Batbayar Khuyagbaatar

Conversion Equation between the Drop Height in the New York University Impactor and the Impact Force in the Infinite Horizon Impactor in the Contusion Spinal Cord Injury Model

There are several widely used devices for controlled contusion of the spinal cord, including the Ohio State University device, the University of British Columbia multi-mechanisms injury device, the New York University (NYU) impactor, and the Infinite Horizon (IH) impactor. Although various devices and protocols have been used to generate consistent injury severities, further investigation of the relationship between the key parameters of different spinal cord injury (SCI) contusion devices (e.g., drop height in the NYU impactor and impact force in the IH impactor) will improve our understanding of SCI mechanisms. A three-dimensional finite element model of the rat spinal cord from T9 to T10 that included the white and gray matters, dura mater, and cerebrospinal fluid was developed to investigate the von-Mises stress, maximum principal strain, and maximum displacement of the spinal cord for the drop height in the NYU impactor and the impact force in the IH impactor. A quantitative relationship was established as a conversion equation between two key parameters--i.e., the drop height and the impact force--in the NYU and IH impactors from regression equations for peak von-Mises stress, peak maximum principal strain, and maximum displacement in the spinal cord with respect to drop height and impact force with very high coefficients of determination. The consistent correlation was represented as a simple equation (Force = (28.2 ± 3.2) · Height((0.83 ± 0.07))) under the experimental conditions of a 10-g rod in the NYU impactor and an impact velocity of 125 mm/sec in the IH impactor. Thus, the key biomechanical parameter for a contusion device can be converted or translated to that of another device to analyze experimental results from multiple contusion devices.

Effect of bone fragment impact velocity on biomechanical parameters related to spinal cord injury: A finite element study

Several experimental and computational studies have investigated the effect of bone fragment impact on the spinal cord during trauma. However, the effect of the impact velocity of a fragment generated by a burst fracture on the stress and strain inside the spinal cord has not been computationally investigated, even though spinal canal occlusion and peak pressure at various impact velocities were provided in experimental studies. These stresses and strains are known factors related to clinical symptoms or injuries. In this study, a fluid-structure interaction model of the spinal cord, dura mater, and cerebrospinal fluid was developed and validated. The von-Mises stress distribution in the cord, the longitudinal strain, the cord compression and cross-sectional area at the impact center, and the obliteration of the cerebrospinal fluid layer were analyzed for three pellet sizes at impact velocities ranging from 1.5m/s to 7.5m/s. The results indicate that stress in the cord was substantially elevated when the initial impact velocity of the pellet exceeded a threshold of 4.5m/s. Cord compression, reduction in cross-sectional area, and obliteration of the cerebrospinal fluid increased gradually as the velocity of the pellet increased, regardless of the size of the pellet. The present study provides insight into the mechanisms underlying spinal cord injury.

Biomechanical effects of spinal cord compression due to ossification of posterior longitudinal ligament and ligamentum flavum: a finite element analysis.

Ossification of the posterior longitudinal ligament (OPLL) and ossification of the ligamentum flavum (OLF) have been recognized as causes of myelopathy due to thickening of the ligaments resulting in narrowing of the spinal canal and compression of the spinal cord. However, few studies have focused on predicting stress distribution under conditions of OPLL and OLF based on clinical aspects such as the relationship between level of stress and severity of neurologic symptoms because direct in vivo measurement of stress is very restrictive. In this study, a three-dimensional finite element model of the spinal cord in T12-L1 was developed based on MR images. The von-Mises stresses in the cord and the cross-sectional area of the cord were investigated for various grades and shapes of spinal cord compression in OPLL and OLF. Substantial increases in maximum stresses resulting in the manifestation of spinal cord symptoms occurred when the cross-sectional area was reduced by 30-40% at 60% compression of the antero-posterior diameter of the cord in OPLL and at 4mm compression in OLF. These results indicate that compression greater than these thresholds may induce spinal symptoms, which is consistent with clinical observations.

Biomechanical Behaviors in Three Types of Spinal Cord Injury Mechanisms.

Clinically, spinal cord injuries (SCIs) are radiographically evaluated and diagnosed from plain radiographs, computed tomography (CT), and magnetic resonance imaging. However, it is difficult to conclude that radiographic evaluation of SCI can directly explain the fundamental mechanism of spinal cord damage. The von-Mises stress and maximum principal strain are directly associated with neurological damage in the spinal cord from a biomechanical viewpoint. In this study, the von-Mises stress and maximum principal strain in the spinal cord as well as the cord cross-sectional area (CSA) were analyzed under various magnitudes for contusion, dislocation, and distraction SCI mechanisms, using a finite-element (FE) model of the cervical spine with spinal cord including white matter, gray matter, dura mater with nerve roots, and cerebrospinal fluid (CSF). A regression analysis was performed to find correlation between peak von-Mises stress/peak maximum principal strain at the cross section of the highest reduction in CSA and corresponding reduction in CSA of the cord. Dislocation and contusion showed greater peak stress and strain values in the cord than distraction. The substantial increases in von-Mises stress as well as CSA reduction similar to or more than 30% were produced at a 60% contusion and a 60% dislocation, while the maximum principal strain was gradually increased as injury severity elevated. In addition, the CSA reduction had a strong correlation with peak von-Mises stress/peak maximum principal strain for the three injury mechanisms, which might be fundamental information in elucidating the relationship between radiographic and mechanical parameters related to SCI.

Effect of posterior decompression extent on biomechanical parameters of the spinal cord in cervical ossification of the posterior longitudinal ligament.

Ossification of the posterior longitudinal ligament is a common cause of the cervical myelopathy due to compression of the spinal cord. Patients with ossification of the posterior longitudinal ligament usually require the decompression surgery, and there is a need to better understand the optimal surgical extent with which sufficient decompression without excessive posterior shifting can be achieved. However, few quantitative studies have clarified this optimal extent for decompression of cervical ossification of the posterior longitudinal ligament. We used finite element modeling of the cervical spine and spinal cord to investigate the effect of posterior decompression extent for continuous-type cervical ossification of the posterior longitudinal ligament on changes in stress, strain, and posterior shifting that occur with three different surgical methods (laminectomy, laminoplasty, and hemilaminectomy). As posterior decompression extended, stress and strain in the spinal cord decreased and posterior shifting of the cord increased. The location of the decompression extent also influenced shifting. Laminectomy and laminoplasty were very similar in terms of decompression results, and both were superior to hemilaminectomy in all parameters tested. Decompression to the extents of C3–C6 and C3–C7 of laminectomy and laminoplasty could be considered sufficient with respect to decompression itself. Our findings provide fundamental information regarding the treatment of cervical ossification of the posterior longitudinal ligament and can be applied to patient-specific surgical planning.

Biomechanical investigation of post-operative C5 palsy due to ossification of the posterior longitudinal ligament in different types of cervical spinal alignment

Post-operative C5palsies are among the most common complications seen after cervical surgery for ossification of the posterior longitudinal ligament (OPLL). Although C5 palsy is a well-known complication of cervical spine surgery, its pathogenesis is poorly understood and depends on many other factors. In this study, a finite element model of the cervical spine and spinal cord-nerve roots complex structures was developed. The changes in stress in the cord and nerve roots, posterior shift of the spinal cord, and displacement and elongation of the nerve roots after laminectomy for cervical OPLL were analyzed for three different cervical sagittal alignments (lordosis, straight, and kyphosis). The results suggest that high stress concentrated on the nerve roots after laminectomy could be the main cause of C5 palsy because ossification of ligaments increases spinal cord shifting and root displacement. The type of sagittal alignment had no influence on changes in cord stress after laminectomy, although cases of kyphosis with a high degree of occupying ratio resulted in greater increases in nerve root stress after laminectomy. Therefore, kyphosis with a high OPLL occupying ratio could be a risk factor for poor surgical outcomes or post-operative complications and should be carefully considered for surgical treatment.

Influence of sagittal and axial types of ossification of posterior longitudinal ligament on mechanical stress in cervical spinal cord: A finite element analysis

BACKGROUND There are few studies focusing on the prediction of stress distribution according to the types of ossification of the posterior longitudinal ligament, which can be fundamental information associated with clinical aspects such as the relationship between stress level and neurological symptom severity. In this study, the influence of sagittal and axial types of ossification of the posterior longitudinal ligament on mechanical stress in the cervical spinal cord was investigated. METHODS A three-dimensional finite element model of the cervical spine with spinal cord was developed and validated. The von Mises stresses in the cord and the reduction in cross-sectional areas and volume of the cord were investigated for various axial and sagittal types according to the occupying ratio of ossification of the posterior longitudinal ligament in the spinal canal. FINDINGS The influence of axial type was less than that of the sagittal type, even though the central type showed higher maximum stresses in the cord, especially for the continuous type. With a 60% occupying ratio of ossification of the posterior longitudinal ligament, the maximum stress was significantly high and the cross-sectional area of the spinal cord was reduced by more than 30% of the intact area regardless of sagittal or axial types. Finally, a higher level of sagittal extension would increase the peak cord tissue stress, which would be related to the neurological dysfunction and tissue damage. INTERPRETATION Quantitative investigation of biomechanical characteristics such as mechanical stress may provide fundamental information for pre-operative planning of treatment for ossification of the posterior longitudinal ligament.

Interjoint coordination of the lower extremities in short-track speed skating

In short-track speed skating, the three-dimensional kinematics of the lower extremities during the whole skating cycle have not been studied. Kinematic parameters of the lower extremities during skating are presented as joint angles versus time. However, the angle–time presentation is not sufficient to describe the relationship between multi-joint movement patterns. Thus, angle–angle presentations were developed and used to describe interjoint coordination in sport activities. In this study, 15 professional male skaters’ full body motion data were recorded using a wearable motion capture system during short-track speed skating. We investigated the three-dimensional kinematics of the lower extremities and then established the interjoint coordination between hip–knee and knee–ankle for both legs during the whole skating cycle. The results demonstrate the relationship between multi-joint movements during different phases of short-track speed skating. This study provides fundamentals of the movement mechanism of the lower extremities that can be integrated with physiotherapy to improve skating posture and prevent injuries from repetitive stress since physiological characteristics play an important role in skating performance.

Biomechanical Effects on Cervical Spinal Cord and Nerve Root Following Laminoplasty for Ossification of the Posterior Longitudinal Ligament in the Cervical Spine: A Comparison Between Open-Door and Double-Door Laminoplasty Using Finite Element Analysis

Many clinical case series have reported the predisposing factors for C5 palsy and have presented comparisons of the two types of laminoplasty. However, there have been no biomechanical studies focusing on cervical spinal cord and nerve root following laminoplasty. The purpose of this study is to investigate biomechanical changes in the spinal cord and nerve roots following the two most common types of laminoplasty, open-door and double-door laminoplasty, for cervical ossification of the posterior longitudinal ligament (OPLL). A finite element (FE) model of the cervical spine and spinal cord with nerve root complex structures was developed. Stress changes in the spinal cord and nerve roots, posterior shift of the spinal cord, and displacement of the cervical nerve roots were analyzed with two types of cervical laminoplasty models for variations in the degree of canal occupying ratio and shape of the OPLL. The shape and degree of spinal cord compression caused by the OPLL had more influence on the changes in stress, posterior shift of the spinal cord, and displacement of the nerve root than the type of laminoplasty. The lateral-type OPLL resulted in imbalanced stress on the nerve roots and the highest nerve root displacement. Type of laminoplasty and shape and degree of spinal cord compression caused by OPLL were found to influence the changes in stress and posterior displacement of the cervical spinal cord and nerve roots. Lateral-type OPLL might contribute to the development of C5 palsy due to the imbalanced stress and tension on the nerve roots after laminoplasty.

Comparative evaluation between anatomic and non-anatomic lateral ligament reconstruction techniques in the ankle joint: A computational study

Biomechanical studies have indicated that the conventional non-anatomic reconstruction techniques for lateral ankle sprain (LAS) tend to restrict subtalar joint motion compared to intact ankle joints. Excessive restriction in subtalar motion may lead to chronic pain, functional difficulties, and development of osteoarthritis. Therefore, various anatomic surgical techniques to reconstruct both the anterior talofibular and calcaneofibular ligaments have been introduced. In this study, ankle joint stability was evaluated using multibody computational ankle joint model to assess two new anatomic reconstruction and three popular non-anatomic reconstruction techniques. An LAS injury, three popular non-anatomic reconstruction models (Watson-Jones, Evans, and Chrisman-Snook), and two common types of anatomic reconstruction models were developed based on the intact ankle model. The stability of ankle in both talocrural and subtalar joint were evaluated under anterior drawer test (150 N anterior force), inversion test (3 Nm inversion moment), internal rotational test (3 Nm internal rotation moment), and the combined loading test (9 Nm inversion and internal moment as well as 1800 N compressive force). Our overall results show that the two anatomic reconstruction techniques were superior to the non-anatomic reconstruction techniques in stabilizing both talocrural and subtalar joints. Restricted subtalar joint motion, which mainly observed in Watson-Jones and Chrisman-Snook techniques, was not shown in the anatomical reconstructions. Evans technique was beneficial for subtalar joint as it does not restrict subtalar motion, though Evans technique was insufficient for restoring talocrural joint inversion. The anatomical reconstruction techniques best recovered ankle stability.