Impact of Metal Density on Deformity Correction for Adolescent Idiopathic Scoliosis
Condition: Adolescent Idiopathic Scoliosis
MeSH terms: Scoliosis
Study type: Observational

Summary: 
      A retrospective analysis to ascertain the correlation between metal density and deformity
      correction among individuals with adolescent idiopathic scoliosis.
    

Detailed description: 
      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.
    

Intervention name(s): Posterior spinal instrumentation
Intervention type(s): Other
Intervention description(s): A fusion construct consisting of all pedicle screws except at uppermost instrumented vertebra. Contoured dual 6-mm stainless steel rods were used to connect the construct. Pedicle screw location and density was determined by the surgeon based on perceived curve stiffness and fusion length with an even distribution of fixation points along the construct. Pedicle screw instrumentation was performed by the free hand technique with biplanar fluoroscopic and direct screw EMG impedance testing for confirmation of placement. Reduction was via cantilever-segmental-translation maneuver in all cases.
Observational model: Cohort
Time perspective: Retrospective
Sampling method: Non-Probability Sample
Study population: 
        Retrospective review of all patients with Adolescent Idiopathic Scoliosis patients operated
        at our hospital during study period
      
Keywords: Adolescent idiopathic scoliosis; posterior instrumentation; metal density; correction; Pakistan