Federal Scientific Clinical Center of Miners’ Health Protection,

 Leninsk-Kuznetsky, Russia

 

The femoral head (caput ossis femoris) is the proximal femoral epiphysis participating in formation of hip joint. Articular surface of the head is covered with hyaline cartilage layer. The bone tissue structure in the femoral head is directly conditioned by its functional features associated with significant load. The bone rods of spongy substance are located in concordance with direction of compression and tension forces and are characterized with strict geometric structure [1].

The femur head solidity is non-uniform in the different locations. The maximal solidity is in its central part (0.6-1.2 kgf/mm²). The lowest solidity is associated with spongy substance in the subchondral departments (0.42-0.75 kgf/mm²) [2].

According to our opinion, the maximal solidity in the central part of the femoral head is related to appearance of primary points (centers) of ossification during 2^th-8^th months of life and hydroxyapatite initiation during osteogenesis of enchondral type [3-5].

For supporting structure and saving possibility for realization of the functions in the femur head tissue the remodeling processes are constant and consist of resorption of “old” tissue and synthesis of new one, considering the functional adaptation. So, after age of 20 during one year of life only 3 % of cortical tissue and 25 % of spongy bone tissue regenerate [6].

The disorders of balance in the gentle remodeling system are one of the causes leading to development of different pathologic states in bone tissue, including coxarthrosis development [7]. In patients with coxarthrosis the changes in mineral metabolism are characterized with decreasing calcium, phosphorus and hormonal activity (calcitonin, somatotropic hormone) at the background of constant level of parathormone in the blood serum. It testifies decrease in bone matrix synthesis and salvation of bone tissue resorption processes [8].

Coxarthrosis has a great influence on patient’s quality of life. It is one of the main causes of temporary or persistent incapacitation. According to the modern opinions, osteoarthrosis is considered as heterogenic group of diseases of different etiology, but with basic biologic, morphologic and clinical outcomes, with pathologic involvement of both cartilage tissue and all joint structures [9].

At the present time the descriptive characteristics of round ligament, articular surface, femoral subchondral departments and chemical composition of spongy substance are investigated closely. Conversely, there is no enough information about comparative morphometric characteristics of femoral head bone tissue in the normal state and in coxarthrosis [10, 11].

Objective ‒ to give comparative assessment of morphometric values of femoral head bone tissue structure in coxarthrosis and without it.

 

MATERIALS AND METHODS

The study includes 16 patients with clinical diagnosis of coxarthrosis of degrees III-IV (mean age of 53.0 ± 3) who were admitted to the department of traumatology and orthopedics in Scientific Clinical Center of Miners’ Health protection and received hip joint endoprosthetics. The duration of disease was 9.5 ± 3.94 years. The morphologic study included 16 femoral heads which were removed during hip joint endoprosthetics. The heads were transported from the operating room to the histology laboratory of the anatomic pathology department in Clinical Center of Miners’ Health Protection.

The exclusion criteria were evident deformation of the femoral head, cysts and posttraumatic etiology of coxarthrosis.

The comparison group included 10 died patients who were prosected in the pathologic anatomy department during 2010-2013. Their histories were used for examination of absence of hip joint diseases. The morphologic study subjects were 10 femoral heads from the dead patients. The mean age was 57 ± 5.6. This group included the materials with macroscopically unchangeable articular surface and absent bone deformation.

From the given materials, according to a method described in the literature [12], three  bone tissue fragments were sawed out, with their volume of 0.75 cm³ (1.5 x 1.0 x 0.5 cm) and the marks (I ‒ articular surface, II ‒ middle department, III ‒ in-depth department of the head). Then the samples were fixed in 10 % formaline and were prepared in electrolytic decalcificator (Medax, Germany). After decalcification the histological preparation was performed with placement into wax. The serial histological sections (4-6 sections from one fragment), 5-6 µm in thickness, were prepared on the sliding microtome (MS-2, Russia) and stained with hematoxylin-eosin and hematoxylin-picrofuxin (according to Van-Gison) [13]. The study was performed with the optical microscope (Biomed-6, Russia) with using a camera (Panasonic DMC-LS80). The special software (PhotoM, Russia) was used for measuring thickness in the bone rods and their square in histological sections of marked parts.                                 

The statistical analysis was performed with Statistica 6.0. The normalcy of distribution of the qualitative data was tested with Kolmogorov-Smirnov's test. In case of statistically significant values the null hypothesis about concordance of analyzed data to the normal probability law was rejected. The data is presented as Me (LQ-UQ), with Me ‒ median, (LQ-UQ) – interquartile range. For identification of intergroup differences in quantitative values the non-parametric Mann-Whitney and Kruskal-Wallis tests were used. The differences were statistically significant with p < 0.05 [14].

 

RESULTS AND DISCUSSION

The histological study of the samples from the comparison group showed the uniform thickness of cartilage tissue in articular surface with salvation of all regions: cell free, superficial, transitional, region of isogenous group, column region, region of hypertrophic cells and region of calcification (Fig. 1). In all three examined femoral head parts the spongy substance consists of continuously connected boned rods, which form the closed voids ‒ lacunes.

Figure 1

Articular surface of the femur head. Staining with hematoxylin-eosin, õ50  

 

In the lacunes of superficial and middle parts the bone marrow with low amount of fat tissue is identified. The deep lacunes are free from the bone marrow and include insignificant amount of fat tissue. There no identified fibrous tissue spreading (Fig. 2).

Figure 2

The femur head bone tissue in superficial (a), middle (b) and deep (c) regions in the comparison group. Staining with hematoxylin-eosin, õ100  

 

The morphometric examination of the femoral head samples in the comparison group and the femoral heads with coxarthrosis yielded the results, which demonstrate the cartilage tissue thickness in articular surface, the thickness of the bone rods and their square in all examined locations (table 1).

Table
The morphometric indices of bone tissue structure in the examined groups (Ìå (LQ –UQ))

Index	Femur heads with coxarthrosis (n = 16)	Comparison group (n = 10)
Articular surface thickness, µm	722.14 (656.55–887.16) *	1156.097 (1094.69–1225.52)
Bone rod thickness in region I, µm	270.22 (209.28–329.98)	229.391 (227.52–231.71)
Bone rod thickness in region II, µm	265.34 (232.43–299.15) *	226.945 (219.25–237.53)
Bone rod thickness in region III, µm	230.43 (181.39–283.25) *	158.64 (156.41–160.64) a, b
Bone rod square in region I, %	42.63 (38.88–49.49)	44.191 (42.62–46.28)
Bone rod square in region II, %	33.98 (31.27–38.4) *	42.368 (39.85–43.47)
Bone rod square in region III, %	28.13 (22.96–32.48) 1, 2, *	33.083 (32.61–34.25) a, b

In the comparison group the examination of the above mentioned values showed the decrease in bone rod thickness by 30 % in the department III compared to the departments I and II, but the square of bone rods in the department III is 25 % lower than in the department I and 22 % lower than in the department II. There were no statistically significant differences between the thickness and the square of bone rods in the departments I and II. Despite of lower thickness and the square of bone rods in the deep part of a healthy femoral bone, the mechanical strength is insufficient for supporting normal functioning that may be related to its qualitative composition by means of saved remodeling processes.

The morphologic examination of femoral head bone tissue with coxarthrosis showed non-uniform thickness of articular surface in different parts. It is manifested with disordered stratification and architectonics in chondrocyte groups, different expressiveness of fibrous tissue spreading, locations of cartilage fragmentation and different ability to color receptivity (Fig. 3). In the subchondral departments of bone tissue the sites of chondrogenesis are identified. The main and the most interesting process was fibrosis (of different degrees) in bone lacunes in subchondral departments of spongy substance (Fig. 4).

Figure 3

Articular surface of the femur head in coxarthrosis. Staining with hematoxylin-eosin, õ50

Figure 4

The subchondral department of the femur head bone tissue in coxarthrosis. Staining with hematoxylin-eosin, õ100

 

The obtained histological picture does not contradict to earlier investigations and testifies degenerative dystrophic changes in bone and cartilage tissues in the examined samples [15].

The performed morphometric studies showed the absence of statistically significant differences in all three examined regions of the femoral head bone tissue with coxarthrosis. The bone rod square was 34 % lower in the department III compared to the department I, and 17 % lower than in the department II. It testifies the prevailing resorption processes over synthesis in this region.

The results of comparative analysis of morphometric values of femoral head bone tissue structure with coxarthrosis and without it showed that the thickness of articular surface in arthrosis femoral head was 37.5 % lower than in the comparison group. The thickness of bone rods in the department II with coxarthrosis is 14 % higher, and in the department III ‒ 31 % higher than in the comparison group. The square of bone rods in the department II is 20 % lower, and 15 % lower in the department III compared to the comparison group.

CONCLUSION

In coxarthrosis the morphometric values of bone tissue are characterized with decreasing square of bone rods, despite of increasing thickness.  It testifies predominance of resorption processes over synthesis in bone tissue. The predominance of resorption processes is also confirmed by disordered integrity of bone lacunes that result in decreasing mechanical strength in arthrosis femur head.

One can use the evaluation of such morphometric values as thickness in bone rods and their square in different femur head parts with coxarthrosis for assessment of remodeling processes in bone tissue.