Subchondral bone morphology in the metacarpus of racehorses in training changes with distance from the articular surface but not with age

The repetitive large loads generated during high‐speed training and racing commonly cause subchondral bone injuries in the metacarpal condyles of racehorses. Adaptive bone modelling leads to focal sclerosis at the site of highest loading in the palmar aspect of the metacarpal condyles. Information on whether and how adaptive modelling of subchondral bone changes during the career of a racehorse is sparse. The aim of this cross‐sectional study was to describe the changes in subchondral bone micromorphology in the area of highest loading in the palmar aspect of the metacarpal condyle in thoroughbred racehorses as a function of age and training. Bone morphology parameters derived from micro‐CT images were evaluated using principal component analysis and mixed‐effects linear regression models. The largest differences in micromorphology were observed in untrained horses between the age of 16 and 20 months. Age and duration of a training period had no influence on tissue mineral density, bone volume fraction or number and area of closed pores to a depth of 5.1 mm from the articular surface in 2‐ to 4‐year‐old racehorses in training. Horses with subchondral bone injuries had more pores in cross‐section compared with horses without subchondral bone injuries. Differences in bone volume fraction were due to the volume of less mineralised bone. Tissue mineral density increased and bone volume fraction decreased with increasing distance from the articular surface up to 5.1 mm from the articular surface. Further research is required to elucidate the biomechanical and pathophysiological consequences of these gradients of micromorphological parameters in the subchondral bone.     

Complete pterygoidectomy--a novel method for the topographical investigation of the deep masticator space and its contents.

The complexity of the topographical anatomy of the infratemporal fossa (=masticator space) remains underappreciated because of limitations of the methods used to expose it; these methods are described and critiqued. The disposition of the lateral pterygoid (LPt) muscle in the masticator space obscures the anatomical relations of clinically significant neurovascular structures. Controversies regarding the nerve supply and actions of the two LPt heads are summarized. Since the LPt has been implicated in temporomandibular (joint) dysfunction (TMD), its precise relationships to the mandibular neurovascular structures is essential in understanding its role in TMD. We recently developed a method involving the en bloc removal of the LPt-tensor veli palatini complex along with all vital neurovascular structures. Further investigations using our method--in conjunction with contemporary imaging techniques (CT, MRI)--should help describe the detailed topography of masticatory structures. This information should help in understanding, differential diagnosis, and treatment of TMD.     

Influence of food consistency on growth and morphology of the mandibular condyle

The objective of this study was to determine if variation in the shape and mineralization of the mandibular condyle are the result of natural adaptation in response to different functional loading demands. Eight female Kuni Kuni piglets were randomly assigned to two groups of four, receiving either a soft or hard diet. Each animal was given three separate doses of vital stains intravenously at set time points during the study. At 8.5 months, animals were euthanized and temporomandibular joints (TMJs) were excised. Histological analysis was used to measure the amount of new bone deposition in the anterior, central, and posterior regions of the mandibular condyle. Backscatter electron (BSE) imaging was used as a semiquantitative estimate of bone mineralization in these two diet groups. Histology revealed that the degree of new bone deposition in the hard-diet group was significantly (n = 4, P < 0.001, paired t-test) higher than that of the soft-diet group. Also, the majority (87%) of animals fed a hard diet tended to show greater new bone deposition on the leftside in comparison to the right, indicating a chewing preference for the left side. In both groups, the degree of new bone deposition was significantly (P < 0.01) higher in the posterior area than in other regions. BSE imaging corroborated basic histology results, with significantly (P < 0.01) higher mineralization levels detected in the hard-diet group. These findings indicate that diet consistency has a small but significant effect on the rate of bone deposition in the mandibular condyle.     

In situ hybridization and immunohistochemistry of bone sialoprotein and secreted phosphoprotein 1 (osteopontin) in the developing mouse mandibular condylar cartilage compared with limb bud cartilage

Mandibular condylar cartilage is often classified as a secondary cartilage, differing from the primary cartilaginous skeleton in its rapid progress from progenitor cells to hypertrophic chondrocytes. In this study we used in situ hybridization and immunohistochemistry to investigate whether the formation of primary (tibial) and secondary (condylar) cartilage also differs with respect to the expression of two major non‐collagenous glycoproteins of bone matrix, bone sialoprotein (BSP) and secreted phosphoprotein 1 (Spp1, osteopontin). The mRNAs for both molecules were never expressed until hypertrophic chondrocytes appeared. In the tibial cartilage, hypertrophic chondrocytes first appeared at E14 and the expression of BSP and Spp1 mRNAs was detected in the lower hypertrophic cell zone, but the expression of BSP mRNA was very weak. In the condylar cartilage, hypertrophic chondrocytes appeared at E15 as soon as cartilage tissue appeared. The mRNAs for both molecules were expressed in the newly formed condylar cartilage, although the proteins were not detected by immunostaining; BSP mRNA in the condylar cartilage was more extensively expressed than that in the tibial cartilage at the corresponding stage (first appearance of hypertrophic cell zone). Endochondral bone formation started at E15 in the tibial cartilage and at E16 in the condylar cartilage. At this stage (first appearance of endochondral bone formation), BSP mRNA was also more extensively expressed in the condylar cartilage than in the tibial cartilage. The hypertrophic cell zone in the condylar cartilage rapidly extended during E15–16. These results indicate that the formation process of the mandibular condylar cartilage differs from that of limb bud cartilage with respect to the extensive expression of BSP mRNA and the rapid extension of the hypertrophic cell zone at early stages of cartilage formation. Furthermore, these results support the hypothesis that, in vivo, BSP promotes the initiation of mineralization.     

Visualization of 3D osteon morphology by synchrotron radiation micro-CT

Cortical bone histology has been the subject of scientific inquiry since the advent of the earliest microscopes. Histology - literally the study of tissue - is a field nearly synonymous with 2D thin sections. That said, progressive developments in high-resolution X-ray imaging are enabling 3D visualization to reach ever smaller structures. Micro-computed tomography (micro-CT), employing conventional X-ray sources, has become the gold standard for 3D analysis of trabecular bone and is capable of detecting the structure of vascular (osteonal) porosity in cortical bone. To date, however, direct 3D visualization of secondary osteons has eluded micro-CT based upon absorption-derived contrast. Synchrotron radiation micro-CT, through greater image quality, resolution and alternative contrast mechanisms (e.g. phase contrast), holds great potential for non-destructive 3D visualization of secondary osteons. Our objective was to demonstrate this potential and to discuss areas of bone research that can be advanced through the application of this approach. We imaged human mid-femoral cortical bone specimens derived from a 20-year-old male (Melbourne Femur Collection) at the Advanced Photon Source synchrotron (Chicago, IL, USA) using the 2BM beam line. A 60-mm distance between the target and the detector was employed to enhance visualization of internal structures through propagation phase contrast. Scan times were 1 h and images were acquired with 1.4-μm nominal isotropic resolution. Computer-aided manual segmentation and volumetric 3D rendering were employed to visualize secondary osteons and porous structures, respectively. Osteonal borders were evident via two contrast mechanisms. First, relatively new (hypomineralized) osteons were evident due to differences in X-ray attenuation relative to the surrounding bone. Second, osteon boundaries (cement lines) were delineated by phase contrast. Phase contrast also enabled the detection of soft tissue remnants within the vascular pores. The ability to discern osteon boundaries in conjunction with vascular and cellular porosity revealed a number of secondary osteon morphologies and provided a unique 3D perspective of the superimposition of secondary osteons on existing structures. Improvements in resolution and optimization of the propagation phase contrast promise to provide further improvements in structural detail in the future.     

Lateral pterygoid muscle: a three-dimensional analysis of neuromuscular partitioning

The lateral pterygoid (LP) has been implicated in temporomandibular joint (TMJ) pathology. Few studies have examined muscle architecture of the superior (SLP) and inferior (ILP) heads of LP; moreover, the pattern of intramuscular innervation is poorly defined. The purpose of this study was to determine patterns of intramuscular innervation of LP using 3D modeling. The superior and lateral aspects of LP were exposed in 10 embalmed cadaveric specimens. Nerves entering the muscle, all branches of the mandibular nerve (V₃), were followed intramuscularly in short segments and sequentially digitized. Muscle volume, surrounding bone, and the TMJ disc were also digitized. The data were reconstructed into 3D models (Maya®) that were used to determine patterns of intramuscular innervation. It was found that the SLP had independent sources of innervation to each of the quadrants in its superior part (masseteric/posterior deep temporal/middle deep temporal/buccal) and one primary source of innervation (buccal) to the quadrants of the inferior part. This difference in innervation is significant as the superior part attaches to the TMJ disc‐capsule complex, whereas the inferior part attaches to the mandibular condylar neck. Differing sites of attachment and sources of innervation for each part suggests that movement of the TMJ disc‐capsule complex, independent of the condyle, may be possible. The buccal nerve supplied both the medial and lateral quadrants of the ILP, with the medial quadrants receiving additional innervation from V₃ muscular branches. Results of this study could be used to direct EMG/ultrasound studies of LP function as related to TMJ disorders. Clin. Anat. 25:576–583, 2012. © 2011 Wiley Periodicals, Inc.     

Phenotypic switching of in vitro mandibular condylar cartilage during matrix mineralization

In order to analyze the phenotypic conversion of chondrocytes, mandibular condyles of mice and rabbits were cultured under cell and organ culture systems, and then examined by a combination of morphological and biochemical procedures. In organ culture, mandibular condylar cartilage (MCC) obtained from newborn mice began to mineralize from the central zone and then progressively widened towards the peripheral zone. Electron microscopic observations showed that with the increasing duration of the organ culture, chondrocytes at the central zone converted into spindle-shaped osteoblastic cells accompanying the formation of the bone type of thick-banded collagen fibrils. To obtain a better understanding of the chondrocytic conversion, immunolocalizations for type I and type X collagens and osteocalcin (OC) were examined in mouse MCC cells in cell culture. Type X collagen and OC were expressed almost simultaneously at the late stage of culture, and type I collagen was detected along the calcified nodues after the production of these proteins. Northern blot analysis in cell cultures of rabbit MCC indicated that type II collagen and alkaline phosphatase (ALPase) messenger ribonucleic acids (mRNAs) were highly expressed at day 7, but subsequently decreased. In contrast, mRNA for type I collagen was expressed at a low level on day 7 and peaked on day 12. The present results suggest that, morphologically and biochemically, cellular modification in MCC cells under culture conditions occurs at a cellular morphological level and also at marker-gene-expression level.     

The effects of immobilization on vascular canal orientation in rat cortical bone

It is well established that bone is capable of adapting to changes in loading; however, little is known regarding how loading specifically affects the internal 3D microarchitecture of cortical bone. The aim of this study was to experimentally test the hypothesis that loading is a determinant of the 3D orientation of primary vascular canals in the rat tibial diaphysis. Left tibiae from 10 rats (30 weeks old) that had been immobilized (sciatic neurectomy) for 27 weeks, right SHAM-operated tibiae from these same rats (internal control) and right tibiae from 10 normal age-matched rats (external control) were scanned by micro-CT. Mean canal orientation (for the whole bone segment and by region), percent porosity, canal diameter and canal separation were quantitatively assessed in 3D. Canal orientation in the immobilized tibiae was significantly (P < 0.001) more radial (by 9.9°) compared to the external controls but did not differ from the internal controls (P = 0.310). Comparing the external and internal controls, orientation was significantly (P < 0.05) more radial in the internal control group (by 6.8°). No differences were found for percent porosity and canal separation. Canal diameter was significantly greater in the immobilized vs. internal (P < 0.001) and external control (P < 0.001) tibiae. The differences in orientation relative to the external controls indicated that the organization of cortical bone in the rat is affected by loading. Although the predicted difference in canal orientation was not detected between immobilized and internal control groups, the distributions of individual canal orientations, from which the mean values were derived, revealed distinctive patterns for all three groups. The internal controls exhibited an intermediate position between the immobilized and external controls, suggesting that paralysis on the contralateral side resulted in altered loading relative to the normal state represented by the external control. This was also evident in a regional analysis by quadrant. The loaded bones had the same cross-sectional shape; however, their internal structure differed. These results provide novel insights into the impact of loading on the 3D organization of primary cortical bone and have implications for understanding the relation between cortical bone adaptation, disease and mechanical properties.     

Histological and histomorphometric investigation of the condylar cartilage of juvenile pigs after anterior mandibular displacement

The condylar cartilage of the mandible is considered a secondary growth center and represents a joint cartilage different from other cartilage structures regarding its histological structure, its histochemical and immunohistochemical properties and its growth pattern. This study aimed to histologically and histomorphometrically investigate the condylar cartilage after anterior mandibular displacement similar to functional orthopedic treatment. A total of 12 pigs (sus scrofa domesticus) aged 10 weeks were divided into an experimental group and a control group comprising 6 animals each. The experimental animals were provided bilaterally with synthetic occlusal build-ups in the posterior area which induced anterior displacement of the mandible in terminal occlusion. After 4 weeks, the temporomandibular structures were removed en bloc and the condylar cartilage was analyzed histologically and histomorphometrically. As a result, the experimental animals displayed a significantly increased total cartilage thickness of the posterocranial mandibular condyle which was primarily caused by an increase in thickness of the hypertrophic and chondogenic layers. Similarly, the proliferative layer showed a significant increase, whereas significant differences in thickness were absent in the articular layer. Increased cell proliferation was not observed in the experimental animals as compared to the controls. The changes found in the condylar cartilage area suggest that the zonal structure of the condylar cartilage may be modified by an altered spatial relationship between the mandibular condyle and the glenoid fossa.     

Positional relationships between the masticatory muscles and their innervating nerves with special reference to the lateral pterygoid and the midmedial and discotemporal muscle bundles of temporalis

For an accurate assessment of jaw movement, it is crucial to understand the comprehensive formation of the masticatory muscles with special reference to the relationship to the disc of the temporomandibular joint. Detailed dissection was performed on 26 head halves of 14 Japanese cadavers in order to obtain precise anatomical information of the positional relationships between the masticatory muscles and the branches of the mandibular nerve. After complete removal of the bony elements, the midmedial muscle bundle in all specimens and the discotemporal muscle bundle in 6 specimens, derivatives of the temporalis, which insert into the disc were observed. On the anterior area of the articular capsule and the disc of the temporomandibular joint, the upper head of the lateral pterygoid, the midmedial muscle bundle of temporalis and the discotemporal bundle of temporalis were attached mediolaterally, and in 3 specimens the posterosuperior margin of the zygomaticomandibularis was attached to the anterolateral area of the disc. It is suggested that these muscles and muscle bundles contribute to various mandibular movements. Although various patterns of the positional relationships between the muscles and muscle bundles and the their innervating nerves are observed in the present study, relative positional relationships of the muscles and muscle bundles and of nerves of the mandibular nerve are consistent. A possible scheme of the developmental formation of the masticatory muscles based on the findings of the positional relationships between the muscles and the nerves is presented.     

Effect of Food Consistency on the Degree of Mineralization in the Rat Mandible

A switch to a soft diet, associated with reduced forces applied to the mandible during mastication, may result in an alteration of the degree of mineralization in the mandible. This alteration may be regionally different. The aim of this study was to analyze this alteration by examination of the degree of mineralization in the mandible of growing rats fed with a hard or soft diet. Fifteen Wistar male rats were used in this investigation. After weaning, six rats were fed with a hard diet and the remaining nine rats with a soft diet. After 9 weeks, three-dimensional reconstructions of the cortical and trabecular bone of their mandibles were obtained using a microCT system. The degree of mineralization was determined for the trabecular bone in the condyle and for the cortical bone in the anterior and posterior areas of the mandibular body. In both diet groups the degree of mineralization was significantly (p < 0.01) lower in the trabecular than in the cortical bone. In the mandibular body, the anterior area showed a significantly (p < 0.01) higher degree of mineralization than the posterior area in both diet groups. In both areas the soft diet group had a significantly (p < 0.05 or 0.01) higher degree of mineralization than the hard diet group. The trabecular bone in the condyle of the hard diet group showed a significantly (p < 0.01) higher degree of mineralization than in the soft diet group. The present results indicate the importance of proper masticatory muscle function for craniofacial growth and development.     

The Influence of Mineralization on Intratrabecular Stress and Strain Distribution in Developing Trabecular Bone

The load-transfer pathway in trabecular bone is largely determined by its architecture. However, the influence of variations in mineralization is not known. The goal of this study was to examine the influence of inhomogeneously distributed degrees of mineralization (DMB) on intratrabecular stresses and strains. Cubic mandibular condylar bone specimens from fetal and newborn pigs were used. Finite element models were constructed, in which the element tissue moduli were scaled to the local DMB. Disregarding the observed distribution of mineralization was associated with an overestimation of average equivalent strain and underestimation of von Mises equivalent stress. From the surface of trabecular elements towards their core the strain decreased irrespective of tissue stiffness distribution. This indicates that the trabecular elements were bent during the compression experiment. Inhomogeneously distributed tissue stiffness resulted in a low stress at the surface that increased towards the core. In contrast, disregarding this tissue stiffness distribution resulted in high stress at the surface which decreased towards the core. It was concluded that the increased DMB, together with concurring alterations in architecture, during development leads to a structure which is able to resist increasing loads without an increase in average deformation, which may lead to damage.     

Fetal developmental change in topographical relationship between the human lateral pterygoid muscle and buccal nerve

In adults, the lateral pterygoid muscle (LPM) is usually divided into the upper and lower heads, between which the buccal nerve passes. Using sagittal or horizontal sections of 14 fetuses and seven embryos (five specimens at approximately 20-25 weeks; five at 14-16 weeks; four at 8 weeks; seven at 6-7 weeks), we examined the topographical relationship between the LPM and the buccal nerve. In large fetuses later than 15 weeks, the upper head of the LPM was clearly discriminated from the lower head. However, the upper head was much smaller than the lower head in the smaller fetuses. Thus, in the latter, the upper head was better described as an 'anterior slip' extending from the lower head or the major muscle mass to the anterior side of the buccal nerve. The postero-anterior nerve course seemed to be determined by a branch to the temporalis muscle (i.e. the anterior deep temporal nerve). At 8 weeks, the buccal nerve passed through the roof of the small, fan-like LPM. At 6-7 weeks, the LPM anlage was embedded between the temporobuccal nerve trunk and the inferior alveolar nerve. Therefore, parts of the LPM were likely to 'leak' out of slits between the origins of the mandibular nerve branches at 7-8 weeks, and seemed to grow in size during weeks 14-20 and extend anterosuperiorly along the infratemporal surface of the prominently developing greater wing of the sphenoid bone. Consequently, the topographical relationship between the LPM and the buccal nerve appeared to 'change' during fetal development due to delayed development of the upper head.     

In situ hybridisation study of type I, II, X collagens and aggrecan mRNAs in the developing condylar cartilage of fetal mouse mandible

The aim of this study was to investigate the developmental characteristics of the mandibular condyle in sequential phases at the gene level using in situ hybridisation. At d 14.5 of gestation, although no expression of type II collagen mRNA was observed, aggrecan mRNA was detected with type I collagen mRNA in the posterior region of the mesenchymal cell aggregation continuous with the ossifying mandibular bone anlage prior to chondrogenesis. At d 15.0 of gestation, the first cartilaginous tissue appeared at the posterior edge of the ossifying mandibular bone anlage. The primarily formed chondrocytes in the cartilage matrix had already shown the appearance of hypertrophy and expressed types I, II and X collagens and aggrecan mRNAs simultaneously. At d 16.0 of gestation, the condylar cartilage increased in size due to accumulation of hypertrophic chondrocytes characterised by the expression of type X collagen mRNA, whereas the expression of type I collagen mRNA had been reduced in the hypertrophic chondrocytes and was confined to the periosteal osteogenic cells surrounding the cartilaginous tissue. At d 18.0 of gestation before birth, cartilage-characteristic gene expression had been reduced in the chondrocytes of the lower half of the hypertrophic cell layer. The present findings demonstrate that the initial chondrogenesis for the mandibular condyle starts continuous with the posterior edge of the mandibular periosteum and that chondroprogenitor cells for the condylar cartilage rapidly differentiate into hypertrophic chondrocytes. Further, it is indicated that sequential rapid changes and reductions of each mRNA might be closely related to the construction of the temporal mandibular ramus in the fetal stage.     

以串连血管为蒂的股骨外侧髁骨(膜)瓣的应用解剖

目的：为治疗股骨干骨不连、骨缺损提供一种新的骨（膜）瓣供区。方法：在５０侧成人下肢标本上,解剖观察了膝上外侧动脉的起始、走行、分支分布及其与旋股外侧动脉降支的吻合类型。结果：膝上外侧动脉于股骨外侧髁上方（２．５ ± ０．５）ｃｍ处起自于腘动脉外侧壁,分出升支、横支和降支。升支和／或横支与旋股外侧动脉降支有 ３种类型的吻合,吻合率为 ９２％（４６侧）,吻合处外径为（１．３ ± ０．３）ｍｍ。结论：以旋股外侧动脉降支与膝上外侧动脉升支和／或横支串连为蒂可截取股骨外侧髁骨（膜）瓣用于修复股骨干骨不连及骨缺损。     

应用Micro CT测量下颌第二磨牙牙根尖到颊侧骨板的距离

目的运用Micro CT技术测量牙根尖到颊侧骨板的解剖距离。方法应用Micro CT(Skyscan 1072,Antwerpen,Belgium)及cutome计算机软件分析三维骨结构。结果下颌第二磨牙,近中根和远中根到颊侧骨板的距离平均为5.18mm和4.09mm。上颌骨的颊根中,上颌第二磨牙近中颊根和远中颊根到颊侧骨板的距离最大,分别是4.63mm和3.61mm。结论Micro CT是一种快速、准确、不损伤样本内部结构有效的评价方法。     

Mineralization of ground substance of new bone tissue in mouse marrow organ cultures

Laboratory of Immunomorphology, N. F. Gamaleya Research Institute of Epidemiology and Microbiology, Academy of Medical Sciences of the USSR, Moscow. Laboratory of Medical Biophysics, Institute of Chemical Physics, Academy of Sciences of the USSR, Moscow. (Presented by Academician of the Academy of Medical Sciences of the USSR S. V. Prozorovskii.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 106, No. 11, pp. 614–616, November, 1988.