Impact of Metal Density on Deformity Correction in Posterior Fusions for Adolescent Idiopathic Scoliosis

Posterior spinal fusion with pedicle screws has become the "gold standard" for the management of adolescent idiopathic scoliosis (AIS). Pedicle screws provide three column fixation through the strongest part of vertebra thereby enhancing surgeon's ability to do a 3-dimensional deformity correction. The higher pullout strength results in less long-term loss of correction, shorter fusions resulting in preservation of motion segments, lower pseudarthrosis rates and lower implant failures compared with these alternative posterior instrumentation systems. However, studies are contradictoryregarding the effect of metal density on coronaland sagittal curve corrections. Multiple factors including curve flexibility, instrumentation and rod types, reduction strategies and curve types, affect outcomes. Given this, intraoperative decisions regarding the number of anchorage points remain difficult, with considerable inter-surgeon variability.

The rationale for using a high implant density constructs is to obtain more rigid fixation and to limit potential stress concentration at any one screw. Furthermore, health-related quality of life instruments such as the SRS 22, 24, or 30 seem to show little correlation with curve correction. The placement of every additional pedicle screw is associated with increased operative time, risk of neurological deterioration and increased implant cost. If implant density can be lowered without compromising clinical results, reducing the number of screws may improve the efficiency and cost effectiveness of scoliosis surgery. Several authors have demonstrated successful results with low-density instrumentation for the treatment of scoliosis. The purpose of this retrospective review is to describe the demographics of our patient population and to ascertain correlation between metal density and correction achieved.