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 annular 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.