title: Stabilization of the craniocervical junction after an internal dislocation injury: an in vitro study.
abstract: BACKGROUND
  Reconstructive surgeries at the occipitocervical (OC) junction have been studied in treating degenerative conditions. There is a paucity of data for optimal fixation for a traumatically unstable OC joint. In clinical OC dislocations, segmental fixation may be impossible because of vertebral artery injury or fracture. Segmental fixation of the occiput, C1, and C2 demonstrated maximum biomechanical stability in fixation of an unstable craniocervical dislocation. A biomechanical study comparing various points of cervical posterior screw fixation after recreating traumatic injury would illuminate relative advantages between the various techniques.
  
  
  OBJECTIVE
  To determine the rigidity lost, if any, of segmental C0-C2 posterior screw fixation versus fixation skipping C1 at the OC junction, with or without a cross-connector.
  
  
  METHODS
  This study is a cadaveric biomechanical investigation.
  
  
  METHODS
  Intervertebral motions and translations were recorded in seven specimens under conditions in the following order: intact, OC dislocation model with complete disruption of the cruciate ligaments, alar ligaments, and occipitoatlantal/atlantoaxial capsules (injury), segmental posterior fixation (SPF) with posterior instrumentation (ELLIPSE; Globus Medical, Inc., Audubon, PA, USA) at occiput, C1, and C2 levels, endpoint fixation (EPF) with posterior instrumentation at occiput and C1 level skipping C1, and endpoint fixation with a cross-connector (EPFC). Motion was applied through a custom spine simulator with a pure moment load of 2.5 Nm and measured with motion capture markers attached to occiput (C0), anterior C1 ring, and C2. Flexion-extension (FE), lateral bending (LB), axial rotation (AR), and cranial-caudal (CC) motions were recorded in terms of C0-C2. Results were reported as a percentage of injured motion (injury=100%), unless otherwise stated.
  
  
  RESULTS
  The injury significantly increased the motion to 165%, 263%, and 130%, during FE, LB, and AR, respectively, of intact. The CC translations increased to 164%, 254%, and 121% during FE, LB, AR, respectively, of intact. Segmental posterior fixation significantly reduced motion to 7%, 8%, and 1%, during FE, LB, and AR, respectively, of injury. Endpoint fixation significantly increased motion in FE, resulting in 12%, 6%, and 4% during FE, LB, and AR, respectively, of injury when compared with SPF. The EPFC construct decreased the motion compared with its counterpart to 8.6%, 5.7%, and 3.2% during FE, LB, and AR, respectively.
  
  
  CONCLUSIONS
  All fixation constructs significantly reduced motion in all loading modes and CC translations, compared with intact and injury. The construct with the greatest stability against craniocervical dislocation included SPF with instrumentation at the occiput, C1, and C2. By skipping C1 using the EPF, FE and cephalad-caudal translations significantly increased compared with posterior fixation at every level. The addition of a cross-connector increased the stability but was not statistically significant.
authors: Rothman Institute, 2500 English Creek Ave., Building 1300, Egg Harbor Township, NJ 08234, USA.
authors: Kris E
authors: KE
authors: Radcliff
authors: MERC, Globus Medical, Inc., 2560 General Armistead Ave., Audubon, PA 19403, USA. Electronic address: mhussain@globusmedical.com.
authors: Mir M
authors: MM
authors: Hussain
authors: MERC, Globus Medical, Inc., 2560 General Armistead Ave., Audubon, PA 19403, USA.
authors: Mark
authors: M
authors: Moldavsky
authors: MERC, Globus Medical, Inc., 2560 General Armistead Ave., Audubon, PA 19403, USA.
authors: Noelle F
authors: NF
authors: Klocke
authors: Rothman Institute, 925 Chestnut St, 5th Floor, Philadelphia, PA 19107, USA.
authors: Alexander
authors: A
authors: Vaccaro
authors: Rothman Institute, 925 Chestnut St, 5th Floor, Philadelphia, PA 19107, USA.
authors: Todd J
authors: TJ
authors: Albert
authors: MERC, Globus Medical, Inc., 2560 General Armistead Ave., Audubon, PA 19403, USA.
authors: Saif
authors: S
authors: Khalil
authors: MERC, Globus Medical, Inc., 2560 General Armistead Ave., Audubon, PA 19403, USA.
authors: Brandon S
authors: BS
authors: Bucklen
mesh_terms: D001268:Atlanto-Axial Joint / Q000601:surgery*; D001696:Biomechanical Phenomena; D001863:Bone Screws; D006801:Humans; D004204:Joint Dislocations / Q000601:surgery*; D016059:Range of Motion, Articular; D013123:Spinal Fusion / Q000295:instrumentation / Q000379:methods*
keywords: Biomechanics; Cervical screw fixation; Craniocervical; Dislocation; Range of motion; Subluxation