title: Fixation Strength of Caudal Pedicle Screws after Posterior Lumbar Interbody Fusion with the Modified Cortical Bone Trajectory Screw Method.
abstract: METHODS
  Clinical case series.
  
  
  OBJECTIVE
  In the posterior lumbar interbody fusion (PLIF) procedure in our institute, the cephalad screw trajectory follows a mediolateral and caudocephalad directed path according to the original cortical bone trajectory (CBT) method. However, the starting point of the caudal screw is at the medial border of the pedicle on an articular surface of the superior articular process, and the trajectory takes a mediolateral path parallel to the cephalad endplate. The incidence of caudal screw loosening after PLIF with this modified CBT screw method was investigated, and significant risk factors for caudal screw loosening were evaluated.
  
  
  BACKGROUND
  A biomechanical study of this modified caudal screw trajectory using the finite element method reported about a 20% increase in uniaxial yield pullout load compared with the traditional trajectory. However, there has been no clinical study concerning the fixation strength of this modified caudal screw trajectory.
  
  
  METHODS
  The subjects were 193 consecutive patients who underwent single-level PLIF with modified CBT screw fixation. Caudal screw loosening was checked in computed tomography at 6 months after surgery, and screw loosening was defined as a radiolucency of 1 mm or more at the bone-screw interface.
  
  
  RESULTS
  The incidence of caudal screw loosening after lumbosacral PLIF (46.2%) was significantly higher than that after floating PLIF (6.0%). No significant differences in sex, brand of the instruments, and diameter and length of the caudal screw were evident between patients with and without caudal screw loosening. Patients with caudal screw loosening were significantly older at the time of surgery than patients without caudal screw loosening.
  
  
  CONCLUSIONS
  Fixation strength of the caudal screw after floating PLIF with this modified CBT screw technique was sufficiently acceptable. Fixation strength after the lumbosacral procedure was not.
authors: Department of Orthopaedic Surgery, Kansai Rosai Hospital, Amagasaki, Japan.
authors: Hironobu
authors: H
authors: Sakaura
authors: Department of Orthopaedic Surgery, Kansai Rosai Hospital, Amagasaki, Japan.
authors: Toshitada
authors: T
authors: Miwa
authors: Department of Orthopaedic Surgery, Osaka Rosai Hospital, Osaka, Japan.
authors: Tomoya
authors: T
authors: Yamashita
authors: Department of Orthopaedic Surgery, Kansai Rosai Hospital, Amagasaki, Japan.
authors: Yusuke
authors: Y
authors: Kuroda
authors: Department of Orthopaedic Surgery, Kansai Rosai Hospital, Amagasaki, Japan.
authors: Tetsuo
authors: T
authors: Ohwada
keywords: Caudal screw loosening; Cortical bone trajectory; Less-invasive approach; Posterior lumbar interbody fusion; Risk factors