title: Are Collapsed Cervical Discs Amenable to Total Disc Arthroplasty?: Analysis of Prospective Clinical Data With 2-Year Follow Up.
abstract: METHODS
  Analysis of prospectively collected radiographic data.
  
  
  OBJECTIVE
  To investigate the influence of preoperative index-level range of motion (ROM) and disc height on postoperative ROM after cervical total disc arthroplasty (TDA) using compressible disc prostheses.
  
  
  BACKGROUND
  Clinical studies demonstrate benefits of motion preservation over fusion; however, questions remain unanswered as to which preoperative factors have the ability to identify patients who are most likely to have good postoperative motion, which is the primary rationale for TDA.
  
  
  METHODS
  We analyzed prospectively collected data from a single-arm, multicenter study with 2-year follow up of 30 patients with 48 implanted levels. All received compressible cervical disc prostheses of 6 mm-height (M6C, Spinal Kinetics, Sunnyvale, CA). The influence of index-level preoperative disc height and ROM (each with two levels: below-median and above-median) on postoperative ROM was analyzed using 2 x 2 ANOVA. We further analyzed the radiographic outcomes of a subset of discs with preoperative height less than 3 mm, the so-called "collapsed" discs.
  
  
  RESULTS
  Shorter (3.0 ± 0.4 mm) discs were significantly less mobile preoperatively than taller (4.4 ± 0.5 mm) discs (6.7° vs. 10.5°, P = 0.01). The postoperative ROM did not differ between the shorter and taller discs (5.6° vs. 5.0°, P = 0.63). Tall discs that were less mobile preoperatively had significantly smaller postoperative ROM than short discs with above-median preoperative mobility (P < 0.05). The "collapsed discs" (n = 8) were less mobile preoperatively compared with all discs combined (5.1° vs. 8.6°, P < 0.01). These discs were distracted to more than two times the preoperative height, from 2.6 to 5.7 mm, and had significantly greater postoperative ROM than all discs combined (7.6° vs. 5.3°, P < 0.05).
  
  
  CONCLUSIONS
  We observed a significant interaction between preoperative index-level disc height and ROM in influencing postoperative ROM. Although limited by small sample size, the results suggest discs with preoperative height less than 3 mm may be amenable to disc arthroplasty using compressible disc prostheses.
  
  
  METHODS
  2.
authors.affiliation: Edward Hines Jr. VA Hospital, Hines, IL.|Loyola University Stritch School of Medicine, Maywood, IL.
authors.forename: Avinash G
authors.initials: AG
authors.lastname: Patwardhan
authors.affiliation: Edward Hines Jr. VA Hospital, Hines, IL.
authors.forename: Gerard
authors.initials: G
authors.lastname: Carandang
authors.affiliation: Edward Hines Jr. VA Hospital, Hines, IL.|Loyola University Stritch School of Medicine, Maywood, IL.
authors.forename: Leonard I
authors.initials: LI
authors.lastname: Voronov
authors.affiliation: Edward Hines Jr. VA Hospital, Hines, IL.|Loyola University Stritch School of Medicine, Maywood, IL.
authors.forename: Robert M
authors.initials: RM
authors.lastname: Havey
authors.affiliation: Spinal Kinetics, San Jose, CA.
authors.forename: Gary A
authors.initials: GA
authors.lastname: Paul
authors.affiliation: NeuroTexas Brain and Spinal Surgery, Austin, TX.
authors.forename: Carl
authors.initials: C
authors.lastname: Lauryssen
authors.affiliation: Carolina Neurosurgery and Spine Associates, Charlotte, NC.
authors.forename: Domagoj
authors.initials: D
authors.lastname: Coric
authors.affiliation: Triangle Orthopedic Associates, Durham, NC.
authors.forename: Thomas
authors.initials: T
authors.lastname: Dimmig
authors.affiliation: Triangle Orthopedic Associates, Durham, NC.
authors.forename: David
authors.initials: D
authors.lastname: Musante
mesh_terms: D000328:Adult; D001178:Arthroplasty / Q000379:methods; D002574:Cervical Vertebrae / Q000601:surgery*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007403:Intervertebral Disc / Q000601:surgery*; D007405:Intervertebral Disc Displacement / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D016059:Range of Motion, Articular / Q000502:physiology*; D059145:Total Disc Replacement / Q000379:methods; D016896:Treatment Outcome