237. Individual plates vs single plate for multilevel fixation results in superior biomechanics in anterior cervical fusion surgery

Abstract

BACKGROUND CONTEXT Anterior cervical discectomy and fusion (ACDF) has been the gold standard surgical treatment for degenerative conditions of the cervical spine, including degenerative disc disease, cervical spondylotic myelopathy, and cervical disc prolapse. This procedure remains the preferred treatment technique particularly for more elderly patients or those with a contraindication to total disc replacement. Multilevel anterior cervical spine fusion with single plates are associated with hardware failure and screw pullout due to stress shielding and excessive loading. Given the lever arm of longer plates and multiple fusion surfaces, pseudarthrosis rates are higher than single level cases. The biomechanics of a new approach using segmental fixation versus convention fixation using a long plate is compared using computational modeling. PURPOSE To compare the biomechanics of multilevel cervical spine fixation using segmental plating versus single plating. STUDY DESIGN/SETTING Computational modeling using cadaver-validated finite element model of cervical spine PATIENT SAMPLE N/A OUTCOME MEASURES Biomechanical data including segmental range of motion and pull-out load on screws METHODS A cadaver-validated finite element (FE) model of C3-C7 spine was used. The model included all crucial anatomical components including, vertebral bones, intervertebral ligaments and connecting tissues, intervertebral disc, facet joints and uncinate processes. The model was validated by comparison of segmental range of motion against data obtained from a cadaver experiment of cervical spine. The validated model was then used to simulate the fixation across C4-C6 using anterior plating, screw and interbody fixation with PEEK cages following simulation of the surgical procedure including total annulectomy and removal of ACL ligaments and the index levels. Two surgical cases were simulated: fixation with two individual plates (each with three screws) vs fixation with single long plate and 6 screws. Anatomical loading of 70N compressive follower load plus 1.5Nm bending moment were applied to the constructs to simulate physiological flexion, extension, lateral bending and axial rotation motions. Segmental motion and screw load data were compared among constructs. RESULTS Fixation at the index levels resulted in significant reduction in range of motion with 60% reduction in extension,85% in left and right axial rotation (LR&RR),63% in left and right lateral bending (LB&RB) and 80% in flexion. The range of motion in the multi-plate construct was similar to the long plate construct in all loadings. At the upper adjacent segment, both constructs yielded a slight increase in ROM in flexion, extension and lateral bending motions (3-10%). The screws in the long plate construct had significantly greater pull out force ranging from 35-82N in extension versus 10-60N in the multi-plate constructs. In axial rotation the ranges of forces were 18-139N in long plate versus 15-70N in multi-plate constructs. The load ranges were similar in both constructs in flexion and lateral bending. CONCLUSIONS Cervical segmental plating allows the ability to treat each level individually yielding in improvement in ability of restoring natural lordosis and biomechanics. When instrumenting across more than one level in ACDF, the individual multi-plates demonstrate superior biomechanics versus the conventional single long plate constructs by ensuring load sharing versus stress shielding. The screw in segmental plating experience lower axial forces resulting in lower risk of screw pull-out post-surgery. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.