title: Sagittal balance influences range of motion: an in vivo study with the ProDisc-C.
abstract: BACKGROUND
  Cervical arthroplasty is designed to maintain cervical motion of the functional spinal unit after cervical discectomy. The impact of the ProDisc-C (Synthes Spine, Paoli, PA) on in vivo kinematics and sagittal alignment requires further assessment.
  
  
  OBJECTIVE
  The purpose of this study is to test the hypothesis that the ProDisc-C increases range of motion (ROM) in flexion and extension at the surgical level, and assess its impact on cervical alignment.
  
  
  METHODS
  Clinical study.
  
  
  METHODS
  Fifteen patients with a mean age of 49 years were included in this study. Each patient had a single-level arthroplasty. Patients with multilevel arthroplasty, previous cervical spine surgery, and length of follow-up less than 6 months were excluded from this study.
  
  
  METHODS
  Lateral dynamic radiographs of the cervical spine were analyzed using quantitative measurement analysis (QMA) preoperatively and postoperatively. QMA software was also used to determine the ROM and sagittal translation at the surgical level.
  
  
  METHODS
  Flexion/extension lateral radiographs of the cervical spine were prospectively collected and reviewed in 15 patients preoperatively and at early (1-3 months) and late (6-14 months) follow-up after placement of the ProDisc-C. Shell angle (SA) and C2-C7 Cobb angles were measured. Sagittal translation and ROM were calculated at each time point. Preoperative values were compared with early and late follow-up values using paired Student t tests and Pearson's correlation.
  
  
  RESULTS
  The C2-C7 Cobb angle did not change significantly after surgery. Segmental ROM increased significantly from neutral to flexion (p=.02) and neutral to extension (p=.002) at late follow-up. SA correlated significantly with ROM from neutral to extension (Pearson's r=-0.55; p=.02) and translation from neutral to extension (Pearson's r=-0.58; p=.02).
  
  
  CONCLUSIONS
  The ProDisc-C increased overall segmental ROM. A lordotic SA may be associated with restricted segmental ROM and translation in extension. This study did not detect any change in overall cervical spinal alignment after insertion of the device.
authors.affiliation: Division of Neurosurgery, London Health Sciences Center, Ontario, Canada.
authors.forename: Doron
authors.initials: D
authors.lastname: Rabin
authors.forename: Rudolf
authors.initials: R
authors.lastname: Bertagnoli
authors.forename: Nicholas
authors.initials: N
authors.lastname: Wharton
authors.forename: Gwynedd E
authors.initials: GE
authors.lastname: Pickett
authors.forename: Neil
authors.initials: N
authors.lastname: Duggal
mesh_terms: D000328:Adult; D019643:Arthroplasty, Replacement / Q000295:instrumentation*; D002574:Cervical Vertebrae; D017586:Diskectomy; D005260:Female; D006801:Humans; D007595:Joint Prosthesis; D008297:Male; D008875:Middle Aged; D004856:Postural Balance / Q000502:physiology*; D016059:Range of Motion, Articular / Q000502:physiology*