Analysis of collagen profile and orientation in a chronic ruptured extensor pollicis longus tendon

Purpose: The purpose of this study is to examine the collagen profile and orientation in a ruptured extensor pollicis longus (EPL) tendon, in order to better understand the collagen response to loss of tensile forces. Methods: A 76-year-old male with a history of rheumatoid arthritis required surgical reconstruction of a chronic EPL rupture using EIP tendon transfer; the refreshed tip of the distal EPL tendon, along with the intervening tubular scar and EIP tendon were further analyzed. Picrosirus red (PSR) staining was performed, and the levels of collagen isoform were determined with western blotting. Results: The results obtained from PSR staining under polarized microscopy showed thin, weakly birefringent, green fibers (collagen III-like) and thick, yellow-red, strongly birefringent fibers (collagen I-like). The arrangement was noted to be much less organized and directional in the ruptured tendon compared to the EIP tendon. Western blotting results showed the presence of collagen I, II, III, V, VI and X, with the ratio comparison to collagen I markedly different between a normal EIP tendon and the ruptured EPL tendon. Conclusion: EPL tendon rupture is accompanied by collagen disorganization and significant alteration in the collagen isoform expression, postulated to be a consequence of the loss of tensile forces.