Histology and ultrastructure of the human flexor tendon sheath

Twenty human flexor tendons and their sheaths were studied to determine the gross, microscopic, and ultrastructural morphology of their surfaces. Specimens were obtained at the time of autopsy or at the time of reconstructive and reparative surgery. The flexor tendon sheath consists of a noninterrupted layer of parietal synovium reinforced externally at intervals by dense bands of collagen, the annular and cruciform pulleys, and the palmar plates of the respective finger joints. The sheath contents are independently covered by a second similar layer of visceral synovium. These two layers are continuous at the proximal cul-de-sac, the vincula origins, and the tendon insertions. While the synovial cells lining the pulleys and tendons differ quantitatively from those of the membranous portion of the sheath, they are morphologically identical. The presence of a visceral synovial layer covering each tendon may indicate a key role of the synovial cell in tendon healing.