Application of design-based stereology for estimation of absolute volume and surface area of the articular and calcified cartilage compartments of undecalcified human femoral heads

Calcified cartilage differs in patients with end-stage primary osteoarthritis and secondary osteoarthritis due to rheumatoid arthritis of the hip joint

Objectives: Despite distinct aetiologies, the end-stages of primary osteoarthritis (OA) and secondary OA are described by common radiological features. However, the morphology of the bone-cartilage unit may differ depending on the pathogenesis. In this cross-sectional study, we aimed to investigate the histological differences in the bone-cartilage unit of the femoral head between patients with primary OA and secondary OA due to rheumatoid arthritis (RA).Method: Femoral heads were obtained from 12 patients with primary OA, six patients with secondary OA due to RA, and 12 control subjects. The femoral heads were investigated using stereological methods to ensure unbiased quantification.Results: The volume (mean difference [95% confidence interval]) (2.1 [0.5;3.8] cm³, p = 0.016) and thickness (413 [78.9;747] µm, p = 0.029) of the articular cartilage and the thickness of the calcified cartilage (56.4 [0.4;113] µm, p = 0.017) were larger in patients with primary OA than in patients with secondary OA due to RA. Femoral head volume (1.2 [-3.6;6.1] cm³, p = 0.598), bone volume fraction (-1.1 [-2.8;5.1] cm³, p = 0.553), subchondral bone thickness (-2.5 [-212;207] µm, p = 0.980), and osteophyte area (25.3 [-53.6;104] cm², p = 0.506) did not differ between patients.Conclusion: The thicker calcified cartilage in primary OA preceding the loss of articular cartilage can be attributed to endochondral ossification. Patients with secondary OA due to RA had severely thinner calcified cartilage as the pathogenesis is driven by inflammation and is characterized by a generalized and more severe loss of articular cartilage.

Calcified cartilage in patients with osteoarthritis of the hip compared to that of healthy subjects. A design-based histological study

OBJECTIVE

Calcified cartilage is suggested to be involved in the pathogenesis of osteoarthritis (OA) by facilitating endochondral ossification at the bone-cartilage unit. Therefore, the objective was to quantify the volume and surface area of the calcified cartilage in the femoral head in OA patients and healthy subjects.

MATERIALS AND METHODS

We used design-based stereological principles, i.e., systematic uniform random sampling and vertical uniform random sections of the entire femoral head. We investigated the articular and calcified cartilage and femoral head surface area and volume, excluding fovea capitis and marginal osteophytes, in 20 patients with OA and 15 healthy subjects.

RESULTS

The volume of the calcified cartilage was significantly larger for the patients with OA compared with the healthy subjects (mean difference [95% CI]) (284 [110,457] mm³, p = 0.002). The upper and lower surface area of the calcified cartilage, i.e. the tidemark and cement line, were both significantly larger for OA patients compared with the healthy subjects (17.8 [8.4,27.3] cm², p < 0.001) and (38.7 [20.8,56.7] cm², p = 0.002), respectively. The volume of the calcified cartilage and the volume of the femoral head were significantly correlated for the patients with OA (Spearman's ρ = 0.51, p = 0.021), but not for the healthy subjects (ρ = 0.41, p = 0.123).

CONCLUSIONS

Patients with OA had a larger femoral head surface area and more calcified cartilage compared to healthy subjects. The volume of the calcified cartilage correlated positively with the volume of the femoral head for patients with OA, but not for healthy subjects. This strongly supports the existing view that bone growth in OA is associated with endochondral ossification.

Histomorphometric case-control study of subarticular osteophytes in patients with osteoarthritis of the hip

Objective

The objective of this cross-sectional case-control study was to determine the prevalence and size of marginal and subarticular osteophytes in patients with osteoarthritis (OA), and to compare these to that of a control group.

Design

We investigated femoral heads from 25 patients with OA following hip replacement surgery, and 25 femoral heads from a control group obtained post-mortem. The area and boundary length of the femoral head, marginal osteophytes, and subarticular osteophytes were determined with histomorphometry. Marginal osteophytes were defined histologically as bony projections at the peripheral margin of the femoral head, while subarticular osteophytes were defined as areas of bone that expanded from the normal curvature of the femoral head into the articular cartilage.

Results

The prevalence of OA patients with marginal- and subarticular osteophytes were 100 and 84%, respectively. Whereas the prevalence of the participants in the control group with marginal- and subarticular osteophytes were 56 and 28%, respectively.

The area and boundary length of marginal osteophytes was (median (Interquartile range)) 165.3mm² (121.4–254.0) mm² and 75.1 mm (50.8–99.3) mm for patients with OA compared to 0 mm² (0–0.5) mm² and 0 mm (0–0.5) mm for the control group (P <  0.001). For the subarticular osteophytes, the area and boundary length was 1.0 mm² (0–4.4) mm² and 1.4 mm (0–6.5) mm for patients with OA compared to 0 mm² (0–0.5) mm² and 0 mm (0–0.5) mm for the control group (P <  0.001).

Conclusion

As expected, both marginal- and subarticular osteophytes at the femoral head, were more frequent and larger in patients with OA than in the control group. However, in the control group, subarticular osteophytes were more prevalent than expected from the minor osteophytic changes at the femoral head margin, which may suggest that subarticular osteophytes are an early degenerative phenomenon that ultimately might develop into clinical osteoarthritis.

Age-related histological changes in calcified cartilage and subchondral bone in femoral heads from healthy humans

OBJECTIVE

Age is the most important risk factor for osteoarthritis (OA). It is suggested that changes in subchondral bone and calcified cartilage may occur in early OA. Therefore, the aim was to investigate age-related changes in the femoral head composition. We hypothesise that the thickness of the subchondral bone plate decreases with age, while the thickness of the calcified cartilage increases with age as seen in early-stage OA.

METHODS

Femoral heads from 29 women (20-74 years) and 32 men (23-78 years), who had died suddenly and unexpectedly, were obtained at autopsy. Individuals with bone or joint diseases or macroscopic abnormal cartilage were excluded. Using design-based stereology, femoral head volume as well as thickness and volume of the calcified cartilage and subchondral bone plate were estimated and correlated to sex and age.

RESULTS

The thickness and volume of the subchondral bone plate were not correlated with age. Calcified cartilage thickness and volume correlated positively with age in women, while the femoral head volume was correlated positively with age in men.

CONCLUSION

In human femoral heads obtained from a cross-sectional population without macroscopic OA changes, the thickness of the subchondral bone plate did not change with age, which differs from the thinning seen in early OA. Surprisingly, the age-related changes of the volume and thickness of the calcified cartilage and of the volume of the femoral head were different for women and men. This indicate that cartilage and bone metabolism is sex-specific, which may influence ageing of the hip joint.

Thickness of the bone-cartilage unit in relation to osteoarthritis severity in the human hip joint

Objective

Bone formation is a hallmark of osteoarthritis (OA). It has been speculated that bone formation may occur because of ossification at the bone-cartilage unit, that is, bone formation directly involving the calcified cartilage (CC). This study aimed to investigate the thickness of the CC and subchondral bone (SCB) in relation to the severity of the overlying articular cartilage (AC) degeneration.

Design

We investigated femoral heads from 20 patients with OA and 15 healthy subjects with design-based stereology using systematic uniform random sampling of the entire joint surface. This was combined with the Osteoarthritis Research Society International (OARSI) OA cartilage histopathology assessment system, thus obtaining focal OARSI grades paired with thickness measurements of AC, CC and the SCB.

Results

The patients with OA had thicker CC (mean 159; 95% CI 144 to 177 µm) compared with the healthy subjects (mean 132; 95% CI 113 to 1550 µm; p=0.036), and this difference was even higher in areas without loss of AC thickness (OARSI grade ≤3); 187 (95% CI 164 to 214) µm vs 132 (95% CI 113 to 155) µm (p=0.001). In the patients with OA, a thicker SCB was observed in areas with loss of AC thickness (OARSI grade ≥4), but not in areas without loss of AC thickness (OARSI grade ≤3).

Conclusion

The study showed that thicker CC is present in early stages of OA, suggesting that bone formation by endochondral ossification is an early phenomenon of OA. Thickening of the SCB was present, but only in areas with denuded bone. Suggesting that also appositional bone growth occurs and that it may be a consequence of changed biomechanics.

Histological Osteoarthritic Changes in the Human Cervical Spine Facet Joints Related to Age and Sex

STUDY DESIGN

Cross-sectional autopsy study.

OBJECTIVE

Quantify histological changes in the lower cervical spine facet joints with regard to age and sex using systematic random sampling of entire joints.

SUMMARY OF BACKGROUND DATA

Neck pain is a common debilitating musculoskeletal condition and one of the highest ranked causes of years lived with disability. The cause of neck pain is multifactorial and osteoarthritis is one potential cause. The cervical spine facet joints have been implicated in the etiology of chronic neck pain. Hence, a detailed description of their anatomy and age- and sex-related changes is needed.

METHODS

The lower four cervical spine segments (C4-C7 included) were obtained from 72 subjects during autopsy; 29 women (median age 53 years [22-77]) and 43 men (median age 38 years [20-78]). A total of 1132 articular facets were embedded in toto in hard plastic and sliced into 3-mm thick sections from where 10 μm thick histological sections were produced. Morphological variables were evaluated microscopically and histomorphometric variables were retrieved using random sampling methods. Data were analyzed with a linear regression model.

RESULTS

Significant associations were found between increasing age and in particular splitting, fissures, osteophytes, thickness of the calcified cartilage, and subchondral bone plate. The thickness of the calcified cartilage and subchondral bone plate increased with increasing age, whereas the hyaline cartilage thickness decreased. Males had more extensive degenerative changes in the cartilage.

CONCLUSION

Using semiquantitative histological methods, degenerative findings were observed at all spinal levels involving the articular cartilage and the osseous structures of the cervical spine facet joints similar to those observed in larger weight-bearing joints. In particular, the thickening of the calcified cartilage and the subchondral bone identified the osteocartilaginous junction as an important area in osteoarthritis. These findings may be relevant for the pathogenesis of osteoarthritis.

LEVEL OF EVIDENCE

3.

Design-Based Stereology for Evaluation of Histological Parameters

Valid quantification of organ volume and total cell numbers are crucial parameters for morphometric studies. The number of a specific cell type cannot be simply deduced from the number of its profiles found in thin tissue sections, as this parameter also depends on cell volume, tissue orientation as well as tissue atrophy. Design-based stereology has become the method of choice for unbiased, reproducible total cell number quantification. Steps described in this protocol include transcardial perfusion of mice, postfixation, and cryoprotection of the region of interest (ROI), followed by the preparation of a systematically and randomly sampled series of thick sections through the entire ROI. Furthermore, it is described how to perform immuno-histochemical staining of such thick cryo-sections, followed by providing a guidance for quantification of the ROI volume, the generation of unbiased virtual counting spaces, and steps to work with these counting spaces to obtain an unbiased estimate of total cell numbers.

First and second order stereology of hyaline cartilage: Application on mice femoral cartilage

Stereological techniques could be considered in research on cartilage to obtain quantitative data. The present study aimed to explain application of the first- and second-order stereological methods on articular cartilage of mice and the methods applied on the mice exposed to cadmium (Cd). The distal femoral articular cartilage of BALB/c mice (control and Cd-treated) was removed. Then, volume and surface area of the cartilage and number of chondrocytes were estimated using Cavalieri and optical dissector techniques on isotropic uniform random sections. Pair-correlation function [g(r)] and cross-correlation function were calculated to express the spatial arrangement of chondrocytes-chondrocytes and chondrocytes-matrix (chondrocyte clustering/dispersing), respectively. The mean±standard deviation of the cartilage volume, surface area, and thickness were 1.4±0.1mm³, 26.2±5.4mm², and 52.8±6.7μm, respectively. Besides, the mean number of chondrocytes was 680±200 (×10³). The cartilage volume, cartilage surface area, and number of chondrocytes were respectively reduced by 25%, 27%, and 27% in the Cd-treated mice in comparison to the control animals (p<0.03). Estimates of g(r) for the cells and matrix against the dipole distances, r, have been plotted. This plot showed that the chondrocytes and the matrix were neither dispersed nor clustered in the two study groups. Application of design-based stereological methods and also evaluation of spatial arrangement of the cartilage components carried potential advantages for investigating the cartilage in different joint conditions. Chondrocyte clustering/dispersing and cellularity can be evaluated in cartilage assessment in normal or abnormal situations.

Subchondral bone turnover, but not bone volume, is increased in early stage osteoarthritic lesions in the human hip joint

OBJECTIVE

The pathogenesis of osteoarthritis (OA) is not fully understood, but bone changes are suggested to be important. Bone turnover and bone volume (BV) in human hip OA were investigated in relation to the overlying cartilage degeneration using design-based stereological estimators.

MATERIALS AND METHODS

Femoral heads were obtained from 25 end-stage OA patients and 24 controls (CTL). Design-based stereological methods were used for sampling and quantification to obtain absolute estimates of volume and surface in the central trabecular and the subarticular bone region. The subarticular bone was further subdivided into regions according to the OARSI-score of the overlying articular cartilage in which erosion and osteoid surfaces were estimated.

RESULTS

In the subarticular region, bone volume (BV/TV) was 15.0% higher in OA patients compared to CTL; The fraction of erosive (ES/BS) and osteoid surfaces (OS/BS) were 56.2% and 72.8% higher in OA compared to CTL. In subarticular regions with none to mild cartilage degeneration (OARSI grade 0-2), ES/BS and OS/BS were 48.6% and 59.9% higher in OA compared to CTL, whereas BV/TV did not differ between OA and CTL.

CONCLUSION

In human end-stage hip OA, BV and bone turnover correlate with the degree of local cartilage degeneration. Subarticular bone sclerosis was only present in regions corresponding to end-stage OA. However, in regions with only none to mild cartilage degeneration the underlying bone had significantly higher turnover in OA patients compared to the control group, suggesting that high bone turnover may contribute to the early pathogenesis of OA.