Can an expansion device be used in anterior cruciate ligament reconstruction? An in vitro study of soft tissue graft tibial fixation

Background: The purpose of this study was to compare the mechanical properties of an interference screw with an expansion device in anterior cruciate ligament (ACL) reconstruction.

Methods: A total of 52 porcine tibia and 20 polyurethane foam blocks (0.16g/cm³) were used. Forty pullout tests were carried out to combine the two types of bones - surrogate and porcine - with the two fixation systems: interference screw and expansion device (n=10 per group). Thirty-two cyclic tests (n=8 per group) were carried out with both fixation devices in porcine bone at two different force amplitudes (100N and 200N).

Results: Stiffness and load values (mean±SD) at six millimeters of displacement for the expansion device and the interference screw were 74±33N/mm, 318±135N, and 52±28N/mm, 205±70N, respectively, showing a difference in stiffness (P=0.016) and load at six millimeters of displacement (P=0.001). No correlation between insertion torque and the ultimate failure load was found for both fixation devices tested. In cyclic tests, significantly higher (P<0.001) numbers of cycles (mean±SD) were reached with the expansion device (81,014±30,291 at 100N; 13,462±11,351 at 200N) than with the interference screw (15,100±8623 at 100N; 343±113 at 200N) at six millimeters of displacement.

Conclusion: The use of an expansion device for ACL reconstructions seemed to be a promising alternative to an interference screw. Insertion torque alone was not a useful predictor of graft fixation strength in ACL reconstructions.