Computer simulation and image guidance for individualised dynamic spinal stabilization

Quantifying the Impact of Spinal Fusion Systems by Multibody Simulation

The established surgical procedure of spinal fusion, in which two or more spinal vertebrae are permanently connected, is constantly increasing worldwide due to new developments in fusion procedures and surgical techniques, as well as improved implants, even though there is still no consensus on whether fusion leads to subsequent degeneration of adjacent spinal segments. We outline the potential biomechanical impacts of mono-segmental and multi-segmental fusion on the spinal structures, especially on the adjacent functional spinal units (FSU), using MultiBody Simulation (MBS). In addition, we investigated the influence of the implant size on the loading situation of the spinal structures by analyzing suitable human MBS models, focusing on a highly detailed spinal region. Our results showed no significant increase in the load on adjacent intervertebral discs (IVD) in the present specific model configurations due to mono-segmental and multi-segmental fusion. Instead, the load was redistributed to the disadvantage of the posterior facet joints in the lumbar spine's upper section. Analysis of the influence of different implant sizes on the spinal structures' load revealed that choosing an implant size that did not correspond to the original IVD space led to a massive increase in the IVD loads.Clinical relevance: gaining new insights to improve surgical outcomes to minimize the risk of adverse effects.

Multibody Models of the Thoracolumbar Spine: A Review on Applications, Limitations, and Challenges

Numerical models of the musculoskeletal system as investigative tools are an integral part of biomechanical and clinical research. While finite element modeling is primarily suitable for the examination of deformation states and internal stresses in flexible bodies, multibody modeling is based on the assumption of rigid bodies, that are connected via joints and flexible elements. This simplification allows the consideration of biomechanical systems from a holistic perspective and thus takes into account multiple influencing factors of mechanical loads. Being the source of major health issues worldwide, the human spine is subject to a variety of studies using these models to investigate and understand healthy and pathological biomechanics of the upper body. In this review, we summarize the current state-of-the-art literature on multibody models of the thoracolumbar spine and identify limitations and challenges related to current modeling approaches.

Muscle-driven and torque-driven centrodes during modeled flexion of individual lumbar spines are disparate

Lumbar spine biomechanics during the forward-bending of the upper body (flexion) are well investigated by both in vivo and in vitro experiments. In both cases, the experimentally observed relative motion of vertebral bodies can be used to calculate the instantaneous center of rotation (ICR). The timely evolution of the ICR, the centrode, is widely utilized for validating computer models and is thought to serve as a criterion for distinguishing healthy and degenerative motion patterns. While in vivo motion can be induced by physiological active structures (muscles), in vitro spinal segments have to be driven by external torque-applying equipment such as spine testers. It is implicitly assumed that muscle-driven and torque-driven centrodes are similar. Here, however, we show that centrodes qualitatively depend on the impetus. Distinction is achieved by introducing confidence regions (ellipses) that comprise centrodes of seven individual multi-body simulation models, performing flexion with and without preload. Muscle-driven centrodes were generally directed superior–anterior and tail-shaped, while torque-driven centrodes were located in a comparably narrow region close to the center of mass of the caudal vertebrae. We thus argue that centrodes resulting from different experimental conditions ought to be compared with caution. Finally, the applicability of our method regarding the analysis of clinical syndromes and the assessment of surgical methods is discussed.

A review of computer-assisted orthopaedic surgery systems

BACKGROUND

Computer-assisted orthopaedic surgery systems have great potential, but no review has focused on computer-assisted surgery systems for the spine, hip, and knee.

METHODS

A systematic search was performed in Web of Science and PubMed. We searched the literature on computer-assisted orthopaedic surgery systems from 2008 to the present and focused on three aspects of systems: training, planning, and intraoperative navigation.

RESULTS AND DISCUSSION

In this review study, we reviewed 34 surgical training systems, 31 surgical planning systems, and 41 surgical navigation systems. The functions and characteristics of the surgical systems were compared and analysed, and the current concerns about and the impact of the surgical systems on doctors and surgery were clarified.

CONCLUSION

Computer-assisted orthopaedic surgery systems are still in the development stage. Future surgical training systems should include synthetic models with patient anatomy. Surgical planning systems with automatic planning should be developed, and surgical navigation systems with multimodal fusion, robotic assistance and imaging should be developed.

Semirigid Waved Rod System for the Treatment of the Degenerative Lumbar Diseases

BACKGROUND

The semirigid pedicle screw instrumentation has gained wide popularity in recent decennium in lumbar fusion surgery. However, few data were documented to compare the clinical efficacy between semirigid and traditional rigid pedicle screw systems.

MATERIALS AND METHODS

A total of 96 patients with degenerative lumbar diseases were selected to perform operations between 2008 and 2013. The patients were prospectively randomized into 2 groups: 50 patients were managed by semirigid waved rod systems and 46 patients were intervened by traditional rigid straight stiff rod systems. X-rays and computed tomography were utilized to examine the interbody fusion status in the follow-up in detail. Surgical parameters such as operative time, blood loss, and total hospital stay were calculated and compared. Visual Analog Scale and Oswestry Disability Index were used to assess clinical efficacy postoperatively.

RESULTS

No significant differences were found about demographic data between groups. There were no significant differences regarding the surgical parameters including operative time, blood loss, and total hospital stay. Visual Analog Scale and Oswestry Disability Index postoperatively were also similar between the 2 instrumentations (P>0.05). The fusion rate was higher in the semirigid group (45/50) than in the traditional group (34/46) (P=0.039) at the final follow-up.

CONCLUSIONS

Waved rod may be better in facilitating interbody fusion compared with traditional straight rod, although waved rod and straight stiff rod can both get similar clinical efficacy. Meanwhile, waved rod is likely superior in alleviating adjacent degeneration segments.

Three-dimensional Cross-Platform Planning for Complex Spinal Procedures: A New Method Adaptive to Different Navigation Systems

STUDY DESIGN

A feasibility study.

OBJECTIVE

To develop a method based on the DICOM standard which transfers complex 3-dimensional (3D) trajectories and objects from external planning software to any navigation system for planning and intraoperative guidance of complex spinal procedures.

SUMMARY OF BACKGROUND DATA

There have been many reports about navigation systems with embedded planning solutions but only few on how to transfer planning data generated in external software.

MATERIALS AND METHODS

Patients computerized tomography and/or magnetic resonance volume data sets of the affected spinal segments were imported to Amira software, reconstructed to 3D images and fused with magnetic resonance data for soft-tissue visualization, resulting in a virtual patient model. Objects needed for surgical plans or surgical procedures such as trajectories, implants or surgical instruments were either digitally constructed or computerized tomography scanned and virtually positioned within the 3D model as required. As crucial step of this method these objects were fused with the patient's original diagnostic image data, resulting in a single DICOM sequence, containing all preplanned information necessary for the operation. By this step it was possible to import complex surgical plans into any navigation system.

RESULTS

We applied this method not only to intraoperatively adjustable implants and objects under experimental settings, but also planned and successfully performed surgical procedures, such as the percutaneous lateral approach to the lumbar spine following preplanned trajectories and a thoracic tumor resection including intervertebral body replacement using an optical navigation system. To demonstrate the versatility and compatibility of the method with an entirely different navigation system, virtually preplanned lumbar transpedicular screw placement was performed with a robotic guidance system.

CONCLUSIONS

The presented method not only allows virtual planning of complex surgical procedures, but to export objects and surgical plans to any navigation or guidance system able to read DICOM data sets, expanding the possibilities of embedded planning software.