Determination of the biomechanical effect of an interspinous process device on implanted and adjacent lumbar spinal segments using a hybrid testing protocol: a finite-element study.
OBJECT The authors evaluated the biomechanical effects of an interspinous process (ISP) device on kinematics and load sharing at the implanted and adjacent segments. METHODS A 3D finite-element (FE) model of the lumbar spine (L1-5) was developed and validated through comparison with published in vitro study data. Specifically, validation was achieved by a flexible (load-control) approach in 3 main planes under a pure moment of 10 Nm and a compressive follower load of 400 N. The ISP device was inserted between the L-3 and L-4 processes. Intact and implanted cases were simulated using the hybrid protocol in all motion directions. The resultant motion, facet load, and intradiscal pressure after implantation were investigated at the index and adjacent levels. In addition, stress at the bone-implant interface was predicted. RESULTS The hybrid approach, shown to be appropriate for adjacent-level investigations, predicted that the ISP device would decrease the range of motion, facet load, and intradiscal pressure at the index level relative to the corresponding values for the intact spine in extension. Specifically, the intradiscal pressure induced after implantation at adjacent segments increased by 39.7% and by 6.6% at L2-3 and L4-5, respectively. Similarly, facet loads at adjacent segments after implantation increased up to 60% relative to the loads in the intact case. Further, the stress at the bone-implant interface increased significantly. The influence of the ISP device on load sharing parameters in motion directions other than extension was negligible. CONCLUSIONS Although ISP devices apply a distraction force on the processes and prevent further extension of the index segment, their implantation may cause changes in biomechanical parameters such as facet load, intradiscal pressure, and range of motion at adjacent levels in extension.
Departments of 1 Mechanical Engineering and.|Neurosurgery, Koc University, Istanbul, Turkey.
Deniz U
DU
Erbulut
Departments of 1 Mechanical Engineering and.
Iman
I
Zafarparandeh
Departments of 1 Mechanical Engineering and.
Chaudhry R
CR
Hassan
Departments of 1 Mechanical Engineering and.
Ismail
I
Lazoglu
Neurosurgery, Koc University, Istanbul, Turkey.
Ali F
AF
Ozer
D000328:Adult; D001696:Biomechanical Phenomena / Q000502:physiology*; D006801:Humans; D007403:Intervertebral Disc / Q000601:surgery*; D008159:Lumbar Vertebrae / Q000601:surgery*; D008161:Lumbosacral Region / Q000601:surgery*; D008297:Male; D009038:Motion; D019736:Prostheses and Implants; D016059:Range of Motion, Articular; D013123:Spinal Fusion / Q000379:methods
ALE = adjacent-level effect; FE = finite element; FN = flying node; IDP = intradiscal pressure; ISL = interspinous ligament; ISP = interspinous process; ROM = range of motion; SSL = supraspinous ligament; interspinous device; lumbar spine; posterior stabilization