Aims. Osteoarthritis (OA) is the most prevalent systemic musculoskeletal disorder, characterized by articular cartilage degeneration and subchondral bone (SCB) sclerosis. Here, we sought to examine the contribution of accelerated growth to OA development using a murine model of excessive longitudinal growth. Suppressor of cytokine signalling 2 (SOCS2) is a negative regulator of growth hormone (GH) signalling, thus mice deficient in SOCS2 (Socs2. -/-. ) display accelerated bone growth. Methods. We examined vulnerability of Socs2. -/-. mice to OA following surgical induction of disease (destabilization of the medial meniscus (DMM)), and with ageing, by histology and micro-CT. Results. We observed a significant increase in mean number (wild-type (WT) DMM: 532 (SD 56); WT sham: 495 (SD 45); knockout (KO) DMM: 169 (SD 49); KO sham: 187 (SD 56); p < 0.001) and density (WT DMM: 2.2 (SD 0.9); WT sham: 1.2 (SD 0.5); KO DMM: 13.0 (SD 0.5); KO sham: 14.4 (SD 0.7)) of growth plate bridges in Socs2. -/-. in comparison with WT. Histological examination of WT and Socs2. -/-. knees revealed articular cartilage damage with DMM in comparison to sham. Articular cartilage lesion severity scores (mean and maximum) were similar in WT and Socs2. -/-. mice with either DMM, or with ageing. Micro-CT analysis revealed significant decreases in SCB thickness, epiphyseal trabecular number, and thickness in the medial compartment of Socs2. -/-. , in comparison with WT (p < 0.001). DMM had no effect on the SCB thickness in comparison with sham in either genotype. Conclusion. Together, these data suggest that enhanced GH signalling through SOCS2 deletion accelerates growth plate fusion, however this has no effect on OA vulnerability in this model. Cite this article: Bone Joint Res 2022;11(3):162–170

Matrix metalloproteinases (MMPs), responsible for extracellular matrix remodelling and angiogenesis, might play a major role in the response of the growth plate to detrimental loads that lead to overuse injuries in young athletes. In order to test this hypothesis, human growth plate chondrocytes were subjected to mechanical forces equal to either physiological loads, near detrimental or detrimental loads for two hours. In addition, these cells were exposed to physiological loads for up to 24 hours. Changes in the expression of MMPs -2, -3 and -13 were investigated. We found that expression of MMPs in cultured human growth plate chondrocytes increases in a linear manner with increased duration and intensity of loading. We also showed for the first time that physiological loads have the same effect on growth plate chondrocytes over a long period of time as detrimental loads applied for a short period. These findings confirm the involvement of MMPs in overuse injuries in children. We suggest that training programmes for immature athletes should be reconsidered in order to avoid detrimental stresses and over-expression of MMPs in the growth plate, and especially to avoid physiological loads becoming detrimental. Cite this article: Bone Joint J 2013;95-B:568–73

Objectives. The aim of this experimental study on New Zealand’s white rabbits was to investigate the transplantation of autogenous growth plate cells in order to treat the injured growth plate. They were assessed in terms of measurements of radiological tibial varus and histological characteristics. . Methods. An experimental model of plate growth medial partial resection of the tibia in 14 New Zealand white rabbits was created. During this surgical procedure the plate growth cells were collected and cultured. While the second surgery was being performed, the autologous cultured growth plate cells were grafted at the right tibia, whereas the left tibia was used as a control group. . Results. Histological examinations showed that the grafted right tibia presented the regular shape of the plate growth with hypertrophic maturation, chondrocyte columniation and endochondral calcification. Radiological study shows that the mean tibial deformity at the left angle was 20.29° (6.25 to 33) and 7.21° (5 to 10) in the right angle. . Conclusion. This study has demonstrated that grafting of autogenous cultured growth plate cells into a defect of the medial aspect of the proximal tibial physis can prevent bone bridge formation, growth arrest and the development of varus deformity. Cite this article: Bone Joint Res 2014;3:310–16

Objectives. The aim of this study was to examine whether asymmetric loading influences macrophage elastase (MMP12) expression in different parts of a rat tail intervertebral disc and growth plate and if MMP12 expression is correlated with the severity of the deformity. Methods. A wedge deformity between the ninth and tenth tail vertebrae was produced with an Ilizarov-type mini external fixator in 45 female Wistar rats, matched for their age and weight. Three groups were created according to the degree of deformity (10°, 30° and 50°). A total of 30 discs and vertebrae were evaluated immunohistochemically for immunolocalisation of MMP12 expression, and 15 discs were analysed by western blot and zymography in order to detect pro- and active MMP12. Results. No MMP12 expression was detected in the nucleus pulposus. Expression of MMP12 in the annulus progressively increased from group I to groups II and III, mainly at the concave side. Many growth plate chondrocytes expressed MMP12 in the control group, less in group I and rare in groups II and III. Changes in cell phenotype and reduction of cell number were observed, together with disorganisation of matrix microstructure similar to disc degeneration. ProMMP12 was detected at the area of 54 kDa and active MMP12 at 22 kDa. Conclusions. Expression of MMP12 after application of asymmetric loading in a rat tail increased in the intervertebral disc but decreased in the growth plate and correlated with the degree of the deformity and the side of the wedged disc. Cite this article: Bone Joint Res 2014;3:273–9

The mammalian growth plate is a complex structure which is essential for the elongation of long bones. However, an understanding of how the growth plate functions at the cellular level is lacking. This review, summarises the factors involved in growth-plate regulation, its failure and the consequence of injury. We also describe some of the cellular mechanisms which underpin the increase in volume of the growth-plate chondrocyte which is the major determinant of the rate and extent of bone lengthening. We show how living in situ chondrocytes can be imaged using 2-photon laser scanning microscopy to provide a quantitative analysis of their volume. This approach should give better understanding of the cellular control of bone growth in both healthy and failed growth plates

Sex hormones play important roles in the regulation of the proliferation, maturation and death of chondrocytes in the epiphyseal growth plate. We have investigated the effects of male castration on the cell kinetics of chondrocytes as defined by the numbers of proliferating and dying cells. The growth plates of normal rabbits and animals castrated at eight weeks of age were obtained at 10, 15, 20 and 25 weeks of age. Our study suggested that castration led to an increase in apoptosis and a decrease in the proliferation of chondrocytes in the growth plate. In addition, the number of chondrocytes in the castrated rabbits was less than that of normal animals of the same age

Chondromodulin-I (ChM-I) is a bifunctional autocrine regulator of cartilage, initially isolated from fetal bovine epiphyseal cartilage. 1. ChM-I stimulates matrix synthesis of chondrocytes, but inhibits the growth of endothelial cells. 1,. 2. thus ChM-I may be one of the anti-angiogenic molecules present in cartilage. In fetal bovine bone, ChM-I was expressed by all epiphyseal and growth plate chondrocytes except hypertrophic chondrocytes and was present in the matrix throughout the epiphysis and the growth plate, except the hypertrophic zone . 2,. 3. , consistent with its proposed role as anti-angiogenic factor. To examine the possible role of chondromodulin-I in relation to angiogenesis at the vascular front, we studied the immunolocalisation in femoral growth plates from young and mature rats (2–16 weeks) as well as aged rats (62–80 weeks), using a rabbit polyclonal antibody raised against the entire region of mature human recombinant ChM-I. In 2-week old rats, ChM-I was synthesised by all epiphyseal chondrocytes and strong immunostaining was found in the matrix. In the growth plates, ChM-I staining was present in chondrocytes and matrix of the reserve, proliferating and maturing zones with loss of staining in the hypertrophic zone. However, ChM-I was also present where cartilage canals had penetrated into the chondroepiphysis. In 4–16 week old rats, there was a progressive change in the localisation of ChM-I. Hypertrophic chondrocytes also became positive for ChM-I, while cellular staining gradually disappeared from the other zones. By 12–16 weeks, very strong immunostaining was present almost exclusively on the inner perimeter of the lacunae of hypertrophic chondrocytes. As lacunae were opened at the vascular front, ChM-I initially remained on the cartilage-side of the lacunae, and then disappeared completely. In aged rats, very little ChM-I was present in the cells and matrix of the growth plates, except where remodelling had occurred or chondrocytes had become re-activated. The rate of longitudinal growth in rats is high between 1–5 weeks, then declines until skeletal maturity at approximately 12 weeks, after which a very slow rate of growth continues until 26 weeks. In young rats, the loss of ChM-I in the hypertrophic zone was as expected for an anti-angiogenic factor, i.e. loss was required before vascular invasion could take place. However, the same did not apply to cartilage canal formation, since there was no loss of ChM-I around cartilage canals. The change in the localisation of ChM-I in mature rats, in particular the very intense immunolocalisation around hypertrophic chondrocytes, might be related to the reduced rate of growth. It is possible that rapid vascular invasion must be slowed down in these growth plates and that ChM-I prevented vascular invasion until degraded by proteases, such as MMP-9. The relative absence of ChM-I in the stationary growth plates of aged rats suggests that other anti-angiogenic factors prevent vascular invasion in these growth plates

Cohort studies in humans have suggested that the peak bone mass attained at skeletal maturity may be programmed in utero. To investigate which aspects of bone development might be influenced in utero, we utilised a rat model of maternal protein insufficiency, which has previously been used to demonstrate the fetal origin of adult hypertension. In rodents, a growth plate remains present throughout life, even after longitudinal growth ceases. Generally, the height of the growth plate is related to the rate of bone growth. Fast growing bones have maximal height growth plates, and as bone growth slows down the height decreases until it remains stationary. The aim of this study was to compare the morphology of long bones in aged rats that had been subjected to protein insufficiency in utero with that of controls. Rat dams were fed either an 18% casein control diet or a 9% casein low protein diet from conception until the end of pregnancy. The offspring were fed a normal diet until death (~72 weeks), when bone density was measured by dual energy X-ray absorptiometry (DEXA) and the tibiae and femurs were processed for histology. The offspring of rats from the low protein group had a significantly lower bone mass, as assessed by DEXA. The major differences in bone structure were found in the growth plates, which were very irregular without the usual zones of resting, proliferating and hypertrophic chondrocytes. A number of unusual cellular events were noted to have taken place subsequent to cessation of growth, including: a) elimination of all chondrocytes in a number of regions, resulting in vast acellular areas; b) formation of chondroid bone and/or transdifferentiation of chondrocytes to bone-forming cells in other regions; c) partial resorption of those latter regions while the acellular regions were not resorbed; d) ‘horizontal’ apposition of bone against a smooth metaphyseal edge of the growth plate. To compare the growth plates from the low and high protein groups semi-quantitatively, the degrees of the above features were scored. In addition, the heights of the growth plates were were assessed by two independent measurements. In the low protein group, the height of the growth plate were found to be significantly greater (p< 0.001). Additionally, the growth plates from this group of animals were observed to be more irregular with regards to all the features outlined above. These findings are consistent with the hypothesis that growth trajectory and bone mass are programmed in early life. The increased height of the growth plate in animals undernourished in utero may reflect the cessation of growth at an earlier age. The increased irregularity of the growth plate in this group of animals may infer an earlier onset of age-related changes within the growth cartilage

INTRODUCTION. Endochondral ossification in the growth plate is directly responsible for skeletal growth and its de novo bone-generating activity. Growth plates are vulnerable to disturbances that may lead to abnormal skeletal development. Non-steroidal anti-inflammatory drugs (NSAIDs) are widely used analgesics but have been reported to impair endochondral ossification-driven fracture healing. Despite the general awareness that NSAIDs affect endochondral ossification, the consequences of NSAIDs on skeletal development are unknown. We hypothesise that the NSAID celecoxib leads to impaired growth plate development and consequently impairs skeletal development. METHODS. Healthy skeletally immature (5 weeks old) C57BL/6 mice were treated for ten weeks with celecoxib (daily oral administration 10 mg/kg) or placebo (water) (institutional approval 2013–094) (n=12 per group). At 15 weeks postnatally, total growth plate thickness, the thickness of specific growth plate zones, (immuno)histological analysis of extracellular matrix composition in the growth plate, cell number and cell size, longitudinal bone growth and bone micro-architecture by micro-CT were analysed. Inhibition of COX-2 activity was confirmed by determining PGE2 levels in plasma using an ELISA. RESULTS. No significant difference in total growth plate thickness or thickness of the resting zone, proliferative or hypertrophic zone was found between groups. Staining of growth plate extracellular matrix components revealed, however, a significantly higher proteoglycan content and less collagen type II staining in the proliferative zone. In the hypertrophic zone of the growth plates of celecoxib treated mice collagen type X was hardly detectable as compared to placebo mice. In addition, a significantly decreased cell number was observed in the hypertrophic zone of the growth plate and cells were significantly smaller in the celecoxib group. Micro-CT analysis of the subchondral bone region directly beneath the growth plate showed significantly higher bone density, bone volume density and trabecular thickness following celecoxib treatment. Despite the detected differences in extracellular matrix composition of the growth plate, no difference was found in the length of the tibia in celecoxib treated mice. DISCUSSION. In summary, there are no measurable differences found in murine skeletal formation as a result of treatment with celecoxib in this study. However, there are notable phenotypic features found in the maturation of the growth plate (hypertrophic zone and subchondral bone) as a result from the celecoxib treatment, of which the potential consequences we do not yet understand. SIGNIFICANCE. When follow-up actions from the use of celecoxib on the growing individual are found this may warrant re-evaluation for the use of celecoxib in these individuals

Introduction. Kinematically or anatomically aligned total knee arthroplasty (TKA) has been reported to provide improved clinical outcomes by replicating patient's original joint line [1][2]. It has been known that tibial (joint line) varus varies among patients, and the tibial varus would increase over progression of arthritis and bone remodeling. For those patients with significant deformity, the current tibial varus may significantly differ from its pre-diseased state. In this exploratory study, geometry and alignment of the tibial growth plate were measured with respect to tibial anatomical landmarks in order to better understand modes of tibial deformity and seek possible application in reconstructing pre-diseased joint alignment. Methods. CT scans of sixteen healthy Japanese knees (M6:F10, Age 31.9±13.9 years) were studied. Three-dimensional reconstruction models were created using Mimics 17 (Materialise, Leuven, Belgium). First, a mid-sagittal tibial reference plane, for comparing the varus/valgus orientation of the tibial plateau to that of the growth plate, was defined by the medial margin of the tibial tuberosity, origin of the PCL and center of the foot joint. The tibial plateau (or joint line plane) was determined from three points; dwell point of femur (aligned in extension) on lateral tibial articular surface, and two points at anterior and posterior rim of medial tibial articular surface sampled in the sagittal view and coinciding with dwell point of femur on medial tibia. Then, a three-dimensional model of the tibial growth plate was extracted using the Livewire function and mask editing tools in Mimics. To determine 3D orientation of the growth plate (GP), the vertical mass moment of inertia axis was calculated for the 3D model. The inertia axes were also determined for medial and lateral half of the GP (Figure 1). Results. Tibial plateau (TP) had 2.39±1.72 degrees of varus in coronal view and 11.12±3.90 degrees of posterior inclination in sagittal view. The shape of the GP is noticeably different between medial and lateral. The medial half tends to incline posteriorly towards medial, while the lateral half is twisted anteriorly. In coronal view, GP axis was in 1.27±1.49 degrees valgus to midsagittal plane. Normal axis of the TP was in varus to the GP axis by 3.66±1.79 degrees. The GP medial half was in 5.81±2.49 degrees valgus and 1.63±2.59 degrees anteriorly inclined with respect to the TP. The GP lateral half was in 11.65±2.07 degrees varus and 18.66±4.44 degrees anteriorly inclined relative to the TP. Discussion. The preliminary results from 16 healthy knees suggested that the tibial growth plate is aligned to midsagittal plane and tibial plateau in varus/valgus orientations with relatively small variations. More study samples will be required to validate usefulness of this method in surgical planning. Distinctive shape difference for medial and lateral half of the growth plate was also observed. Future study should also include diseased knees with various levels of deformities

Physeal bar resection for partial growth plate arrest was first described by Langenskjold in 1967. The initial enthusiasm by Peterson (1989) who found that 83% of patients resumed physeal growth was tempered by Birch (1992) who only had 33% success. Poor results were due to failure to resume growth or premature growth arrest. We retrospectively reviewed 21 physeal bar resections performed in 19 children from 1987 to 2003. The average age at surgery was 8.2 years (range 3–12 years). The aetiology of the physeal arrest was : growth plate fracture (8), meningococcal septicaemia (5), osteitis (3; 2 neonatal), dysplasia (3), gunshot (1) and idiopathic (1). The commonest site was the distal femur (12; 5 due to growth plate fracture), followed by the proximal tibia (5; 3 due to meningococcal septicaemia), and the distal tibia (4; 2 due to growth plate fractures). Assessment of the size and location of the bar was with biplanar tomography in 7, MRI in 5 and both in 7. We found equal accuracy with both modalities, but currently prefer MRI. The bar was plotted on an anterior-posterior and lateral map of the growth plate. The average size of the bar was 25% (range 15 to 50%) of the area of the growth plate. Only 3 bars were larger than 30%. Fifteen of the bars were peripheral, 5 linear and 1 central. Results were classified poor if there was no resumption of growth or if premature growth plate arrest occurred, good if there was resumption of growth which continued to maturity or to follow-up, and excellent if the growth exceeded the expected growth. There were 5 (24%) poor results; all failed to resume growth. Three bars exceeded 30% and 2 were due to meningococcal septicaemia. The remaining 16 bars were followed up for a range of 2 to 12 years; 10 to maturity. Four (19%) had an excellent and 12 (57%) had a good result. The authors conclude that physeal bar resection is a worthwhile procedure if the size of the bar is equal to or less than 30% of the area of the growth plate. In growth arrest due to meningococcal septicaemia we only had a 60% success rate

Purposes:. See if permanent damage of the growth plate after physeal distraction is the rule and. Identify factors with influence on the viability of the physis after physeal distraction. Introduction: Surgeons have always been concerned about the fate of the growth plate after physeal distraction and for that reason this technique has usually been considered only in patients nearing maturity. Previous experimental work has shown that the velocity of distraction has an influence on the viability of the growth plate at follow-up (recommended rate: 0.5 mm/day). Clinically, it has also been our observation that the condition of the physis prior to distraction is another important factor related to physeal function in the long term. Patients and methods: Since 1987 we have used low velocity physeal distraction in 43 bone segments of which 37 cases have been followed-up at least for 24 months and this has been the group included in this study. The indications were lengthening (14), angular deformity correction (19) and resection of benign bone tumours (4). Most patients (24) were older than 10 y.o. and 22 of them were followed-up until maturity. We have retrospectively reviewed these patients looking at the radiological morphology and function of the distracted growth plate at follow-up. Results: Out of the 24 children older than 10 y.o., twenty showed a premature complete physeal closure. We looked with interest at the 13 cases younger than 10 y.o. since the repercussions of iatrogenic physeal damage would obviously be bigger in this age group. Five out of the 13 showed premature closure and in the remnant eight an open growth plate was observed at follow-up. All patients with open and/or functioning physes after distraction had no local injuries in the growth plate prior to distraction (4 congenital short femora and 4 normal physes). On the contrary, four out of the five cases with prematurely closed physes, had a local physeal damage prior to distraction (3 bony bridges and one non-union), and the remnant was a congenitally short femur. Growth after distraction was difficult to assess in the congenitally short femora but it has been very satisfactory in the 4 cases of previously normal physes (2 benign tumours and 2 femoral shortenings due to hip disorders). In three cases of congenital short femur in pre-teenagers we were able to repeat distraction twice through the same physis, since it had remained open after the first distraction. Conclusions: Physeal premature closure often follows physeal distraction, but not always. The condition of the physis prior to lengthening is an important factor with influence on its viability after distraction

Rodents are often used as preclinical models for investigating the biomechanical consequences of spinal pathologies and interventions. Growth plates are present within rat vertebrae throughout life and may alter the vertebral biomechanics. This study investigates the biomechanical response of rat-tail vertebrae to axial compressive loading using μCT imaging and image registration to spatially resolve strain fields. The sixth caudal vertebrae of eight immunocompromised (rnu/rnu) rats were μCT scanned (17.5 ×17.5×17.5μm/pixel) in both loaded (27N-32N axial compression) and unloaded configurations. Image registration was used to calculate strain and displacement fields in the bone due to the applied load by finding a spatial mapping between the two scans. Strain was resolved to varying spatial resolutions; high strain gradient regions, such as the growth plates, were analyzed to higher spatial resolutions. Axial strains calculated by image registration ranged from 2% in tension to 16% in compression with an average axial strain of 1.6% in compression. In seven rats the majority of the strain measured within the vertebrae was concentrated in the growth plate. Very soft growth plates in three specimens resulted in maximum axial strains from 10–16% in compression. The remaining four rats with strain concentrations in the growth plate had maximum axial strains ranging from 2.2%–3.2%. Centrally located strain concentrations of lower magnitudes and more limited spatial extent were observed in the trabecular bone. The majority of the strain within the rat vertebrae was absorbed by the growth plates. The amount of strain within the growth plate is important to consider when interpreting biomechanical data on rat vertebrae. Load application to rodent vertebrae will first compress the growth plate and only following compression of this structure cause significant development of displacement and strains within the trabecular and cortical bone. This insight into the biomechanical response of rat vertebrae is apparent through the application of image registration to analyse vertebral body behaviour; such information would not be evident in analysing preclinical whole vertebral body response using finite element modeling or experimental testing protocols

Introduction: In the growth plate, chondrocyte swelling (hypertrophy) is a crucial event during endochondral ossification and bone lengthening, accounting for ~80% of the increase in bone length (. 1. ,. 3. ). The swelling is dramatic (~10x) and closely regulated. Failure of chondrocyte hypertrophy may underlie the chondrodysplasias of the vertebrate skeleton (. 1. ). However, the mechanisms which control cell swelling are poorly understood although there must be a key role for chondrocyte osmolyte transporters which are sensitive to an increase in cell volume. We have used confocal scanning laser microscopy (CLSM) to study volume regulation by living in situ growth plate chondrocytes at varying degrees of hypertrophy. Methods: Bovine growth plates were taken from the ends of young (~12d) bovine ribs. In situ growth plate chondrocytes at the proliferative through to hypertrophic stages were fluorescently-labelled (calcein-AM; 5μM), imaged (Zeiss CLSM510) and volumes determined quantitatively as described (. 2. ). An acute osmotic challenge (280-140mOsm) was delivered by perfusion to determine volume-regulatory capacity by cells in the various zones. Results: The resting volumes of proliferative and hypertrophic cells were 550±63μm. 3. and 5227±1974μm. 3. respectively. Reducing osmolarity resulted in a rapid (within ~1min) cell swelling, proliferative and hypertrophic chondrocytes increasing in volume by 126±2% and 146±5% (n=5) respectively. Chondrocytes within the proliferative zone then recovered in volume by ~60% over the following 20mins (p=0.04), whereas no volume recovery was detected in hypertrophic cells (p=0.94). Conclusions: For the increase in growth plate chondrocyte volume to produce hypertrophy it is essential that the membrane transporters which normally prevent cell swelling are suppressed, otherwise the increase in volume will be compromised. These results suggest that chondrocyte hypertrophy is associated with reduced activity of the swelling-stimulated osmolyte transporter whereas the pathway is active in proliferating chondrocytes. Changes in the activity of this pathway are likely to be an important component in the control of chondrocyte hypertrophy. It is clear that the contributions of other membrane transporters in mediating chondrocyte swelling must be identified in order to understand the overall hypertrophic process

The parameters of cellular proliferation and growth in the growth plates of immature rats were measured after unilateral tibial osteotomy and used to calculate growth rates. Distal osteotomy of one tibia was followed by a bilateral increase in the calculated growth rate of the distal growth plates. However, the ipsilateral distal growth plate grew faster than the contralateral between 12 and 18 days after operation, which appeared to be related to increased cell proliferation and height. Proximal osteotomy led to an increase in growth rates proximally which was more marked on the contralateral side. The lesser response of the ipsilateral growth plate may have been due to local impairment of blood supply, or to greater local release of metabolites after bony damage. Distal tibial osteotomy gave similar results to circumferential release of the distal tibial periosteum. Proximal osteotomy, however, produced a relative impairment of growth on the operated side. This may be of importance in the correction of childhood deformities associated with inequality of leg length

The growth plates of rapidly growing animals have been studied extensively. Nevertheless, several questions remain unanswered, partly because many events happen simultaneously, especially at the vascular front. Terminal chondrocytes are thought to undergo programmed cell death, but the fate of the cell remnants remains unclear. Are the dying cells released into the vascular space and phagocytosed by macrophages, as one would expect for apoptosis? Or are the cells eliminated prior to opening of the lacunae, leaving empty lacunae? Do all terminal chondrocytes die or do some become bone-forming cells? Rodents maintain a growth plate into old age, long after longitudinal growth has ceased. These stationary growth plates have several features not found in the growth plates of rapidly growing animals and closer study of these features may provide answers to the above questions. Femurs and tibiae from 4–16 week-old and 62–80 week-old rats were decalcified, processed into paraffin, and the morphological changes were documented. Between 4–16 weeks, the heights of the growth plates decreased due to loss of the large hypertrophic chondrocytes, but the various zones were still present. In the aged rats, the growth plates were identifiable as a narrow cartilaginous band with some short columns of inactive cells. The vascular front was irregular, the narrow spicules of primary spongiosa were absent and the much thicker spicules, which are normally seen in secondary spongiosa, directly abutted to the cartilage. Horizontal apposition of bone matrix onto the cartilage edge was frequently present. In addition, the following features were noted. 1) Acellular areas: Nearly all growth plates contained regions of cartilage from which all cells and their lacunae had disappeared. In some cases, these acellular regions stretched from the reserve zone to the vascular front and even persisted as a relatively wide core within the spicules of spongiosa, indicating increased resistance of acellular cartilage to resorption. The absence of cells or cell debris was consistent with an autophagic mode of cell death and subsequent collapse of the lacunae. 2) Remodelling within the growth plate; in some growth plates, large regions of growth plate cartilage had been resorbed and new bone had been laid down in a pattern similar to the remodelling of cortical bone. This suggested that the normal resistance of cartilage to vascular invasion had been lost locally, but was maintained in adjacent non-remodelled regions. 3) Trans-differentiation of chondrocytes to bone-forming cells; extensive new medullary bone formation was noted in the diaphysis of approximately 30% of the aged rats, suggesting that they had received an (unknown) osteogenic stimulus. In these rats, bone matrix was identifiable inside chondrocytic lacunae, and spreading beyond the confines of the lacunae, thus directly replacing growth plate cartilage with bone matrix. The results suggest that i) chondrocytes are capable of self-elimination, perhaps by a mechanism similar to the autophagic cell death that occurs during insect metamorphosis; ii) resorption of cartilage and vascular invasion requires the presence of the viable chondrocytes; and iii) chondrocytes have the capacity to transdifferentiate to bone-forming cells, but only do so when receiving an increased osteogenic stimulus

We studied the cellular response to physeal distraction in the growth plates of skeletally immature rabbits. We used a new method of labelling and detection of proliferating cells with bromodeoxyuridine (BUdR) and an anti-BUdR antibody. The application of an external fixator but no distraction force produced no changes in the growth plates. After five days of distraction at a maximum force of 20 N, the growth plate became thicker, mainly because of an increase in the number of hypertrophic chondrocytes, but there was no evidence of increased cell proliferation. Recent fractures were seen at the junction of growth plate and metaphysis but the increase in bone length was insignificant. After ten days of distraction at the same maximum force, the chondrocyte columns had become disorganised and cell proliferation was significantly decreased. There was an increase in bone length due to distraction of the fracture gap. In this model, physeal distraction did not stimulate cell proliferation, but actually inhibited it. The apparent increase in growth-plate thickness produced by distraction is not due to increased cell production, but results from inhibition of endochondral ossification and the consequent accumulation of hypertrophic chondrocytes. Any growth after distraction depends on the ability of growth-plate chondrocytes to divide. The decrease in proliferative activity which we found after ten days of distraction suggests the need for caution in the use of such procedures in young children

This paper describes a study in the human femur of the relationship between cell division in growth cartilage and overall bone growth. Growth rates for the distal femur from birth to eighteen years were determined from serial radiographs available from the Harpenden Growth Study; An average of 1-4 cm/year was found for the ages of five to eight years. The development of the growth plate is illustrated in a series of photomicrographs of femur sections. These sections were also used for quantitative histology; The length of the proliferation zone was estimated from cell counts to be twenty-four cells per column. On the basis of this value and the measured growth rate, an approximate mean cycle time of twenty days was found for the proliferating cells of the human growth plate. Since the corresponding cycle time is two days for rodent growth plates, which also have a different structure, it is unwise to extrapolate the findings in this tissue from mouse to man

Problems of vertebral growth plate metabolism regulation at different stages of ontogenesis are insufficiently covered in the literature. However, the study of function mechanism of provisional cartilage of vertebral growth plate is a practical and theoretical basis of pathogenesis model of idiopathic scoliosis and Scheuermann’s disease both associated with growth disorders. Objective: To investigate the function mechanism of vertebral growth plate structural components during formation and growth. Materials and methods: Fifty vertebral body specimens of children at the age from 1 to 14 years obtained from the forensic medicine department were studied by methods of morphohistochemistry, biochemistry, and ultra-structural analysis. The expression of five proteoglycan genes and their albuminous products was investigated by RT-PCR method. Results: The process of growth represents a sequence of morphogenetic movements ongoing up to the achievement of sexual maturity. But morphofunctional organization and regulation of growth are different in different periods of ontogenesis. Early postnatal growth of vertebral bodies is governed by a radially located zone of growth. The cell population in a just-formed cartilage growth plate is non-uniform: from poorly differentiated chondroblast through the form of highly differentiated ones to degrading chondrocyte. This period of the spine development is characterised by the presence of vessels in provisional cartilage tissue. The concept of “chondro/hematic barrier” suggested and validated by A.M Zaidman explains a conservation of homeostasis at a stage of vertebral bodies differentiation. The process of chondrogenic differentiation of prechondroblasts in the early postnatal period is inducted by the chorda influence. In the late postnatal period (12–14 years) the laws of structural and functional organization of cartilage growth plate of vertebral body remain the same: phenotypic heterogeneity, polarity, and zonality of cells. A metabolic centre of complex architectonics of cartilage tissue is chondroblast. Chondroblast is functioning at the level of chondron which is a functional unit of vertebral growth plate. Chondroblast (chondrocyte) is located in the centre of chondron and surrounded by pericellular matrix presented by diffuse aggrecan molecules, or growth plate aggregates. Due a peculiar architectonics, growth plate molecules have inner spaces comparable in size with Golgi’s vesicles. Metabolites, small molecules, and water freely penetrate through these molecules. Diffuse molecules together with type II thin collagenic fibres, minor collagenes, and structure-forming growth plates perform barrier function. Besides barrier function, diffuse molecules perform information function inside a chondron, forming a kind of information field. Signals of this field are perceived by chondroblast receptors, and the cell gene apparatus expression is carried out through second messengers. Thus, either stimulation of proliferative activity with subsequent differentiation during intensive growth, or interruption of these processes (period of growth delay) occurs. Single chondrons unite into chains in proliferation zones. Cell interaction inside chondron occurs due transmembrane structures, as a contact coordination of functions of cells with inherent high specificity. Concentration of diffuse molecules of growth plate (aggrecan) in proliferation zones is the highest on evidence of histochemical and ultrastructural assays. Besides, diffuse molecules are the short-distance regulators of DNA synthesis the mechanism of action of which is realised through the system of receptors on a cellular membrane. Hence, contact intercellular interactions are one of the mechanisms controlling cell division. These are so-called extracellular factors of chondroblast proliferation regulation. Thus, the process of growth represents a complex two-stage mechanism of proliferation and differentiation of chondroblasts, and adequate osteogenesis. All three processes provide harmonious spine formation, and disturbance of one of them results in pathology development

Our aim was to evaluate the expression of transcription factors CCAAT/enhancer-binding protein-beta (C/EBP. β. ) and C/EBP-homologous protein (CHOP) in the growth plate. Proximal tibial epiphyseal growth plates from ten 15-day-old Wistar rats were used. Additionally, anti-proliferating cell nuclear antigen (PCNA), anti-5-bromo-2’-deoxyuridine (BrdU) immunostaining, terminal transferase dUTP nick end-labelling (TUNEL) and nucleolar organiser region-associated proteins (AgNOR) techniques were peformed. The histological morphology of the growth plate from C/EBP. β. knock-out mice was also analysed. The normal growth plate showed that C/EBP. β. and CHOP factors are expressed both in the germinative/ upper proliferative and in the lower proliferative zones. Furthermore, BdrU+ and PCNA+ cells were present exclusively in the germinative and proliferative zones, while TUNEL+ and AgNOR+ cells were seen in all three zones of the growth plate. Acellular areas, hypocellularity, the increase in cell death and anomalies in the architecture of the cell columns were observed in the growth plates of C/EBP. β. (−/ −) knockout mice. We suggest that C/EBP. β. and CHOP transcription factors may be key modulators participating in the chondrocyte differentiation process in the growth plate