AUTOGENOUS INTRASYNOVIAL AND EXTRASYNOVIAL TENDON GRAFTS - AN EXPERIMENTAL-STUDY OF PRO ALPHA-1(I) COLLAGEN MESSENGER-RNA EXPRESSION IN DOGS

On the basis of recent evidence that the healing processes of tendon g rafts are donor-tissue specific, in situ hybridization, using a 372 bp cDNA fragment complementary to a portion of pro alpha 1(I) collagen m RNA, 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 te ndon 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 hy bridization, autoradiography, and staining levels of procollagen mRNA then were assessed by microscopic examination. The two types of tendon grafts exhibited different levels of pro alpha 1(I) collagen mRNA exp ression at all three time points. Intrasynovial tendon grafts displaye d 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 back ground levels by 6 weeks. The high levels of procollagen mRNA exhibite d by the extrasynovial grafts suggest increased collagen synthetic act ivity, indicative of a cellular response to injury: whereas the preser vation of low levels of expression in the intrasynovial grafts may sig nify a less inflammatory cellular response.