title: Two-piece ALIF cage optimizes the bone-implant interface in a 360° setting.
abstract: Clinical research has documented that cage subsidence and the loss of balance correction is a significant complication related to spinal fusion. Subsidence is a multifactorial complication, where implant design is one important element. The aim of the study is to compare the rigidity and bone-implant relative motion of segments treated with either a conventional one-piece ALIF cage versus a two-piece ALIF cage, which adapts in situ and permits 7°-21° of lordosis.
  
  
  
  Seven lumbosacral (L3-S1) human cadaver specimens were tested in a universal spine tester in the intact condition, the specimens instrumented with a two-piece ALIF cage (Statur®-L, FBC Device, Denmark) and a one-piece ALIF cage (Pezo™-A, Ulrich GmbH & Co. KG., Germany), both supplemented with a pedicle screw system using pure moments of ±7.5 Nm in three principal motion directions. For assessment of the bone-implant interface, fluoroscopic videos were captured during motion and 3D motion was measured using an optical motion capturing system.
  
  
  
  Significantly less motion at the implant-endplate interface was found for the two-piece cage (1.0° ± 0.6°) in comparison to the one-piece cage (4.2° ± 1.7°) in flexion/extension. No significant differences in segment rigidity were found between the one-piece and two-piece cages in the 360° setup, while both configurations significantly reduced the range of motion compared to the intact condition (p < 0.05).
  
  
  
  In comparison to the traditional one-piece ALIF cages, the two-piece cage concept reduced the relative motion at the bone-implant interface without compromising stability.
authors.affiliation: Trauma Research Centre Ulm, Institute of Orthopaedic Research and Biomechanics, University Hospital Ulm, Helmholtzstr. 14, 89081, Ulm, Germany. hans-joachim.wilke@uni-ulm.de.
authors.forename: Hans-Joachim
authors.initials: HJ
authors.lastname: Wilke
authors.affiliation: Trauma Research Centre Ulm, Institute of Orthopaedic Research and Biomechanics, University Hospital Ulm, Helmholtzstr. 14, 89081, Ulm, Germany.
authors.forename: David
authors.initials: D
authors.lastname: Volkheimer
authors.affiliation: FBC Device ApS, Risskov, Denmark.
authors.forename: Bruce
authors.initials: B
authors.lastname: Robie
authors.affiliation: Orthopaedic Research Laboratory, Aarhus University Hospital, Aarhus, Denmark.
authors.forename: Finn B
authors.initials: FB
authors.lastname: Christensen
mesh_terms: D000069343:Bone-Implant Interface / Q000502:physiology*; D006801:Humans; D008159:Lumbar Vertebrae / Q000601:surgery*; D012447:Sacrum / Q000601:surgery*; D013123:Spinal Fusion / Q000379:methods*
keywords: ALIF; Biomechanics; In vitro; Lumbar spine; Sagittal balance