The pseudosynovial sheath--its characteristics in a primate model.

The characteristics and long-term fate of the pseudosynovial sheath formed in response to a gliding tendon implant were examined. A primate model was chosen to reproduce the human clinical situation. Hunter passive gliding implants were implanted in 32 digits of eight Macque monkeys. Surgical syndactylism was created to the adjacent active digits to provide passive range of motion of the digits. No implanted digits demonstrated progressive flexion contractures. Radiographs revealed passive excursion of the implants of an average of 2.5 cm. Biopsies were taken at various time intervals and locations for histological examination. The pseudosynovial sheath has three descriptive layers: an intima, media, and adventitia. This sheath becomes mature and stable at 8 weeks. The intima cells contain a glycosaminoglycan substance and have a secretory capacity. The media cells have large amounts of collagen and provide structural and vascular support. The adventitia is a highly vascular structure composed of loose fibrous tissues that demonstrates clefts that may represent gliding planes. The pseudosynovial sheath was found to be a morphologically stable structure that showed no propensity for longitudinal contracture. The sheath appears to have the characteristics necessary to provide a good bed for a tendon graft.