Fetal tendon healing: development of an experimental model.

An experimental model was developed to study the process of fetal tendon healing. The flexor digitorum profundus tendons of the right hindlimb of 14 fetal lambs were partially lacerated at 100 days' gestation (term 145 days) and then studied macroscopically and histologically at several postinjury intervals (2, 4, 7, 14, 28, 42, and 56 days); two lambs were studied at each interval. A similar procedure was done in 14 adult sheep, who served as a control group. The fetal lambs showed no subcutaneous scarring, the digital sheath and tendon healed 2 weeks after injury, and a smooth, gliding surface was reconstituted. Collagen fibers were randomly arranged at 1 week but became organized along the tendon axis by 2 weeks. No adhesions, ruptures, or triggering was noted in the healing fetal tendons. Normal morphology was restored by 6 weeks. In the adult, dense subcutaneous scarring was noted, the digital sheath healed by 4 weeks and the tendon gap by 6 weeks, but a smooth gliding surface was not restored. Collagen fibers were randomly arranged at 2 weeks and became organized along the tendon axis by 4 weeks after injury. There were no dense adhesions or ruptures, but 25 percent of the tendons showed triggering.