Experimental restoration of the digital synovial sheath.

The digital synovial sheath constitutes an important component of the delicate mechanism of flexor tendon nutrition and gliding function, In the present study the true nature of the inner cell layers of secondary healed defects in the tendon sheath as well as of free tendon sheath autografts were studied. Leghorn chickens were used as experimental animals and the gradual development of the pseudosheath as well as the healing of sheath autografts were studied both macroscopically and histologically including transmission electron miscroscopy. Synovial regeneration by extension from intact parts of the sheath was never observed and the pseudosheath formed around silastic rods consisted of granulation tissue with fibroblasts and macrophages. The free tendon sheath autografts demonstrated a normal process of healing at the edges of the defect. Synovial regeneration appeared to be that of metaplasia and proliferation of fibroblasts and macrophages. This phenomenon was demonstrable both in the secondary healed defects and more convincingly in the sheath autografts. Further, the silastic rod was found to induce foreign body reaction in the healing synovium. It is concluded that grafting of autologous tendon sheath tissue seems to be a promising method for restoration of defects in the digital tendon sheath.