title: Biomechanical assessment of bilateral C1 laminar hook and C1-2 transarticular screws and bone graft for atlantoaxial instability.
abstract: STUDYDESIGN: In vitro biomechanical test was conducted to compare the stability of 5 different atlantoaxial posterior fusion techniques.
  
  
  OBJECTIVE
  To evaluate the biomechanical stability of an atlas laminar hook combined with transarticular (TA) screws relative to 4 different conventional fusion techniques.
  
  
  BACKGROUND
  The atlantoaxial instability caused by fractures, rheumatoid arthritis, congenital deformity, or traumatic lesions of the transverse ligament often result in acute or chronic spinal cord compression, a possible threat to a patient's life. Posterior atlantoaxial fixations are used to reconstruct the stability of atlantoaxial articulation. Conventional posterior atlantoaxial fixations are associated with high rates of pseudoarthrosis and carry the potential risk of neurologic complication. TA screw fixation can provide an excellent biomechanical stability. As a modified 3-point fixation technique, the bilateral C1-2 TA screws have been combined with C1 laminar hook and bone grafts. This modified technique had carried good clinical outcomes.
  
  
  METHODS
  Eight human specimens (C0-C4) were loaded nondestructively with pure moments and the range of motion at the level of C1-C2 was measured. Eight specimens were implanted with each of the following techniques, respectively: Gallie fixation, C1-2 TA screw fixation combined with Gallie fixation, C1-2 TA screw fixation, C1 laminar hook combined with C1-2 TA screw fixation plus bone grafts, and the C1 lateral mass screws in the atlas combined with C2 isthmic screws in axis.
  
  
  RESULTS
  Although the C1-2 TA screws best restricted lateral bending and axial rotation, the modified 3-point fixation technique additionally restricted flexion-extension and provided the excellent stability. Differences in axial rotation and lateral bending (with + or - 1.5 Nm load) were observed when the 3-point fixation techniques (TA + Gallie and TA + hook) were compared with atlas lateral mass screws in the atlas combined with isthmic screws in axis.
  
  
  CONCLUSIONS
  The modified C1 laminar hook combined with C1-2 TA screws and bone graft fixation provided the best biomechanical stability. The C1 lateral mass screws in the atlas combined with isthmic screws in axis fixation is a sound alternative when the C1-2 TA screw fixation is not feasible.
authors: Department of Orthopedics, The Second Affiliated Hospital, The Second Military Medical University, Shanghai, People's Republic of China.
authors: Xiang
authors: X
authors: Guo
authors: Bin
authors: B
authors: Ni
authors: Weidong
authors: W
authors: Zhao
authors: Mingfei
authors: M
authors: Wang
authors: Fengjin
authors: F
authors: Zhou
authors: Songkai
authors: S
authors: Li
authors: Zhongwu
authors: Z
authors: Ren
mesh_terms: D000328:Adult; D001268:Atlanto-Axial Joint / Q000473:pathology / Q000503:physiopathology / Q000601:surgery*; D001368:Axis, Cervical Vertebra / Q000473:pathology / Q000503:physiopathology / Q000601:surgery; D001696:Biomechanical Phenomena; D001863:Bone Screws / Q000592:standards; D016025:Bone Transplantation / Q000379:methods*; D002102:Cadaver; D001270:Cervical Atlas / Q000473:pathology / Q000503:physiopathology / Q000601:surgery; D004867:Equipment Design; D019544:Equipment Failure Analysis; D019416:Head Movements / Q000502:physiology; D006801:Humans; D016268:Internal Fixators / Q000592:standards*; D007593:Joint Instability / Q000473:pathology / Q000503:physiopathology / Q000601:surgery*; D008297:Male; D011183:Postoperative Complications / Q000209:etiology / Q000503:physiopathology / Q000517:prevention & control; D016059:Range of Motion, Articular / Q000502:physiology; D013117:Spinal Cord Compression / Q000209:etiology / Q000503:physiopathology / Q000517:prevention & control; D013123:Spinal Fusion / Q000295:instrumentation* / Q000379:methods*; D016474:Weight-Bearing / Q000502:physiology; D055815:Young Adult; D021801:Zygapophyseal Joint / Q000473:pathology / Q000503:physiopathology / Q000601:surgery