Studies on the arrangement of the collagenous fibers in infant epiphyseal plates using polarized light and the scanning electron microscope

The architecture of the collagenous fibers in epiphyseal plates of infantile long bones was investigated using polarized light and scanning electron microscope. In the zone of columnar cartilage the collagenous fiber bundles are arranged longitudinally in the intercolumnar cartilaginous septa. In addition to this main longitudinal orientation, some of the fibers branch off at an acute angle and flow through the cartilage columns surrounding rhombus-shaped groups of chondrocytes. In the area adjaced to the inert cartilage the collagen fibers become curved and form a network of arcades. In the zone of inert cartilage the collagenous fibers are arranged in a honeycomb-like fashion. The importance of the arrangement of the collagen fibers to the loading strength of the epiphyseal plate is discussed.     

Temporo-spatial distribution of blood vessels in human lumbar intervertebral discs

While there is consensus in the literature that blood vessels are confined to the outer anulus fibrosus of normal adult intervertebral disc, debate continues whether there is a vascular in-growths into inner parts of the intervertebral disc during degeneration. We therefore tested the hypothesis that vascular in-growth is not a distinct feature of disc degeneration. The specific endothelial cell marker CD 31 (PECAM) was used to immunohistochemically investigate 42 paraffin-embedded complete mid-sagittal human intervertebral disc sections of various ages (0–86 years) and varying extent of histomorphological degeneration. Additionally, 20 surgical disc samples from individuals (26–69 years) were included in this study. In discs of fetal to infantile age, blood vessels perforated the cartilaginous end plate and extended into the inner and outer anulus fibrosus, but not into the nucleus pulposus. In adolescents and adults, no blood vessels were seen except for the outer zone of the anulus fibrosus adjacent to the insertion to ligaments. The cartilaginous end plate remained free of vessels, except for areas with circumscribed destruction of the end plate. In advanced disc degeneration, no vessels were observed except for those few cases with complete, scar-like disc destruction. However, some rim lesions and occasionally major clefts were surrounded by a small network of capillary blood vessels extending into deeper zones of the anulus fibrosus. A subsequent morphometric analysis, revealed slightly “deeper” blood vessel extension in juvenile/adolescent discs when compared to young, mature and senile adult individuals with significantly “deeper” extension in the posterior than anterior anulus. The analysis of the surgical specimens showed that only sparse capillary blood vessels which did not extend into the nucleus pulposus even in major disc disruption. Our results show that vascular invasion deeper than the periphery was not observed during disc degeneration, which supports the hypothesis that vascular in-growth is not a distinct feature of disc degeneration. This study was supported by a grant from the AO/ASIF Foundation Switzerland (00-B72) and a grant from the AO Spine (SRN 02/103).     

The relationship between apoptosis of endplate chondrocytes and aging and degeneration of the intervertebral disc.

STUDY DESIGN: Apoptosis in cervical intervertebral disc cells and cartilaginous endplate cells was examined by the nick end labeling (TUNEL) technique during the process of natural aging and in a mouse experimental spondylosis model. OBJECTIVES: To determine the role of apoptosis in aging and degeneration of intervertebral discs by monitoring chronologic changes in the quantity and localization of apoptotic cells. SUMMARY OF BACKGROUND DATA: Apoptosis occurs within human intervertebral discs, but little is known about the pathologic significance of this process. On the other hand, the cartilaginous endplate is known to decrease in thickness and to disappear with aging and degeneration. The cause of this age-related change remains unclear. METHODS: A mouse spondylosis model was prepared via surgical resection of the posterior spinal element in 12 mice to examine the experimentally induced spondylosis process. Eighteen naturally aged mice were also used to examine the influence of aging. Paraffin-embedded midsagittal sections of the cervical spine were obtained 2, 3, 6, and 12 months after surgery in the spondylosis model and in the age-matched naturally aged mice, as well as in 4-week-old and 18-month-old naturally aged mice. Sections were stained with hematoxylin and eosin, safranin-O, and the TUNEL procedure. The number of apoptotic cells and vital cells were counted in the cartilaginous endplate of the intervertebral disc excluding the growth cartilage, and the degree of disappearance of the cartilaginous endplate was evaluated. RESULTS: Apoptosis, particularly noticeable in the cartilaginous endplate, increased with age and resulted in a marked decrease in cell density. Subsequently, the structure of the cartilaginous endplate began to disappear. Apoptosis was more evident and the structure of the cartilaginous endplate began to disappear more rapidly in the surgically treated group than in the naturally aged group. CONCLUSIONS: TUNEL-positive cells in the cartilaginous endplate increased with age, with destruction of the cartilaginous endplate after apoptosis (TUNEL-positive cell death). The application of the spondylosis model increased the incidence of apoptosis preceding the development of spondylosis. This suggests that apoptosis plays a role in the age-related changes seen in the cartilaginous endplate of the intervertebral disc and in the experimentally induced spondylosis process.     

Effects of hydrocortisone on the vertebral cartilage plate in mice. A light and electron microscopic study

Together with other side effects, the clinical use of steroid appears to produce disorders in the spinal column, especially in young patients. However, morphologic details of steroid induced changes in the spinal column are little known. In this study, mice were treated with daily intramuscular injections of hydrocortisone at doses of 1, 5, and 10 mg/kg body weight for 1, 2, or 4 weeks after 2 weeks of age, and the cartilage plates of the lumbar vertebrae were examined, compared with controls, by light and electron microscopy. Cartilage plates consist of an outer zone, abutting the nucleus pulposus and an inner zone oriented toward the vertebral body. The outer zone is divided into a superficial layer and a deep calcified layer. With steroid therapy, chondrocytes in the inner zone and the superficial layer of the outer zone became degenerative or necrotic. In mice treated with 5 and 10 mg hydrocortisone/kg body weight, ossification appeared earlier in the deep calcified layer than in control animals. After 2 weeks of treatment, the cartilage tissue of the inner zone in mice treated with 10 mg hydrocortisone contained ossification gaps, columnar bone tissue, connecting the bony vertebral body, and the deep calcified layer of the outer zone. The thickness of each layer was measured by light microscopy. By hydrocortisone treatment, the whole of the cartilage plate decreased in thickness, the two cartilage layers of the inner zone and the superficial layer of the outer zone became thinner, and the calcified or ossified layer of the outer zone became widened.(ABSTRACT TRUNCATED AT 250 WORDS)     

Immunohistochemical localization of fibroblast growth factor receptors in the rat mandibular condylar cartilage and tibial cartilage

The fibroblast growth factor receptors (FGFRs), members of the tyrosine-kinase receptor family, are known to play a crucial role in the growth and development of cartilaginous tissues. The mandibular condylar cartilage has been suggested to have a characteristic growth pattern compared with the tibial growth plate cartilage, e.g., cell alignment, mode of proliferation and differentiation, and response to humoral and mechanical factors. To examine the mRNA expression and localization of fibroblast growth factor receptor (FGFR)-1, -2, and -3 in the condylar and tibial growth plate cartilages, reversed transcribed polymerase chain reaction (RT-PCR) assay and immunohistochemistry were carried out using growing rats. The enzymatically isolated rat condylar and tibial chondrocytes expressed mRNA of aggrecan and type II collagen, which are together known as the major cartilaginous extracellular matrices. Both types of cells expressed mRNA of FGFR-1, -2, and -3 by RT-PCR. In the neonatal rat, immunolocalization of FGFR-1, -2, and -3 was found in the middle of the condylar cartilage, mainly in the hypertrophic zone of the tibial cartilage. At 3 weeks old, the three FGFRs were broadly observed in both cartilages. At 8 weeks old, localization of FGFR-3 was absent in the hypertrophic cell layer of the condyle, whereas it was still broadly observed in the tibial growth plate cartilage. In the same stage, FGFR-1 and FGFR-2 showed similar localization in both cartilages to that at 3 weeks of age. All these observations suggest that FGFRs play an important role in the differential growth pattern of the condylar cartilage. Received: Jan. 14, 1999 / Accepted: March 3, 1999     

兔椎体软骨终板血管芽增龄性变化

目的 探讨不同年龄段兔椎体软骨终板内血管芽的形态变化与椎间盘退变的关系.方法 15只不同年龄段新西兰兔,2月龄5只,1年龄5只,3年龄5只,雌雄不限.X线观察终板有无钙化及椎体周围有无骨赘形成,组织学观察软骨终板和椎间盘的形态学变化,血管铸型后扫描电镜观察终板各部位血管的形态变化.按Miyamoto等分级标准将椎间盘分为1～5级,分别规定为1～5分.采用t检验,分别对2月龄组和1年龄组髓核区与内层纤维环区,2月龄组及1年龄组兔髓核区、内层纤维环区椎体终板内血管直径进行比较.结果 2月龄组终板无明显钙化、软骨终板结构良好、潮标清晰,髓核及纤维环结构饱满清晰;1年龄组终板轻度钙化,髓核皱缩,纤维环出现裂隙;3年龄组终板钙化明显,密度增高,并可见骨赘形成,髓核消失.随着年龄增加,终板内微血管逐渐减少,最终消失,软骨终板中心部位较周围部血管减少更为明显.组织学显示软骨终板出现钙化,软骨终板退变重于椎间盘;钙化的程度与椎间盘退变程度呈正相关.2月龄组髓核区与内层纤维环区椎体终板内血管直径比较,差异有统计学意义;2月龄组与1年龄组髓核区椎体终板内血管直径比较,差异有统计学意义.结论 随着兔年龄增加终板内血管逐渐减少,终板发生退变,其程度重于椎间盘,提示椎体终板内微血管的变化可能是椎间盘退变的重要促进因素.

Abstract：

Objective To observe the morphologic changes of of vascular buds in vertebral cartilage endplate in age-specific rabbits and also to investigate the correlation between the changes of vascular buds and interverbral disc degeneration. Methods There were 15 New Zealand white rabbits in our study,which include three groups, 2-week-old rabbits, 1-year-old rabbits and 3-year-old rabbits, and each groups had five rabbits. The X-ray radiograph, histology and scanning electron microscope were used to observe the changes of vertebral cartilage endplate. According to Miyamoto standard, the interverbral disc was graded 1-5, and scored 1-5 respectively. Results The changes of micro-vascular structure of vertebral cartilage endplate were observed during aging. Under the scanning electron microscope, the vascular structure degenerated gradually, and disappeared in the end. The blood vessels in the central region of the vertebral cartilage endplate reduced more obviously than those in periphery region. The severe degeneration was found in vertebral endplate, compared with intervertebral disc. The changes of vascular buds in rabbits vertebral cartilage endplate had positive correlation with the vertebral endplate calcification and the interbertebral disc degeneration. Conclusion Changes of vascular buds in vertebral endplate may accelerate intervertebral disc degeneration.     

Distribution of elastic fiber types in the epiphyseal region

Three types of elastic fibers have been described: mature elastic fibers, elaunin fibers, and oxytalan fibers. To our knowledge, their location in the immature epiphysis has never been previously reported. The aim of the present study was to use histochemistry, immunohistochemistry, and electron microscopy to demonstrate the distribution of each type of elastic fiber in the epiphyseal region of growing humans and rabbits. Histological samples were collected from the knees of 10 immature New Zealand White rabbits and four children of various ages. The Weigert resorcin-fuchsin, Gomori aldehyde-fuchsin, Verhoeff iron haematoxylin, and Fullmer-Lillie methods were used for histochemistry; anti-elastin monoclonal antibodies, for immunohistochemistry; and tannic acid, uranyl acetate, and lead citrate stain, for transmission electron microscopy analysis. Elastic fibers were detected in the perichondrium, the epiphyseal vessels, and the outer and middle zones of Ranvier's groove. Their orientation was longitudinal in the outer zone and circumferential in the middle zone of the groove. Oxytalan fibrils (i.e., bundles of filaments of 10–12 nm in diameter that do not contain elastin) and elaunin fibers (i.e., filaments that cross discontinuous aggregates of elastin) were more plentiful in the middle zone and decreased with age, whereas mature fibers were more numerous in the outer zone and increased with age. This organization of elastic fibers seems to indicate an age-related process of maturation of the elastic network. The contribution of these fibers to the mechanical properties of the epiphyseal plate and to the growth process remains to be determined.     

The pathogenesis of Schmorl's nodes

We examined the pathogenesis of Schmorl's nodes, correlating the histological findings from 12 lumbar vertebrae with the corresponding conventional radiographs, tomographs, MR images and CT scans. The last revealed round, often multiple cystic lesions with indistinct sclerotic margins beneath the cartilaginous endplate. The appearances are similar to the typical CT changes of osteonecrosis. Histological examination of en-bloc slices through Schmorl's nodes gave clear evidence of subchondral osteonecrosis. Beneath the cartilage endplate, we found fibrosis within the marrow cavities with the disappearance of fat cells. Osteocytes within bone trabeculae were either dead or had disappeared. We suggest that Schmorl's nodes are the end result of ischaemic necrosis beneath the cartilaginous endplate and that herniation into the body of the vertebra is secondary.     

Middle-vault narrowing in the wide nasal dorsum: the "Reverse Spreader" technique

The middle vault is a transition zone between the nasal tip and nasal bones and plays an important role in profile, tip projection, tip rotation, and tip support. This report presents an alternative to conventional techniques specific to the middle nasal vault for a patient population with particular nasal features. A narrow middle vault with internal nasal valve collapse is functionally and aesthetically addressed by the insertion of spreader grafts. However, the inverse of this situation is sometimes encountered. A patient with a broad middle vault and without internal nasal valve collapse will benefit from reduction of the horizontal width of the cartilaginous dorsum, which is in effect the reverse of spreader grafts. This effect is achieved by excising a vertical wedge-shaped strip of cartilage that follows the length of the upper lateral cartilage at the junction of the upper lateral cartilage and the dorsal nasal septum.     

Tissue engineering of stratified articular cartilage from chondrocyte subpopulations

OBJECTIVE: To test if subpopulations of chondrocytes from different cartilage zones could be used to engineer cartilage constructs with features of normal stratification. ESIGN: Chondrocytes from the superficial and middle zones of immature bovine cartilage were cultured in alginate, released, and seeded either separately or sequentially to form cartilage constructs. Constructs were cultured for 1 or 2 weeks and were assessed for growth, compressive properties, and deposition, and localization of matrix molecules and superficial zone protein (SZP). RESULTS: The cartilaginous constructs formed from superficial zone chondrocytes exhibited less matrix growth and lower compressive properties than constructs from middle zone chondrocytes, with the stratified superficial-middle constructs exhibiting intermediate properties. Expression of SZP was highest at the construct surfaces, with the localization of SZP in superficial-middle constructs being concentrated at the superficial surface. CONCLUSIONS: Manipulation of subpopulations of chondrocytes can be useful in engineering cartilage tissue with a biomimetic approach, and in fabricating constructs that exhibit stratified features of normal articular cartilage.     

Demonstration of blood-vessellike structures in cartilaginous callus by antilaminin and antiheparin sulfate proteoglycan antibodies

The vascularization of the callus of experimental nonfixated tibia fractures in rat was investigated with antibodies against two basement-membrane macromolecules, i.e., laminin and the heparin sulfate, low-buoyant-density proteoglycan. The purpose of the investigation was to study the relationship between the appearance of blood vessels and the development of cartilaginous callus. The ages of the callus were three, five, eight, and 11 days after the fracture, that is, from before the cartilage was demonstrable on Day 5 until the enchondral bone formation started on Day 11. The abundant blood vessels in the differentiating granulation tissue, in the periosteal callus, and in the cortical bone itself were stained, as were the endomysia of the surrounding myofibrils. During the whole course, the cartilaginous callus also contained vessellike structures stained by the antibodies. These structures are apparently nonfunctioning vessels. Also, some of the chondrocytes were stained by antilaminin. This study implies that cartilage is not formed as a result of insufficient blood supply, but rather as a natural link in a predetermined course of the migrating mesenchymal cells.     

胶原酶在髌骨软骨软化中的作用

２４只新西兰兔，随机分４组。右膝髌骨手术方法造成髌骨倾斜状态为实验侧，左膝实施假手术为对照侧，定期处死动物后进行髌骨软骨面接触压力测量、软骨组织病理观察以及胶原酶免疫组化（ＬＡＢ法）定位。结果：实验膝髌骨倾斜后导致髌内侧面软骨接触压力降低，而髌外侧面软骨接触压力无明显变化；组织病理显示：髌内侧面软骨中层至深层明显变性、软化，髌骨外侧面软骨变性不明显；免疫组化染色显示：髌内侧面软骨中层、深层软骨细胞浆与周围软骨基质胶原酶明显增多，且自软骨下骨长入钙化层或深层的血管内皮细胞以及软骨裂隙边缘处胶原酶强阳性。而髌外侧面软骨胶原酶含量无明显增多。表明：软骨胶原酶增多部位与髌骨软骨软化发生部位及其程度相一致。作者认为，胶原酶对髌骨倾斜导致髌软骨软化过程中软骨基质的破坏起重要作用。     

PTH Receptor Signaling in Osteoblasts Regulates Endochondral Vascularization in Maintenance of Postnatal Growth Plate

Longitudinal growth of postnatal bone requires precise control of growth plate cartilage chondrocytes and subsequent osteogenesis and bone formation. Little is known about the role of angiogenesis and bone remodeling in maintenance of cartilaginous growth plate. Parathyroid hormone (PTH) stimulates bone remodeling by activating PTH receptor (PTH1R). Mice with conditional deletion of PTH1R in osteoblasts showed disrupted trabecular bone formation. The mice also exhibited postnatal growth retardation with profound defects in growth plate cartilage, ascribable predominantly to a decrease in number of hypertrophic chondrocytes, resulting in premature fusion of the growth plate and shortened long bones. Further characterization of hypertrophic zone and primary spongiosa revealed that endochondral angiogenesis and vascular invasion of the cartilage were impaired, which was associated with aberrant chondrocyte maturation and cartilage development. These studies reveal that PTH1R signaling in osteoblasts regulates cartilaginous growth plate for postnatal growth of bone. © 2014 American Society for Bone and Mineral Research.     

One‐Stage Anterior Approach with Arch Plate to Treat Lumbosacral Tuberculosis

This article describes the arch plate technique for treating lumbosacral tuberculosis. Lumbosacral tuberculosis often leads to the destruction of anterior vertebral columns and presacral or iliopsoas abscess, which requires an anterior approach to achieve thorough debridement. Due to the complexity of the anatomical structure of lumbosacral spine and the high requirement of fixation stability, a combined posterior approach to perform internal fixation is necessary, which is rather traumatic. On the other hand, most of the current anterior lumbosacral internal fixation systems cannot be applied to spinal tuberculosis patients who have irregular bony endplate destruction. The arch plate was designed as a cephalic narrow and caudal wide trapezoid or triangle outline according to the preliminary anatomic research. In terms of the endplate bony destruction, a multidirectional technique was introduced in the arch screws, which enables surgeons to arbitrarily change the direction of the screw in the range of 5°–20°, which increases the length and the inclination angles in the sagittal plane of the implant screw and makes sure that the autologous iliac bone graft fits the irregular bone destruction for maximum stability. This study demonstrated the effectiveness of one‐stage anterior debridement, bone grafting, and arch plate fixation to treat lumbosacral tuberculosis. The risk of intraoperative and postoperative complications, such as injury to major vessels, could be minimized. This surgical procedure had many advantages, including a shorter operation time, less blood loss, and better functional recovery over the conventional combined anterior and posterior approach.     

Microvascular invasion during endochondral ossification in experimental fractures in rats

In this study morphologic techniques have been used to detail the angiogenic response that accompanies endochondral fracture healing in a clinically relevant, reproducible rat model. In this displaced fracture, the gap fills with cartilage that later is replaced by bone, via endochondral ossification. A transient periosteal circulation, followed by a permanent medullary circulation accompany this progression. From 2 to 6 weeks, vessels grow out from the periosteal tissue and give rise to vascular buds, which abut directly onto the avascular zone corresponding to the fracture defect. From 3 weeks onwards, a second wave of vessels grows out from the marrow to the cartilage-filled fracture defect, terminating as vascular buds and loops lined by endothelial and perivascular cells. The loops and buds stain strongly for laminin but transmission electron microscopy does not demonstrate an identifiable basement membrane, pointing to a region of active extracellular matrix turnover. These vessels are intimately associated with osteoblasts and newly formed woven bone forming finger-like composite structures that protrude into the mineralized cartilage matrix with which they form a clearly demarcated interface. Invading vessels and woven bone successively replace the cartilage matrix to mediate repair. Both the vascular structures and progression of endochondral ossification observed, closely resemble those described in the normal epiphyseal growth plate, indicating that the fundamental processes are similar. However, there is a difference in the spatial orientation of cells such that the healing front in the fracture model is relatively disorganized, compared to the orderly linear array of cells at the epiphyseal growth plate.     

Endochondral ossification in fracture callus during long bone repair: the localisation of 'cavity-lining cells' within the cartilage.

Successful fracture healing typically involves the production of a cartilaginous callus, which is eventually remodelled into new bone. The blood vessels in the advancing front of endochondral ossification are likely to play an important role in the replacement of cartilage with bone within the callus. This was investigated by histology and immunohistochemistry techniques carried out on rabbit tibial osteotomy tissue. Cavities within the cartilage were identified by histology and in many cases, there appeared to be vascular structures within them, identified by the immunolocalisation of the transmembrane proteins CD31 and CD34. Osteocalcin localisation and Alizarin red histology was carried out to identify 'osteoblastic' cells and mineral localisation within the cartilaginous callus respectively. However, it was the identification of a population of cells lining the cavities within the cartilage that became the main focus of this study. These cells were 'osteoblastic' in nature, (positive localisation of osteocalcin), and were also positive for the adhesion proteins CD31 and CD34. It is thought that these cells play a role in the conversion of cartilage to bone during the fracture healing process.     

Functional barrier principle for growth-factor-based articular cartilage repair

OBJECTIVE: Induction of growth-factor-based repair in full-thickness articular cartilage defects can be impaired by the upgrowth of blood vessels and new bone into the cartilaginous compartment. We postulated that if an antiangiogenic factor (suramin) is included in the chondrogenic matrix applied to the cartilaginous compartment of a full-thickness defect, vascular upgrowth and therefore bone formation will be inhibited (functional barrier principle). DESIGN: Full-thickness defects were created in miniature pigs and the bony portion filled with a chondrogenic matrix. The cartilaginous compartment was filled with the same matrix which additionally contained suramin, either in a free form or in free and liposome-encapsulated forms. Animals were sacrificed 8 weeks after surgery and the extent to which bone tissue had encroached on the cartilaginous compartment was graded semiquantitatively using light microscopy. RESULTS: In 63% of the control defects, bone represented more than 50% of the repair tissue present. In 10% of the defects treated with free suramin, bone upgrowth was completely inhibited; in 55%, osseous tissue occupied 1-10% of the cartilaginous space and in the other 35%, it represented 11-50% of the repair tissue present in this compartment. In 69% of the defects treated with free and liposome-encapsulated suramin, bone upgrowth into the cartilaginous compartment was completely inhibited; in the remaining 31%, osseous tissue occupied no more than 1-10% of this space. CONCLUSIONS: To be effective, an antiangiogenic factor needs to be present at a sustained level throughout the chondrogenic treatment course.     

大鼠不同部位软骨细胞的形态及表型特征比较研究

目的:比较研究大鼠椎间盘软骨终板和膝关节软骨的细胞表型特征的相关性.方法:大鼠的软骨终板和关节软骨细胞分别予以消化培养.进行光镜、电镜观察其形态.使用免疫组化技术分别检测不同部位细胞的Ⅱ型胶原表达.结果:大鼠椎间盘软骨终板和关节软骨细胞形状相似,并且均表达Ⅱ型胶原.结论:本研究提示软骨终板表达软骨细胞的特征性胶原,与关节软骨细胞相似.     

Shaped,Stratified, Scaffold-free Grafts for Articular Cartilage Defects

One goal of treatment for large articular cartilage defects is to restore the anatomic contour of the joint with tissue having a structure similar to native cartilage. Shaped and stratified cartilaginous tissue may be fabricated into a suitable graft to achieve such restoration. We asked if scaffold-free cartilaginous constructs, anatomically shaped and targeting spherically-shaped hips, can be created using a molding technique and if biomimetic stratification of the shaped constructs can be achieved with appropriate superficial and middle/deep zone chondrocyte subpopulations. The shaped, scaffold-free constructs were formed from the alginate-released bovine calf chondrocytes with shaping on one (saucer), two (cup), or neither (disk) surfaces. The saucer and cup constructs had shapes distinguishable quantitatively (radius of curvature of 5.5 ± 0.1 mm for saucer and 2.8 ± 0.1 mm for cup) and had no adverse effects on the glycosaminoglycan and collagen contents and their distribution in the constructs as assessed by biochemical assays and histology, respectively. Biomimetic stratification of chondrocyte subpopulations in saucer- and cup-shaped constructs was confirmed and quantified using fluorescence microscopy and image analysis. This shaping method, combined with biomimetic stratification, has the potential to create anatomically contoured large cartilaginous constructs. One or more authors have received funding from the National Football League Charities, Musculoskeletal Transplant Foundation, Howard Hughes Medical Institute, NIH, and NSF (RLS) and from an NSF Graduate Research Fellowship (EHH).     

Histology and pathology of the human intervertebral disc

The intervertebral disc is a highly organized matrix laid down by relatively few cells in a specific manner. The central gelatinous nucleus pulposus is contained within the more collagenous anulus fibrosus laterally and the cartilage end plates inferiorly and superiorly. The anulus consists of concentric rings or lamellae, with fibers in the outer lamellae continuing into the longitudinal ligaments and vertebral bodies. This arrangement allows the discs to facilitate movement and flexibility within what would be an otherwise rigid spine. At birth, the human disc has some vascular supply within both the cartilage end plates and the anulus fibrosus, but these vessels soon recede, leaving the disc with little direct blood supply in the healthy adult. With increasing age, water is lost from the matrix, and the proteoglycan content also changes and diminishes. The disc-particularly the nucleus-becomes less gelatinous and more fibrous, and cracks and fissures eventually form. More blood vessels begin to grow into the disc from the outer areas of the anulus. There is an increase in cell proliferation and formation of cell clusters as well as an increase in cell death. The cartilage end plate undergoes thinning, altered cell density, formation of fissures, and sclerosis of the subchondral bone. These changes are similar to those seen in degenerative disc disease, causing discussion as to whether aging and degeneration are separate processes or the same process occurring over a different timescale. Additional disorders involving the intervertebral disc can demonstrate other changes in morphology. Discs from patients with spinal deformities such as scoliosis have ectopic calcification in the cartilage end plate and sometimes in the disc itself. Cells in these discs and cells from patients with spondylolisthesis have been found to have very long cell processes. Cells in herniated discs appear to have a higher degree of cellular senescence than cells in nonherniated discs and produce a greater abundance of matrix metalloproteinases. The role that abnormalities play in the etiopathogenesis of different disorders is not always clear. Disorders may be caused by a genetic predisposition or a tissue response to an insult or altered mechanical environment. Whatever the initial cause, a change in the morphology of the tissue is likely to alter the physiologic and mechanical functioning of the tissue.