title: Failure of Monoaxial Pedicle Screws at the Distal End of Scoliosis Constructs: A Case Series.
abstract: BACKGROUND
  The goals of instrumented fusion for scoliosis are to correct deformities, stabilize the spine, and achieve arthrodesis. Monoaxial pedicle screws are often used in scoliosis constructs and have shown superiority over other types of pedicle screws in their ability to correct vertebral rotation and lumbar lordosis. However, because of the fixed-angle nature of the monoaxial pedicle screw head, any malalignment at the rod-screw interface could result in less than optimum stability.
  
  
  RESULTS
  This series exhibits 3 cases of set screw loosening with the use of monoaxial pedicle screws at the distal end of long spinal fusion constructs for the management of patients with scoliosis; these complications all occurred within 6 months of the index procedures. The results of a detailed microscopic analysis of the failed components from 1 of the cases are also presented.
  
  
  CONCLUSIONS
  From this evidence, the authors of the current study recommend that surgeons exercise caution when using monoaxial pedicle screws at the distal end of long spinal fusion constructs, especially after compression has been achieved on the convex portion of the curve.
authors.affiliation: Department of Orthopaedic Surgery, University of Pennsylvania, 2 Silverstein Building, 3400 Spruce Street, Philadelphia, PA 19104, USA.
authors.forename: Pramod B
authors.initials: PB
authors.lastname: Voleti
authors.affiliation: Department of Orthopaedic Surgery, University of Virginia, 415 Ray C Hunt Drive, Third Floor, Charlottesville, VA 22908, USA.
authors.forename: Francis H
authors.initials: FH
authors.lastname: Shen
authors.affiliation: Department of Orthopaedic Surgery, Department of Neurosurgery, University of Pennsylvania, Washington Square West Building, 235 South 8th Street, Philadelphia, PA 19106, USA. Electronic address: Vincent.Arlet@uphs.upenn.edu.
authors.forename: Vincent
authors.initials: V
authors.lastname: Arlet
keywords: Idiopathic scoliosis; Monoaxial pedicle screws; Posterior spinal fusion; Set screw loosening