title: Postoperative segmental malalignment after surgery with the Bryan cervical disc prosthesis: is it related to the mechanics and design of the prosthesis?
abstract: METHODS
  In a radiographic study, postoperative segmental alignment was compared between 2 cohorts of 20 consecutive patients operated with a Bryan Cervical Disc Prosthesis. In group 2, patients with severe preoperative kyphosis were excluded for disc replacement surgery and the surgical technique was slightly altered to avoid asymmetric overdrilling of the posterior part of the cranial endplate of the caudal vertebral body.
  
  
  OBJECTIVE
  The aim was to investigate whether this change in patient inclusion criteria and modification of the surgical technique had an influence on postoperative segmental alignment and whether postoperative kyphosis is related to the mechanical properties and/or the design of the prosthesis.
  
  
  BACKGROUND
  Several research groups reported segmental kyphosis after treatment of degenerative disc disease with the Bryan Cervical Disc Prosthesis.
  
  
  METHODS
  On the basis of lateral radiographs, the disc insertion angle (as a postoperative estimate for the intraoperative angle of approach) and the angle of the functional spinal unit (FSU) and disc angle (both as measures for segmental alignment) were calculated.
  
  
  RESULTS
  In group 1, 80% of the patients had a kyphotic FSU angle and 40% had a kyphotic disc angle preoperatively. At follow-up, 65% of the patients had a kyphotic FSU angle, whereas 55% had a kyphotic disc angle. In group 2, 40% of the patients had a kyphotic FSU angle and 5% had a kyphotic disc angle preoperatively. At follow-up, 40% of the patients had a kyphotic FSU angle, whereas 5% had a kyphotic disc angle. Due to the change in patient inclusion criteria, there was a significant difference in preoperative FSU angle between groups 1 and 2; however, no significant difference in preoperative disc angle was found. Owing to the change in surgical technique, the disc insertion angle was significantly different between both the groups. A difference in postoperative FSU angle, however, nonsignificant, between both the groups was observed. There was a significant difference in postoperative disc angle between both the groups; group 1 showed significantly more kyphosis of the shells, than group 2.
  
  
  CONCLUSIONS
  This study shows that segmental malalignment with the Bryan Disc can be reduced and is therefore not device related. Proper patient selection and a modified surgical technique can prevent this adverse outcome.
authors.affiliation: Division of Biomechanics and Engineering Design, University Hospital Gasthuisberg, KU Leuven, Belgium. joris.walraevens@mech.kuleuven.be
authors.forename: Joris R R
authors.initials: JR
authors.lastname: Walraevens
authors.forename: Baoge
authors.initials: B
authors.lastname: Liu
authors.forename: Jozef Vander
authors.initials: JV
authors.lastname: Sloten
authors.forename: Philippe
authors.initials: P
authors.lastname: Demaerel
authors.forename: Jan
authors.initials: J
authors.lastname: Goffin
mesh_terms: D000328:Adult; D002574:Cervical Vertebrae / Q000000981:diagnostic imaging* / Q000503:physiopathology / Q000601:surgery; D017586:Diskectomy / Q000009:adverse effects / Q000295:instrumentation / Q000379:methods; D005260:Female; D006801:Humans; D007403:Intervertebral Disc / Q000000981:diagnostic imaging* / Q000503:physiopathology / Q000601:surgery; D055959:Intervertebral Disc Degeneration / Q000000981:diagnostic imaging* / Q000503:physiopathology / Q000601:surgery; D007405:Intervertebral Disc Displacement / Q000000981:diagnostic imaging / Q000209:etiology* / Q000601:surgery; D007738:Kyphosis / Q000000981:diagnostic imaging* / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D018579:Patient Selection; D011446:Prospective Studies; D019919:Prosthesis Implantation / Q000009:adverse effects* / Q000295:instrumentation / Q000379:methods*; D011859:Radiography; D016059:Range of Motion, Articular; D013123:Spinal Fusion / Q000009:adverse effects / Q000295:instrumentation / Q000379:methods; D016896:Treatment Outcome