Impact of screw design on refixation of solid avulsion fractures of the posterior cruciate ligament-Abiomechanical feasibility study.

Briese T, Peez C, Albert A, Große-Allermann A, Herbst E, Deichsel A, Raschke MJ, Kittl C

Abstract

Purpose: Avulsion fractures of the posterior cruciate ligament (PCL) are commonly treated with refixation. Headless compression screws (HCS) offer benefits, compared to conventional techniques, such as reduced material irritation and option of bioabsorbable materials, possibly avoiding implant removal. Proofing its clinical applicability, the authors hypothesized that (1) biomechanical properties of HCS would be comparable to conventional techniques and (2) magnesium-based HCS would provide comparable properties to titanium HCS. Study DesignControlled laboratory study. Methods: Forty fresh frozen porcine knees were dissected keeping the menisci and ligaments intact. A solid avulsion fracture of the tibial PCL (20 mm [length] x 20 mm [width] x 10 mm [depth]) was created with a chisel. Specimens were randomized into four groups: (1) the native PCL, the tibial PCL avulsion refixed with parallel arranged, (2) two 3.5 mm cortical screws with washer (Ti-CS), (3) two titanium headless compression screws (Ti-HCS) or (4) two magnesium based headless compression screws (Mg-HCS). Femur and tibia were mounted in a universal uniaxial testing machine (Zwick) simulating a posterior drawer testing, by performing axial load on the femur while the tibia was fixed in 90 degrees flexion. After preconditioning, 500 cycles (200 mm/min) were performed with 10-100 N, followed by load-to-failure (LTF). Key parameters measured included stiffness, yield load, LTF and cyclic displacement. Differences were analyzed using an analysis of variance with a significance level of p < 0.05. The macroscopic failure mode was documented. Results: LTF of the intact PCL (1982.0 +/- 285.4 N; p