Histopathological and immunohistochemical aspects of bone tissue in aseptic necrosis of the femoral head

Abstract

Femoral head osteonecrosis, also known as avascular necrosis, is a disease with a multifactorial etiology, characterized by a profound change of bone architecture, which leads to the diminishing of bone resistance and femoral head collapse. The main causes that lead to femoral head necrosis are represented by the decrease of local blood perfusion and increase of intraosseous pressure, because of an excessive development of adipose tissue in the areolas of the trabecular bone tissue in the femoral head. The histopathological and immunohistochemical (IHC) study performed by us showed that most of bone trabeculae were damaged by necrotic-involutive processes, their sizes being reduced, both regarding their length and their diameter; generally, the spans were thin, fragmented, distanced among them, which led to the occurrence of some large areolar cavities, full of conjunctive tissue, rich in adipocytes. Some of the residual bone spans even presented microfractures. In the structure of the trabecular bone tissue, numerous cavities showed lack of content, which indicates the death of osteocytes inside, while the endosteum appeared very thin, with few osteoprogenitor, flattened, difficult to highlight cells. The IHC study showed a low reaction of the bone reparatory processes and a reduced multiplication capacity of bone cells involved in the remodeling and remake of the diseased bone tissue. Nevertheless, there were identified numerous young conjunctive cells (fibroblasts, myofibroblasts), positive to proliferating cell nuclear antigen (PCNA), cells that have a high capacity of multiplication, participating in the formation of a fibrous conjunctive tissue (sclerous) instead of the damaged bone trabeculae. The formation of fibrous conjunctive tissue causes the reduction of mechanical resistance of the femoral head and its collapse. The IHC study of the microvascularization in the femoral head damaged by aseptic osteonecrosis showed the presence of a very low vascular system, both in the residual bone trabeculae and in the sclerous conjunctive tissue. Of the inflammatory cells present in the spongy bone tissue of the femoral head affected by osteonecrosis, the most numerous ones were the macrophages. Both macrophages and T- and B-lymphocytes had a heterogenous distribution.

Figure 1

Area of bone acellular necrosis with a heterogenous aspect and residual bone spans inside (HE staining, ×100). HE: Hematoxylin–Eosin

Figure 2

Microscopic image of trabecular bone from the femoral head, where we may observe the reduction of the number and sizes of bone spans (HE staining, ×40)

Figure 3

Image of isolated, deformed bone trabeculae, with intratrabecular microfractures (HE staining, ×40)

Figure 4

Trabecular bone tissue with numerous empty bonne cavities, because of the death of osteocytes inside (HE staining, ×200).

Figure 5

Overall image of a bone trabeculae where we may observe the heterogenous aspect of the bone and the presence of a low number of osteocytes (GS trichrome staining, ×40). GS: Goldner–Szekely

Figure 6

Image of an area in a trabeculae where there may be observed an almost complete demineralization of the bone tissue and the expression of collagen fibers in the structure of bone blades (GS trichrome staining, ×400)

Figure 7

Area of endosteum with large, hypertrophied, reactive osteoprogenitor cells, specific to areas of bone restoration (HE staining, ×400)

Figure 8

Microscopic image of an isolated bone trabeculae, with a negative reaction of the component osteocytes to anti-PCNA antibody. In the endosteum, there are observed rare cells with a poor positive reaction to anti-PCNA antibody (Immunomarking with anti-PCNA antibody, ×200). PCNA: Proliferating cell nuclear antigen

Figure 9

Fragment of bone tissue with numerous osteoprogenitor cells from the endosteum intensely reactive to anti-PCNA antibody, proving an intense mitotic capacity (Immunomarking with anti-PCNA antibody, ×200)

Figure 10

Conjunctive cells with an intense reaction to anti-PCNA antibody, part of them being transformed into osteoblasts, thus proving their osteotransforming capacity (Immunomarking with anti-PCNA antibody, ×200)

Figure 11

Image of fibrous tissue developed in the necrosis and restoration areas of the bone tissue, rich in fibroblasts, with an intense reaction (+++) to anti-PCNA antibody (Immunomarking with anti-PCNA antibody, ×200)

Figure 12

Myofibroblasts present in a moderate number in the restored conjunctive tissue of the femoral head (Immunomarking with anti-α-SMA antibody, ×200). α-SMA: Alpha-smooth muscle actin

Figure 13

Image of sclerous tissue from the femoral head with rare blood vessels (Immunomarking with anti-CD34 antibody, ×100). CD34: Cluster of differentiation 34

Figure 14

Fibroadipose areolar tissue with low vascularization (Immunomarking with anti-CD34 antibody, ×100)

Figure 15

Immunohistochemical image where we can observe the presence of many foamy cytoplasm cells, specific to macrophages, identified at the edge of the avascular necrosis area (Immunomarking with anti-CD68 antibody, ×200). CD68: Cluster of differentiation 68

Figure 16

Image of fibro-adipose tissue from the bone areoles with a low number of macrophages (Immunomarking with anti-CD68 antibody, ×200)

Figure 17

Abundant inflammatory infiltrate, mostly formed of T-lymphocytes, present in a fibro-adipose area from the spongy tissue areoles affected by aseptic necrosis, arranged mainly perivascularly (Immunomarking with anti-CD3 antibody, ×200). CD3: Cluster of differentiation 3

Figure 18

Fibro-sclerous conjunctive tissue resulting from the restoration of the necrosed bone tissue, where we may observe the presence of a low number of T-lymphocytes (Immunomarking with anti-CD3 antibody, ×200)

Figure 19

Abundant perinecrotic inflammatory infiltrate with a nodular organization, mainly formed of B-lymphocytes (Immunomarking with anti-CD20 antibody, ×200). CD20: Cluster of differentiation 20

Figure 20

Area of areolar, perinecrotic conjunctive tissue, diffusely infiltrated with B-lymphocytes (Immunomarking with anti-CD20 antibody, ×200)