title: Construct Rigidity after Fatigue Loading in Pedicle Subtraction Osteotomy with or without Adjacent Interbody Structural Cages.
abstract: Introduction Studies document rod fracture in pedicle subtraction osteotomy (PSO) settings where disk spaces were preserved above or adjacent to the PSO. This study compares the multidirectional bending rigidity and fatigue life of PSO segments with or without interbody support. Methods Twelve specimens received bilateral T12-S1 posterior fixation and L3 PSO. Six received extreme lateral interbody fusion (XLIF) cages in addition to PSO at L2-L3 and L3-L4; six had PSO only. Flexion-extension, lateral bending, and axial rotation (AR) tests were conducted up to 7.5 Newton-meters (Nm) for groups: (1) posterior fixation, (2) L3 PSO, (3) addition of cages (six specimens). Relative motion across the osteotomy (L2-L4) and entire fixation site (T12-S1) was measured. All specimens were then fatigue tested for 35K cycles. Results Regardingmultiaxial bending, there was a significant 25.7% reduction in AR range of motion across L2-L4 following addition of cages. Regarding fatigue bending, dynamic stiffness, though not significant (p = 0.095), was 22.2% greater in the PSO + XLIF group than in the PSO-only group. Conclusions Results suggest that placement of interbody cages in PSO settings has a potential stabilizing effect, which is modestly evident in the acute setting. Inserting cages in a second-stage surgery remains a viable option and may benefit patients in terms of recovery but additional clinical studies are necessary to confirm this.
authors.affiliation: Biomechanical Testing Facility, San Francisco General Hospital, San Francisco, California ; Department of Orthopaedic Surgery, University of California, San Francisco, California.
authors.forename: Vedat
authors.initials: V
authors.lastname: Deviren
authors.affiliation: Biomechanical Testing Facility, San Francisco General Hospital, San Francisco, California ; Department of Orthopaedic Surgery, University of California, San Francisco, California.
authors.forename: Jessica A
authors.initials: JA
authors.lastname: Tang
authors.affiliation: Biomechanical Testing Facility, San Francisco General Hospital, San Francisco, California ; Department of Orthopaedic Surgery, University of California, San Francisco, California.
authors.forename: Justin K
authors.initials: JK
authors.lastname: Scheer
authors.affiliation: Biomechanical Testing Facility, San Francisco General Hospital, San Francisco, California ; Department of Orthopaedic Surgery, University of California, San Francisco, California ; Department of Neurological Surgery, University of California, San Francisco, California ; San Francisco Orthopaedic Residency Program, St. Mary's Medical Center, San Francisco, California.
authors.forename: Jenni M
authors.initials: JM
authors.lastname: Buckley
authors.affiliation: Biomechanical Testing Facility, San Francisco General Hospital, San Francisco, California ; Department of Orthopaedic Surgery, University of California, San Francisco, California.
authors.forename: Murat
authors.initials: M
authors.lastname: Pekmezci
authors.affiliation: Biomechanical Testing Facility, San Francisco General Hospital, San Francisco, California ; Department of Orthopaedic Surgery, University of California, San Francisco, California.
authors.forename: R Trigg
authors.initials: RT
authors.lastname: McClellan
authors.affiliation: Biomechanical Testing Facility, San Francisco General Hospital, San Francisco, California ; Department of Neurological Surgery, University of California, San Francisco, California.
authors.forename: Christopher P
authors.initials: CP
authors.lastname: Ames
keywords: XLIF; pedicle subtraction osteotomy; revision; rod fracture; spine biomechanics; structuralinterbody cages