Federal Scientific Clinical Center of Miners’ Health Protection, 

Leninsk-Kuznetsky, Russia

 

Osteoarthrosis (OA) is the most common joint pathology resulting in significant worsening patients’ quality of life and is one of the main causes of temporary and persistent loss of function with disability in 11-38 % of the cases, with continuous trend to increasing these values [2]. OA is noted in each 3rd patient at the age of 45-64 and in 60-70 % of patients older 65, with men to women ratio 1:3, and 1:7 for hip joint OA. It is expected that the incidence of the disease will double by 2020. Hip joint OA (coxarthrosis) is the most common and severe type of OA with features of degeneration in articular cartilage with subsequent changes in subchondral bone [12] resulting in progressing disorders in joint function right up to full loss.

According to the modern concepts, OA is considered as the heterogenetic group of diseases of different etiology, but with similar clinical, pathogenetic and histopathologic manifestations [13, 14].

According to the literature data, the main and the most common cause of coxarthrosis is dysplasia (90 %), i.e. inborn disorder of normal anatomic shape of joint-forming ends of the bones and other tissues of the joint [7, 16, 43].

Posttraumatic coxarthrosis is the separate disease according to its etiology [9]. The cause of development of posttraumatic coxarthrosis is single-step or chronical injuries causing impression of bone structures, subchondral plate and spongious bone tissue. Unilateral lesion of the hip joint is the sign of posttraumatic coxarthrosis in most cases that accompanied by anamnesis data.

Aseptic necrosis of the femoral head (ANFH, avascular necrosis) is one of the causes of deforming arthrosis of the hip. ANFH is the disease of pluricausal genesis. Its pathologic process is the result of disordered perfusion in the epiphysis with following necrosis of elements of the bone marrow and bone tissue of the femoral head [15].

Idiopathic coxarthrosis is the disease of the hip with unknown pathology [31, 40].

The histopathologic features of bone tissue of the femoral head in deforming arthrosis

The modern literature describes the histopathologic signs of the articular surface and bone tissue of the femoral head in deforming arthrosis.

The Osteoarthritis Research Society International (OARSI) [11] offered the system for estimating histopathologic changes in articular hyaline cartilage with 6 stages. Pathologic changes in cartilaginous tissue of the joint appear from the superficial region with gradual spreading to deeper regions right up to full abrasion of the articular cartilage. The stage 0 is an intact state of the articular joint. The stage I presents unimpaired integrity of cartilage tissue of the articular surface, however with disappearance of lamina splendens. At the same time, chondrocytes demonstrate the signs of apoptosis, hypertrophy and proliferation. The stage II includes such changes as shallow crevices and horizontal dissociation within the superficial region of the cartilage. There are regions of insignificant thinning of the cartilage. The fibrillar component of the superficial region of the cartilage changes its structure of homogenous matrix to fibrous one. Dissociation of collagen fibers takes place and they become distinguishable. In the superficial region the fibers are located in parallel, and in the central region – perpendicularly to the articular surface. In the stage III the vertical crevices take the central region. Cartilaginous matrix fragments itself in a circumferential direction. Chondrocytes locate in chaotic order with formation of focal accumulations. The border of ossification zone is vague and even untraceable in some parts. At the stage IV of pathologic process the cartilaginous tissues has microvilli, which incidentally branch into the joint cavity. The villi have viable chondrocytes. The superficial part and the part of deep region disappear. The thickness of the cartilage decreases gradually. At the stage V the pathologic process involves the subchondral bone. It is characterized by chaotic location of thinning bone rods with unclear borders and fibrosis in the interred space. Also there are the groups of osteoclasts making bone resorption. In the regions without cartilaginous tissue the subchondral bone thickens and obtains compact cancellous structure. The stage VI of OA is characterized with different degrees of expression of deformation in the articular surfaces and activity of processes of bone remodeling. This stage includes absence of cartilaginous tissue within significant length or in view of separate regions, or in view of extensive regions, exposure of the subchondral bone with its sclerotic rebuilding, rapid thickness and development of cystic cavities in the spongy substance.

This classification is sufficiently informative, available, universal and it decreases misunderstanding between different specialties. However it was developed for osteoarthrosis without consideration of functional features of the specific joint. Considering the anatomic and functional features of the hip joint [3], the morphologic structure of the femoral head has its own specific features in coxarthrosis.

For deforming arthrosis of the hip the range of general histopathologic signs, which characterize intensity of dystrophic and necrotic changes in the articular cartilage, has been described. It manifests itself in view of thinning, dissociation and fragmentation of cartilaginous structures. The isogenous groups of chondrocytes lose their vertical orientation (normal hystoarchitectonics), and the cells are exposed to vacuolization and lysis (blebby chondrocytes) [23]. Interspatial regions of the cartilaginous tissue lose basophily and acquire oxyphilous color. Most chondrocytes are subjected to destructive changes in view of nuclear shrinking (karyopyknosis) and its destruction (karyorhexis). The histochemical composition of chondromucoid alters significantly. Acid glycosaminoglycans and proteoglycans disappear. In the regions of locally thinning and destructed cartilage the spongy fibrous tissue with rough collagenous fibers grows. The same epiphyseal regions contain macrophages, lymphocytes and plasmocytes. Such cells are arranged by groups along periphery of blood vessels of microcirculatory bed. The signs of agglomeration of formed elements, microthrombosis and injuries to endotheliocytes (swelling, vesiculation and desquamation) are noted in the microvascular lumen.

The subchondral bone includes the region of endochondral osteogenesis. This region shows focuses of complete and incomplete osteogenesis. Complete osteogenesis is characterized by presence of the plate of bone tissue separating the cartilaginous tissue from bone marrow structures with vessels and endotoast. Incomplete osteogenesis is identified in view of two structural variants: a – penetration of vessels from bone marrow into the articular cartilage with focuses of resorption of bone tissue, altered cartilaginous tissue and focuses of enchondral osteogenesis; b – preservation of cartilaginous tissue in adjacent bone rods of the region of enchondral osteogenesis, presence of new cartilaginous tissue in these regions [20].                                                                                                 

In the boundary parts of the femoral head the cartilaginous degenerative changes are combined with manifestations of neoosteogenesis. It results in development of bone growth – osteophytes. Applanation of the femoral head covered with bone fragments appears. The parts of reactive osteogenesis are subjected to destruction in the place of changed articular cartilage. Some rare individual regions contain persistent structures of new lamellar bone tissue alternating with small residual focuses of hyaline cartilaginous tissue with signs of calcification. Also here the fragments of low-differentiated connective and fibrous tissue are identified. Fibrous tissue can replace hyaline cartilage, but the thickness of such tissue is quite insignificant [1]. Besides general histopathologic signs of coxarthrosis, some other specific morphologic features of the femoral head structure in dependence on genesis of arthrosis were found. So, posttraumatic coxarthrosis was accompanied by tessellated pattern of histologic structure of the articular cartilage (regions of unchanged hyaline tissue alternate with regions of intense destructive and necrobiotic changes). The regions of destruction of the articular cartilage included cellular dissociation (discoupling) of the isogenous groups of chondrocytes with signs of karyopyknosis, karyorhexis and plasmorrhexis. The dense structured fibrous connective tissue is found in the regions of destruction of the cartilaginous plate [4].

The histologic analysis of the femoral heads from the patients with postischemic coxarthrosis showed that the cartilaginous plate is subjected to necrosis within the greater distance. Trabecules in subchondral region are thinner and less extensional because of absent processes of development of new bone tissue [21]. Also there is aseptic necrosis of fat tissue of bone lacunes, bone marrow and bone rods. Necrosis focuses are presented in view of homogenous eosinophilic masses without inflammatory infiltration in a circumferential direction. The process of necrosis is combined with new apposition growth of bone tissue [34], intense growth of fibrous tissue, fast unsmooth thinning of bone rods, sclerosis in vascular lumen, and sometimes vascular thrombosis, hypertrophy of adipose cells, sequestration of bone rods and multiple events of karyopyknosis in different cells as the sign of apoptosis [27, 35, 50].                                

In deforming arthrosis of dysplastic genesis the microscopic appearance of the femoral head is a sclerotic thickened subchondral bone plate having compact construction and including small focuses of cartilaginous and fibrous tissue. The trabecules of the subjacent spongy bone are also sclerotic and significantly thickened; the interred spaces contain fibroreticular tissue. The focuses of the bone marrow present only in the deeper parts of the head. The different parts of the tissues of the femoral head include small regions of necrosis in view of homogenous eosinophilic masses. The individual regions demonstrate the processes of cyst conversion into the regions of fat degeneration [8].       

Regardless of origin of the pathologic process, the morphometric indexes of bone tissue (in deforming coxarthrosis) are characterized with decreasing square of bone rods. It testifies predominance of the processes of resorption of bone tissue in comparison with its synthesis. The predominance of the resorption processes are also supported by disordered integrity of bone rods resulting in decreasing mechanical strength in the femoral head subjected to arthrosis [5, 6].    

The features of immunohistochemistry examination of bone tissue of the femoral head in deforming arthrosis  

The different immunohistochemical techniques for examination of bone tissue remodeling in the femoral head show significant predominance of resorption processes [10, 33].

The processes of bone tissue remodeling are closely interrelated and are the result of cellular influence of osteoblasts (OB) and osteoclasts (OC) initiating from the precursors of different cellular lines: OB – from mesenchymal stem cells, OC – from macrophage-monocytic cells of the bone marrow [36]. OB is a mononuclear cell participating in the process of formation and mineralization of the bone. Osteoblasts play the fundamental role in bone remodeling and regulation of cellular activity of other cells of bone tissue. OB release the number of the biological active compounds mediating the process of maturation of the precursor cell of OC transforming into the big multinuclear cell participating in resorption, i.e. resolution of bone tissue with only influence on the mineralized bone without changing bone tissue matrix [44]. Multiple research work supported the assumption that activation and regulation of bone tissue remodeling is a consequence of interrelation between OB and OC [26]. Maturation and differentiation of OB is realized by means of different specific factors influencing on the process of transcription. The most important factor is the protein Cbfa1 (core-binding factor alpha1) known as runt related transcription factor 2 (RUNX2), which decreased (with statistical reliability) in deforming arthrosis [17, 18, 41].          

Significant process in understanding the processes of bone remodeling was achieved with discovery of cytokine system RANKL-RANK-OPG [37, 45] playing the key role in formation, differentiation and functional activity of OC. The discovery of this system has become the keystone for understanding the pathogenesis of OA, osteoclastogenesis and regulation of bone resorption and other processes participating in local bone remodeling. Osteoclastogenesis is regulated mainly by means of two cytokines: receptor activator of nuclear factor kappa-B ligand (RANKL) and osteoprotegerin (OPG) [28]. RANKL is a glycoprotein produced by the cells of osteoblast group and activated T-lymphocytes. It relates to the superfamily of ligands of tumor necrosis factor (TNF) [30] and is the main impetus for maturation of OC. The molecular basis for intercellular interrelation with participation of RANKL-RANK-OPG system can be presented as follows: RANKL with expression on the surface of OB binds to RANK-receptor in the membranes of the precursor-cells of OC and induces the process of differentiation and activation of OC [24]. At the same time, stem cells of the bone marrow and OC release the factor stimulating formation of new colonies of macrophages. This polypeptide growth factor interrelates to high affinity transmembrane receptor (c-fms), activates intracellular thiokinase and stimulates the process of proliferation and differentiation of the precursor-cells of OC [38]. Osteoprotegerin is a soluble receptor for RANKL. It is synthesized by osteoblast cells, stroma cells, endothelial cells of the vessels and B-lymphocytes. It functions as endogenous decoy receptor for RANKL and blocks its relationship to the own receptor (RANK) and suppresses formation of the mature multinuclear cells of OC, disorders the process of osteoclastogenesis and activity of bone tissue resorption [25]. RANKL, which is synthesized and released by osteoblasts, is the specific factor obligatory for development and functioning of OC. RANKL relates to the tropic receptor RANK on the membrane of the precursor cell of OC. It results in intracellular cascade genome transformations.

Basing on the main mechanisms of osteogenesis, the estimation of the processes of remodeling in bone tissue became possible by means of immunohistochemistry technique.

The group of the scientists [39] conducted the study of expression of bone modifying protein of type 4 (BMP4) in the spongy substance of the femoral head, with identification of the levels in hip osteoarthrosis. The direct correlation was found between degree of intensity of expression of BMP4 and incidence of sclerosis.

As result of other research work [46] the statistically significant decrease in the levels of expression of vascular endothelial growth factor (VEGF) in the spongy substance of the OA femoral head was found. Thereby, the attention was given to such important manifestation of this pathologic process as hypoxia.

The great attention is given to apoptosis of osteoblasts in the bone tissue of the femoral head in deforming arthrosis [49]. In their research the scientists used TUNEL technique based on the identification of defragmented regions of DNA in apoptotic cells. These regions were identified with use of deoxynucleotidyl transferase (tdt), which connected the modified oligonucleotides (labeled with horseradish peroxidase) to free 3'ОН groups in the regions of DNA fragmentation. The developed persistent complexes were visualized with DAB-chromogene [22, 47]. According to the researchers’ opinion, the intensity of apoptosis was related to hypertrophy of fat cells of bone lacunes and inhibition of the processes of osteogenic differentiation of the stem cells [29].

The greatest interest is associated with the research works dedicated to investigation of activity of the main cells of the process of bone remodeling (OB and OC).

Yamaguchi et al. [48] used immunohistochemistry technique for estimation of OB and OC in the process of bone remodeling of the femoral head in OA. They found that the level of alkaline phosphatase (BAP) released by OB was significantly higher in the group of postischemic OA in comparison with OA of other origin, and the level of tartrate-resistant acid phosphatase 5b (TRAP-5b) released by OC was significantly lower.

Almost at the same time, the research group [19] conducted the study and received the absolutely contrary results. The researchers used the same techniques for estimation of activity of OB and OC in bone tissue of the femoral head. After estimation of expression of alkaline phosphatase (ALP) in osteoblasts and tartrate-resistant acid phosphatase 5b (TRAP-5b) in osteoclasts they noted decreasing levels of expression of alkaline phosphatase and increasing tartrate-resistant acid phosphatase.

 

CONCLUSION

The presented literature review includes the data about the features of the morphological structure and the processes of remodeling in bone tissue of the femoral head in deforming osteoarthrosis of different origin. Despite the fact that the main histopathologic characteristics of the femoral head in osteoarthrosis have been determined, the immunohistochemical features of remodeling processes have not been described to the full degree. Up to the present day we have no clear pathomorphological structure of deforming arthrosis of the hip with consideration of immunohistochemical status.