of the finger can be very serious. These are called flexor tenosynovitis, or a flexor tendon sheath infection.

Prior to our understanding of the importance of surgery and the discovery of antibiotic treatment, flexor tenosynovitis often led to loss of limb or death. Today, these infections can be treated. But, to prevent significant disability, they need to be recognized quickly and treated aggressively.

Doctor examining patient's hand
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Flexor Tendons and the Flexor Sheath

Flexor tendons are the tendons of the fingers. A tendon is a structure that connects a muscle to a bone. When the muscle contracts, the tendon pulls on the bone. In the case of the flexor tendons of the fingers, when the forearm muscles contract, the fingers are pulled by the tendons into a fist.

The flexor tendons run part of their course through a structure called the flexor tendon sheath. The flexor tendon sheath exists for two reasons:

  1. It allows for smooth gliding of the tendon. Because the fingers are constantly moving, smooth motion is critical for dexterous movement.
  2. The flexor sheath prevents the tendons from "bowstringing." Bowstringing would occur if the sheath were not holding the tendon against the bone. In that case, the tendons would be pulled in a straight line, not held against the finger, and would get in the way of grasping objects.

Infection of the Flexor Sheath (Flexor Tenosynovitis)

Most often, a flexor sheath infection occurs after an injury to the finger, a deep cut, or penetrating trauma. If bacteria are introduced into the sheath, the body has limited ability to fight off these infections.

There is no blood supply to the lubricating synovial fluid within the tendon sheath and, therefore, the body's immune system is rendered largely ineffective. The signs of infection usually develop within a week of the injury and are characterized by the following:

  • Swelling of the finger
  • Tenderness along the tendon sheath
  • Limited movement with the finger held slightly bent
  • Pain with attempted movement of the finger

These signs are called "Kanavel's cardinal signs," named after the physician who described them. Patients with these signs should be evaluated by a physician trained to recognize flexor sheath infections. Patients may have fever, abnormal blood work, and other findings, but the physical signs described by Kanavel are the most important when making the diagnosis of a flexor sheath infection.


As stated earlier, the most critical step is to recognize the problem quickly and initiate treatment as soon as possible. Most infections of the flexor sheath will be with bacteria commonly found on our skin surfaces, including staph and strep.

Antibiotic treatment is critical, but not entirely sufficient. Because the body has limited blood supply to the flexor tendon sheath, the antibiotics cannot get to that location easily. Therefore, a surgery is also needed to clean out the infection from the sheath.

Surgery to clean out the flexor sheath can usually be accomplished by making two small incisions, one at the base of the finger and one near the tip. Saline fluid is then washed through the sheath to clean out the infection. Patients with more advanced infection may require the entire sheath to be surgically exposed to clean out the infection.


Flexor sheath infections are significant injuries and they often take months for full recovery. Patients with more severe and more advanced infections may never recover full mobility of the finger.

Because the flexor sheath is important for finger motion, if damage to the sheath occurs or scar tissue develops, the finger motion may never return to 100%. Patients may work with hand therapists after their infection has resolved to help recover mobility.

A Word From Verywell

Infections of the flexor tendon sheath in the hand and fingers are serious problems that can have long-term repercussions. Urgent evaluation and treatment are necessary to ensure the infection is appropriately treated, to give you the best chance of recovery. Even with appropriate treatment, stiffness, swelling, and discomfort can linger for a long time.

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Article Sources
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  2. Ceroni D, Merlini L, Salvo D, Lascombes P, Dubois-Ferrière V. Pyogenic flexor tenosynovitis of the finger due to Kingella kingaePediatr Infect Dis J. 2013;32(6):702-3. doi:10.1097/INF.0b013e3182868f17

  3. Kennedy CD, Huang JI, Hanel DP. In Brief: Kanavel's signs and pyogenic flexor tenosynovitisClin Orthop Relat Res. 2016;474(1):280-4. doi:10.1007/s11999-015-4367-x

  4. Draeger RW, Bynum DK. Flexor tendon sheath infections of the handJ Am Acad Orthop Surg. 2012;20(6):373-82. doi:10.5435/JAAOS-20-06-373

  5. Steinberg DR. Infection of the tendon sheath in the fingers. Merck Manual. Updated August 2018. 

  6. Mamane W, Lippmann S, Israel D, et al. Infectious flexor hand tenosynovitis: State of knowledge. A study of 120 casesJ Orthop. 2018;15(2):701-706. doi:10.1016/j.jor.2018.05.030

Additional Reading
  • Draeger RW and Bynum DK. "Flexor Tendon Sheath Infections of the Hand" J Am Acad Orthop Surg June 2012 ; 20:373-382.