Comparison of Tendon-to-bone Healing Using Extracortical and Anatomic Interference Fit Fixation of Soft Tissue Grafts in a Sheep Model of Acl Reconstruction

INTRODUCTION: The short and long term fate oft soft tissue graft ACL reconstruction relies on a proper osseous graft incorporation. Using conventional extracortical fixation techniques, the tendon-to-bone healing progresses via the development of a fibrous interzone (FIZ) which results in an indirect, periosteal-like insertion site (1). The original ACL insertion, however, is characterized as a direct ligament insertion with a transition zone consisting of mineralized and fibrocartilage. A direct insertion may be more appropriate to transmit tensile forces between the ligament tissue and the underlying bone (2). In contrast, an anatomic interference fit fixation of soft tissue grafts may reduce graft-tunnel motion, thus eliminating a tunnel enlargement. Therefore, it has been suggested that anatomic interference fit fixation promotes tendon-to-bone healing, resulting in the development of a direct type of ligament insertion (3). To test the hypothesis that different healing patterns apply for different soft tissue graft fixation techniques we studied the tendon-to-bone healing histologically in an intraarticular model of soft tissue graft ACL reconstruction using extracortical and anatomic graft fixation.