Early anchoring collagen fibers at the bone-tendon interface are conductedby woven bone formation: light microscope and scanning electron microscopeobservation using a canine model

To clarify the early process of recovery at the bone-tendon interface, we u sed light microscopy and SEM to examine the process of anchoring of collage n fibers to bone in a canine model. At two weeks, tendon. sear tissue, woven bone and lamellar bone were presen t at the insertion site. SEM revealed anchoring of collagen fibril bundles of the scar to the woven bone. By 4 weeks, the number of anchoring fibers h ad increased and a parallel arrangement of fibers was observed. SEM demonst rated deep penetration of fibers into the woven bone layer. In addition, th e fibers were observed to project into and intermingle with the scar tissue . By 6 weeks, the anchoring fibers had developed fully and were distributed densely over the interface. SEM also revealed that the collagen fibril bun dles in the sear tissue had connected with the collagen fibrils of the wove n bone by way of the anchoring bundles. The woven bone was identifiable thr oughout the early stages of recovery as the interface between soft tissue a nd hard tissue. Throughout all experimental periods, no staining was observ ed at the interface of the tendon and bone by Saffranin-O. The formation of woven bone was important during early recovery of the tendon-bone interfac e prior to the completion of fibrocartilage-mediated insertion. (C) 2001 Or thopaedic Research Society. Published by Elsevier Science Ltd. All rights r eserved.