In-vitro Biomechanics of the Cervical Spine: a Systematic Review

Prioritizing biomaterials for spinal disc implants by a fuzzy AHP and TOPSIS decision making method

Considerable research has been focused on identifying the optimum biomaterial for spine implants. New technologies and materials have allowed surgeons to better grasp the biomechanical principles underpinning implant stability and function. An optimal biomaterial for total disc replacement (TDR) should include essential characteristics such as biocompatibility, long-term durability, the capacity to withstand mechanical stresses, and economic viability. Our research has focused on six biomaterials for TDR, including Ti-6Al-4V, CoCr alloy, stainless steel 316L, zirconia toughened alumina (ZTA), polyether ether ketone (PEEK) and ultra-high-molecular weight polyethylene (UHMWPE). Ten common properties, i.e., the Young's modulus, density, tensile strength, the expense of the manufacturing process, the cost of raw material, wear rate, corrosion resistance, thermal conductivity, fracture toughness and compressive strength were utilized to assess these six different materials. The purpose of this study was to evaluate and rank the six alternative biomaterials proposed for use in the endplates and articulating surface of a spinal TDR. To accomplish this, a multi-criteria decision-making approach, namely the fuzzy analytic hierarchy process (fuzzy AHP) and the Technique of Order Preference by Similarity to Ideal Solution (TOPSIS) was adopted to solve the model. For validation and robustness of the proposed method, sensitivity analysis was performed, and comparison was performed with fuzzy-VIKOR and fuzzy-MOORA methods. In light of the study's results, ZTA and Ti-6Al-4V were identified as the best suited materials for the articulating surface and endplates, respectively, in a spinal disc implant.

True Continuous Segment of Ossification of Posterior Longitudinal Ligament is Protective Against Postoperative Early Kyphosis Progression After Laminoplasty

BACKGROUND AND OBJECTIVES

Ossification of the posterior longitudinal ligament (OPLL) is a potentially catastrophic disease. Laminoplasty (LP) is a common surgical intervention, but postoperative kyphosis progression is a major complication, for which various risk factors have been identified and used in surgical decision-making. Our focus is on the ability of OPLL with specific morphological traits, designated as the true continuous segment (TCS), to stabilize alignment and prevent postoperative kyphosis after LP.

METHODS

This retrospective case-control study included patients who underwent cervical LP for OPLL treatment with a minimum 1-year follow-up. Demographic, operative, and radiographic parameters were analyzed. TCS is defined as a continuous segment of OPLL that spans the disk space more than half of the adjacent vertebral body height without crack, or OPLL segment attached to both upper and lower adjacent vertebral bodies by bridging, or obvious interbody autofusion, and is identified from preoperative computed tomography. A subgroup analysis for preoperatively lordotic patients, divided into 2 groups based on cervical alignment at the final follow-up, was conducted to identify risk factors for kyphosis progression. Difference analysis, linear regression analysis for loss of lordosis (LoL), and logistic regression analysis for kyphosis progression were used.

RESULTS

A total of 84 patients were identified. Among them, 78 patients with preoperatively lordotic alignment were divided into 2 groups: those who maintained lordotic alignment (n = 60) and those who progressed to kyphosis (n = 18). Regression analyses revealed a significant protective effect of TCS count against LoL and postoperative kyphosis, with a TCS count of 3 or more conclusively preventing kyphosis (sensitivity 1.000, specificity 0.283, area under the curve 0.629).

CONCLUSION

For patients with OPLL, TCS was shown to protect against the LoL after LP. Therefore, TCS should be identified and considered when planning surgical treatment for OPLL.

Cervical facet capsular ligament mechanics: Estimations based on subject-specific anatomy and kinematics

Background

To understand the facet capsular ligament's (FCL) role in cervical spine mechanics, the interactions between the FCL and other spinal components must be examined. One approach is to develop a subject-specific finite element (FE) model of the lower cervical spine, simulating the motion segments and their components' behaviors under physiological loading conditions. This approach can be particularly attractive when a patient's anatomical and kinematic data are available.

Methods

We developed and demonstrated methodology to create 3D subject-specific models of the lower cervical spine, with a focus on facet capsular ligament biomechanics. Displacement-controlled boundary conditions were applied to the vertebrae using kinematics extracted from biplane videoradiography during planar head motions, including axial rotation, lateral bending, and flexion-extension. The FCL geometries were generated by fitting a surface over the estimated ligament-bone attachment regions. The fiber structure and material characteristics of the ligament tissue were extracted from available human cervical FCL data. The method was demonstrated by application to the cervical geometry and kinematics of a healthy 23-year-old female subject.

Results

FCL strain within the resulting subject-specific model were subsequently compared to models with generic: (1) geometry, (2) kinematics, and (3) material properties to assess the effect of model specificity. Asymmetry in both the kinematics and the anatomy led to asymmetry in strain fields, highlighting the importance of patient-specific models. We also found that the calculated strain field was largely independent of constitutive model and driven by vertebrae morphology and motion, but the stress field showed more constitutive-equation-dependence, as would be expected given the highly constrained motion of cervical FCLs.

Conclusions

The current study provides a methodology to create a subject-specific model of the cervical spine that can be used to investigate various clinical questions by coupling experimental kinematics with multiscale computational models.

Remission of cervicogenic dysphagia associated with biomechanical dysfunction following chiropractic therapy

Cervicogenic dysphagia is a complex condition that can arise from biomechanical dysfunction in the cervical spine. Conventional treatment outcomes are not always guaranteed. Chiropractic treatment is considered an alternative treatment for dysphagia, yet there is a lack of evidence supporting its effectiveness. We present the case of a 48-year-old male who had difficulty swallowing for eight months. He had a feeling of food stuck in his throat when eating hard food but without any pain when swallowing, and eventually, he could not swallow any dry food. He was diagnosed with dysphagia associated with an anxiety disorder and was treated with medication, but there was no improvement in his condition. A full-spine radiograph revealed biomechanical dysfunction, including reduced cervical lordosis and levoscoliosis of the upper thoracic spine. After nine months of conventional physiotherapy, the patient completely recovered from his symptoms, with significantly improved biomechanical parameters. This study highlights the potential mechanism of cervicogenic dysphagia and the effect of chiropractic treatment in managing it. Applying chiropractic treatment, including spinal manipulative therapy, instrument-assisted soft tissue manipulation, and mechanical traction, might bring a positive outcome for dysphagia patients with careful consideration.