Impact of Metal Density on Deformity Correction for Adolescent Idiopathic Scoliosis
Impact of Metal Density on Deformity Correction for Adolescent Idiopathic Scoliosis
A retrospective analysis to ascertain the correlation between metal density and deformity
 correction among individuals with 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.
Inclusion Criteria:

 -  Patients with adolescent idiopathic scoliosis

 -  Age more than 10 years at time of surgery

 -  Posterior instrumentation consisting of all pedicle screw construct except for
 bilateral hooks at the uppermost instrumented vertebra

 -  A major curve magnitude between 45 and 80 degrees.

 Exclusion Criteria:

 -  Scoliosis patients with a diagnosis other than adolescent idiopathic scoliosis

 -  Previous spine surgery

 -  Use of spinal osteotomies in addition to posterior spinal fusion with pedicle screws

 -  ALenke 5 curve

 -  Patients with less than 2 years' follow-up

 -  Use of hooks or wires below the uppermost instrumented level