The elucidation and strategic modification of flexor tendon healing mechanisms.

0.1.1 Introduction and aims: 16,000 flexor tendon repair operations are performed annually in the UK these are frequently complicated by adhesions, causing significant morbidity. The uncertainty over which cells are responsible for the tendon healing mechanisms persists. We aimed to develop a novel experimental model to elucidate the possible role and migratory response of synovial sheath fibroblasts during tendon healing and to determine the effects of differing environment and stimuli on the cellular processes in the healing tendon. 0.1.2 Materials and methods: Rat synovial sheath cells were labelled with a lipophilic tracer dye, and an injury made in the adjacent flexor tendon. Tendons were then harvested at 1,3,5 and 7 days and frozen sectioned. The location of the labelled fibroblasts was determined using ultra-violet microscopy. In a separate experimental series, rat flexor tendons received different injury type / mobilisation or immobilisation / and TGF-pl or saline control application. Tendons were harvested at 7 and 14 days, fixed, sectioned and HandE stained. Cell densities in the injury region were determined. 0.1.3 Results: By 24 hours, labelled synovial fibroblasts were observed to have migrated from the sheath to the zone of injury, with numbers increasing at 3 and 5 days, but diminishing by day 7. In the second experimental model, tendons injured with a superficial scrape, or immobilised post-injury showed a significant increase in relative cellularity in the region of the injury. 0.1.4 Discussion: These results suggest that synovial cells are involved in the early stages of tendon healing, and migrate from the synovial sheath into the healing tendon. Fibroblast density, in the rat model, is modulated by type of injury, immobilisation, but not TGF-p 1 application. This may correlate clinically with collagen deposition and adhesion formation