Autogenous intrasynovial and extrasynovial tendon grafts: An experimental study of pro α1(I) collagen mRNA expression in dogs

On the basis of recent evidence that the healing processes of tendon grafts are donor‐tissue specific, in situ hybridization, using a 372 bp cDNA fragment complementary to a portion of pro α1(I) collagen mRNA, was utilized to compare the cellular responses to transplantation exhibited by autogenous intrasynovial and extrasynovial flexor tendon grafts. Intrasynovial and extrasynovial tendons from the hindpaw were transferred to synovial sheaths in the forepaw of 12 mongrel dogs (24 tendons) and treated with immediate controlled passive motion. The tendon grafts were harvested at 2, 4, and 6 weeks, and each was divided into a proximal, central (8 mm), and distal portion. Sections from the central portion were embedded in paraffin and subjected to in situ hybridization, autoradiography, and staining; levels of procollagen mRNA then were assessed by microscopic examination. The two types of tendon grafts exhibited different levels of pro α1(I) collagen mRNA expression at all three time points. Intrasynovial tendon grafts displayed no areas of increased type‐I procollagen mRNA at 2, 4, and 6 weeks. The extrasynovial tendon grafts displayed increased surface levels of type‐I procollagen mRNA at 2 and 4 weeks; the levels decreased to background levels by 6 weeks. The high levels of procollagen mRNA exhibited by the extrasynovial grafts suggest increased collagen synthetic activity, indicative of a cellular response to injury, whereas the preservation of low levels of expression in the intrasynovial grafts may signify a less inflammatory cellular response.