Subchondral bone microarchitecture and mineral density in human osteoarthritis and osteoporosis: A regional and compartmental analysis

High-resolution microCT analysis of sclerotic subchondral bone beneath bone-on-bone wear grooves in severe osteoarthritis

Osteoarthritis (OA) is associated with sclerosis, a thickening of the subchondral bone plate, yet little is known about bone adaptations around full-thickness cartilage defects in severe knee OA, particularly beneath bone-on-bone wear grooves. This high-resolution micro-computed tomography (microCT) study aimed to quantify subchondral bone microstructure relative to cartilage defect location, distance from the joint space, and groove depth. Ten tibial plateaus with full-thickness cartilage defects were microCT-scanned to determine defect location and size. Wear groove depth was estimated as the thickness from its deepest point to a surface interpolated from the defect edges. Two 5 × 5 mm specimens were sampled from three regions (defect, edge, and cartilage-covered areas) and two from the contralateral condyle, then scanned at higher resolution. Bone density profiles were analyzed as a function of distance from the joint space to identify cortical and trabecular regions of interest and and compute their respective bone density and microstructure. Cortical bone beneath defects was four times thicker under wear grooves than beneath cartilage. Bone density profiles significantly differed between the three specimen types at depths up to 5 mm. Below defects, cortical porosity was 85 % higher, and trabecular density 14 % higher, than in cartilage-covered specimens. Some trabecular spaces were filled with woven bone-like tissue, forming a new cortical layer. These changes were confined to the defect region and ceased abruptly at the defect edge. No correlation was found between bone microstructural indices and the estimated groove depth. Our findings suggest an ongoing migration of the cortical layer during formation of the groove from its original position into the underlying trabecular bone, a process we termed "trabecular corticalization." Under deeper wear grooves, the new cortical layer exhibited large pores connecting bone marrow to the joint space, suggesting physiological limits to corticalization. These results highlight specific bone adaptations beneath cartilage defects in severe OA and provide insights into the progression of subchondral bone changes under bone-on-bone contact areas.

Alterations in compositional and cellular properties of the subchondral bone are linked to cartilage degeneration in hip osteoarthritis

OBJECTIVE

The subchondral bone is an emerging regulator of osteoarthritis (OA). However, knowledge of how specific subchondral alterations relate to cartilage degeneration remains incomplete.

METHOD

Femoral heads were obtained from 44 patients with primary OA during total hip arthroplasty and from 30 non-OA controls during autopsy. A multiscale assessment of the central subchondral bone region comprising histomorphometry, quantitative backscattered electron imaging, nanoindentation, and osteocyte lacunocanalicular network characterization was employed.

RESULTS

In hip OA, thickening of the subchondral bone coincided with a higher number of osteoblasts (controls: 3.7 ± 4.5 mm-1, OA: 16.4 ± 10.2 mm-1, age-adjusted mean difference 10.5 mm-1 [95% CI 4.7 to 16.4], p < 0.001) but a similar number of osteoclasts compared to controls (p = 0.150). Furthermore, higher matrix mineralization heterogeneity (CaWidth, controls: 2.8 ± 0.2 wt%, OA: 3.1 ± 0.3 wt%, age-adjusted mean difference 0.2 wt% [95% CI 0.1 to 0.4], p = 0.011) and lower tissue hardness (controls: 0.69 ± 0.06 GPa, OA: 0.67 ± 0.06 GPa, age-adjusted mean difference -0.05 GPa [95% CI -0.09 to -0.01], p = 0.032) were detected. While no evidence of altered osteocytic perilacunar/canalicular remodeling in terms of fewer osteocyte canaliculi was found in OA, specimens with advanced cartilage degeneration showed a higher number of osteocyte canaliculi and larger lacunocanalicular network area compared to those with low-grade cartilage degeneration. Multiple linear regression models indicated that several subchondral bone properties, especially osteoblast and osteocyte parameters, were closely related to cartilage degeneration (R2 adjusted = 0.561, p < 0.001).

CONCLUSION

Subchondral bone properties in OA are affected at the compositional, mechanical, and cellular levels. Based on their strong interaction with cartilage degeneration, targeting osteoblasts/osteocytes may be a promising therapeutic OA approach.

DATA AND MATERIALS AVAILABILITY

All data are available in the main text or the supplementary materials.

Effect of Romosozumab Treatment in Postmenopausal Women With Osteoporosis and Knee Osteoarthritis: Results From a Substudy of a Phase 3 Clinical Trial

OBJECTIVE

Romosozumab is a bone-forming agent approved for osteoporosis treatment. Here we report results of the protocol-specified, noninferiority osteoarthritis substudy of the fracture study in postmenopausal women with osteoporosis (FRAME), which evaluated the effect of romosozumab versus placebo on knee osteoarthritis in patients with a clinical history of osteoarthritis.

METHODS

Women in FRAME with a history of knee osteoarthritis were eligible for enrollment in the osteoarthritis substudy; key inclusion criteria were osteoarthritis-related signal knee pain, morning stiffness lasting less than 30 minutes, knee crepitus, and knee osteoarthritis confirmed by x-ray within 12 months. The protocol-specified outcomes were change from baseline through month 12 in the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) score, incidence of worsening knee osteoarthritis, and treatment-emergent adverse events (TEAEs) with romosozumab versus placebo. In a post hoc analysis, percentage change from baseline to month 12 in bone mineral density (BMD) was assessed.

RESULTS

Of 7180 women in FRAME, 347 participated in the osteoarthritis substudy (placebo, 177; romosozumab, 170). At month 12, no significant difference in progression of knee osteoarthritis was observed with romosozumab versus placebo (least squares mean total WOMAC score: -2.2 vs. -1.3; P = 0.71). Incidence of worsening symptoms of knee osteoarthritis was comparable between romosozumab (17.1%) and placebo (20.5%) (odds ratio 0.9 [95% confidence interval: 0.5, 1.7]; P = 0.69). Incidence of TEAEs of osteoarthritis was numerically lower with romosozumab (13 [7.7%]) versus placebo (21 [12.0%]). BMD gains were higher with romosozumab.

CONCLUSION

Romosozumab treatment did not impact knee pain or function in postmenopausal women with osteoporosis and knee osteoarthritis and resulted in significant BMD gains in these women.

Subchondral bone remodeling patterns in larger animal models of meniscal injuries inducing knee osteoarthritis - a systematic review

PURPOSE

Elucidating subchondral bone remodeling in preclinical models of traumatic meniscus injury may address clinically relevant questions about determinants of knee osteoarthritis (OA).

METHODS

Studies on subchondral bone remodeling in larger animal models applying meniscal injuries as standardizing entity were systematically analyzed. Of the identified 5367 papers reporting total or partial meniscectomy, meniscal transection or destabilization, 0.4% (in guinea pigs, rabbits, dogs, minipigs, sheep) remained eligible.

RESULTS

Only early or mid-term time points were available. Larger joint sizes allow reporting higher topographical details. The most frequently reported parameters were BV/TV (61%), BMD (41%), osteophytes (41%) and subchondral bone plate thickness (39%). Subchondral bone plate microstructure is not comprehensively, subarticular spongiosa microstructure is well characterized. The subarticular spongiosa is altered shortly before the subchondral bone plate. These early changes involve degradation of subarticular trabecular elements, reduction of their number, loss of bone volume and reduced mineralization. Soon thereafter, the previously normal subchondral bone plate becomes thicker. Its porosity first increases, then decreases.

CONCLUSION

The specific human topographical pattern of a thinner subchondral bone plate in the region below both menisci is present solely in the larger species (partly in rabbits), but absent in rodents, an important fact to consider when designing animal studies examining subchondral consequences of meniscus damage. Large animal models are capable of providing high topographical detail, suggesting that they may represent suitable study systems reflecting the clinical complexities. For advanced OA, significant gaps of knowledge exist. Future investigations assessing the subchondral bone in a standardized fashion are warranted.

Association between radiographic hand osteoarthritis and bone microarchitecture in a population-based sample

Background

Subchondral bone plays an important role in the pathogenesis of radiographic osteoarthritis (OA). However, the bony changes that occur in hand OA (HOA) are much less understood. This study aimed to describe the association between radiographic HOA and high-resolution peripheral quantitative computed tomography (HRpQCT) measures of the hand and radius in a population-based sample.

Methods

A total of 201 participants (mean age 72, 46% female) from the Tasmanian Older Adult Cohort (TASOAC) study underwent HRpQCT assessment of the 2nd distal and proximal interphalangeal (DIP, PIP), 1st carpometacarpal (CMC) joint, and distal radius. Radiographic HOA was assessed at the 2nd DIP, PIP joints, and the 1st CMC joint using the OARSI atlas.

Results

Proximal osteophyte and joint space narrowing (JSN) scores were consistently more strongly associated with HRpQCT measures compared to the distal site with positive associations for indices of bone size (total and trabecular bone area and cortical perimeter but inconsistent for cortical area) and negative associations for volumetric bone mineral density (vBMD). There was a decrease in trabecular number and bone volume fraction with increasing osteophyte and JSN score as well as an increase in trabecular separation and inhomogeneity. Osteophyte and JSN scores in the hand were not associated with HRpQCT measures at the distal radius.

Conclusions

This hypothesis generating data suggests that bone size and trabecular disorganization increase with both osteophyte formation and JSN (proximal more than distal), while local vBMD decreases. This process appears to be primarily at the site of pathology rather than nearby unaffected bone.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13075-022-02907-6.

Effects of testosterone and exercise training on bone microstructure of rats

Background and Aim:

Male hypogonadism results from failure to produce physiological levels of testosterone. Testosterone in men is essential in masculine development, sperm production, and adult man’s health. Osteoporosis is one of the consequences of hypogonadism. Regular physical exercise and exogenous testosterone administration are frequently used to prevent or treat this condition. This study aimed to understand the effects of lifelong exercise training and testosterone levels (isolated and together) in the main bone structure parameters.

Materials and Methods:

A total of 24 rats were used and randomly divided into four groups: Control group (CG; n=6), exercised group (EG, n=6), testosterone group (TG, n=6), and testosterone EG (TEG, n=6). A micro-computed tomography equipment was used to evaluate 15 bone parameters.

Results:

Both factors (exercise training and testosterone) seem to improve the bone resistance and microstructure, although in different bone characteristics. Testosterone influenced trabecular structure parameters, namely, connectivity density, trabecular number, and trabecular space. The exercise promoted alterations in bone structure as well, although, in most cases, in different bone structure parameters as bone mineral density and medullar mineral density.

Conclusion:

Overall, exercise and testosterone therapy seems to have a synergistic contribution to the general bone structure and resistance. Further studies are warranted, comparing different individual factors, as gender, lifestyle, or testosterone protocols, to constantly improve the medical management of hypogonadism (and osteoporosis).

Moving Beyond the Limits of Detection: The Past, the Present, and the Future of Diagnostic Imaging in Canine Osteoarthritis

Osteoarthritis (OA) is the most common orthopedic condition in dogs, characterized as the chronic, painful end-point of a synovial joint with limited therapeutic options other than palliative pain control or surgical salvage. Since the 1970s, radiography has been the standard-of-care for the imaging diagnosis of OA, despite its known limitations. As newer technologies have been developed, the limits of detection have lowered, allowing for the identification of earlier stages of OA. Identification of OA at a stage where it is potentially reversible still remains elusive, however, yet there is hope that newer technologies may be able to close this gap. In this article, we review the changes in the imaging of canine OA over the past 50 years and give a speculative view on future innovations which may provide for earlier identification, with the ultimate goal of repositioning the limit of detection to cross the threshold of this potentially reversible disease.

Subchondral Bone Microarchitectural and Mineral Properties and Expression of Key Degradative Proteinases by Chondrocytes in Human Hip Osteoarthritis

Background: The purpose of this study was to investigate the relationship between the expression of key degradative enzymes by chondrocytes and the microarchitectural and mineral properties of subchondral bone across different stages of cartilage degradation in human hip osteoarthritis (OA). Methods: Osteochondral samples at different stages of cartilage degradation were collected from 16 femoral heads with OA. Osteochondral samples with normal cartilage were collected from seven femoral heads with osteoporosis. Microcomputed tomography was used for the investigation of subchondral bone microarchitecture and mineral densities. Immunohistochemistry was used to study the expression and distribution of MMP13 and ADAMTS4 in cartilage. Results: The microarchitecture and mineral properties of the subchondral plate and trabecular bone in OA varied with the severity of the degradation of the overlying cartilage. Chondrocytes expressing MMP13 and ADAMTS4 are mainly located in the upper zone(s) of cartilage regardless of the histopathological grades. The zonal expression of these enzymes in OA (i.e., the percentage of positive cells in the superficial, middle, and deep zones), rather than their overall expression (the percentage of positive cells in the full thickness of the cartilage), exhibited significant variation in relation to the severity of cartilage degradation. The associations between the subchondral bone properties and zonal and overall expression of these enzymes in the cartilage were generally weak or nonsignificant. Conclusions: Phenotypic changes in chondrocytes and remodelling of subchondral bone proceed at different rates throughout the process of cartilage degradation. Biological influences are more important for cartilage degradation at early stages, while biomechanical damage to the compromised tissue may outrun the phenotypic change of chondrocytes and is critical in the advanced stages.