title: A functional classification of spinal instrumentation.
abstract: BACKGROUND
  Spinal instrumentation systems have evolved far beyond the original Harrington design, with increasing complexity and capabilities. This review attempts to de-emphasize the "product names," as systems are often generically and inappropriately referred to as "Harrington rods," by introducing a functional classification for current systems.
  
  
  OBJECTIVE
  The aim of this paper is to review the intended design purpose of current spinal instrumentation systems for more accurate interpretations of radiographs and complications.
  
  
  METHODS
  The principles involved in each type of instrumentation system are described, followed by the characteristic components and the normal appearance radiographically, with examples of complications, which should be recognized.
  
  
  METHODS
  The historical contribution of specific systems in the developing art of internal fixation of the spine is provided as a background to understand the biomechanical forces imparted by spinal hardware. Recognizing the functional intent of spinal constructs will enhance descriptions of those images.
  
  
  RESULTS
  Spinal instrumentation has been categorized into five functional types: Distraction and compression, segmental stabilization, coupled or derotation systems, translational or pedicle screw systems, and anterior instrumentation.
  
  
  CONCLUSIONS
  Analysis of radiographs from a functional viewpoint can enhance the descriptive interpretation and specifically allow assessment of the success or of the presence of complications, which are crucial to the analysis of instrumentation effectiveness.
authors.affiliation: Cherry Way Orthopaedics, P.C., 425 First Avenue @ Cherry Way, Pittsburgh, PA 15219, USA. cherryway@pol.net
authors.forename: Mark R
authors.initials: MR
authors.lastname: Foster
mesh_terms: D004867:Equipment Design; D016267:External Fixators / Q000145:classification*; D006801:Humans; D016268:Internal Fixators / Q000145:classification*; D019857:Osteogenesis, Distraction / Q000145:classification* / Q000295:instrumentation*; D013123:Spinal Fusion / Q000145:classification* / Q000295:instrumentation*; D013131:Spine / Q000601:surgery