The biomechanical effect on the adjacent L4/L5 segment of S1 superior facet arthroplasty: a finite element analysis for the male spine

Finite element mechanical analysis of ipsilateral approach and contralateral approach in unilateral bilateral endoscopic spine surgery

BACKGROUND

Unilateral bilateral endoscopic spine surgery (UBE) is often performed to treat lumbar spinal stenosis and disc herniation. It has become a prominent method in endoscopic spine surgery because of its very low learning curve and broader operative field of vision. Currently, the ipsilateral approach and contralateral approach have been established for disc herniation in the foraminal area, intervertebral foramen region, or pedicle region. The contralateral method offers many benefits over the ipsilateral approach, including less bone labour during microsurgical decompression and the preservation of facet joints. However, because it uses the interlaminar window approach, it inevitably involves osteotomy of the patient's superior and inferior articular processes, which may result in corresponding deterioration in the spine's biomechanical stability and subsequent adjacent facet joint diseases caused by facet joint degeneration postoperatively.

OBJECTIVE

As a result, the purpose of this work is to use a finite element model to evaluate how the ipsilateral approach and contralateral approach in unilateral bilateral endoscopic spine surgery affect spinal stability while treating identical intervertebral disc herniation.

STUDY DESIGN

In this study, a three-dimensional lumbar-sacral spine model was built and verified. Osteotomies were conducted for armpit-type lumbar disc herniation (LDH), periradicular-type LDH, and shoulder-type LDH. Postoperative lumbar spine models of the ipsilateral approach and contralateral approach in unilateral bilateral endoscopic spine surgery were developed. The von Mises stress on the endplate, shear force on the annulus fibrosus, pressure inside the intervertebral disc, and range of motion (ROM) of the L3 segment were all determined. The results of our well-validated model showed that osteotomy done in the ipsilateral approach deteriorated most biomechanical metrics.

RESULTS

In the majority of loading conditions, the contralateral approach caused the intervertebral disc's biomechanical properties to increase, and the ipsilateral approach caused the intervertebral disc's biomechanical properties to increase sharply more than the contralateral approach.

CONCLUSION

The contralateral approach, which is now extensively employed in unilateral bilateral endoscopic spine surgery, may be regarded as an ideal surgical alternative for treating lumbar disc herniation without producing iatrogenic instability. This approach has a low facet joint reduction rate, minimum soft tissue injury, and precisely identifies the midline of the central spinal canal during the retraction of the thecal sac and nerve roots.

Effect of seat tilting on biomechanics of L4 in tractor drivers

The tilting of the tractors' seat during deep tillage operations affects the drivers' sitting position, which can lead to lumbar spine injuries. To investigate the effect of seat tilting on the driver's L4 biomechanics, we built a tractor-driver musculoskeletal model in AnyBody™. The maximum activity of the driver's erector spinae at different tilted angles were measured by sEMG and compared with the simulation results to validate the model. The spatial position of the driver's spine at different tilted angles were obtained by 3 D motion capture. The model simulated the driver's spine posture during the actual tilt and investigated the effects of different tilted angles and vibration on the biomechanics of the driver's L4 . The results showed that as the tilt angle of the tractor increased, the load on the driver's L4 also increased, especially the shear force increased at a faster rate than the axial and normal forces, with the shear force on the driver's L4 increasing from 0 N to 138.7 N when the tractor was tilted from 0° to 15°. When vibration was applied to the musculoskeletal model, the maximum value of the shear force on the driver became progressively greater as the angle of tilt of the tractor increased. Overall, tilting the tractor can have a large impact on the biomechanics of the driver's L4, and tilting the tractor may be an important cause of lumbar spine injuries for tractor drivers.