A comprehensive finite element model of surgical treatment for cervical myelopathy

BackgroundCervical myelopathy is a common and debilitating chronic spinal cord dysfunction. Treatment includes anterior and/or posterior surgical intervention to decompress the spinal cord and stabilize the spine, but no consensus has been made as to the preferable surgical intervention. The objective of this study was to develop an finite element model of the healthy and myelopathic C2-T1 cervical spine and common anterior and posterior decompression techniques to determine how spinal cord stress and strain is altered in healthy and diseased states.MethodsA finite element model of the C2-T1 cervical spine, spinal cord, pia, dura, cerebral spinal fluid, and neural ligaments was developed and validated against in vivo human displacement data. To model cervical myelopathy, disc herniation and osteophytes were created at the C4-C6 levels. Three common surgical interventions were then incorporated at these levels.FindingsThe finite element model accurately predicted healthy and myelopathic spinal cord displacement compared to motions observed in vivo. Spinal cord strain increased during extension in the cervical myelopathy finite element model. All surgical techniques affected spinal cord stress and strain. Specifically, adjacent levels had increased stress and strain, especially in the anterior cervical discectomy and fusion case.InterpretationsThis model is the first biomechanically validated, finite element model of the healthy and myelopathic C2-T1 cervical spine and spinal cord which predicts spinal cord displacement, stress, and strain during physiologic motion. Our findings show surgical intervention can cause increased strain in the adjacent levels of the spinal cord which is particularly worse following anterior cervical discectomy and fusion.     

Magnetic resonance imaging of the spine. Normal anatomy.

Standard anatomy of the spine may be found in anatomy and radiology textbooks. However, there are aspects of spinal anatomy that are of particular importance to magnetic resonance imaging (MRI). The structure and orientation of the facet joints and their relationship to the neural foramina receive relatively little attention in standard anatomic works, but they are of great importance in evaluating nerve root compression syndromes. Similarly, the relationships between the cross-sectional diameters of the spinal canal, the subarachnoid space, and the spinal cord assume a great deal of significance when evaluating patients with signs or symptoms of spinal stenosis. Changes in the configurations and composition of the spinal cord will become increasingly important to the radiologists as it becomes possible to identify and distinguish spinal cord grey and white matter. Degenerative syndromes of the spinal cord may be more thoroughly evaluated once MRI permits identification of the specific regions or structures of the cord in which the tissue loss has been most severe.     

Anterior spinal cord syndrome after initiation of treatment with atenolol

Anterior spinal cord syndrome is a rare condition with a variety of precipitating factors. Patients typically complain of weakness or paralysis of the extremities, often accompanied by pain, but frequently without a history of trauma. A 48-year-old man presented to the emergency department complaining of neck pain and inability to move his legs in the absence of trauma. Several hours prior he had seen his private physician and was given a dose of atenolol for elevated blood pressure. He had not previously been on medications for hypertension. His neurological examination revealed bilateral paralysis of the lower extremities. In the upper extremities he had weakness and sensory loss at the level of C6. Rectal tone was decreased and without sensation. Cervical and thoracic spine magnetic resonance imaging showed spondylotic disc disease, with disc herniation at C6-7 causing severe spinal canal stenosis. Despite i.v. methylprednisolone, pressors, and a prolonged intensive care unit course, the patient was discharged 5 weeks later with continued neurological deficits. Anterior spinal cord syndrome results from compression of the anterior spinal artery and often occurs in the absence of traumatic injury. The recognition, management, and prognosis of this condition are discussed.     

MRI观察成人无骨折、脱位型颈髓损伤

目的 分析成人无骨折、脱位颈椎外伤合并颈脊髓损伤的MR表现及其临床意义.方法 收集该病患者38例,入院时均行颈椎X线、CT及MR检查,其中男32例,女6例,年龄24～62岁,平均(42.0±0.4)岁.结果 本组病例X线、CT及MR检查均未见颈椎骨折及脱位.脊髓MRI信号改变包括脊髓信号无改变4例,髓内水肿30例,髓内出血9例,脊髓软化或囊性变4例以及增强后有强化13例.其他MRI表现包括颈椎后纵韧带骨化或颈椎间盘退变或损伤后突出等,为脊髓受压迫的原因.结论 MRI可为无骨折、脱位型颈脊髓损伤患者的诊断与正确治疗提供依据.MRI无信号改变或仅有水肿表现者预后较好,髓内出血或者异常强化者预后较差.     

Numerical investigation of the relative effect of disc bulging and ligamentum flavum hypertrophy on the mechanism of central cord syndrome

BackgroundThe pathogenesis of the central cord syndrome is still unclear. While there is a consensus on hyperextension as the main traumatic mechanism leading to this condition, there is yet to be consensus in studies regarding the pathological features of the spine (intervertebral disc bulging or ligamentum flavum hypertrophy) that could contribute to clinical manifestations.MethodsA comprehensive finite element model of the cervical spine segment and spinal cord was used to simulate high-speed hyperextension. Four stenotic cases were modelled to study the effect of ligamentum flavum hypertrophy and intervertebral disc bulging on the von Mises stress and strain.FindingsDuring hyperextension, the downward displacement of the ligamentum flavum and a reduction of the spinal canal diameter (up to 17%) led to a dynamic compression of the cord. Ligamentum flavum hypertrophy was associated with stress and strain (peak of 0.011 Mpa and 0.24, respectively) in the lateral corticospinal tracts, which is consistent with the histologic pattern of the central cord syndrome. Linear intervertebral disc bulging alone led to a higher stress in the anterior and posterior funiculi (peak 0.029 Mpa). Combined with hypertrophic ligamentum flavum, it further increased the stress and strain in the corticospinal tracts and in the posterior horn (peak of 0.023 Mpa and 0.35, respectively).InterpretationThe stenotic typology and geometry greatly influence stress and strain distribution resulting from hyperextension. Ligamentum flavum hypertrophy is a main feature leading to central cord syndrome.     

MR imaging of cerebrospinal fluid flow and spinal cord motion in neurologic disorders of the spine.

In summary, MR imaging of CSF and cord motion helps to evaluate diseases affecting cord and CSF motion and to identify the specific pathophysiology involved. A number of significant points have been made. First, MR imaging flow studies can be useful in evaluating CSF spaces and cystic diseases. Second, longitudinal and transverse motions occur in the spinal cord and CSF. Traveling wave motion occurs along the length of the spinal cord. Third, spinal cord tethering is associated with decreased cord velocity and loss of cord displacement at tethering site. Decreased transverse velocities occur with lateral cord tethering to the spinal canal. Fourth, in spinal dysraphism, longitudinal cord velocity is decreased by tethering, and is normal in asymptomatic patients with low conus. Normal cord motion helps to rule out possible tethering in symptomatic dysraphism with hydromyelia. Fifth, in acquired and nonmyelodysplastic symptomatic tethering, spinal cord motion is decreased. Sixth, in symptomatic cord compression, CSF flow and cord motion decrease, but recover after surgical decompression and after compensatory atrophy. Seventh, in asymptomatic spinal stenosis, cord motion is normal or increased. Diffuse spinal stenosis with cord atrophy leads to diffuse cord acceleration and prolonged cord caudal velocity, possibly related to the loss of the transverse mobility of the cord. Finally, focal spinal stenosis leads to focal dynamic cord deformation and can be associated with prominent intramedullary deformations. When compression is severe or symptomatic, cord motion is significantly decreased. Postoperative cases demonstrate good recovery of cord and CSF motion, unless compression or obstruction is still present.     

Does pedicle screw fixation of the subaxial cervical spine provide adequate stabilization in a multilevel vertebral body fracture model? An in vitro biomechanical study

BackgroundCervical vertebral body fractures generally are treated through an anterior-posterior approach. Cervical pedicle screws offer an alternative to circumferential fixation. This biomechanical study quantifies whether cervical pedicle screws alone can restore the stability of a three-column vertebral body fracture, making standard 360° reconstruction unnecessary.MethodsRange of motion (2.0 Nm) in flexion-extension, lateral bending, and axial rotation was tested on 10 cadaveric specimens (five/group) at C2–T1 with a spine kinematics simulator. Specimens were tested for flexibility of intact when a fatigue protocol with instrumentation was used to evaluate construct longevity. For a C4–6 fracture, spines were instrumented with 360° reconstruction (corpectomy spacer + plate + lateral mass screws) (Group 1) or cervical pedicle screw reconstruction (C3 and C7 only) (Group 2).FindingsResults are expressed as percentage of intact (100%). In Group 1, 360° reconstruction resulted in decreased motion during flexion-extension, lateral bending, and axial rotation, to 21.5%, 14.1%, and 48.6%, respectively, following 18,000 cycles of flexion-extension testing. In Group 2, cervical pedicle screw reconstruction led to reduced motion after cyclic flexion-extension testing, to 38.4%, 12.3%, and 51.1% during flexion-extension, lateral bending, and axial rotation, respectively.InterpretationThe 360° stabilization procedure provided the greatest initial stability. Cervical pedicle screw reconstruction resulted in less change in motion following cyclic loading with less variation from specimen to specimen, possibly caused by loosening of the shorter lateral mass screws. Cervical pedicle screw stabilization may be a viable alternative to 360° reconstruction for restoring multilevel vertebral body fracture.     

Dynamics of spinal cord compression with different patterns of thoracolumbar burst fractures: Numerical simulations using finite element modelling

BackgroundIn thoracolumbar burst fractures, spinal cord primary injury involves a direct impact and energy transfer from bone fragments to the spinal cord. Unfortunately, imaging studies performed after the injury only depict the residual bone fragments position and pattern of spinal cord compression, with little insight on the dynamics involved during traumas. Knowledge of underlying mechanisms could be helpful in determining the severity of the primary injury, hence the extent of spinal cord damage and associated potential for recovery. Finite element models are often used to study dynamic processes, but have never been used specifically to simulate different severities of thoracolumbar burst fractures.MethodsPreviously developed thoracolumbar spine and spinal cord finite element models were used and further validated, and representative vertebral fragments were modelled. A full factorial design was used to investigate the effects of comminution of the superior fragment, presence of an inferior fragment, fragments rotation and velocity, on maximum Von Mises stress and strain, maximum major strain, and pressure in the spinal cord.FindingsFragment velocity clearly was the most influential factor. Fragments rotation and presence of an inferior fragment increased pressure, but rotation decreased both strains outputs. Although significant for both strains outputs, comminution of the superior fragment isn't estimated to influence outputs.InterpretationThis study is the first, to the authors' knowledge, to examine a detailed spinal cord model impacted in situ by fragments from burst fractures. This numeric model could be used in the future to comprehensively link traumatic events or imaging study characteristics to known spinal cord injuries severity and potential for recovery.     

Analysis of the mechanical response of damaged human cervical spine ligaments

BackgroundCervical spine ligaments that protect the spinal cord and stabilize the spine are frequently injured in motor vehicle collisions and other traumatic situations. These injuries are usually incomplete, and often difficult to notice. The focus of the presented study is placed on analysis of the effect of subfailure load on the mechanical response of the three main cervical spine ligaments: the anterior and the posterior longitudinal ligament and the ligamentum flavum.MethodsA total of 115 samples of human cadaveric ligaments removed within 24–48 h after death have been tested. Uniaxial tension tests along the fiber direction were performed in physiological conditions on a custom designed test equipment. The ligaments were loaded into an expected damage zone at two different subfailure values (based on previously reported reference group of 46 samples), and then reloaded to failure.FindingsThe main effect of a high subfailure load has proven to be the toe elongation change. The toe elongation increase is affected by the subfailure load value. While anterior and posterior longitudinal ligament showed similar changes, the smallest subfailure effect was found in ligamentum flavum.InterpretationsThe normal physiological region of the cervical spine ligaments mechanical response is modified by a high subfailure load. The observed ligament injury significantly compromises ligament ability to give tensile support within physiological spinal motion.     

Football Equipment Removal Improves Chest Compression and Ventilation Efficacy

Objective: Airway access recommendations in potential catastrophic spine injury scenarios advocate for facemask removal, while keeping the helmet and shoulder pads in place for ensuing emergency transport. The anecdotal evidence to support these recommendations assumes that maintaining the helmet and shoulder pads assists inline cervical stabilization and that facial access guarantees adequate airway access. Our objective was to determine the effect of football equipment interference on performing chest compressions and delivering adequate ventilations on patient simulators. We hypothesized that conditions with more football equipment would decrease chest compression and ventilation efficacy. Methods: Thirty-two certified athletic trainers were block randomized to participate in six different compression conditions and six different ventilation conditions using human patient simulators. Data for chest compression (mean compression depth, compression rate, percentage of correctly released compressions, and percentage of adequate compressions) and ventilation (total ventilations, mean ventilation volume, and percentage of ventilations delivering adequate volume) conditions were analyzed across all conditions. Results: The fully equipped athlete resulted in the lowest mean compression depth (F_5,154 = 22.82; P < 0.001; Effect Size = 0.98) and delivery of adequate compressions (F_5,154 = 15.06; P < 0.001; Effect Size = 1.09) compared to all other conditions. Bag-valve mask conditions resulted in delivery of significantly higher mean ventilation volumes compared to all 1- or 2-person pocketmask conditions (F_5,150 = 40.05; P < 0.001; Effect Size = 1.47). Two-responder ventilation scenarios resulted in delivery of a greater number of total ventilations (F_5,153 = 3.99; P = 0.002; Effect Size = 0.26) and percentage of adequate ventilations (F_5,150 = 5.44; P < 0.001; Effect Size = 0.89) compared to one-responder scenarios. Non-chinstrap conditions permitted greater ventilation volumes (F_3,28 = 35.17; P < 0.001; Effect Size = 1.78) and a greater percentage of adequate volume (F_3,28 = 4.85; P = 0.008; Effect Size = 1.12) compared to conditions with the chinstrap buckled or with the chinstrap in place but not buckled. Conclusions: Chest compression and ventilation delivery are compromised in equipment-intense conditions when compared to conditions whereby equipment was mostly or entirely removed. Emergency medical personnel should remove the helmet and shoulder pads from all football athletes who require cardiopulmonary resuscitation, while maintaining appropriate cervical spine stabilization when injury is suspected. Further research is needed to confirm our findings supporting full equipment removal for chest compression and ventilation delivery.     

基于正侧位锥束CT投影快速构建脊椎三维模型

目的 探讨基于C形臂的两张正侧位2D锥束CT（CBCT）投影图像进行3D模型重建的效果。方法 采用半自动化的二维投影图像特征点提取算法,选定18点的特征点集并提取其对应的正侧位二维投影图像平面坐标,然后针对C形臂CBCT系统建立坐标系,推导特征点三维空间坐标与其在投影图像中平面坐标之间的几何关系,代入转换公式获得特征点集的三维空间坐标。利用薄板样条法对三维脊椎基础模型进行空间非刚性插值获得三维脊椎目标模型。将L3石膏模型置入C形臂CBCT系统,获取375幅圆周扫描图像,利用FDK算法重建三维模型并进行表面重采样得到三维脊椎参考模型,对其进行不规则形状调制得到三维脊椎基础模型,利用本文方法对三维脊椎基础模型进行空间非刚性插值得到三维脊椎目标模型,并设置对照组对本文方法的精度进行评价。结果 相对于特征点手动提取和边缘增强提取算法,采用半自动化特征点提取算法构建获得的三维脊椎目标模型与参考模型的误差降低至1 mm以内。结论 采用本文方法可构建出近似的、精度较高的脊椎三维模型,为基于C形臂CBCT的手术导航提供3D图像支持。     

强直性脊柱炎脊柱骨折的影像学表现

目的 探讨强直性脊柱炎(AS)脊柱骨折的多种影像学特征和影像诊断的价值.方法 回顾性分析20例AS合并脊柱骨折患者的影像学和临床资料.结果 损伤节段位于颈椎5例(25.00%),胸腰椎15例(75.00%),其中屈曲型损伤11例(55.00%),屈曲过伸型损伤9例(45.00%),前中后三柱同时损伤14例(70.00%),伴脊髓损伤8例(40.00%).X线平片共发现脊柱损伤征象43个,多层螺旋CT(MSCT)发现93个,MRI发现102个.结论 AS脊柱骨折常表现为累及三柱的贯通性骨折,MRI和MSCT是早期诊断的重要手段,MRI显示脊髓损伤和后柱损伤有明显优势,是评估AS合并脊柱骨折的首选影像学检查方法.     

Speed impacts frontal-plane maneuver stability of individuals with incomplete spinal cord injury

BackgroundFollowing incomplete spinal cord injury, people often move slowly in an effort to maintain stability during walking maneuvers. Here we examine how maneuver speed impacts frontal-plane stability in people with incomplete spinal cord injury. We hypothesized that the challenge to control frontal-plane stability would increase with maneuver speed; specifically, the minimum lateral margin of stability would be smaller and the required coefficient of friction to avoid a slip would be greater during fast vs. preferred speed maneuvers.MethodsWe measured kinematics and ground reaction forces as 12 individuals with incomplete spinal cord injury performed side-step, lateral maneuvers at preferred and fast speeds. We examined four sequential steps: the Setup and Pushoff steps initiated the maneuver, and the Landing and Recovery steps arrested the maneuver.FindingsOur hypotheses were partially supported. Maneuver time was shorter during fast vs. preferred speed maneuvers (p = 0.003). Minimum lateral margin of stability was smaller during the Setup step of fast vs. preferred speed maneuvers (p = 0.026). We found no differences in minimum lateral margin of stability between speeds for the Landing and Recovery steps (p > 0.05). The required coefficient of friction was not different between fast and preferred speed maneuvers (p = 0.087).InterpretationThe greatest effect of increasing maneuver speed occurred during the Setup step; as speed increased, participants reduced their minimum lateral margin of stability ipsilateral to the maneuver direction. This action allowed maneuvers to be performed more quickly without requiring a greater lateral impulse during the Pushoff step. However, this strategy reduced passive stability.     

广州管圆线虫病患者头颈部MR检查

目的 分析广州管圆线虫感染人体后有症状患者的头颈部MRI表现.方法 对74例有症状患者进行MRI和CT检查.MRI检查包括常规T1WI、T2WI、T2-FLAIR序列以及静脉注射钆对比剂后T1WI增强扫描.脑部CT检查均为平扫, 分析CT和MRI所见.对影像表现异常的患者,MR 随访1~3次.结果 33例患者MRI表现异常,包括单纯软脑膜异常强化17例,单纯脑实质异常信号3例,单纯脊髓异常信号1例,脑实质与软脑膜同时受累11例,脊髓与软脊膜同时受累1例.脑实质与脊髓内病变多表现为长T1、长T2信号,灶性分布;T1WI增强扫描时病灶多呈结节状强化.5例脑实质和脊髓的长T1、长T2异常信号无强化表现.结论 头颈部MRI检查有助于了解中枢神经系统广州管圆线虫病的病变程度,但绝大多数MRI所见缺乏特征性.     

适合磁共振成像的羊颈脊髓压迫性损伤模型的建立与病理学观察

目的 探讨建立一种新的适合MRI研究的羊颈髓压迫损伤模型,并对其进行影像学和神经功能评价.方法 12只20～25 kg山羊随机分为实验组和对照组,每组6只,通过椎间孔把导管球囊插入羊颈髓的硬膜外腔.手术10天后,实验组注入0.2 ml生理盐水,持续压迫40天,对照组不注生理盐水.利用MRI、运动功能评分和病理学检查对模型进行评价.结果 实验组MR影像表现为脊髓受压变扁,运动功能评分下降.病理学显示神经元变性,胶质细胞增生,炎性细胞浸润,有髓神经髓鞘部分板层状结构紊乱,部分明显分层.对照组各项检查未见明显异常.结论 经颈椎间孔置入导管球囊制作的羊颈髓压迫性损伤的动物模型适合进行急性和慢性脊髓压迫性损伤的研究,为利用MR深入研究颈髓压迫症的病理生理变化奠定了基础.     

Extraosseous spinal epidural plasmocytoma associated with multiple myeloma: Two case reports

BACKGROUNDMultiple myeloma is a malignant hematological disease characterized by proliferation of monoclonal plasma cells mainly in the bone marrow. Extraosseous epidural plasmacytoma associated with myeloma arises from lymphoid tissue in the epidural space without focal vertebral involvement, and is rare.CASE SUMMARYA 52-year-old woman was diagnosed with kappa subtype nonsecretory multiple myeloma and presented with bilateral arm weakness 11 mo after completing multiple courses of chemotherapy. Spinal magnetic resonance imaging (MRI) showed a posterior C7–T3 epidural mass with spinal cord compression. After five courses of chemotherapy, follow-up MRI showed resolution of cord compression. A 54-year-old man presented with paraplegia 15 mo after a diagnosis of IgD kappa subtype multiple myeloma and completing multiple courses of chemotherapy. He underwent Th11 and L1 laminectomies for tumor resection because MRI showed an epidural mass causing cord compression. His-topathologic examination was consistent with IgD multiple myeloma. The patients have currently survived for 33 mo and 19 mo, respectively.CONCLUSIONIsolated extraosseous epidural plasmacytoma associated with multiple myeloma without bony involvement is difficult to diagnose by imaging. Definitive diagnosis requires pathological and immunohistochemical examination.     

Spinal cord injury syndrome with motor sparing in the absence of all sensation

This paper describes the anatomic basis for the unusual presentation in a spinal cord injured subject of preservation of motor power in the absence of all sensation. The patient was examined at four hours, and daily thereafter, after a motorcycle accident in which he was thrown over the handle bars. He had trace ankle dorsi and plantar flexors, but light touch, pin, position, and vibratory sensation were absent below the level of C4 bilaterally. There was no physical evidence to differentiate whether he suffered a flexion or extension injury. Cervical spine films showed no evidence of fracture or dislocation, but anterior and posterior osteophytes involving C3 to C4, C4 to C5, and C5 to C6 were present. Magnetic resonance imaging showed evidence of cervical cord edema at C3 to C4 with possible hemorrhage and severe spinal stenosis at C3 to C4 and C4 to C5. This patient received a compression injury with resulting classic anterior spinal artery syndrome. Because of his spinal stenosis with a decreased anterior-posterior (AP) diameter of the canal, the posterior circulation was also compromised. The extensive pial anastomotic network provided relative sparing of the most peripheral components of the lateral corticospinal tracts. This case report demonstrates a unique clinical picture that cannot be anatomically classified by current American Spinal Injury Association (ASIA) standards as central cord syndrome. It can be explained by the lamination of the ascending and descending tracts in relation to the vascular supply of the cervical cord in conjunction with the narrowing of the AP diameter of the canal due to spinal stenosis.     

MULTIDISCIPLINARY PAIN ABSTRACTS: 50

Degenerative disease of the spine is one of the most common clinical entities and affects the intervertebral discs, including opposing vertebral endplates, the intervertebral posterior joints and the ligaments. The most severe primary spinal degenerative changes are found in the lower cervical and lumbar spine regions. The spine contains three different types of joints, each of which presents its own pattern of degenerative disease: cartilaginous joints, synovial joints, and fibrous joints. With regard to radicular pain, root compression alone does not fully account for root pain following disc-root conflict, but it is, nevertheless, considered to be the main cause of pain. The authors pointed out that the origin of pain is multi-factorial and that inflammation probably predominates over merely mechanical mechanisms. They also considered whether vertebral arthrosis can be construed as the body's decision to favor the spine's static function over its dynamic role when joint "hypermobility" linked to chronic load in old age could cause severe structural damage to the bony vertebral structures.     

198例四川地震中脊柱脊髓损伤的临床分析

目的分析四川地震脊柱脊髓损伤类型构成情况及临床特点。方法将198例伤员按照年龄段分为4组,收集骨折类型、神经损害程度、复合伤及多个部位脊柱骨折的数据,分析其临床特点。结果骨折类型以压缩骨折最多见(占49.3%),其次是爆裂骨折(占45.9%)。198例伤员中,脊髓损伤105例,ASIA分级：A级20例,B级18例,C级25例,D级42例。发生复合伤41例。发生多个椎体损伤的部位以T₁₂、L₁、L₂最多见。结论四川地震脊柱损伤类型以压缩骨折和爆裂骨折为主,主要集中在18～65岁年龄段,脊髓损伤占脊柱损伤的53.03%。     

A patient specific computational biomechanical model for the entire lumbosacral spinal unit with imposed spondylolysis

BackgroundA biomechanical model of the lumbosacral spinal unit between L1-S1 was developed to investigate the behavior of normal and select pathological states. Our aims were to generate predictive structural models for mechanical deformation including critical stresses in the spine components and to investigate the probability of subsequent lumbar spine fractures in the presence of unilateral spondylolysis.MethodsA non-linear three-dimensional finite element pathology-free model of the L1-S1 lumbosacral unit was generated using patient-specific computerized tomography scans and calibrated by comparing it to experimental data of a range of motion modes consisting of flexion, extension, left and right lateral bending, and left and right axial rotation. Unilateral and bilateral pars defects were created on the isthmus of L5 to simulate spondylolysis.FindingsResults showed that under flexion, left lateral bending and right axial rotation, stresses were higher on the contralateral L5 pars-interarticularis, whereas, no significant changes occurred on the left-right isthmus of the L2-L4 and S1. Significant changes in the range of motion compared to the pathology-free model were observed in bilateral spondylolysis not only adjacent to the pars defect area but also in other lumbar spine levels.InterpretationThe proposed pathology-free lumbosacral unit model showed good correlation with experimental tests for all loading cases. In unilateral spondylolysis, a subsequent pars defect was observed within the same vertebra. The overall modeling approach can be used to study different pathological states.