Abstract
The new distractable titanium implant (Synex) is designated for replacement of the vertebral body following fracture, posttraumatic kyphosis or tumor.
Synex was compared with the “Harms” cage (MOSS, 22x28 mm, stabilising ring) in two test series.
Test A: Measurement of the compressive strength of the vertebral body end-plate in uniaxial loading via both implants; Test B: Analysis of the bisegmental stability after corpectomy, replacement of L1 and stabilisation.
Materials and methods: In testseries A human vertebral specimens (L1) were matched according to bone mineral density (BMD). They were axially loaded (v=5mm/min) to failure via Synex (n=6) or MOSS (n=6) in an electrohydraulic testing device with load-displacement recording.
In test series B the bisegmental motion (T12-L2) of 12 spinal specimens were tested in a 3D loading simulator with moments of 0–7.5 Nm for the six directions. After testing the intact spine, we replaced L1 and stabilised with Fixateur interne (USS) or Ventrofix (VFix). Analysis of the range of motion (ROM), elastic zone (EZ) and neutral zone (NZ) for five conditions: 1) Intact specimen, 2) USS+Synex, 3) USS+MOSS, 4) VFix+Synex, 5) VFix+MOSS (randomized order).
Results: With Synex, significantly higher compression forces were recorded at 1–2 mm deformation. Ultimate compression force (Fmax) was higher (3396 N vs. 2719 N) and the distance until point of failure (Dmax) was significantly less using Synex. A significant correlation (R=0.89) between Fmax and BMD was found.
Significantly higher stability was noted with USS+Synex for extension, lateral bending, and axial rotation. No differences between Synex and MOSS were observed in combination with VFix. The combined instrumentation (USS) was superior to the anterior one (VFix).
The possibility of secondary dislocation, loss of correction, or posttraumatic kyphosis can be decreased using Synex for replacement of the vertebral body, compared with MOSS. A combined anterior-posterior stabilisation provides higher biomechanical stability compared with an anterior construct.
