title: Stability of transforaminal lumbar interbody fusion in the setting of retained facets and posterior fixation using transfacet or standard pedicle screws.
abstract: BACKGROUND
  The transforaminal lumbar interbody fusion (TLIF) technique supplements posterior instrumented lumbar spine fusion and has been tested with different types of screw fixation for stabilization. Transforaminal lumbar interbody fusion is usually placed through a unilateral foraminal approach after unilateral facetectomy, although extraforaminal entry allows the facet to be spared.
  
  
  OBJECTIVE
  To characterize the biomechanics of L4-L5 lumbar motion segments instrumented with bilateral transfacet pedicle screw (TFPS) fixation versus bilateral pedicle screw-rod (PSR) fixation in the setting of intact facets and native disc or after discectomy and extraforaminal placement of a TLIF technology graft.
  
  
  METHODS
  Human cadaveric lumbar spine segments were biomechanically tested in vitro to provide a nonpaired comparison of four configurations of posterior and interbody instrumentation.
  
  
  METHODS
  Fourteen human cadaveric spine specimens (T12-S1) underwent standard pure moment flexibility tests with intact L4-L5 disc and facets. Seven were studied with intact discs, after TFPS fixation, and then with TLIF and TFPS fixation. The others were studied with intact discs, after PSR fixation, and then combined with extraforaminally placed TLIF. Loads were applied about anatomic axes to induce flexion-extension, lateral bending, and axial rotation. Three-dimensional specimen motion in response to applied loads during flexibility tests was determined. A nonpaired comparison of the four configurations of posterior and interbody instrumentation was made.
  
  
  RESULTS
  Transfacet pedicle screw and PSR, with or without TLIF, significantly reduced range of motion during all directions of loading. Transfacet pedicle screw provided greater stability than PSR in all directions of motion except lateral bending. In flexion, TFPS was more stable than PSR (p=.042). A TLIF device provided less stability than the intact disc in constructs with TFPS and PSR.
  
  
  CONCLUSIONS
  These results suggest that fixation at L4-L5 with TFPS is a promising alternative to PSR, with or without TLIF. A TLIF device was less stable than the native disc with both methods of instrumentation presumably because of a fulcrum effect from a relatively small footplate. Additional interbody support may be considered for improved biomechanics with TLIF.
authors.affiliation: Charles E. Schmidt College of Medicine at Florida Atlantic University, 777 Glades Rd, Building 71, Boca Raton, FL 33431, USA; Department of Orthopaedic Surgery, The LES Spine Institute, 1100 W. Oakland Park Blvd., Suite #3, Fort Lauderdale, FL 33311, USA. Electronic address: kingsleychin@imissurgery.com.
authors.forename: Kingsley R
authors.initials: KR
authors.lastname: Chin
authors.affiliation: Department of Neurosurgery, Barrow Neurological Institute, St Joseph's Hospital and Medical Center, 350 W Thomas Rd, Phoenix, AZ 85013, USA.
authors.forename: Marco T
authors.initials: MT
authors.lastname: Reis
authors.affiliation: Department of Neurosurgery, Barrow Neurological Institute, St Joseph's Hospital and Medical Center, 350 W Thomas Rd, Phoenix, AZ 85013, USA.
authors.forename: Phillip M
authors.initials: PM
authors.lastname: Reyes
authors.affiliation: Department of Neurosurgery, Barrow Neurological Institute, St Joseph's Hospital and Medical Center, 350 W Thomas Rd, Phoenix, AZ 85013, USA.
authors.forename: Anna G U
authors.initials: AG
authors.lastname: Newcomb
authors.affiliation: Department of Neurosurgery, Barrow Neurological Institute, St Joseph's Hospital and Medical Center, 350 W Thomas Rd, Phoenix, AZ 85013, USA.
authors.forename: Anda
authors.initials: A
authors.lastname: Neagoe
authors.affiliation: Department of Orthopedics, Grant Medical Center, 111 South Grant Ave, Columbus, OH 43215, USA.
authors.forename: Josue P
authors.initials: JP
authors.lastname: Gabriel
authors.affiliation: The Spine Center at The Colorado Springs Orthopaedic Group, 3010 North Circle Dr, Suite 200, Colorado Springs, CO 80909, USA.
authors.forename: Roger D
authors.initials: RD
authors.lastname: Sung
authors.affiliation: Department of Neurosurgery, Barrow Neurological Institute, St Joseph's Hospital and Medical Center, 350 W Thomas Rd, Phoenix, AZ 85013, USA.
authors.forename: Neil R
authors.initials: NR
authors.lastname: Crawford
mesh_terms: D000328:Adult; D000368:Aged; D005260:Female; D006801:Humans; D008159:Lumbar Vertebrae / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D065289:Pedicle Screws; D013123:Spinal Fusion / Q000295:instrumentation / Q000379:methods*
keywords: Facet; LES; Less Exposure Surgery; Transfacet pedicle screws; Transforaminal lumbar interbody fusion