Interference Screw versus Cement Fixation in Anterior Cruciate Ligament Soft Tissue Grafts: A Biomechanical Study

Abstract

INTRODUCTION: Shortcomings of fixation has been reported as a source of graft failure in ACL reconstruction. While interference screws have long been used as fixation devices for ACL reconstruction, they are not without complication. Previous studies have highlighted the use of bone void filler as a fixation method, however no biomechanical comparisons using soft tissue grafts with interference screws exist to our knowledge. The purpose of this study is the studies to evaluate the fixation strength of a calcium phosphate cement bone void filler compared to screw fixation in an ACL reconstruction bone replica model with human soft tissue grafts. METHODS: 10 ACL grafts were constructed using semitendinosus and gracilis tendons harvested from 10 donors. Grafts were affixed with either an 8-10mmx23mm PEEK interference screw (n=5) or with approximately 8mL of calcium phosphate cement (n=5) into open cell polyurethane blocks. Graft constructs were tested to failure in cyclic loading under displacement control at a rate of 1mm per second. RESULTS: When compared to screw construct, cement construct showed a 978% higher load at yield, 228% higher load at failure, 181% higher displacement at yield, 233% higher work at failure, and a 545% higher stiffness. Normalized data for the screw constructs relative to the cement constructs from the same donor showed 14±11% load at yield, 54±38% load at failure, and 172±14% graft elongation. DISCUSSION: The results of this study indicate that cement fixation of ACL grafts may result in a stronger construct compared to the current standard of fixation with interference screws. This method could potentially reduce the incidence of complications associated with interface screw placement such as bone tunnel widening, screw migration and screw breakage.