title: Spinal cord intramedullary pressure in cervical kyphotic deformity: a cadaveric study.
abstract: METHODS
  In vitro cadaveric study of cervical spinal cord intramedullary pressure (IMP) in kyphotic deformity.
  
  
  OBJECTIVE
  To define the relationship between cervical spinal kyphotic deformity and spinal cord IMP.
  
  
  BACKGROUND
  Previous studies of asymptomatic volunteers have revealed that the greatest variation in regional sagittal neutral upright spinal alignment occurs in the cervical spine with "normal" alignment ranging up to +15 to +20° kyphosis. We sought to determine whether IMP changes in response to increasing cervical kyphosis.
  
  
  METHODS
  In eight fresh-frozen cadavers, a progressive kyphotic deformity was created. Cadavers were positioned sitting with cervical lordosis, with head stabilized using a skull clamp. The C1 posterior arch was removed, dura was opened, and three pressure sensors were advanced caudally to C7, C4-C5, and C2 within the cord parenchyma. A stepwise kyphotic deformity was then induced by sequentially releasing and retightening the skull clamp while distracting posterior short segment rods and closing anterior segmental osteotomies. After each step, fluoroscopic images and pressure measurements were obtained. The C2-C7 Gore angle and horizontal displacement of the odontoid plumb line relative to C7 (C2-C7 sagittal vertical axis [SVA]) were measured.
  
  
  RESULTS
  Minor IMP increases of 2 to 5 mm Hg were observed at one or more spinal cord levels in one of eight cadavers when the Gore angle was <+7.5° and in three of eight cadavers when the Gore angle was >+7.5° and <+21°. At Gore angles exceeding +21°, change in pressure (ΔIMP) progressively increased at one or more spinal cord levels in eight of eight cadavers. Gore angles ranging from +21° to +78° resulted in statistically significant increases in IMP ranging to >50 mm Hg, as did C2-C7 SVA >+75 mm. ΔIMP did not correlate with segmental spinal canal diameter (stenosis).
  
  
  CONCLUSIONS
  Cervical lordosis and kyphosis less than +7.5° resulted in no meaningful increase in IMP. Minor cervical kyphosis measuring +7.5° to +21° resulted in 2 to 5 mm Hg increases in IMP. As the cervical kyphotic deformity exceeded +21°, IMP increased significantly. ΔIMP with spinal alignment may help to explain the wide range of "normal" cervical neutral upright sagittal alignment in studies of asymptomatic individuals and may help further define cervical kyphotic deformity.
authors.affiliation: UC Neuroscience Institute, Department of Neurosurgery, University of Cincinnati College of Medicine, Mayfield Clinic and Spine Institute, Cincinnati, OH, USA.
authors.forename: Albert
authors.initials: A
authors.lastname: Chavanne
authors.forename: David B
authors.initials: DB
authors.lastname: Pettigrew
authors.forename: Jeffrey R
authors.initials: JR
authors.lastname: Holtz
authors.forename: Neal
authors.initials: N
authors.lastname: Dollin
authors.forename: Charles
authors.initials: C
authors.lastname: Kuntz
mesh_terms: D000368:Aged; D002102:Cadaver; D002574:Cervical Vertebrae / Q000000981:diagnostic imaging / Q000473:pathology / Q000503:physiopathology*; D005260:Female; D006801:Humans; D007738:Kyphosis / Q000150:complications / Q000473:pathology / Q000503:physiopathology*; D008297:Male; D011312:Pressure / Q000009:adverse effects; D011859:Radiography; D013116:Spinal Cord / Q000000981:diagnostic imaging / Q000473:pathology / Q000503:physiopathology*; D013117:Spinal Cord Compression / Q000209:etiology / Q000473:pathology / Q000503:physiopathology*; D055009:Spondylosis / Q000150:complications / Q000473:pathology / Q000503:physiopathology*; D014160:Transducers, Pressure / Q000592:standards