Flexor Tendons and the Flexor SheathFlexor 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. First, it allows for smooth gliding of the tendon. Because the fingers are constantly moving, smooth motion is critical for dexterous movement. Second, 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 SheathMost 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
Treatment of the InfectionAs 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.
Complications of Flexor Sheath InfectionsFlexor 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.
Draeger RW and Bynum DK. "Flexor Tendon Sheath Infections of the Hand" J Am Acad Orthop Surg June 2012 ; 20:373-382.