Arthrotome: a specific joint forming compartment in the avian somite.

Somitocoele cells previously have been shown to form the proximal part of the ribs, the intervertebral discs, and the intervertebral joints (synovial joints). To determine whether the somitocoele cells are necessary for the development of axial skeleton joints, we microsurgically ablated the somitocoele cells in epithelial somites of 2-day-old chick embryos. The operated embryos were analyzed after whole-mount skeletal preparations and in sections. Removal of the somitocoele cells led to two major outcomes: (1) Intervertebral joints failed to develop and resulted in the fusion of the superior articular process and the inferior articular process; (2) Adjacent vertebral bodies fused and lacked the intervertebral disc. These results demonstrate that somitocoele cells specifically give rise to intervertebral joints and discs. Furthermore, these results suggest that neighboring sclerotome cells cannot adapt to form vertebral joints in the absence of the somitocoele compartment. Thus, we provide for the first time experimental evidence for the existence of a joint forming compartment in the somites, which we term the "arthrotome."     

Geometry of the Intervertebral Volume and Vertebral Endplates of the Human Spine

Replacement of a degenerated vertebral disc with an artificial intervertebral disc (AID) is currently possible, but poses problems, mainly in the force distribution through the vertebral column. Data on the intervertebral disc space geometry will provide a better fit of the prosthesis to the vertebrae, but current literature on vertebral disc geometry is very scarce or not suitable. In this study, existing CT-scans of 77 patients were analyzed to measure the intervertebral disc and vertebral endplate geometry of the lumbar spine. Ten adjacent points on both sides of the vertebrae (S1-superior to T12-inferior) and sagittal and transverse diameters were measured to describe the shape of the caudal and cranial vertebral planes of the vertebrae. It was found that the largest endplate depth is located in the middle or posterior regions of the vertebra, that there is a linear relationship between all inferior endplate depths and the endplate location (p < 0.0001) within the spinal column, and that the superior endplate depth increases with age by about 0.01 mm per year (p < 0.02). The wedge angle increases from T12-L1 to L5-S1. The results allow for improvement of the fit of intervertebral disc-prostheses to the vertebrae and optimized force transmission through the vertebral column.     

Modeling intervertebral articulation: The rotule à doigt mechanical joint (RAD) in birds and mammals

The vertebrate skeleton is composed of articulated bones. Most of the articulations are classically described using mechanical joints, except the intervertebral joint. The aim of this study was to identify a joint model with the same mechanical features as the cervical joints. On the neck vertebrae, six articular surfaces participate in the joint: the cranial part of the centrum and the facets of the two prezygapophyses of a vertebra articulate on the caudal part of the centrum and the two articular facets of the postzygapophyses of the previous vertebra. We used the intervertebral joints of the birds neck to identify the mechanical joint representing intervertebral linkage. This link was described in the literature as a joint allowing two or three rotations and no translation. These features correspond to the rotule à doigt (RAD) joint, a ball and socket joint with a pin. We compared the RAD joint to the postaxial intervertebral joints of the avian neck and found it a suitable model to determine the geometrical features involved in the joint mobility. The difference in the angles of virtual axes linking the geometrical center of the centrum to the zygapophysis surfaces determines the mean dorsoventral flexion of the joint. It also helps to limit longitudinal rotation. The orientation of the zygapophysis surfaces determines the range of motion in both dorsoventral and lateral flexion. The overall system prevents dislocation. The model was validated on 13 joints of a vulture neck and 11 joints of a swallow neck and on one joint (C6–C7) in each of three mammal species: the wolf (Canis lupus), mole (Talpa europaea), and human (Homo sapiens). The RAD mechanical joint was found in all vertebral articulations. This validation of the model on different species shows that the RAD intervertebral joint model makes it possible to extract the parameters that guide and limit the mobility of the cervical spine from the complex shape of the vertebrae and to compare them in interspecific studies.     

颈椎人工椎间盘置换有限元分析

目的　建立C4~5节段PrestigeTM-LP颈椎人工椎间盘植入后的三维有限元模型,进行手术节段的运动分析。 方法 采用对成年男性的新鲜尸体的颈椎标本进行CT三维扫描方法建立C4~5节段和PrestigeTM-LP人工间盘有限元,模拟完成C4~5人工椎间盘置换手术。测量生理加载下手术节段前屈/后伸、侧弯及轴向旋转运动角度。结果 有限元模型对颈椎的结构,包括椎体间韧带、颈椎关节突关节、钩椎关节等均进行了精确的重建,并较好地模拟手术操作进行PrestigeTM-LP人工间盘植入。运动加载后运动角度,前屈5.7°,后伸3.5°,侧弯5.0°,旋转11.3°,与文献报道结果较为接近。 结论　有限元模型具有精确度高,手术模拟真实的特点,可作为颈椎人工椎间盘生物力学研究的一种较好途径。PrestigeTM-LP颈椎人工椎间盘置换可较好地保留手术节段的运动功能。     

Differentiation and classification of thoracolumbar transitional vertebrae

The literature states that transitional vertebrae at any junction are characterized by features retained from two adjacent regions in the vertebral column. Currently, there is no published literature available that describes the prevalence or morphology of thoracolumbar transitional vertebrae (TLTV). The aim of this study was to identify the qualitative characteristics of transitional vertebrae at the thoracolumbar junction and establish a technique to differentiate the various subtypes that may be found. A selection of vertebral columns from skeletal remains (n = 35) were evaluated in this study. Vertebrae were taken based on features that are atypical for vertebrae in each relative region. The transitional vertebrae were qualitatively identified based on overlapping thoracic and lumbar features of vertebrae at the thoracolumbar junction. The following general overlapping characteristics were observed: aplasia or hypoplasia of the transverse process, irregular orientation on the superior articular process and atypical mammillary bodies. The results show that the most frequent location of the transitional vertebrae was in the thoracic region (f = 23). The second most frequent location was in the lumbar region (f = 10). In two specimens of the selection (f = 2), an additional 13th thoracic vertebra was present which functioned as a transitional vertebra. This study concluded that one can accurately identify the characteristics of transitional vertebrae at the thoracolumbar junction. In addition, the various subtypes can be differentiated according to the region in the vertebral column the vertebra is located in and the relative number of vertebral segments in the adjacent regions of the vertebral column. This provides a qualitative tool for researchers to differentiate the transitional vertebrae from distinctly different typical thoracic or lumbar vertebrae at the thoracolumbar junction.     

Radiographic and Magnetic Resonance Imaging Identification of Thoracolumbar Spine Variants with Implications for the Positioning of the Conus Medullaris in Rhesus Macaques

The anatomy of the vertebral column in mammals may differ between species and between subjects of the same species, especially with regards to the composition of the thoracolumbar spine. We investigated, using several noninvasive imaging techniques, the thoracolumbar spine of a total of 44 adult rhesus macaques of both genders. Radiographic examination of the vertebral column showed a predominant spine phenotype with 12 rib‐bearing thoracic vertebrae and 7 lumbar vertebrae without ribs in 82% of subjects, whereas a subset of subjects demonstrated 13 rib‐bearing thoracic vertebrae and 6 lumbar vertebrae without ribs. Computer tomography studies of the thoraco‐lumbar spine in two cases with a pair of supernumerary ribs showed facet joints between the most caudal pair of ribs and the associated vertebra, supporting a thoracic phenotype. Magnetic resonance imaging (MRI) studies were used to determine the relationship between the lumbosacral spinal cord and the vertebral column. The length of the conus medullaris portion of the spinal cord was 1.5 ± 0.3 vertebral units, and its rostral and caudal positions in the spinal canal were at 2.0 ± 0.3 and 3.6 ± 0.4 vertebral units below the thoracolumbar junction, respectively (n = 44). The presence of a set of supernumerary ribs did not affect the length or craniocaudal position of the conus medullaris, and subjects with13 rib‐bearing vertebrae may from a functional or spine surgical perspective be considered as exhibiting12 thoracic vertebrae and an L1 vertebra with ribs. Anat Rec, 300:300–308, 2017. © 2016 Wiley Periodicals, Inc.     

基于3Dslier及3dsmax的人腰椎侧隐窝前后径虚拟测量的可行性与精确性分析

目的 探讨人腰椎侧隐窝前后径虚拟测量的可行性与精确性。方法 CT数据包括正常腰椎1例,椎间盘突出2例;腰椎干标本（骨性+椎间盘假体）8例。在3D Slicer 4.4基于CT数据重建出虚拟模型,在3ds max中用欧氏距离测算出L1~L5侧隐窝前后径大小。利用游标卡尺对腰椎干标本的L1~L5侧隐窝前后径进行测量。对所得数据进行双样本等方差t检验,得出虚拟正常腰椎与干标本,虚拟正常腰椎与虚拟椎间盘突出病例在腰椎侧隐窝前后径上的差异。结果 正常组与病例1,病例2及干标本组对比地,侧隐窝前后径均无统计学差异（P＞0.05）。结论 基于三维模型的虚拟测量方法在人椎间孔径测量中有着较高的可行性与可靠性。     

后凸成形术疗效评估中椎体高度与椎序的关系

目的：探讨椎体高度与椎序的关系，为后凸成形术治疗骨质疏松性椎体压缩骨折的临床研究提供解剖学与影像学依据。方法：选8套干燥成人胸腰椎标本，按解剖序列拍摄X线侧位片，分别测量标本及其X线图片各椎体前、中、后高度。以椎序为自变量，椎体高度为应变量进行直线回归与相关分析。结果：胸腰椎高度逐渐增大，无论是解剖学测量，还是影像学测量，3个椎体高度与椎序分别呈直线关系，P=0．0001；各高度影像学测量与解剖学测量值呈斜率相同、但截距不同的平行线，相关分析为极度相关，r〉0．9。结论：椎体前、中、后高度与椎序分别呈直线关系，表明椎体高度的变化符合脊柱运动及依次从上至下负重递增的要求；椎体影像学与解剖学测量之间无显著性差异，表明X线投照中心对椎体高度与椎序间关系无影响。     

From somites to vertebral column.

We report on the development and differentiation of the somites with respect to vertebral column formation in avian and human embryos. The somites, which are made up of different compartments, establish a segmental pattern which becomes transferred to adjacent structures such as the peripheral nervous system and the vascular system. Each vertebra arises from three sclerotomic areas. The paired lateral ones give rise to the neural arches, the ribs and the pedicles of vertebrae, whereas the vertebral body and the intervening disc develop from the axially-located mesenchyme. The neural arches originate from the caudal half of one somite, whereas the vertebral body is made up of the adjacent parts of two somites. Interactions between notochord and axial mesenchyme are a prerequisite for the normal development of vertebral bodies and intervening discs. The neural arches form a frame for the neural tube and spinal ganglia. The boundary between head and vertebral column is located between the 5th and 6th somites. In the human embryo, proatlas, body of the atlas segment, and body of the axis fuse to form the axis.     

Vertebral Comparative Anatomy and Morphological Differences in Anguine Lizards With a Special Reference to Pseudopus apodus

The article reports on the first detailed vertebral and rib morphology of anguine taxon Pseudopus apodus using micro-computed tomography. A comparison shows significant morphological differences of vertebrae of Pseudopus relative to those of Anguis and Ophisaurus. Usually, there are 55 presacral vertebrae, two sacral, and 95–97 caudal vertebrae. Pseudopus apodus can be defined by 23 diagnostic features concerning the vertebral column. Although zygapophyseal articulation between atlas and axis is well developed in limbed anguid gerrhonotine lizards like Abronia or Barisia, it is absent in the extant representatives of the clade Anguinae, which are limbless. Thus, our study brings further support to the hypothesis about the complete reduction of this articulation in forms with reduced or absent limbs. Comparison of adult and juvenile morphology of vertebrae of P. apodus was also analyzed. Heterochrony in the evolution of this taxon was previously confirmed by its skull morphology and it can be also documented on the basis of vertebrae. Our data suggest that a peramorphic heterochronic process played a role in the evolution of this largest extant anguine species. Geometric morphometric analyses revealed a pattern of high vertebral disparity among species. We found a clear separation of limbless forms in morphospace. Pseudopus apodus always clusters within Ophisaurus-species confirming molecular and some morphological phylogenies. Only the first tail vertebra shows a distinct difference to those of other anguids, which might be related to altered locomotion associated to the larger body size in this species. Anat Rec, 302:232–257, 2019. © 2018 Wiley Periodicals, Inc.     

Advanced template matching method for estimation of intervertebral kinematics of lumbar spine

Diagnosis of low back pain and other degenerative spinal pathologies can be extremely difficult and, so far, there are not accepted standards. In general, such pathologies are associated with alteration of mechanical properties of spine and, in particular, with the instability of spinal motion. Intervertebral kinematics can be a valuable, objective method to assess the functionality of spinal segments. Fluoroscopic imaging system can provide continuous screening of lumbar tracts during patient's motion, with an acceptable low X-ray dose. Estimation of intervertebral kinematics relies on accurate recognition of vertebrae positions throughout the fluoroscopic sequence: specific vertebrae features are identified and tracked either by manual selection or by automated methods. This study presents a new method of vertebra tracking, based on image template matching of the contour of the vertebral body for an accurate intervertebral kinematics analysis. An image gradient operator was utilized to obtain the vertebral contours; it operates after an edge-preserving smoothing filter designed to reduce low dose X-ray image noise. Once a template is defined for each vertebra, this is used to determine the best vertebral location in each image throughout the fluoroscopic sequence. Accuracy of the proposed method was tested using images of a calibration model. Average error achieved for the intervertebral angle is of the order of 0.4° and approximately 2 mm for the intervertebral centre of rotation. Five fluoroscopic lumbar sequences of healthy volunteers undergoing passive flexion–extension motion were processed. The intervertebral kinematics was compared with other methods (automated and manual) by an estimation of measurement error. Results showed that the current method provides a better representation of the evolution over time of kinematic parameters. In particular, root mean square differences between the current method and a manual selection procedure performed by an experienced and trained clinician resulted 1.3° for the intervertebral angles and 0.9 mm for the intervertebral trajectory. The proposed method provides an effective, automated and objective technique for estimation of intervertebral kinematics of lumbar spine.     

Posterior distraction forces of the posterior longitudinal ligament stratified according to vertebral level

Introduction Although considered significant in resisting midline intervertebral disc herniation, the posterior longitudinal ligament (PLL) has had relatively few studies performed regarding its morphology and function. We performed the present experiment to discern the amount of posterior tensile force necessary to disrupt the PLL at each vertebral level. Materials and methods Twenty-five adult cadavers underwent laminectomies of vertebrae C1 to S1. After removal of the spinal cord, nerve roots, and dura mater, the PLL was identified for each vertebral level and a steel wire placed around its waist in the midline and a tensile gauge attached and posterior tension applied perpendicular to the spine. Forces necessary to failure of the PLL were noted for each vertebral level. Results The PLL was found to be stronger in the thoracic spine compared to the cervical and lumbar vertebrae (P < 0.05). Dividing the vertebral levels in this manner, we found an average posterior distraction force to failure of 48.3 N in the cervical region, 61.3 N in the thoracic region, and 48.8 N in the lumbar region. Conclusions These findings support clinical observations that thoracic disc herniation is rare. We hypothesize that this clinical observation is partially due to a stronger PLL in the thoracic spine.     

Effects of Advanced Age on the Morphometry and Degenerative State of the Cervical Spine in a Rat Model

Aging causes changes in the geometry of the human cervical spine that may influence the tissue response to applied loads. Rat models are often used to study spinal cord injuries (SCI) and have the potential to enhance our understanding of the effect of age on SCI. The goal of this study was to characterize the morphometry and degenerative state of the cervical spine in Fisher 344 rats, and to determine the influence of age on these variables. Fifteen rats were split into three age groups: young adult (3 months of age), aged (12–18 months) and geriatric (30 months). Following tissue harvest we used a μCT scanner to image the cervical and upper thoracic spine from each specimen. Analysis software was used to measure variables including canal pinch diameter (the most rostral point on the dorsal aspect of a vertebral body to the most caudal aspect of the lamina on the immediately rostral vertebra), vertebral canal depth, width, and area, vertebral body height, depth, width, and area, and intervertebral disc thickness. Orthopaedic surgeons used midsagittal images to rate the degenerative state of the intervertebral discs. For all measures except disc thickness there was a significant increase (mean (SD) = 15.0 (9.7)%) for the aged compared to young specimens (P < 0.05). There were significant differences between the aged and geriatric specimens for only vertebral body depth (P = 0.016) and area (P = 0.020). Intervertebral disc degeneration was significantly greater on the ventral aspect of the spinal column (P < 0.001), with a trend toward increased degeneration in the geriatric specimens (P = 0.069). The results suggest that age‐related morphometric differences may need to be accounted for in experimental aging models of SCI in rats. Anat Rec, 2011. © 2011 Wiley‐Liss, Inc.     

Finite element modeling of the cervical spine: role of intervertebral disc under axial and eccentric loads

An anatomically accurate, three-dimensional, nonlinear finite element model of the human cervical spine was developed using computed tomography images and cryomicrotome sections. The detailed model included the cortical bone, cancellous core, endplate, lamina, pedicle, transverse processes and spinous processes of the vertebrae; the annulus fibrosus and nucleus pulposus of the intervertebral discs; the uncovertebral joints; the articular cartilage, the synovial fluid and synovial membrane of the facet joints; and the anterior and posterior longitudinal ligaments, interspinous ligaments, capsular ligaments and ligamentum flavum. The finite element model was validated with experimental results: force–displacement and localized strain responses of the vertebral body and lateral masses under pure compression, and varying eccentric anterior-compression and posterior-compression loading modes. This experimentally validated finite element model was used to study the biomechanics of the cervical spine intervertebral disc by quantifying the internal axial and shear forces resisted by the ventral, middle, and dorsal regions of the disc under the above axial and eccentric loading modes. Results indicated that higher axial forces (compared to shear forces) were transmitted through different regions of the disc under all loading modes. While the ventral region of the disc resisted higher variations in axial force, the dorsal region transmitted higher shear forces under all loading modes. These findings may offer an insight to better understand the biomechanical role of the human cervical spine intervertebral disc.     

胸腰段后凸畸形对相邻椎间盘力学影响的三维有限元分析

目的：了解胸椎后凸畸形对相邻椎间盘(IVD)的影响，从生物力学方面探讨椎间盘退变及椎间盘突出的机制。方法：选取结构正常的脊柱作为实验材料，通过CT扫描获取脊柱的二维图像，然后进行三维重建，转化为有限元模型(FEM)。利用FreeFonm成形软件构建胸椎后凸畸形模型。分别对正常结构和胸椎后凸的脊柱有限元模型进行载荷试验，分析比较椎间盘和小关节应力分布情况。结果：胸椎后凸畸形后椎间盘应力分布发生明显的改变，椎间盘前部的压应力明显增加，后部出现张应力，小关节面的压应力减小。椎体的应力分布也发生了改变，由后向前应力越来越大。结论：(1)有限元方法是脊柱生物力学研究中很有效及很有前途的方法，但是要使其与人体达到近乎真实的模拟则还有不少问题有待完善。有些组织的材料性质了解不够，有限元模型的逼真度有一定影响。(2)利用FreeForm成形软件构建脊柱畸形的有限元模型是富有创意的建模方法。(3)脊柱胸腰段后凸畸形改变了相应椎间盘的载荷应力应变分布，这可能加快椎间盘退变及使后方纤维环易受损破坏。     

Temporal sequence in the formation of midline dermis and dorsal vertebral elements in avian embryos

Somites compartmentalize into a dorsal epithelial dermomyotome and a ventral mesenchymal sclerotome. While sclerotomes give rise to vertebrae and intervertebral discs, dermomyotomes contribute to skeletal muscle and epaxial dermis. Bone morphogenetic protein (BMP)-signals from the lateral mesoderm induce the lateral portion of the dermomyotome to form chondrogenic precursor cells, forming the cartilage of the scapula blade. The fact that BMPs are expressed in the roof plate of the neural tube where they induce cartilage formation led to the question why cells migrating from the medial part of the dermomyotome do not undergo chondrogenic differentiation and do not contribute to the dorsal part of the vertebrae. In the present study, we traced dermomyotomal derivatives by using the quail-chick marker technique. Our study reveals a temporal sequence in the formation of the vertebral cartilage and the midline dermis. The dorsal mesenchyme overlying the roof plate of the neural tube is formed prior to the de-epithelialization of the dermomyotome. Dermomyotomal cells start to migrate medially into the sub-ectodermal space to form the midline dermis after chondrogenesis of the dorsal mesenchyme has occurred. This time delay between chondrogenesis of the dorsal vertebra and dermal formation allows an undisturbed development of these two tissue components within a narrow region of the embryo.     

骨保护素基因敲除小鼠腰椎间盘退变与腰椎骨质疏松

背景：骨保护素基因敲除小鼠已被证明会表现出明显的骨质疏松及骨关节炎表型。 目的：观察骨保护素基因敲除小鼠随年龄增长腰椎间盘退变和骨质疏松的动态变化关系。 方法：分别取出生后4,8,12周的骨保护素基因敲除纯合子小鼠及正常对照组小鼠的L3椎体和L4/5椎间盘,运用Micro-CT检测L3椎体松质骨微结构指标;用苏木精-伊红染色法观察L4/5椎间盘形态学,测量椎间盘及软骨终板高度。 结果与结论：骨保护素基因敲除纯合子小鼠组L3椎体骨小梁数量、骨小梁厚度、骨体积分数较正常组均明显下降(P < 0.05),而骨小梁分离度、结构模型指数较正常小鼠增高(P < 0.05)。8周及12周的骨保护素基因敲除纯合子小鼠的L4/5椎间盘软骨终板出现退变征象,软骨终板排列不规则,并有骨髓腔组织进入软骨终板及外层纤维环。提示骨保护素基因在维持椎间盘正常的结构和功能方面起到重要作用,骨保护素基因缺失后可导致椎间盘退变和椎体骨质疏松。     

采用“双侧垂直错位穿刺法”与“双侧水平裂隙穿刺法”行经皮椎体成形术在治疗Ⅰ期Kümmell病的疗效对比

目的 探究采用“双侧垂直错位穿刺法”与“双侧水平裂隙穿刺法”行经皮椎体成形术（PVP）在治疗I期Kümmell病中的疗效对比。方法 回顾性分析2014年1月至2021年1月在中国人民解放军火箭军特色医学中心接受PVP治疗的I期Kümmell病患者53例，其中采取“双侧垂直错位穿刺法”治疗25例（A组），采取“双侧水平裂隙穿刺法”治疗28例（B组）。比较两组的手术时间、骨水泥注入量、骨水泥渗漏率、骨水泥分布及并发症情况，并记录术前与术后1 d、1个月、3个月、6个月视觉评分量表（VAS）和Oswestry功能障碍指数（ODI），通过X线或CT检查测量并记录术前、术后伤椎前缘与中线高度和Cobb角，并观察骨水泥松动或移位及伤椎再骨折发生情况，末次随访采用改良MacNab标准评估手术的优良率。结果 两组患者均顺利完成手术，均获定期随访。A组较B组手术时间相当（P＞0.05），骨水泥注入量更多（P＜0.05）；A组术中2例出现骨水泥渗漏，渗入椎间盘1例、椎体前侧１例，无临床症状；B组术中9例出现骨水泥渗漏，渗入椎间盘6例、椎体前侧3例，无临床症状；A组术中骨水泥渗漏率较低（P＜0.05），术后椎体裂隙及骨折线周围骨水泥分布更广泛（P＜0.05）；两组术中均无脊髓、椎前大血管损伤，无肺栓塞等并发症发生。与术前比较，两组患者术后1 d、1个月、3个月、6个月VAS、ODI显著降低（P＜0.05）；A组与B组比较，术前、术后VAS、ODI在两组间差异无统计学意义（P＞0.05）；与术前比较，两组患者术后1 d、1个月、3个月、6个月伤椎前缘与中线高度显著增加（P＜0.05），Cobb角测量值显著降低（P＜0.05）；A组与B组比较，术后1 d、1个月、3个月、6个月伤椎前缘与中线高度变化、伤椎Cobb角变化差异无统计学意义（P＞0.05）；末次随访时两组患者均无骨水泥松动或移位及伤椎再骨折情况发生，采用改良MacNab标准评定临床疗效：A组优23例、良2例，B组优19例、良9例，A组优秀率高于B组（P＜0.05）。结论 治疗Ⅰ型Kümmell病时，与“双侧水平裂隙穿刺法”经皮椎体成形术相比，“双侧垂直错位穿刺法”经皮椎体成形术术中的骨水泥渗漏率更低，骨水泥分布更广泛，术后早期治疗效果相当，中期效果更确切。     

Considering the inferior surface area of lower lumbar vertebrae: determining weight transmission pattern at the lumbosacral junction

The biomechanical function of the lumbosacral junction (LSJ) is obscure, but its medical significance is not, as it is the most common site of low back pain. In this study, we analyzed the difference between the mean values of the surface areas of the inferior body and total inferior facet areas of the fourth and fifth lumbar vertebrae. We aimed to define the function of the LSJ during weight transmission and clarify its mechanical significance. Vertebral columns of 45 adult male human cadavers from five anatomy departments in Nigeria were cut at the L3–L4 intervertebral disc and macerated. Using the graph paper method, the mean values of the surface area of the inferior body and total facet area of the fourth and fifth lumbar vertebrae were 1356 ± 26 and 329 ± 6 and 1277 ± 27 and 418 ± 8 mm², respectively. The relationships between the fourth and fifth lumbar vertebrae paired variables were highly significant (P < 0.001). A sudden reduction in the surface area of the inferior body of the fifth lumbar vertebra was compensated for by a corresponding increase in its total inferior facet area, which indicated that corresponding weight was diverted from the anterior column to the posterior column at the LSJ. This pattern of weight transmission may be a beneficial functional adaptation in man to protect the relatively large intervertebral disc of the LSJ in bipedal posture, or it may predispose the LSJ synovial zygapophyseal joints to mechanical stress.