Age‐related spontaneous lumbar intervertebral disc degeneration in a mouse model

The pathogenesis of intervertebral disc degeneration is unclear, but it is a major cause of several spinal diseases. Animal models have historically provided an appropriate benchmark for understanding the human spine. However, there is little information about when intervertebral disc degeneration begins in the mouse or regarding the relationship between magnetic resonance imaging and histological findings. The aim for this study was to obtain information about age‐related spontaneous intervertebral disc degeneration in the mouse lumbar spine using magnetic resonance imaging and a histological score regarding when the intervertebral disc degeneration started and how rapidly it progressed, as well as how our histological score detected the degeneration. The magnetic resonance imaging index yielded a moderate correlation with our Age‐related model score. The Pfirrmann grade and magnetic resonance imaging index had moderate correlations with age. However, our Age‐related model score had a high correlation with age. Intervertebral disc level was not a significant variable for the severity of disc degeneration. Both Pfirrmann grade and the Age‐related model score were higher in the ≥14‐month‐old group than in the 6‐month‐old group. The present results indicated that mild but significant intervertebral disc degeneration occurred in 14‐month‐old mice, and the degree of degeneration progressed slowly, reaching a moderate to severe condition for 22‐month‐old mice. At least a 14‐month follow‐up is mandatory for evaluating spontaneous age‐related mouse intervertebral disc degeneration. The histological classification score can precisely detect the gradual progression of age‐related spontaneous intervertebral disc degeneration in the mouse lumbar spine, and is appropriate for evaluating it. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:224–232, 2018.     

Bone morphogenic protein-2 signaling in human disc degeneration and correlation to the Pfirrmann MRI grading system

BACKGROUND CONTEXTBack and neck pain secondary to disc degeneration is a major public health burden. There is a need for therapeutic treatments to restore intervertebral disc (IVD) composition and function.PURPOSETo quantify ALK3, BMP-2, pSMAD1/5/8 and MMP-13 expression in IVD specimens collected from patients undergoing surgery for disc degeneration, to correlate ALK3, BMP-2, pSMAD1/5/8 and MMP-13 expression in IVD specimens to the 5-level Pfirrmann MRI grading system, and to compare ALK3, BMP-2, pSMAD1/5/8 and MMP-13 expression between cervical and lumbar degenerative disc specimens.STUDY DESIGNAn immunohistochemical study assessing ALK3, BMP-2, pSMAD1/5/8, and MMP-13 expression levels in human control and degenerative IVD specimens.METHODSHuman IVD specimens were collected from surgical patients who underwent discectomy and interbody fusion at our institution between 1/2015 and 8/2017. Each patient underwent MRI prior to surgery. The degree of disc degeneration was measured according to the 5-level Pfirrmann MRI grading system. Patients were categorized into either the 1) control group (Pfirrmann grades I-II) or 2) degenerative group (Pfirrmann grades III-V). Histology slides of the collected IVD specimens were prepared and immunohistochemical staining was performed to assess ALK3, BMP-2, pSMAD1/5/8, and MMP-13 expression levels in the control and degenerative specimens. Expression levels were also correlated to the Pfirrmann criteria. Lastly, the degenerative specimens were stratified according to their vertebral level and expression levels between the degenerative lumbar and cervical discs were compared.RESULTSFifty-two patients were enrolled; however, 2 control and 2 degenerative patients were excluded due to incomplete data sets. Of the remaining 48 patients, there were 12 control and 36 degenerative specimens. Degenerative specimens had increased expression levels of BMP-2 (p=.0006) and pSMAD1/5/8 (p<.0001). Pfirrmann grade 3 (p=.0365) and grade 4 (p=.0008) discs had significantly higher BMP-2 expression as compared to grade 2 discs. Pfirrmann grade 4 discs had higher pSMAD1/5/8 expression as compared to grade 2 discs (p<.0001). There were no differences in ALK3 or MMP-13 expression between the control and degenerative discs (p>.05). Stratifying the degenerative specimens according to their vertebral level showed no significant differences in expression levels between the lumbar and cervical discs (p>.05).CONCLUSIONSBMP-2 and pSMAD1/5/8 signaling activity was significantly upregulated in the human degenerative specimens, while ALK3 and MMP-13 expression were not significantly changed. The expression levels of BMP-2 and pSMAD1/5/8 correlate positively with the degree of disc degeneration measured according to the Pfirrmann MRI grading system.CLINICAL SIGNIFICANCEBMP-SMAD signaling represents a promising therapeutic target to restore IVD composition and function in the setting of disc degeneration.     

The porcine cervical spine as a model of the human lumbar spine: an anatomical, geometric, and functional comparison.

Animal models for analysis of spine injury and orthopaedic issues are common given concerns about bone integrity, disc degeneration, and controlled studies of identical specimens matched for age, weight, physical activity and genetic background. Given this asset, the question is asked: "Is the porcine cervical spine a reasonable model of the human lumbar spine?" Three porcine cervical spines (C2-C7) were assessed for geometric characteristics, with a larger cohort (N = 24) loaded to failure under compressive or shear loading. In addition, in vivo loading was estimated and compared between the human low back (biped) and the porcine neck (quadruped). Generally, the porcine vertebrae are smaller in all dimensions. The porcine vertebrae have anterior processes unlike humans; however, they possess similar ligamentous structure and facet joint orientation. Stiffness values (compression and shear) are similar, and comparable injuries resulted from applied compressive and shear loads. Given the scarcity of healthy, young human lumbar spines, porcine cervical spines may be a useful model for studying human lumbar injury because of the similarity of mechanical characteristics and the resulting injuries, particularly of the adolescent or young adult who has not experienced disc degeneration or calcified end-plates.     

Disc degeneration contributes to the denser bone in the subendplate but not in the vertebral body in patients with lumbar spinal stenosis or disc herniation

BACKGROUND CONTEXTIt is commonly believed that decreased bone quality would lead to endplate degeneration and arthritic changes in the facet joints, and thus accelerated disc degeneration (DD). However, some more detailed studies of vertebral bone structure have found that bone mineral density (BMD) in the vertebral body is increased rather than decreased in moderate or greater disc degeneration. The relationship between BMD and DD still needs further study. MRI-based vertebral bone quality scores have been shown to be effective in reflecting BMD, rendering a new way to evaluate the changes of vertebral body bone with DD using MRI alone.PURPOSETo evaluate MRI-based vertebral bone quality and Pfirrmann grades in patients with lumbar spinal stenosis or disc herniation, and to identify if DD is associated with denser bone around the endplate.STUDY DESIGN/SETTINGA single-center, retrospective cohort study.PATIENT SAMPLEA total of 130 patients with lumbar disc herniation and lumbar spinal stenosis from January 2019 to November 2020 who had a complete dual-energy X-ray absorptiometry scan and noncontrast lumbosacral spine MRI data.OUTCOME MEASURESThe vertebral bone quality score (VBQ) and sub-endplate bone quality score (EBQ) was calculated as a ratio of the signal intensity of the vertebral bodies and sub-endplate regions to the signal intensity of the cerebrospinal fluid at L3 on the mid-sagittal T1-weighted MRI images, respectively. The Pfirrmann grades of the lumbar discs were assessed as well.METHODSThe age, gender, body mass index, and T-score of the lumbar spine of the patients were collected. The degeneration grades of the lumbar discs were evaluated according to the Pfirrmann classification. VBQ and EBQ were measured through T1-weighted lumbar MRI. The VBQ and EBQ scores were compared between cranial and caudal sides. The correlation between MRI-based bone quality and DD was calculated. A linear regression model was used to examine the association between DD and adjacent EBQ and VBQ.RESULTSThis study included 569 lumbar segments from 130 inpatients. Cranial and caudal EBQ decreased with the increase of the Pfirrmann grade. The discs with Pfirrmann grade 5 had significantly lower caudal EBQ than the discs with Pfirrmann grades 2, 3, and 4. In the osteoporosis patients, the Pfirrmann grades negatively correlated both with the cranial EBQ and caudal EBQ. Pfirrmann grade greater than 4 was an independent contributor to the cranial EBQ, whereas greater than 3 was an independent contributor to the caudal EBQ.CONCLUSIONSDisc degeneration grades correlated with the EBQ but not with the VBQ. In patients with lumbar spinal stenosis or disc herniation, DD contributes to the denser bone in the sub-endplate, but not in the whole vertebral body.     

Even mild intervertebral disc degeneration reduces the flexibility of the thoracic spine: an experimental study on 95 human specimens

BACKGROUND CONTEXTIntervertebral disc degeneration represents one of multiple potential trigger factors for reduced passive spinal mobility and back pain. The effects of age-related degenerative intervertebral disc changes on spinal flexibility were however mainly investigated for the lumbar spine in the past, while intervertebral disc degeneration is also highly prevalent in the thoracic spine.PURPOSETo evaluate the effect of the degeneration grade on the range of motion and neutral zone of the thoracic spine.STUDY DESIGNExperimental study including combined radiological grading of intervertebral disc degeneration and biomechanical testing of 95 human thoracic functional spinal units (min. n=4 per level from T1–T2 to T11–T12) from 33 donors (15 female / 18 male, mean age 56 years, age range 37–80 years).METHODSDegeneration grades of the intervertebral discs were assessed using the validated x-ray grading scheme of Liebsch et al. (0=no, 1=mild, 2=moderate, 3=severe degeneration). Motion segments were loaded with pure moments in flexion/extension, lateral bending, and axial rotation to determine range of motion and neutral zone at 5 Nm.RESULTSAll tested specimens exhibited degeneration grades between zero and two. Range of motion significantly decreased for grades one and two compared with grade zero in any motion direction (p<.05), showing the strongest decrease in extension comparing grade two with grade zero (-42%), while no significant differences were detected between grades one and two. Similar trends were found for the neutral zone with the strongest decrease in extension also comparing grade two with grade zero (-47%). Donor age did not significantly affect the range of motion, whereas the range of motion was significantly reduced in specimens from male donors due to the significantly higher degeneration grade in this study.CONCLUSIONSEven mild intervertebral disc degeneration reduces the range of motion and neutral zone of the thoracic spine in any motion plane, whereas progressing degeneration does not further affect its flexibility. This is in contrast to the lumbar spine, where a more gradual decrease of flexibility was found in prior studies, which might be explained by differences between thoracic and lumbar intervertebral disc morphologies.CLINICAL SIGNIFICANCEThoracic intervertebral disc degeneration should be considered as one of multiple potential causal factors in patients showing reduced passive mobility and middle back pain.     

MRI evaluation of spontaneous intervertebral disc degeneration in the alpaca cervical spine

Animal models have historically provided an appropriate benchmark for understanding human pathology, treatment, and healing, but few animals are known to naturally develop intervertebral disc degeneration. The study of degenerative disc disease and its treatment would greatly benefit from a more comprehensive, and comparable animal model. Alpacas have recently been presented as a potential large animal model of intervertebral disc degeneration due to similarities in spinal posture, disc size, biomechanical flexibility, and natural disc pathology. This research further investigated alpacas by determining the prevalence of intervertebral disc degeneration among an aging alpaca population. Twenty healthy female alpacas comprised two age subgroups (5 young: 2–6 years; and 15 older: 10+ years) and were rated according to the Pfirrmann‐grade for degeneration of the cervical intervertebral discs. Incidence rates of degeneration showed strong correlations with age and spinal level: younger alpacas were nearly immune to developing disc degeneration, and in older animals, disc degeneration had an increased incidence rate and severity at lower cervical levels. Advanced disc degeneration was present in at least one of the cervical intervertebral discs of 47% of the older alpacas, and it was most common at the two lowest cervical intervertebral discs. The prevalence of intervertebral disc degeneration encourages further investigation and application of the lower cervical spine of alpacas and similar camelids as a large animal model of intervertebral disc degeneration. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 33:1776–1783, 2015.     

腰椎椎间隙高度与上位椎体高度的比值与椎间盘退行性变Pfirrmann分级的相关性

目的 探讨腰椎椎间隙高度与上位椎体高度的比值与椎间盘退行性变程度之间的关系,为腰椎椎间盘退行性疾病的诊断和治疗提供客观准确的依据。方法 回顾性分析2019年1月—2019年6月来本院就诊的61例腰椎椎间盘退行性变患者临床资料。在腰椎侧位X线片上测量腰椎椎间隙及相应上位椎体的高度,并计算椎间隙高度与上位椎体高度的比值;在腰椎矢状位MRI上评估腰椎椎间盘退行性变Pfirrmann分级;比较不同Pfirrmann分级椎间盘的椎间隙高度与上位椎体高度比值的差异,并采用Spearman相关分析研究椎间隙高度与上位椎体高度比值与相应节段椎间盘Pfirrmann分级之间的相关性。结果 除L₁/L₂节段,其余各节段椎间隙高度与上位椎体高度比值均随着Pfirrmann分级增加而逐渐减小,差异均有统计学意义（P < 0.05）。相同Pfirrmann分级的不同节段椎间盘之间椎间隙高度与上位椎体高度比值差异无统计学意义（P > 0.05）。Spearman相关分析结果显示,L₂/L₃、L₃/L₄、L₄/L₅、L₅/S₁节段Pfirrmann分级与椎间隙高度与上位椎体高度比值呈负相关（r =-0.568,P < 0.05）。结论 临床上测量L₂/L₃、L₃/L₄、L₄/L₅、L₅/S₁节段椎间隙高度与上位椎体高度比值对腰椎椎间盘退行性疾病的诊断可能具有重要意义。     

围绝经期女性腰椎椎间盘退变程度的MRI观察

目的探讨围绝经期女性腰椎椎间盘MRI特点及相关退变规律。方法随机选择2014年1月—12月来本院就诊的成年男女患者各420例,记录患者年龄、身高、体质量指数(BMI)、吸烟史、高血压史、糖尿病史、月经史、职业等,每位患者均行腰椎MRI检查。女性患者按照月经史分为5个组:绝经前组(n=76),绝经0年且6年组(n=98),绝经≥6年且11年组(n=82),绝经≥11年且≤15年组(n=80),绝经15年组(n=84)。用Pfirrmann分级系统对腰椎椎间盘退变程度进行分级,用SPSS 19.0软件进行相关数据分析。结果男女患者年龄、BMI、糖尿病史、高血压史、职业等差异无统计学意义(P0.05);男性吸烟率明显高于女性,差异有统计学意义(P0.05)。男性患者Pfirrmann分级≥Ⅲ级的椎间盘比例高于女性(男78.2%,女60.8%),差异有统计学意义(P0.05);PfirrmannⅣ、Ⅴ级时差异更显著。在女性亚组中,绝经前组各椎间盘水平Pfirrmann平均分均显著低于各绝经组,差异有统计学意义(P0.05)。绝经≤15年时,绝经年限越高,L_1/L_2、L_2/L_3、L_4/L_5及L_5/S_1椎间盘Pfirrmann平均分越高,差异有统计学意义(P0.05);绝经≥11年且≤15年组与绝经15年组间各节段椎间盘Pfirrmann平均分差异均无统计学意义(P0.05)。结论男性患者腰椎椎间盘退变较女性严重。绝经后女性腰椎椎间盘退变较绝经前严重,且在绝经≤15年时,绝经年限越长,退变越严重;绝经15年后,腰椎椎间盘退变进程减缓。因此,雌激素水平下降可能是腰椎椎间盘退变的危险因素。     

Motion in lumbar functional spine units during side bending and axial rotation moments depending on the degree of degeneration

STUDY DESIGN: Human lumbar spine specimens were tested in axial rotation and side bending. Motion was related to the grade of degeneration. OBJECTIVES: To determine the degree to which degeneration with fissure formation in the disc affects axial rotation of the lumbar functional spine unit. SUMMARY OF BACKGROUND DATA: There is controversy in the literature regarding the influence of severe degeneration and fissures of the disc on the range of axial rotation. METHODS: Thirty-six lumbar spine specimens were tested in axial rotation and side bending, by applying pure moments in an unconstrained setting. The motion in 6 df was recorded by dial gauges. The grade of degeneration was established by the grading schemes of Nachemson, Thompson, Adams, and Mimura. RESULTS: A significant increase of axial rotation and lateral translation under torque was found. This increase mainly took place between Grade 3 according to the schemes of Nachemson, Thompson, and Adams (no fissure formation) and the higher grades of degeneration (defined by fissure formation). Reduced disc height was always associated with fissures. CONCLUSIONS: A reduced lumbar disc height in radiographs seems to be associated with fissure formation in the disc. In this case, the range axial rotation after torque is increased in comparison with cases with less degeneration.     

Analysis of the influence of species,intervertebral disc height and Pfirrmann classification on failure load of an injured disc using a novel disc herniation model

Background ContextAnnular repair devices offer a solution to recurrent disc herniations by closing an annular defect and lowering the risk of reherniation. Given the significant risk of neurologic injury from device failure it is imperative that a reliable preclinical model exists to demonstrate a high load to failure for the disc repair devices.PurposeTo establish a preclinical model for disc herniation and demonstrate how changes in species, intervertebral disc height and Pfirrmann classification impacts failure load on an injured disc. We hypothesized that: (1) The force required for disc herniation would be variable across disc morphologies and species, and (2) for human discs the force to herniation would inversely correlate with the degree of disc degeneration.Study designAnimal and human cadaveric biomechanical model of disc herniation.MethodsWe tested calf lumbar spines, bovine tail segments and human lumbar spines. We first divided individual lumbar or tail segments to include the vertebral bodies and disc. We then hydrated the specimens by placing them in a saline bath overnight. A magnetic resonance images were acquired from human specimens and a Pfirrmann classification was made. A stab incision measuring 25% of the diameter of the disc was then done to each specimen along the posterior intervertebral disc space. Each specimen was placed in custom test fixtures on a servo-hydraulic test frame (MTS, Eden Prarie, MN) such that the superior body was attached to a 10,000 lb load cell and the inferior body was supported on the piston. A compressive ramping load was placed on the specimen in load control at 4 MPa/sec stopping at 75% of the disc height. Load was recorded throughout the test and failure load calculated. Once the test was completed each specimen was sliced through the center of the disc and photos were taken of the cut surface.ResultsFifteen each of calf, human, and bovine tail segments were tested. The failure load varied significantly between specimens (p<.001) with human specimens having the highest average failure load (8154±2049 N). Disc height was higher for lumbar/bovine tail segments as compared to calf specimens (p<.001) with bovine tails having the highest disc height (7.1±1.7 mm). Similarly, human lumbar discs had a cross sectional area that was greater than both bovine tail/calf lumbar spines (p<.001). There was no correlation between disc height and failure load within each individual species (p>.05). Cross sectional area and failure load did not correlate with failure load for human lumbar spine and bovine tails (p>.05) but did correlate with calf spine (r=0.53, p=.04). There was a statistically significant inverse correlation between disc height and Pfirrmann classification for human lumbar spines (r=?0.84, p<.001). There was also a statistically significant inverse relationship between Pfirrmann classification and failure load (r=?0.58, p=.02).ConclusionsWe have established a model for disc herniation and have shown how results of this model vary between species, disc morphology, and Pfirrmann classification. Both hypotheses were accepted: The force required for disc herniation was variable across species, and the force to herniation for human spines was inversely correlated with the degree of disc degeneration. We recommend that models using human intervertebral discs should include data on Pfirrmann classification, while biomechanical models using calf spines should report cross sectional area. Failure loads do not vary based on dimensions for bovine tails.Clinical SignificanceOur analysis of models for disc herniation will allow for quicker, reliable comparisons of failure forces required to induce a disc herniation. Future work with these models may facilitate rapid testing of devices to repair a torn/ruptured annulus.     

In vitro study of shear force on interbody implants

OBJECTIVE: The lordosis of the lumbar spine and body weight result in significant shear forces through the lumbosacral disc spaces. These forces result in translational motion across the disc space, which is resisted but not completely abolished by pedicle screw stabilization. It is postulated that this motion may be a factor in the development of nonunion of lumbar interbody fusions. An in vitro study of the micromotion of porcine specimens implanted with serrated or smooth interbody spacers and subjected to shear forces under compressive preload was conducted to determine whether the surface serrations on vertebral interbody implants significantly resist shear forces and resulting sagittal translation. METHODS: Measurements of anterior vertebral translation were recorded on porcine cervical spine segments, subjected to 25 N of anteroposterior shear load while under a 300-N compressive preload. Baseline testing was performed on intact specimens and partially destabilized specimens (facet joints removed). Following partial discectomy, the specimens were divided into two groups for testing: one using smooth-surfaced and one using serrated interbody spacers. RESULTS: Under 25-N shear load, the specimens tested with the serrated spacers showed anterior vertebral translation of 0.046 +/- 0.013 mm, whereas those tested with the smooth spacers measured 0.152 +/- 0.075 mm (P < 0.01). CONCLUSIONS: The presence of surface serrations on the interbody implants significantly increased the resistance to shear forces in this model. In the clinical setting, we postulate that micromotion at interbody fusion sites will be substantially less when serrated implants are used and may help reduce the incidence of nonunion.     

The external spinal fixator does not reduce anterior column motion under axial compressive loads. A mechanical in vitro study

We performed an in vitro study to investigate the effect of external spinal fixation on anterior column motion under physiological axial compression loading. The AO external spinal fixator (ESF) was applied to 5 human cadaveric lumbar spine specimens (L3-S1) at levels L4 to S1. All specimens were tested in 4 configurations: i) intact, ii) ESF in a neutral position, iii) ESF in distraction (12 mm), and iv) ESF in compression (8-12 mm). Cyclic sinusoidal axial compressive loads from 60 to 600 N were applied for 10 cycles in each test condition. The axial displacement of the load application point was recorded as an indicator of anterior column axial translation. The axial motion with the fixator in distraction was significantly greater than all other conditions, including intact. Compression of the fixator resulted in the least axial displacement. External fixation in the neutral position did not significantly affect the overall axial translation, when compared to the intact state. In conclusion, the external spinal fixator did not significantly reduce anterior column axial translation and, in distraction, this motion exceeded that of the intact specimen. Since pain relief is frequently observed during distraction of the painful segment/s with the external fixator, the mechanical basis of the pain relief is not well understood.     

BNIP3与LC3B在椎间盘退行性变过程中的作用

目的研究BCL2/腺病毒E1B19k Da相互作用蛋白3(BNIP3)基因及微管相关蛋白轻链3B(LC3B)基因在退变椎间盘中的表达情况,探讨其与椎间盘退行性变分级之间的相关性。方法收集2016年4月—2016年7月因腰椎椎间盘突出症于本院接受手术治疗的21例患者的退变腰椎椎间盘标本25个,依据Pfirrmann分级分成5组,分别采用实时荧光定量PCR技术和蛋白质印迹法检测BNIP3、LC3B的m RNA和蛋白表达量,用实时荧光定量PCR技术检测Bcl-2、Bax、Caspase-3的mRNA表达量,并分析BNIP3表达量、LC3B表达量、细胞自噬、细胞凋亡与Pfirrmann分级之间的关系。结果退变椎间盘组织中BNIP3、LC3B在mRNA和蛋白水平的表达均随椎间盘退行性变程度加重而减少。Bcl-2 m RNA的表达随椎间盘退行性变程度加重而减少,Bax与Casepase-3 mRNA的表达随椎间盘退行性变程度加重而增多。结论随着椎间盘退行性变程度的加重,BNIP3与LC3B的表达减少,组织内细胞凋亡水平升高,细胞自噬对组织的保护作用逐渐下降。提示BNIP3与LC3B在腰椎椎间盘退行性变过程中具有重要的调节作用,可能是细胞自噬和凋亡之间的桥梁蛋白。     

Effects of aging and spinal degeneration on mechanical properties of lumbar supraspinous and interspinous ligaments.

BACKGROUND CONTEXT: The effects of aging and spinal degeneration on the mechanical properties of spinal ligaments are still unknown, although there have been several studies demonstrating those of normal spinal ligaments. PURPOSE: To investigate the mechanical properties of the human posterior spinal ligaments in human lumbar spine, and their relation to age and spinal degeneration parameters. STUDY DESIGN/SETTING: Destructive uniaxial tensile tests were performed on the human supraspinous and interspinous ligaments at L4-5 level. Their mechanical properties were compared with age and spinal degeneration using several imaging modalities. PATIENT SAMPLE: Twenty-four patients with lumbar degenerative diseases on whom posterior surgeries were performed, with the age ranging from 18 to 85 years. OUTCOME MEASURES: The ultimate load and elastic stiffness as structural properties, the degree of disc degeneration, range of segmental motion, the disc height, disc space narrowing ratio and degree of facet degeneration as the parameters of spinal degeneration. METHODS: Twenty-four supraspinous and interspinous ligaments at the L4-5 level were obtained from posterior surgeries of patients with lumbar degenerative disease. The mechanical tests of bone-ligament-bone complexes were performed in a uniaxial tensile fashion with a specially designed clamp device. The ultimate load and elastic stiffness were calculated as structural properties. The degree of disc degeneration, range of segmental motion, the disc height, disc space narrowing ratio and degree of facet degeneration were examined by using radiographs, computed tomography and magnetic resonance imaging. RESULTS: The average and SD value of ultimate load, elastic stiffness, tensile strength and elastic modulus were 203+/-102.9 N, 60.6+/-36.7 N/mm, 1.2+/-0.6 Mpa and 3.3+/-2.1 Mpa, respectively. A significant negative correlation was found between age and tensile strength (p= 0.02). The specimens with facet degeneration showed lower values in tensile strength and elastic modulus than those without facet degeneration (p<0.04). However, no correlation was found between disc-related parameters and tensile strength. CONCLUSIONS: The mechanical strength of human lumbar posterior spinal ligaments decreases with age and facet degeneration, particularly in the ligament substance.     

Assessment of apparent diffusion coefficient in lumbar intervertebral disc degeneration

Objective

The aim of this study was to determine the relationship between the apparent diffusion coefficient (ADC) and lumbar intervertebral disc degeneration using diffusion-weighted magnetic resonance imaging (DWI).

Materials and methods

Using a 3 T magnetic resonance scanner, DWI of the lumbar spine was assessed in 109 patients, with a total of 545 lumbar discs analyzed. Apparent diffusion coefficient values were recorded for each disc, and all discs were visually graded by two independent observers using Pfirrmann’s grading system. Apparent diffusion coefficient values of disc were tested by correlation with qualitative clinical grading of degeneration severity, patient age, and sex. Correlations were investigated using Pearson’s and Spearman’s rank correlation analysis, and multiple regression analysis.

Results

Intervertebral disc degeneration was negatively correlated with ADC values of all levels (Spearman’s correlation coefficient ranged from ?0.381 to ?0.604, p < 0.001). There was a significant negative association between age and ADC values at all spinal levels (Pearson’s correlation coefficient ranged from ?0.353 to ?0.650, p < 0.001). When stepwise regression models were analyzed, both disc degeneration and age remained negatively associated with ADC values at each lumbar level (standardized coefficients ranged from ?0.231 to ?0.505, p < 0.01 and standardized coefficients ranged from ?0.179 to ?0.523, p < 0.05 respectively).

Conclusion

Apparent diffusion coefficient values obtained using DWI can assess lumbar intervertebral disc degeneration, and the ADC values were negatively correlated with the degree of disc degeneration.     

Thoracic spinal kinematics is affected by the grade of intervertebral disc degeneration,but not by the presence of the ribs: An in vitro study

BACKGROUND CONTEXTThoracic spinal three-dimensional kinematics is widely unknown. For the evaluation of surgical treatments and the complete validation of numerical models, however, kinematic data of the thoracic spine are essential.PURPOSETo identify possible effects of rib presence and grade of intervertebral disc degeneration on thoracic spinal kinematics including three-plane helical axes and instantaneous centers of rotation.DESIGN/SETTINGRadiological grading of intervertebral disc degeneration and in vitro tests using n=8 human thoracic functional spinal units of the segmental levels T1–T2, T3–T4, T5–T6, T7–T8, T9–T10, and T11–T12, respectively, were performed with as well as without ribs to analyze the specific kinematic properties.METHODSSpecimens were loaded with pure moments of 5 Nm and constant loading rates of 1°/s in flexion/extension, lateral bending, and axial rotation. Optical motion tracking was performed to visualize helical axes and instantaneous centers of rotation on three-plane X-rays and to evaluate primary ranges of motion (ROMs) and coupled motions.RESULTSMotion segments with no or mild disc degeneration showed reproducible kinematics in all motion planes, whereas medium or severely degenerated specimens offered high variations and shifts of the rotational axes to the distal direction as well as lower ROM. Coupled motions were generally not detected.CONCLUSIONSWith progressing disc degeneration, the rotational axes show higher variation and tend to shift in distal direction, especially in flexion/extension with a shift to the anterior direction, whereas rib resection does not affect thoracic spinal kinematics but its stability. Rib resections as part of spinal deformity treatment destabilize the thoracic spine, but do not alter its kinematics. Young and healthy discs, however, could be affected by surgical treatments of the thoracic spine regarding thoracic spinal kinematics.     

Is T9-11 the true thoracolumbar transition zone?

ObjectiveDegenerative thoracic stenosis has been shown to most frequently involve the lower thoracic segments (T9-T12) where there is greater mobility and vulnerability due to flexion, extension and rotation of the spine. The thoracolumbar junction is considered anatomically to be T12-L1; the anatomical transition between the relatively immobile thoracic spine and relatively mobile lumbar spine. From anecdotal experience at our institution, we hypothesise that the true thoracolumbar junction is higher, at T10-11; the point of transition from floating to false ribs resulting in increased mobility at T10-11.Methods and materialsA retrospective review was performed of MRI lumbar and whole spine performed on patients aged 10–40 years in our institution over a 5-year period. Patients with previous surgery, chronic spinal disorders and congenital abnormalities were excluded from the study. Intervertebral discs from T8-9 to L1-2 were assessed for evidence of degeneration using the Pfirrmann grading system. Data obtained from a study using computer-based models to assess mean resultant loads in flexion, sitting and standing from T8-9 to L1-2 on patients aged 18–35 years was also analysed. The mean load gradients between two consecutive discs from T8 to L2 were analysed. Statistical analysis was performed with SPSS (p < 0.05 was considered statistically significant).ResultsThree-hundred and twenty-two MRI studies were reviewed. Mean Pfirrmann grade was highest at T8-9 and T9-10 (1.35 ± 0.99 and 1.32 ± 0.93 respectively).Pfirrmann grade differed significantly at each level (χ² = 45.137 p = 0.001). Difference in mean load gradient from T9 to T11 was significantly higher than mean load gradient across T11 to L1 in both sitting and standing (0.095 ± 0.062 vs 0.050 ± 0.044 kN; p = 0.007, and 0.101 ± 0.061 kN vs 0.040 ± 0.054 kN; p = 0.007).ConclusionThe changes in segmental loads and more severe disc degeneration at T9-11 compared to T11-L1 support our hypothesis that the true thoracolumbar transition is higher than expected, at T10-11; where the rib cage transitions from floating to false ribs.     

Quantitative MRI analysis of the surface area, signal intensity and MRI index of the central bright area for the evaluation of early adjacent disc degeneration after lumbar fusion

Purpose

The aim of this study was to evaluate early ASD at short-term follow-up in fused and unoperated patients with degenerative disc disease, using quantitative magnetic resonance imaging (MRI) analysis of the area, signal intensity and their product, i.e., MRI index of the central bright area of the disc as well as measures of intervertebral disc height and Pfirrmann grading scale. The further purpose was to determine whether fusion accelerates ASD compared with non-surgical treatment in short-term follow-up.

Methods

One hundred and eight chronic low back patients diagnosed as L4/L5 degeneration undertook either one-level instrumented posterior lumbar interbody fusion or conservative treatment. They were followed up for about 1?year. Finally 46 fused and 45 conservatively treated patients with MRI follow-up were included. Pre- and post-treatment MRIs were compared to determine the progression of disc degeneration at the two cranial adjacent segments.

Results

The area, signal intensity and MRI index of the central bright area of the adjacent discs decreased in the operated and unoperated groups from pre-treatment to follow-up, except for an insignificant decrease of signal intensity at the second adjacent segment in the unoperated group. The changes in these parameters were statistically greater at the first than the second adjacent segment in the fused group, but not in the unoperated group. And the changes in the fused group were more pronounced than those at both neighbouring levels in the unoperated group. However, the Pfirrmann grading scale and intervertebral disc height did not detect any changes at adjacent discs in either group.

Conclusions

Decrease in the parameters of quantitative MRI analysis indicated early degeneration at discs adjacent to lumbar spinal fusion. Fusion had an independent effect on the natural history of ASD during short-term follow-up. Continued longitudinal follow-up is required to determine whether these MRI changes lead to pathologic changes.     

Lumbar spine endplate fractures: Biomechanical evaluation and clinical considerations through experimental induction of injury

Lumbar endplate fractures were investigated in different experimental scenarios, however the biomechanical effect of segmental alignment was not outlined. The objectives of this study were to quantify effects of spinal orientation on lumbar spine injuries during single‐cycle compressive loads and understand lumbar spine endplate injury tolerance. Twenty lumbar motion segments were compressed to failure. Two methods were used in the preparation of the lumbar motion segments. Group 1 (n = 7) preparation maintained pre‐test sagittal lordosis, whereas Group 2 (n = 13) specimens had a free‐rotational end condition for the cranial vertebra, allowing sagittal rotation of the cranial vertebra to create parallel endplates. Five Group 1 specimens experienced posterior vertebral body fracture prior to endplate fracture, whereas two sustained endplate fracture only. Group 2 specimens sustained isolated endplate fractures. Group 2 fractures occurred at approximately 41% of the axial force required for Group 1 fracture (p < 0.05). Imaging and specimen dissection indicate endplate injury consistently took place within the confines of the endplate boundaries, away from the vertebral periphery. These findings indicate that spinal alignment during compressive loading influences the resulting injury pattern. This investigation identified the specific mechanical conditions under which an endplate breach will take place. Development of endplate injuries has significant clinical implication as previous research identified internal disc disruption (IDD) and degenerative disc disease (DDD) as long‐term consequences of the axial load‐shift that occurs following a breach of the endplate. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1084–1091, 2016.     

Strain of the facet joint capsule during rotation and translation range-of-motion tests: an in vitro porcine model as a human surrogate

BACKGROUND CONTEXTPrior data about the modulating effects of lumbar spine posture on facet capsule strains are limited to small joint deviations. Knowledge of facet capsule strain during rotational and translational intervertebral joint motion (ie, large joint deviations) under physiological loading could be useful as it may help explain why visually normal lumbar spinal joints become painful.PURPOSEThis study quantified the strain tensor of the facet capsule during rotation and translation range-of-motion tests.STUDY DESIGN/SETTINGStrain was calculated in isolated porcine functional spinal units. Following a preload, each specimen underwent a flexion/extension rotation (F/E) followed by an anterior/posterior translation (A/P) range-of-motion test while under a 300 N compression load.METHODSTwenty porcine spinal units (10 C3–C4, 10 C5–C6) were tested. Joint flexion/extension was imposed by applying a ±8 Nm moment at a rate of 0.5°/s, and translation was facilitated by loading the caudal vertebra with a ±400 N shear force at a rate of 0.2 mm/s. Points were drawn on the exposed capsule surface and their coordinates were optically tracked throughout each test. Strain was calculated as the displacement of the point configuration with respect to the configuration in a neutral joint position.RESULTSCompared to a neutral posture, superior-inferior strain increased and decreased systematically during flexion and extension, respectively. Posterior displacement of the caudal vertebra by more than 1.3 mm was associated with negative strains, which was significantly lower than the +4.6% strain observed during anterior displacement (p≥.199). The shear strain associated with anterior translation was, on average, −1.1% compared to a neutral joint posture.CONCLUSIONSThese results demonstrate that there is a combination of strain types within the facet capsule when spinal units are rotated and translated. The strains documented in this study did not reach the thresholds associated with nociception.CLINICAL RELEVANCEThe magnitude of flexion-extension rotation and anterior-translation may glean insight into the facet capsule deformation response under low compression (300 N) loading scenarios. Further, intervertebral joint motion alone, even under low compression loading, does not appear to initiate a clinically relevant pain response in the lumbar facet capsule of a nondegenerated spinal joint.