Rescue of reapproximated flexor profundus tendons in vitro following segmental irradiation

Segments of rabbit flexor profundus tendon were transected at their zone II midpoints. Before reapproximation, proximal and/or distal segment halves received 10,000 rads of x-radiation. Four treatment groups were examined with light and electron microscopy after 2, 4, and 8 weeks in culture: group XX had proximal and distal tendon halves irradiated, group PX had only distal tendon halves irradiated, group XD had only proximal tendon halves irradiated, and group PD served as nonirradiated control tendons. After 2 weeks, the epitenons of all nonirradiated segments had proliferated to become several cell layers thick with migratory-type cells. By 4 weeks these cells in groups PX and XD crossed the repair site and invaded the opposing irradiated segments in a previously undescribed pattern. By 8 weeks, bridging and remodeling of the repair site were evident in groups PX and XD, yet not to the extent noted in the nonirradiated control group PD. No histologically evident difference in mechanism or completeness of healing was observed between groups PX and XD, and no comparable proliferation, bridging, or remodeling was observed in the completely irradiated group XX. These observations allowed for conclusions to be drawn regarding regional involvement during intrinsic tendon healing and confirmed the pluripotency of poorly differentiated epitenocytes.