J. of Orthopedic Research.

Liang R, Woo SL-Y, Takakura Y, Moon D, Jia F, Abramowitch S.


Porcine small intestine submucosa (SIS) has been used to repair musculoskeletal tissue injuries. In the laboratory, it has been shown that SIS could enhance the mechanical properties of healing medial collateral ligaments (MCL) in rabbits. Further, the histomorphological appearance and collagen type V/I ratio of the healing ligaments were found to be closer to those of the normal MCL. The purpose of this study was to examine whether these positive results would persist to a longer term - as long as 26 weeks after injury. Our hypotheses were that 1) SIS could guide neo-ligament formation to be better organized and limit the cross-sectional growth, which would form a basis for an increase in the mechanical properties of the healing MCL; 2) These changes could be associated to an increased diameter of collagen fibrils possibly mediated by a reduction in collagen type V.

A 6 mm gap injury in the right MCL was surgically created in 38 rabbits while the intact MCL of the left knee served as a sham-operated control. In the SIS-treated group (N=19), a single strip of SIS was sutured onto the two ends of the gap. In the non-treated group (N=19), no SIS was applied. The cross-sectional area (CSA) of the ligament was determined with a laser micrometer system. The femur-MCL-tibia complex (FMTC) was tensile tested and the mechanical properties of MCLs were measured in uniaxial tension. The histomorphology of the healing ligaments and collagen fibrils were determined through H & E staining, immunofluorescent staining of collagen type V and nuclei, and transmission electron microscopy (TEM). Sodium-dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) was used to determine the collagen type V/I ratio.

The SIS-treated MCLs displayed a 28% reduction in cross-sectional area, with a corresponding 33% increase in tangent modulus and a 50% increase in tensile strength compared with the non-treated group (p<0.05). TEM showed that groups of collagen fibrils with larger diameters appeared in the SIS-treated ligaments in comparison with uniformly small fibrils for the non-treated group. H&E staining showed the collagen fibers in the SIS-treated group appeared more densely stained and aligned along the longitudinal axis of the ligament with more interspersed spindle-shaped cells. In addition, immunofluorescent staining showed that there were less collagen type V signals and these changes were confirmed by a 5% lower ratio of collagen type V/I compared with the non-treated controls (p<0.05).

The findings of this multidisciplinary study extend the positive results of a shorter term 12 week study and further support the potential application of porcine SIS as a bioscaffold to enhance the healing of ligaments and tendons.