跨骺钢板固定一定周期取出：继续观察一段时间后骺板的生长抑制情况

文题释义： 骨骺损伤：骺板软骨细胞共分为4层,骨骺损伤后骺软骨的结构发生了一系列修复重建性改变,其中骺板软骨增生层和肥大细胞层的细胞增生、分化、代谢活跃。由于肥大细胞层细胞增大,基质稀少,形成了骺板中最薄弱部位,故受到压力时变化最为显著。 骺板厚度变化率：为随着时间延长,骺板厚度逐渐增加,单位时间内骺板厚度增长的比率。主要是指不同时间节点,骺板厚度生长变化情况。用于观察跨骺板钢板内固定一段时间,取出内固定物后骺板厚度的生长变化情况。 背景：临床上儿童干骺端、骺板周围骨折比较常见,跨骺板钢板内固定对稳定骨折有较为重要的作用。但内固定一定周期后取出内固定物,继续观察一定时间骺板的发育恢复情况鲜有报道。 目的：设计骺板周围骨折动物模型,分析跨骺板置入锁定钢板一定周期取出钢板,继续观察一段时间后骺板的生长抑制情况。 方法：建立32只幼兔右股骨远端骺板上方5 mm骨折模型,随机分4组,每组8只。应用相同型号钢板和螺钉,跨骺板周围骨折线行钢板置入内固定。术后2,4,8,12周取出内固定物,继续观察2周处死幼兔。取出股骨标本,测量股骨长度;作病理切片,测量骺板厚度及肥大细胞计数;观察形态学中肥大细胞及骺板厚度变化情况。将骨折模型作为实验组,以左股骨远端骺板作为对照。 结果与结论：①实验组在内固定2周后,取出钢板继续观察2周,股骨长度、骺板厚度、肥大细胞计数等与对照组对比,差异无显著性意义;②实验组内固定4,8,12周,取出钢板继续观察2周,与对照组相比,实验组股骨长度、骺板厚度、肥大细胞计数等指标未能完全恢复至正常,差异有显著性意义(P < 0.05);③结果表明,在内固定物不伤及骺板的前提下,跨骺板钢板内固定初期(≤2周)取出钢板继续观察2周,适当压力作用对骺板生长发育未产生显著影响;④但持续过久压力限制时(≥4周),内固定对骺板压力限制时间过长,虽然也及时取出内固定,但肢体长度、骺板厚度、肥大细胞计数等指标均未能完全恢复正常,可导致骺板生长部分或者完全阻滞,引起肢体畸形及骺板发育停滞。 ORCID: 0000-0003-2448-9683(崔庆达) 中国组织工程研究杂志出版内容重点：人工关节;骨植入物;脊柱;骨折;内固定;数字化骨科;组织工程     

碱性成纤维细胞生长因子对离心管内培养骺板细胞生成软骨组织的作用

背景：采用离心管技术体外培养骺板细胞的报道已很多。 目的：观察碱性成纤维细胞生长因子对离心管内培养的骺板细胞生成类骺板组织的影响。 方法：获取3周龄新西兰白兔股骨远端的骺板组织,利用组织块纱巾培养法获得骺板细胞,加入含有10 μg/L碱性成纤维细胞生长因子的DMEM培养液,连续培养4周。 结果与结论：离心管内聚集的骺板细胞在含有碱性成纤维细胞生长因子的DMEM培养液中形成类骺板样组织块。在组织块外周形成类似骺软骨的生发层,中心的骺板细增殖情况良好,向肥大细胞方向分化。类骺板样组织甲苯胺蓝及番红“O”染色阳性,Ⅱ型胶原免疫组织化学染色呈强阳性。说明碱性成纤维细胞生长因子能够促进离心管中的骺板细胞形成富含蛋白聚糖及Ⅱ型胶原等细胞外基质的类骺板样软骨组织。     

Treatment of rabbit growth plate injuries with an autologous tissue-engineered composite. An experimental study

Tissue engineering has become a promising way of treating growth plate injuries. In this study, we attempted investigating the role of the autologous tissue-engineered composite in the treatment of rabbit growth plate injuries. Growth plate chondrocytes from iliac crest epiphyseal cartilage of immature New Zealand rabbits were obtained by dissection and sequential digestion with 0.2% collagenase (type II). After proliferating in monolayer culture in vitro for 3 weeks, the cells were harvested and seeded onto the demineralized bone matrix (DBM) scaffold to construct the composite. The autologous tissue-engineered composites were finally implanted into the proximal right tibia defects of the growth plate created in 12 rabbits (group A underwent the operation after obtaining chondrocytes 3 weeks beforehand), another 12 rabbits were implanted with only the DBM scaffold (group B), and the defects in group C (12 rabbits) were not implanted. The left tibias of all animals were left undone as the normal control. Two weeks after the operation, severe shortness and angulation deformity of the right tibia evaluated by X-ray were gradually observed in groups B and C. However, there were no obvious changes in group A and there were significant differences between group A and groups B and C (p < 0.05) at the 4-, 8-, and 16-weeks time points. 16 weeks after operation, histological examination revealed that the defects of the right tibias in group A had restored to almost the normal columnar structure of the growth plate. The results demonstrate that tissue-engineered composite established by combination of autologous growth plate chondrocytes and DBM can prevent the formation of a bone bridge and restore the growth of damaged growth plate.     

Dysplastic Histogenesis of Cartilage Growth Plate by Alteration of Sulphation Pathway: A Transgenic Model

Mutations in the diastrophic dysplasia sulphate transporter (dtdst) gene causes different forms of chondrodysplasia in the human. The generation of a knock-in mouse strain with a mutation in dtdst gene provides the basis to study developmental dynamics in the epiphyseal growth plate and long bone growth after impairment of the sulphate pathway. Our microscopical and histochemical data demonstrate that dtdst gene impairment deeply affects tissue organization, matrix structure, and cell differentiation in the epiphyseal growth plate. In mutant animals, the height of the growth plate was significantly reduced, according to a concomitant decrease in cell density and proliferation. Although the pathway of chondrocyte differentiation seemed complete, alteration in cell morphology compared to normal counterparts was detected. In the extracellular matrix, it we observed a dramatic decrease in sulphated proteoglycans, alterations in the organization of type II and type X collagen fibers, and premature onset of mineralization. These data confirm the crucial role of sulphate pathway in proteoglycan biochemistry and suggest that a disarrangement of the extracellular matrix may be responsible for the development of dtdts cartilage dysplasia. Moreover, we corroborated the concept that proteoglycans not only are structural components of the cartilage architecture, but also play a dynamic role in the regulation of chondrocyte growth and differentiation.     

Abnormality of epiphyseal plate induced by selenium deficiency diet in two generation DA rats

This study aimed to observe the effects of Se deficiency on epiphyseal plates of two generation DA rats fed with artificial total synthetic low Se diet. All F0 and F1 DA rats were fed with synthetic low Se diet (SeD group) and low Se diet supplied with Se (SeS group). The levels of selenium and enzyme activities of GPx were detected in plasma of the rats. General growth of bone and articular cartilage was measured macroscopically and microscopically. The epiphyseal plate of femur heads or tibia were obtained to histological and immunohistochemical examinations. The cartilage from left knee joints and femur heads was used to detect the gene expression of collagens, ADAMTSs and several selenoproteins by RT‐qPCR. Two generation SeD rats showed Se insufficiency status. The thicknesses of the femur and tibial epiphyseal plates in both F0 and F1 SeD rats were significantly less than that of SeS rats. In F1 generation, SeD rats showed much fewer proliferative chondrocyte layers than SeS ones. Importantly, two generation SeD rats both showed significantly more serious pathological changes of epiphyseal plates. In two generation rats, gene expressions of COL II, GPx1 and GPx4 were significantly down‐regulated in SeD rats than SeS ones; meanwhile ADAMTS‐4 showed an up‐regulated expression in cartilage. Dietary Se deficiency can apparently cause epiphyseal plate lesion and decrease cartilage type II collagen production and GPx1 activity in two generation DA rats fed with the artificial total synthesis low Se diet.     

Does the epiphyseal cartilage of the long bones have one or two ossification fronts?

Epiphyseal cartilage is hyaline cartilage tissue with a gelatinous texture, and it is responsible for the longitudinal growth of the long bones in birds and mammals. It is located between the epiphysis and the diaphysis. Epiphyseal cartilage also is called a growth plate or physis. It is protected by three bone components: the epiphysis, the bone bar of the perichondrial ring and the metaphysis. The epiphysis, which lies over the epiphyseal cartilage in the form a cupola, contains a juxtaposed bone plate that is near the epiphyseal cartilage and is in direct contact with the epiphyseal side of the epiphyseal cartilage. The germinal zone corresponds to a group of cells called chondrocytes. These chondrocytes belong to a group of chondral cells, which are distributed in rows and columns; this architecture is commonly known as a growth plate. The growth plate is responsible for endochondral bone growth. The aim of this study was to elucidate the causal relationship between the juxtaposed bone plate and epiphyseal cartilage in mammals. Our hypothesis is that cells from the germinal zone of the epiphyseal side of the epiphyseal cartilage are involved in forming a second ossification front that is responsible for the origin of the juxtaposed bone plate. We report the following: (a) The juxtaposed bone plate has a morphology and function that differs from that of the epiphyseal trabeculae; (b) on the epiphyseal edge of the epiphyseal cartilage, a new ossification front starts on the chondrocytes of the germinal area, which forms the juxtaposed bone plate. This ossification front is formed by chondrocytes from the germinal zone through a process of mineralisation and ossification, and (c) the process of mineralisation and ossification has a certain morphological analogy to the process of ossification in the metaphyseal cartilage of amphibians and differs from the endochondral ossification process in the metaphyseal side of the growth plate. The close relationship between the juxtaposed bone plate and the epiphyseal cartilage, in which the chondrocytes that migrate from the germinal area play an important role in the mineralisation and ossification process of the juxtaposed bone plate, supports the hypothesis of a new ossification front in the epiphyseal layer of the epiphyseal plate. This hypothesis has several implications: (a) epiphyseal cartilage is a morphological entity with two different ossification fronts and two different functions, (b) epiphyseal cartilage may be a morphological structure with three parts: perichondrial ring, metaphyseal ossification front or growth plate, and epiphyseal ossification front, (c) all disease (traumatic or dysplastic) that affects some of these parts can have an impact on the morphology of the epiphyseal region of the bone, (d) there is a certain analogy between metaphyseal cartilage in amphibians and mammalian epiphyseal cartilage, although the former is not responsible for bone growth, (e) comparative histological and anatomy studies are also warranted, to shed light on the phylogenetic study of epiphyseal cartilage throughout the changes that occur in the animal species.     

Morphological alterations in the growth plate cartilage of ovariectomized mice

The effects of ovariectomy on growth and estrogen receptor (ER) expression level in the epiphyseal growth plate in mice have been estimated by histomorphometry and immunohistochemistry. Twelve female ddY mice, 8–9 weeks of age, were subjected to bilateral ovariectomy and 12 others were sham operated. They were then killed 8 weeks later. Ovariectomy significantly increased the total thickness of the distal femoral and proximal tibial growth plate cartilage. Ovariectomy caused a 1.4-fold increase in the thickness of the proliferative layer in the distal growth plate of the femur and a 1.3-fold increase in the thickness of the proliferative layer in the proximal growth plate of the tibia. ERα and ERβ immunoreactivity was detected in chondrocytes of the growth plate and the expression level of ERs in epiphyseal plates was increased in ovariectomized mice compared with controls. These data suggest that ERα and ERβ are coexpressed in the growth plates of the mice and that the cartilage growth and the level of expression of ERs in these tissues are hormonally regulated.     

Proteoglycan Synthesis in Vitamin D-Deficient Cartilage: Recovery from Vitamin D deficiency

Vitamin D appears to be required for mineralization of skeletal elements. There is also evidence that cartilage proteoglycans may be involved in the regulation of mineralization. Previous studies have shown an alteration in the structure of the proteoglycans of the epiphyseal growth cartilage as a result of the decrease in serum calcium related to deficiency of dietary vitamin D. Vitamin D deficiency also induces a thickening of the epiphyseal growth plate presumably because of the inhibition of maturation of the growth plate chondrocytes. In order to compare the effect on proteoglycan structure with that on growth plate morphology, the proteoglycans of healing epiphyseal cartilage were characterized. The results indicate that, consistent with previous data, in vitamin D-deficient hatchling chicks, the proteoglycans of the growth cartilage, but not of the articular cartilage, are smaller in monomer size with slightly smaller chondroitin sulfate chains whose sulfation pattern is unaltered. Sternal cartilage proteoglycans are unaffected. During recovery from vitamin D deficiency, the proteoglycans isolated from the growth cartilage are still not completely normal one day after supplementation with vitamin D, but are indistinguishable from normal by four days. In addition, the results conflict with those of a previous study in which only growth cartilage of hatchling chicks, not sternal or articular cartilage, was reported to synthesize large proteoglycans. Instead, all of these cartilages in the normal chicken have been found in this study to produce large proteoglycans of a size typical for mammalian cartilage and embryonic chick cartilage.     

Proteoglycan synthesis in vitamin D-deficient cartilage: recovery from vitamin D deficiency

Vitamin D appears to be required for mineralization of skeletal elements. There is also evidence that cartilage proteoglycans may be involved in the regulation of mineralization. Previous studies have shown an alteration in the structure of the proteoglycans of the epiphyseal growth cartilage as a result of the decrease in serum calcium related to deficiency of dietary vitamin D. Vitamin D deficiency also induces a thickening of the epiphyseal growth plate presumably because of the inhibition of maturation of the growth plate chondrocytes. In order to compare the effect on proteoglycan structure with that on growth plate morphology, the proteoglycans of healing epiphyseal cartilage were characterized. The results indicate that, consistent with previous data, in vitamin D-deficient hatching chicks, the proteoglycans of the growth cartilage, but not of the articular cartilage, are smaller in monomer size with slightly smaller chondroitin sulfate chains whose sulfation pattern is unaltered. Sternal cartilage proteoglycans are unaffected. During recovery from vitamin D deficiency, the proteoglycans isolated from the growth cartilage are still not completely normal one day after supplementation with vitamin D, but are indistinguishable from normal by four days. In addition, the results conflict with those of a previous study in which only growth cartilage of hatchling chicks, not sternal or articular cartilage, was reported to synthesize large proteoglycans. Instead, all of these cartilages in the normal chicken have been found in this study to produce large proteoglycans of a size typical for mammalian cartilage and embryonic chick cartilage.     

Rearrangement of the metaphyseal vasculature of the rat growth plate in rickets and rachitic reversal: A model of vascular arrest and angiogenesis renewed

The morphology of the metaphyseal microvasculature at the epiphysis was examined at both the light and electron microscopic level in rickets and rachitic reversal. The animals studied were normal, rachitic, and rachitic reversed at 8, 24, and 96 hours post-vitamin D administration. The overall architecture of the metaphyseal vessels was significantly altered throughout the intervals examined. In the rachitic animal, arterioles, venules, and capillaries were found adjacent to the growth plate, either directly apposed to the hypertrophic chondrocytes or separated from them by bone-forming cells. These vessels are in many ways similar to the larger arterioles and venules that normally supply the metaphyseal capillary sprouts, but in the normal growing animal are usually located 350–500 μm from the epiphyseal cartilage. The rachitic capillaries appear relatively well differentiated with a partial basement membrane and a perivascular cell lining. In early rachitic reversal, small vascular projections are induced to grow from the large diameter venules that border upon the hypertrophic chondrocytes. These vascular sprouts that invade the epiphyseal cartilage are quite undifferentiated, with no basement membrane or pericyte lining at the sprout apex and occasional abluminal endothelial cell projections. Within 96 hours, the metaphyseal microvasculature has returned to an apparently normal state with only capillaries at the cartilage-vascular interface and larger vessels (arterioles and venules) located several hundred microns deeper into the metaphysis. The sequential processes of differentiation and cessation of capillary growth followed by dedifferentiation and reinitiation of microvascular growth make the rachitic system a unique one in which to study angiogenesis.     

The histological and ultrastructural features of the epiphyseal plate in Morquio type A syndrome (mucopolysaccharidosis type IVA)

Tissue from the epiphyseal plate of a patient with Morquio type A syndrome (mucopolysaccharidosis type IVA) was studied by undecalcified histological and electron microscopical techniques. Cartilage cells in the plate were vacuolated to a variable degree. The orderly proliferating structure of the epiphyseal plate was absent and calcification was markedly reduced. The related bone tissue was morphologically normal although reduced in quantity.     

Rearrangement of the metaphyseal vasculature of the rat growth plate in rickets and rachitic reversal: a model of vascular arrest and angiogenesis renewed.

The morphology of the metaphyseal microvasculature at the epiphysis was examined at both the light and electron microscopic level in rickets and rachitic reversal. The animals studied were normal, rachitic, and rachitic reversed at 8, 24, and 96 hours post-vitamin D administration. The overall architecture of the metaphyseal vessels was significantly altered throughout the intervals examined. In the rachitic animal, arterioles, venules, and capillaries were found adjacent to the growth plate, either directly apposed to the hypertrophic chondrocytes or separated from them by bone-forming cells. These vessels are in many ways similar to the larger arterioles and venules that normally supply the metaphyseal capillary sprouts, but in the normal growing animal are usually located 350-500 microns from the epiphyseal cartilage. The rachitic capillaries appear relatively well differentiated with a partial basement membrane and a perivascular cell lining. In early rachitic reversal, small vascular projections are induced to grow from the large diameter venules that border upon the hypertrophic chondrocytes. These vascular sprouts that invade the epiphyseal cartilage are quite undifferentiated, with no basement membrane or pericyte lining at the sprout apex and occasional abluminal endothelial cell projections. Within 96 hours, the metaphyseal microvasculature has returned to an apparently normal state with only capillaries at the cartilage-vascular interface and larger vessels (arterioles and venules) located several hundred microns deeper into the metaphysis. The sequential processes of differentiation and cessation of capillary growth followed by dedifferentiation and reinitiation of microvascular growth make the rachitic system a unique one in which to study angiogenesis.     

Animal model of experimentally induced ectopic enchondral ossification in nude mice with xenograft of porcine epiphyseal cartilage

In a specific animal model the induction of heterologous enchondral ossification was examined in long term follow-up. Physiologically normal and devitalized frozen porcine epiphyseal cartilage as a control group were transplanted as s.c. xenograft into athymic nude mice (nu/nu). 15 weeks after transplantation the porcine growth plate cartilage showed the development of viable cartilage tissue in the recipients, further differentiating to juvenile longe bone with epiphysis, diaphysis and growth plate. Porcine growth plate cartilage increased s.c. in the recipient nude mice, showing enchondral ossification without any physiological load, and finally an unexpected development towards complete juvenile long bone.     

兔股骨骺板生长与阻滞压力关系式的探讨

本文用三组压力固定模式的预压值对兔股骨骺板加压，测试阻止兔骺板生长的阻滞压力，以指数函数表达骨骺板生长时间的关系，由此得到二者的关系方程。     

Vascular invasion of the epithyseal growth plate: Analysis of metaphyseal capillary ultrastructure and growth dynamics

Metaphyseal blood vessels which invade the calcifying epiphyseal growth plate were examined by a variety of techniques to determine their morphology, cell division, and growth patterns as they relate to endochondral ossification. Four regions of these vessels were characterized: 1) sprout tips—the terminal ends of the capillary sprouts which impinge upon the hypertrophic chondrocytes of the growth plate; 2) region of extended calcified cartilage—those deeper vessels within the metaphysis which are surrounded by an extracellular matrix predominantly composed of extended septa of calcified cartilage; 3) region of bone deposition—further still from the epiphysis these microvessels are contained within a network of active bone deposition laid upon a scaffold of calcified cartilage; 4) region of primary vessels—at a distance of 350–500 μm from the epiphysis are dilated vessels with one or two layers of smooth muscle in their walls, which supply and drain the metaphyseal capillary plexus. The sprout tips are continuous blind-ended vessels lined with an attenuated endothelium with no underlying basement membrane. Dividing endothelial cells are most frequently found in the region of bone deposition 175–200 μm behind the apices of the growing sprout tips. A time-coursed, autoradiographic examination of cytokinesis revealed radio-labelled endothelial cells to appear at the epiphysis after a 24 hr period. The metaphyseal capillary sprouts represent a continuous, unidirectional angiogenic vascular network which grows by elongation from the region of bone deposition; this region remians a fixed distance behind the sprout tips. These findings are discussed in light of the growth dynamics between this vascular plexus and the epiphyseal growth plate.     

Matrix synthesis in high density cultures of bovine epiphyseal plate chondrocytes

Bovine epiphyseal plate chondrocytes were cultured by a method combining both suspension culture and high density monolayers. The matrix synthesized by the cultured cells was analyzed at fifteen days for glycosaminoglycan, proteoglycan, and collagen content. In the cell culture product glycosaminoglycan distribution was: 65% chondroitin-6-sulfate, 18% chondroitin-4-sulfate, 15% keratan sulfate, and less than 2% dermatan sulfate. Essentially all the radioactive sulfate in labelled specimens was present in high molecular weight aggregates. The collagen which was synthesized co-migrated with Type II collagen standard. Parallel analysis showed the matrix of cultured cells to be similar to that of intact epiphyseal plate tissue. This study demonstrates the ability to grow epiphyseal plate chondrocytes in a cell culture system which allows matrix synthesis similar to that seen in vivo.     

Unilateral premature closure of distal radial growth plate due to hematogenous osteomyelitis in a German shepherd dog

Premature closure of a growth plate can result in angular deformity, limb shortening, or both. The condition, particularly in the distal radius and ulna, is not uncommon in dogs; the distal ulnar physis is commonly affected. Causes of premature closure may include growth plate trauma, abnormal nutrition, hereditary factors, and infection. A 6-month-old male German shepherd dog, weighting 19 kg, was referred to the Veterinary Teaching Hospital of the Shahrekord University, with a 5-day history of lethargy, anorexia, and persistent pyrexia associated with left forelimb lameness. Survey radiography revealed the premature closure of distal radial growth plate and moth-eaten osteolysis pattern of affected limb in comparison of normal forelimb. The present report describes clinical, paraclinical, and radiological findings of premature growth plate due to osteomyelitis conditions.     

Vascular invasion of the epiphyseal growth plate: analysis of metaphyseal capillary ultrastructure and growth dynamics

Metaphyseal blood vessels which invade the calcifying epiphyseal growth plate were examined by a variety of techniques to determine their morphology, cell division, and growth patterns as they relate to endochondral ossification. Four regions of these vessels were characterized: 1) sprout tips--the terminal ends of the capillary sprouts which impinge upon the hypertrophic chondrocytes of the growth plate; 2) region of extended calcified cartilage--those deeper vessels within the metaphysis which are surrounded by an extracellular matrix predominantly composed of extended septa of calcified cartilage; 3) region of bone deposition--further still from the epiphysis these microvessels are contained within a network of active bone deposition laid upon a scaffold of calcified cartilage; 4) region of primary vessels--at a distance of 350-500 microns from the epiphysis are dilated vessels with one or two layers of smooth muscle in their walls, which supply and drain the metaphyseal capillary plexus. The sprout tips are continuous blind-ended vessels lined with an attenuated endothelium with no underlying basement membrane. Dividing endothelial cells are most frequently found in the region of bone deposition 175-200 microns behind the apices of the growing sprout tips. A time-coursed, autoradiographic examination of cytokinesis revealed radio-labelled endothelial cells to appear at the epiphysis after a 24 hr period. The metaphyseal capillary sprouts represent a continuous, unidirectional angiogenic vascular network which grows by elongation from the region of bone deposition; this region remains a fixed distance behind the sprout tips. These findings are discussed in light of the growth dynamics between this vascular plexus and the epiphyseal growth plate.     

Immunolocalization of the cleavage of the aggrecan core protein at the Asn341–Phe342 bond,as an indicator of the location of the metalloproteinases active in the lysis of the rat growth plate

In view of the extensive lysis of hyaline cartilage known to take place during endochondral bone formation, the current study was designed to test the hypothesis that metalloproteinases are the agents that mediate this lysis. Since these enzymes have been shown in vitro to cleave the core protein of the major proteoglycan of cartilage, aggrecan, at the Asn³⁴¹–Phe³⁴² bond, an immunohistochemical method has been developed to find out whether or not there are sites in the growth plate of the rat tibia where cleavage of this bond takes place. The cleavage of aggrecan by metalloproteinases is followed by the retention of the fragment known as G1, for it includes the G1 domain. Since the G1 fragment terminates in the amino acid residues ...FVDIPEN, we prepared an antiserum against FVDIPEN, confirmed its specificity, then applied it to the growth plate of 21-day-old rat tibia in the hope of localizing the G1 fragments. The antiserum specificity was shown by its recognition of the ...FVDIPEN sequence at the C-terminus of peptides and of G1 fragments produced by aggrecan cleavage. When the antiserum was applied to Western blots of guanidinium chloride extracts prepared from epiphyseal growth plate, it recognized two species (56 and 52 kDa), which differed only in the degree of glycosylation. These fragments were comparable in size to the G1 fragments generated by the action of recombinant metalloproteinase in vitro, thus confirming antiserum specificity for these fragments. Applying the antiserum to cryosections of 21-day-old rat tibiae revealed immunostaining at two intensities within the growth plate matrix: a strong staining was observed in a 1–5 μm-wide layer designated “peripheral” matrix, which borders the epiphyseal and metaphyseal marrow spaces as well as the perichondrium, while a weak staining was found in the rest of the plate, designated “central” matrix. The abundance of G1 fragments terminating in ...FVDIPEN in the peripheral matrix indicates that this is where the growth plate is lysed to achieve longitudinal and latitudinal bone growth. The site where metalloproteinases exert their main lytic activity is a thin layer of matrix separating central from peripheral matrix. Anat. Rec. 252:117–132, 1998. © 1998 Wiley-Liss, Inc.