title: Effect of uncovertebral joint excision on the motion response of the cervical spine after total disc replacement.
abstract: METHODS
  In vitro biomechanical study.
  
  
  OBJECTIVE
  To quantify the effects of uncinatectomy on cervical motion after total disc replacement (TDR).
  
  
  BACKGROUND
  The effect of uncinatectomy on TDR motion is unknown. Partial uncinatectomy may be required to decompress the foramen; however, the residual uncinates can potentially limit TDR motion and serve as a source of progressive spondylosis. Complete resection of the uncinates may decrease this risk yet endanger destabilizing the segment.
  
  
  METHODS
  Seven human cervical spines (C3-C7) (age, 63.4 +/- 6.9 years) were tested first intact and then after implantation of a metal-on-polyethylene ball-and-socket semiconstrained prosthesis at C5-C6. Following this, gradually increased uncinatectomy was performed in the following order: 1) right partial-posteromedial (two thirds), 2) right complete, and 3) bilateral complete resection. Specimens were tested in flexion-extension, lateral bending, and axial rotation (+/-1.5 Nm). Flexion-extension was tested under 150 N follower preload.
  
  
  RESULTS
  TDR without uncinatectomy increased C5-C6 flexion-extension range of motion from 8.4 degrees +/- 3.5 degrees to 11.6 degrees +/- 3.4 degrees, but statistical significance was not reached (P > 0.05). Lateral bending decreased from 6.2 degrees +/- 2.2 degrees to 3.1 degrees +/- 1.4 degrees, with a trend for statistical significance (P = 0.07). Axial rotation decreased from 5.5 degrees +/- 2.4 degrees to 4.3 degrees +/- 1.4 degrees after the implantation (P > 0.05). Both right partial and right complete uncinatectomy resulted in nearly symmetrical restoration of lateral bending to intact values and significantly increased flexion-extension compared with intact (P < or = 0.05); however, axial rotation still did not differ from intact (P > 0.05). Complete bilateral resection also restored lateral bending to intact values (7.3 degrees +/- 2.7 degrees, P > 0.05); however, it resulted in significant increase in range of motion in flexion-extension (14.1 degrees +/- 3.0 degrees, P < or = 0.05) and axial rotation (8.7 degrees +/- 2.4 degrees, P < or = 0.05).
  
  
  CONCLUSIONS
  Unilateral complete or even partial uncinatectomy can normalize lateral bending after TDR. Bilateral complete uncinatectomy is not necessary to restore lateral bending and may result in significantly increased range of motion in flexion-extension and axial rotation compared with intact values.
authors: Department of Orthopaedic Surgery and Rehabilitation, Loyola University Medical Center, Maywood, IL 60153, USA.
authors: Joshua T
authors: JT
authors: Snyder
authors: Michael N
authors: MN
authors: Tzermiadianos
authors: Alexander J
authors: AJ
authors: Ghanayem
authors: Leonard I
authors: LI
authors: Voronov
authors: Anthony
authors: A
authors: Rinella
authors: Andrew
authors: A
authors: Dooris
authors: Gerard
authors: G
authors: Carandang
authors: Susan M
authors: SM
authors: Renner
authors: Robert M
authors: RM
authors: Havey
authors: Avinash G
authors: AG
authors: Patwardhan
mesh_terms: D000368:Aged; D001696:Biomechanical Phenomena / Q000295:instrumentation / Q000379:methods; D002574:Cervical Vertebrae / Q000473:pathology / Q000502:physiology* / Q000601:surgery*; D006801:Humans; D007403:Intervertebral Disc / Q000473:pathology / Q000502:physiology / Q000601:surgery; D007405:Intervertebral Disc Displacement / Q000473:pathology / Q000601:surgery; D008875:Middle Aged; D019919:Prosthesis Implantation / Q000295:instrumentation / Q000379:methods*; D016059:Range of Motion, Articular / Q000502:physiology*