BIOMECHANICAL ANALYSIS OF MULTILEVEL FIXATION METHODS IN THE LUMBAR SPINE

Study Design, The authors measured and compared the stiffness of cadav eric,lumbar spines stabilized with several anterior interbody fusion d evices. The information obtained provides a foundation for determining how methods of anterior lumbar fixation can maximize rigidity and pro mote development of bony fusion.Objectives. To compare the utility of three-anterior spinal instrumentation systems for Stabilizing the lumb ar spine. Summary of Background Data. Anterior spinal instrumentation is used to prevent progressive spinal deformity and maintain correctio n after spinal fusion surgery. Newer instrumentation systems-developed for anterior interbody fusions can be inserted by minimally, invasive procedures. The-stability of these systems has not been tested adequa tely in human cadaveric specimens. Methods. Fusion constructs were eva luated in 12 human cadaveric specimens sequentially loaded in axial co mpression and torsion, flexion and extension, and lateral bending. The fusion constructs used were 1) two anterior bilateral threaded interb ody fusion devices, 2) lateral hollow interbody screws (Texas Scottish Rite Hospital-B screws), and 3) femoral allograft and conventional an terior Texas Scottish Rite Hospital instrumentation. Results. The cons truct with Texas Scottish Rite Hospital-B screws connected by a rod pr oduced stiffness comparable with that produced by conventional Texas S cottish Rite Hospital instrumentation with femoral ring allografts. Th e threaded interbody fusion-device stiffness tested in axial rotation was comparable with that achieved with Texas Scottish Rite Hospital in strumentation. Conclusions. Our data demonstrate the effectiveness of threaded interbody fusion device and the Texas Scottish Rite Hospital- B screw in immobilizing the L3-L4 and L4-L5 disc spaces. Rigidity of f ixation in the lumbar spine may aid in the maintenance of lordosis.