Lumbar spine stability after combined application of interspinous fastener and modified posterior lumbar interbody fusion: a biomechanical study

Introduction

Posterior lumbar interbody fusion (PLIF) and internal fixation are commonly performed for the treatment of lower back pain due to lumbar spinal degeneration. We have developed a novel interspinous fixation device, the interspinous fastener (ISF) for potential use in the surgical management of degenerative spinal disease. The aim of this study was to assess the in vitro biomechanical characteristics of calf lumbar spine specimens after ISF fixation with modified PLIF.

Materials and methods

Ten lumbar spine (L3–L6) specimens from ten fresh calf cadavers (8–10 weeks of age) were used. Each specimen underwent sequential testing for each of the following four groups: no instrumentation (INTACT); interspinous fusion device fixation + PLIF (ISF); unilateral pedicle screw and titanium rod fixation + PLIF (UPS); bilateral pedicle screw and titanium rod fixation + PLIF (BPS). Outcome measures included angular range of motion (ROM) during unloaded and loaded (8 Nm) flexion, extension, left bending, right bending, left torsion and right torsion.

Results

For all unloaded and loaded assessments, ROM was significantly higher in the INTACT group compared with all other groups (P < 0.05). Similarly, ROM was significantly higher in the UPS group (indicating decreased stability) compared with the ISF and BPS groups (P < 0.05). The only significant difference between the ISF and BPS groups was in the ROM with unloaded extension (higher in the BPS group, P = 0.006).

Conclusions

We found that ISF fixation with PLIF of the lower lumbar spine provided biomechanical stability that was equivalent to that associated with bilateral pedicle screw/rod fixation with PLIF. The ISF shows potential as an alternative means of fixation in the surgical management of degenerative spinal disease.