Initial stability of two PLIF-techniques.: A biomechanical in-vitro-comparison

Objective: The purpose of this biomechanical in-vitro-study was to compare two different PLIF-techniques with two types of implants on human lumbar spine: PLIF with threaded cages, (Bagby and Kuslich, Spinetech, Minneapolis, USA) and PLIF with the Moss-Miami-implants, (DePuy International Limited, Leeds, Great Britain). Methods: Six cadaveric human lumbar spine segments L2-5 were explanted, frozen at -20 degrees C and thawed before preparation. They were cut in two parts by discectomie and arthrotomie L3/4, so six specimen L2/3 and six specimen L4/5 were obtained and used in a crossover-trial. Analysis included testing in a tension-torsion-machine under axial compression with 600 N, rotation (left-right) with 25 Nm and shearing forces with 250 N without preload. This was first done in the intact and then in the fused specimen. Results: Stiffness before treatment was comparable in both groups irrespective of location. Posttreatment stiffness was higher with MOSS-MIAMI-implants as compared to PLIF with BAK-cages. Average relative superiority (and 95%-confidence intervall) were 1,98 (1,01-3,69) for compression, 2,30 (0,85-6,24) for rotation and 1,73 (0,78-3,84) for shearing. Statistical comparison of log posttreatment: stiffness was significant for compression but not for rotation and shearing (2-sided independent crossover t-test). Conclusion: This biomechanical in-vitro-study demonstrates the higher initial stability of PLIF with titanium surgical mesh and posterior instrumentation when compared to PLIF with threaded cages alone.