Abstract
This study investigated the biomechanical stiffness of Anterior Lumbar Interbody Fusion (ALIF) with an interbody fusion cage. The objectives of this study were to clarify the changes of segmental stiffness after insertion of interbody cages anteriorly. The interbody fusion cage was packed experimentally with bone graft and inserted between the vertebral bodies through either an anterior or a posterior approach. Ten fresh frozen and thawed juvenile pig cadaveric lumbar L3-4, L4-5 osteoligamentous spines were used. The segmental stiffness and laxity after implantation of the interbody cages were studied and the direction of placement and the number of cages were compared.Mechanical properties were determined by testing lumbar verteral motion segments in flexion, extension, lateral bending and torsion. The five simulated conditions were, (A) an intact, (B) a single cage placed centrally and anteriorly, (C) a single cage placed laterally, (D) a single cage placed anterolaterally and, (E) two cages inserted anteriorly. There were significant effects of ALIF (surgery) on the configuration for each loading of flexion, extension, or lateral bending. The results indicate that under torsional stress, the stiffness of the (B) and (C) groups was less than that of the intact condition. The stiffness of the (D) and (E) groups was greater than that of the intact condition for all loading modes. A single cage placed anterolaterally had greater stiffness for all loading modes and had an effective configuration. Under stress of sagital and lateral bending and further torsion, the stiffness was greatest in the two cages inserted anteriorly.
