What is the pathophysiology of infectious flexor tenosynovitis?

Updated: Aug 27, 2018
  • Author: Mark R Foster, MD, PhD, FACS; Chief Editor: Harris Gellman, MD  more...
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Infection can be introduced directly into the tendon sheaths through a skin wound (most often) or via hematogenous spread, as occurs with gonococcal tenosynovitis.

Infectious FT is a closed-space infection. Sheaths of the index, middle, and ring fingers run from the metacarpal neck at the level of the first anular (A1) pulley proximally to the insertion of the flexor digitorum profundus distally. The small finger and thumb sheaths are continuous with the ulnar and radial bursae in the palm, respectively (see the image below). Because the radial and ulnar bursae are contiguous, infections in either the small finger or the thumb are at risk of communicating and potentially progressing to the carpal tunnel.

Flexor tendon sheaths and radial and ulnar bursae. Flexor tendon sheaths and radial and ulnar bursae.

Infection in any of the fingers may spread proximally into the wrist and forearm (Parona space). The initial infection also may move into the fascial spaces within the hand, adjacent osseous structures, or synovial joint spaces, or it may erode through the layers of the skin and exit superficially.

The tendon sheath is made up of an inner visceral layer and an outer parietal layer. Between the two layers is the synovial space, which is filled with synovial fluid. The visceral layer is in close approximation to the flexor tendon. The parietal layer is reinforced by a series of five anular pulleys (A1-5) and three cruciform pulleys (C1-3). The A2 and A4 pulleys are critical for flexor tendon function and should be avoided during surgical manipulation of the infected sheath. (See the image below.)

Location of annular and cruciform pulleys on the v Location of annular and cruciform pulleys on the volar finger.

With the accumulation of pus in flexor tendon sheath infections, pressure can increase within the closed-space compounds of the flexor tendon sheath, thus inhibiting the inflammatory response. In one study, eight of 14 patients with flexor tendon sheath infections had hand tendon sheath pressure in excess of 30 mg Hg. The increased pressure also inhibits blood flow and adds to the destructive process. Tendon ischemia increases the likelihood of tendon necrosis and rupture.

Flexor tendons of the fingers receive their nutrient supply from a combination of direct vascular sources and diffusion from synovial fluid. An avascular segment of the flexor digitorum superficialis has been found at the proximal phalangeal level. The flexor digitorum superficialis has two distinct vascular supplies, and three have been identified for the flexor digitorum profundus. As a result, the profundus has two avascular segments, which are located over the proximal and middle phalangeal regions.

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