Software-Assisted Quantitative Measurement of Osteoarthritic Subchondral Bone Thickness
March 18th, 2022
This methodology article presents a software-assisted quantitative measurement protocol to quantify histologic subchondral bone thickness in murine osteoarthritic knee joints and normal knee joints as controls. This protocol is highly sensitive to subtle thickening and is suitable for detecting early osteoarthritic subchondral bone changes.
Subchondral bone thickening, or sclerosis, is one of the hallmarks of osteoarthritis, both in animal models and in humans. Currently, the severity of histologic subchondral bone thickening is mostly determined by visual estimation based on semi-quantitative grading systems. This study aim to develop a reproducible and easily executed protocol to quantitatively measure subchondral bone thickness in a mouse model of knee OA induced by destabilization of the medial meniscus.
We created a mouse model for knee osteoarthritis by surgical destabilization of the medial meniscus which is performed under surgical microscope and the sterile condition. The histological process of mouse knee joints include tissue fixation, decalcification, trimming, processing, embedding, sectioning, and staining, followed by microscopic imaging. The image on the screen shows mouse knee osteoarthritis with articular cartilage lesions, osteophyte formation, and subchondral bone thickening Quantitative measurement of osteoarthritic subchondral bone with ImageJ software.
Download ImageJ from imagej.nih.gov/ij. Open ImageJ. Click the File tab and then click Open option to open the histologic image.
Find the file directory address, select the picture file, and click Open. Use the straight line tool to sketch one unit of length, a micrometer, and click Analyze, then Set Scale. Set the known distance and the pixel aspect ratio to one and click Ok.ImageJ can convert the pixel length to the unit length, a micrometer.
Set the measured factor to area. Click Analyze then Set Measurement and check Area and Limit to Threshold box under the new window. This step sets ImageJ to measure parameter area within selected threshold.
Defined total subchondral bone area of interest as shown in radio which covers the subchondral cortical plate and a portion of the underlying trabecular bone adjacent to cortical plate. Sketch the outline of total subchondral bone area by using the selection tool under the main window of image. The selection tools gives the system a threshold to limit the measurement after threshold being selected.
Click Analyze then Measure. A result window with area measurement will open. Click Edit then Clear Outside to exclude the area outside total subchondral bone area.
Only total subchondral bone area is visible after clicking Clear Outside option. Click Image then Adjust then Color Threshold to open the threshold color window. Click Original at the bottom of threshold color window to restore picture to original status.
Use selection tools to draw a small box in the bone substance region. Click Sample Option at the bottom of window to define the bone substance area. Selected bone substance area will turn to red.
Click Select at the bottom of threshold color window to create area measurement threshold. Click Analyze then Measure in ImageJ main menu. The bone substance area measurement result will show on result window.
Save the data of total subchondral bone area and bone substance area. The inter and intraobserver variability and the reproducibility were determined by Pearson's correlation coefficient analysis. The significance of difference between study groups were determined by using Student t-test or one-way ANOVA, followed by post-hoc test.
This figure shows upper and lower panels. The upper panel shows photomicrographs of histologic images from Sham and DMM groups for visual estimate-based subchondral bone grading. The lower panels show photomicrographs of histologic images from Sham and DMM groups for ImageJ-assisted, quantitative subchondral bone measurement.
The boxes outlined with a dotted yellow line made with Adobe Illustrator defines the total subchondral bone area of interest. The area of bone substance within the boxes is highlighted in orange. Remarkable subchondral bone thickening in the medial femoral condyle and medial tibial plateau can be quantified using ImageJ software.
In this figure, interobserver variation tests indicate a high reproducibility between observers for both the first and second measurements of subchondral bone thickness in the medial tibial plateau and the medial femoral condyle regions of interest. In this figure, intraobserver variation tests indicate a high reproducibility between the first and second subchondral bone thickness measurements in the medial tibial plateau and medial femoral condyle regions of interest. Table 1 shows comparative analysis of reproducibility between the visual grading and ImageJ-assisted quantitative measurement of subchondral bone thickness.
Correlation coefficient test suggests that the quantitative measurement was relatively more reproducible than the visual grading system. This figure shows comparative sensitivity analysis of visual grading and ImageJ-assisted quantitative measurement of subchondral bone thickness in the medial femoral condyle and the medial tibial plateau. The histologic images for visual estimate grading were divided into three groups.
The quantitative subchondral bone thickness value from all three observers for the DMM images with a zero visual score were significantly higher than that of the Sham images with a zero visual score, indicating that the quantitative measurement is more sensitive than the visual grading to mild subchondral bone thickening. The newly developed protocol for quantitative measurement of osteoarthritic subchondral bone thickness is more sensitive to mild subchondral bone changes than the widely used visual grading systems. And this protocol can be used for detecting early osteoarthritic subchondral bone changes and for assessing in vivo efficacy of osteoarthritis treatments in concert with osteoarthritis cartilage grading.
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Overview
This methodology article presents a software-assisted quantitative measurement protocol to quantify histologic subchondral bone thickness in murine osteoarthritic knee joints and normal knee joints as controls. The protocol is designed to be highly sensitive to subtle thickening, making it suitable for detecting early osteoarthritic changes.
Key Study Components
Area of Science
- Neuroscience
- Osteoarthritis Research
- Histology
Background
- Subchondral bone thickening is a hallmark of osteoarthritis.
- Current methods rely on visual estimation and semi-quantitative grading.
- A reproducible protocol is needed for accurate measurement.
- The study uses a mouse model induced by destabilization of the medial meniscus.
Purpose of Study
- To develop a quantitative measurement protocol for subchondral bone thickness.
- To improve the sensitivity of detecting early osteoarthritic changes.
- To provide a standardized method for future research.
Methods Used
- Surgical destabilization of the medial meniscus in mice.
- Histological processes including fixation, decalcification, and staining.
- Microscopic imaging for analysis.
- Quantitative measurement using ImageJ software.
Main Results
- Successful creation of a mouse model for knee osteoarthritis.
- Demonstration of articular cartilage lesions and osteophyte formation.
- Quantitative assessment of subchondral bone thickening achieved.
- Protocol shows high sensitivity to changes in bone thickness.
Conclusions
- The developed protocol allows for accurate measurement of subchondral bone thickness.
- This method can enhance understanding of osteoarthritis progression.
- Future studies can utilize this protocol for further research in osteoarthritis.
Frequently Asked Questions
Executive Industry Relevance
Quantitative measurement of subchondral bone thickness addresses a critical gap in osteoarthritis target validation by replacing subjective visual grading with reproducible, software-assisted analysis. This approach enhances predictive confidence in preclinical models by enabling detection of early, subtle structural changes that precede overt cartilage degradation. The method supports mechanistic de-risking of OA therapeutics by providing a standardized, translatable biomarker for bone remodeling pathways.
Strategic Applications in Biopharma R&D
Early Discovery & Target Validation
- Scientific Value: Enables interrogation of therapeutic hypotheses targeting subchondral bone remodeling pathways in osteoarthritis.
- Operational Value: Provides quantitative, reproducible readouts for functional target validation in murine OA models.
- Predictive Value: Supports portfolio triage by detecting mild bone thickening invisible to visual grading systems.
Screening & Assay Development
- Assay Readiness: Prepares validated histologic samples for standardized, high-throughput analysis using ImageJ.
- Quantitative Output: Generates continuous, threshold-independent measurements of subchondral bone area for compound screening.
- Scalability: Enables platform reuse across OA studies with consistent region-of-interest definitions in medial femoral condyle and tibial plateau.
Translational & Preclinical Research
- Disease Relevance: Aligns with human OA pathology where subchondral sclerosis is a hallmark of progression.
- Translational Continuity: Bridges discovery and preclinical workflows by providing a biomarker compatible with cartilage grading.
- Risk-Adjusted Decisions: Supports go/no-go criteria based on quantitative bone thickness changes in treatment efficacy studies.
Pipeline & Workflow Integration
The protocol fits within the osteoarthritis discovery continuum from target validation through lead optimization to preclinical efficacy assessment, particularly when bone remodeling is a mechanistic focus.
- Discovery Biology: Supports hypothesis testing of targets involved in subchondral bone sclerosis and mechanotransduction.
- Screening: Delivers assay-ready, reproducible quantitative outputs for evaluating compound effects on bone thickness.
- Analytics: Enables statistical comparison of bone thickness across groups using Pearson correlation and t-test/ANOVA as described.
- Translational Research: Connects to preclinical validation by offering a biomarker that mirrors clinical OA progression metrics.
- Enterprise Reuse: Establishes a reusable histology analysis workflow applicable across multiple OA models and treatment arms.
Operational & Enterprise Impact
- Scientific Value: Increases target validation confidence by reducing ambiguity in bone phenotype assessment.
- Operational Value: Standardizes measurement across observers and sessions with low intra- and inter-variability.
- Strategic Value: Improves go/no-go decisions by detecting early structural changes missed by semi-quantitative scoring.
- Portfolio Impact: Enables risk-adjusted advancement based on sensitive, quantitative bone remodeling endpoints.
Implementation Considerations
- Requires expertise in histologic preparation and ImageJ threshold analysis.
- Dependent on calibrated microscopy and consistent region-of-interest definition.
- Necessitates cross-team standardization of measurement protocols for reproducibility.
- Adaptation considerations include model-specific bone anatomy and staining protocols.
- Practical limitation: Manual outlining may introduce variability if region-of-interest definitions are not strictly standardized.
