Subchondral bone trabecular integrity predicts and changes concurrently with radiographic and magnetic resonance imaging-determined knee osteoarthritis progression

Sexual dimorphism in peri-articular tissue anatomy - More keys to understanding sex-differences in osteoarthritis?

Objective

Osteoarthritis prevalence differs between women and men; whether this is the result of differences in pre-morbid articular or peri-articular anatomical morphotypes remains enigmatic. Albeit sex within humans cannot be reduced to female/male, this review focusses to the sexual dimorphism of peri-articular tissues, given lack of literature on non-binary subjects.

Methods

Based on a Pubmed search and input from experts, we selected relevant articles based on the authors' judgement of relevance, interest, and quality; no "hard" bibliometric measures were used to evaluate the quality or importance of the work. Emphasis was on clinical studies, with most (imaging) data being available for the knee and thigh.

Results

The literature on sexual dimorphism of peri-articular tissues is reviewed: 1) bone size/shape, 2) subchondral/subarticular bone, 3) synovial membrane and infra-patellar fad-pad (IPFP), 4) muscle/adipose tissue, and 5) peri-articular tissue response to treatment.

Conclusions

Relevant sex-specific differences exist for 3D bone shape and IPFP size, even after normalization to body weight. Presence of effusion- and Hoffa-synovitis is associated with greater risk of incident knee osteoarthritis in overweight women, but not in men. When normalized to bone size, men exhibit greater muscle, and women greater adipose tissue measures relative to the opposite sex. Reduced thigh muscle specific strength is associated with incident knee osteoarthritis and knee replacement in women, but not in men. These observations may explain why women with muscle strength deficits have a poorer prognosis than men with similar deficits. A "one size/sex fits all" approach must be urgently abandoned in osteoarthritis research.

Subchondral bone in knee osteoarthritis: bystander or treatment target?

The subchondral bone is an important structural component of the knee joint relevant for osteoarthritis (OA) incidence and progression once disease is established. Experimental studies have demonstrated that subchondral bone changes are not simply the result of altered biomechanics, i.e., pathologic loading. In fact, subchondral bone alterations have an impact on joint homeostasis leading to articular cartilage loss already early in the disease process. This narrative review aims to summarize the available and emerging imaging techniques used to evaluate knee OA-related subchondral bone changes and their potential role in clinical trials of disease-modifying OA drugs (DMOADs). Radiographic fractal signature analysis has been used to quantify OA-associated changes in subchondral texture and integrity. Cross-sectional modalities such as cone-beam computed tomography (CT), contrast-enhanced cone beam CT, and micro-CT can also provide high-resolution imaging of the subchondral trabecular morphometry. Magnetic resonance imaging (MRI) has been the most commonly used advanced imaging modality to evaluate OA-related subchondral bone changes such as bone marrow lesions and altered trabecular bone texture. Dual-energy X-ray absorptiometry can provide insight into OA-related changes in periarticular subchondral bone mineral density. Positron emission tomography, using physiological biomarkers of subchondral bone regeneration, has provided additional insight into OA pathogenesis. Finally, artificial intelligence algorithms have been developed to automate some of the above subchondral bone measurements. This paper will particularly focus on semiquantitative methods for assessing bone marrow lesions and their utility in identifying subjects at risk of symptomatic and structural OA progression, and evaluating treatment responses in DMOAD clinical trials.

Biomarkers in osteoarthritis: current status and outlook - the FNIH Biomarkers Consortium PROGRESS OA study

Currently, no disease-modifying therapies are approved for osteoarthritis (OA) use. One obstacle to trial success in this field has been our existing endpoints' limited validity and responsiveness. To overcome this impasse, the Foundation for the NIH OA Biomarkers Consortium is focused on investigating biomarkers for a prognostic context of use for subsequent qualification through regulatory agencies. This narrative review describes this activity and the work underway, focusing on the PROGRESS OA study.

Radiographic Biomarkers for Knee Osteoarthritis: A Narrative Review

Conventional radiography remains the most widely available imaging modality in clinical practice in knee osteoarthritis. Recent research has been carried out to develop novel radiographic biomarkers to establish the diagnosis and to monitor the progression of the disease. The growing number of publications on this topic over time highlights the necessity of a renewed review. Herein, we propose a narrative review of a selection of original full-text articles describing human studies on radiographic imaging biomarkers used for the prediction of knee osteoarthritis-related outcomes. To achieve this, a PubMed database search was used. A total of 24 studies were obtained and then classified based on three outcomes: (1) prediction of radiographic knee osteoarthritis incidence, (2) knee osteoarthritis progression and (3) knee arthroplasty risk. Results showed that numerous studies have reported the relevance of joint space narrowing score, Kellgren-Lawrence score and trabecular bone texture features as potential bioimaging markers in the prediction of the three outcomes. Performance results of reviewed prediction models were presented in terms of the area under the receiver operating characteristic curves. However, fair and valid comparisons of the models' performance were not possible due to the lack of a unique definition of each of the three outcomes.

Subchondral tibial bone texture of conventional X-rays predicts total knee arthroplasty

Lacking disease-modifying osteoarthritis drugs (DMOADs) for knee osteoarthritis (KOA), Total Knee Arthroplasty (TKA) is often considered an important clinical outcome. Thus, it is important to determine the most relevant factors that are associated with the risk of TKA. The present study aims to develop a model based on a combination of X-ray trabecular bone texture (TBT) analysis, and clinical and radiological information to predict TKA risk in patients with or at risk of developing KOA. This study involved 4382 radiographs, obtained from the OsteoArthritis Initiative (OAI) cohort. Cases were defined as patients with TKA on at least one knee prior to the 108-month follow-up time point and controls were defined as patients who had never undergone TKA. The proposed TKA-risk prediction model, combining TBT parameters and Kellgren–Lawrence (KL) grades, was performed using logistic regression. The proposed model achieved an AUC of 0.92 (95% Confidence Interval [CI] 0.90, 0.93), while the KL model achieved an AUC of 0.86 (95% CI 0.84, 0.86; p < 0.001). This study presents a new TKA prediction model with a good performance permitting the identification of at risk patient with a good sensitivy and specificity, with a 60% increase in TKA case prediction as reflected by the recall values.

Study of the Efficacy of Artificial Intelligence Algorithm-Based Analysis of the Functional and Anatomical Improvement in Polynucleotide Treatment in Knee Osteoarthritis Patients: A Prospective Case Series

Knee osteoarthritis (OA) is one of the most common degenerative diseases in old age. Recent studies have suggested new treatment approaches dealing with subchondral remodeling, which is a typical feature of OA progression. However, diagnostic tools or therapeutic approaches related to such a process are still being researched. The automated artificial intelligence (AI) algorithm-based texture analysis is a new method used for OA-progression detection. We designed a prospective case series study to examine the efficacy of the AI algorithm-based texture analysis in detecting the restoration of the subchondral remodeling process, which is expected to follow therapeutic intervention. In this study, we used polynucleotide (PN) filler injections as the therapeutic modality and the treatment outcome was verified by symptom improvement, as well as by the induction of subchondral microstructural changes. We used AI algorithm-based texture analysis to observe these changes in the subchondral bone with the bone structure value (BSV). A total of 51 participants diagnosed with knee OA were enrolled in this study. Intra-articular PN filler (HP cell Vitaran J) injections were administered once a week and five times in total. Knee X-rays and texture analyses with BSVs were performed during the screening visit and the last visit three months after screening. The Visual Analogue Scale (VAS) and Korean-Western Ontario MacMaster (K-WOMAC) measurements were used at the screening visit, the fifth intra-articular injection visit, and the last visit. The VAS and K-WOMAC scores decreased after PN treatment and lasted for three months after the final injection. The BSV changed in the middle and deep layers of tibial bone after PN injection. This result could imply that there were microstructural changes in the subchondral bone after PN treatment, and that this change could be detected using the AI algorithm-based texture analysis. In conclusion, the AI- algorithm-based texture analysis could be a promising tool for detecting and assessing the therapeutic outcome in knee OA.

Prediction of knee osteoarthritis progression using radiological descriptors obtained from bone texture analysis and Siamese neural networks: data from OAI and MOST cohorts

Background

Trabecular bone texture (TBT) analysis has been identified as an imaging biomarker that provides information on trabecular bone changes due to knee osteoarthritis (KOA). In parallel with the improvement in medical imaging technologies, machine learning methods have received growing interest in the scientific osteoarthritis community to potentially provide clinicians with prognostic data from conventional knee X-ray datasets, in particular from the Osteoarthritis Initiative (OAI) and the Multicenter Osteoarthritis Study (MOST) cohorts.

Patients and methods

This study included 1888 patients from OAI and 683 patients from MOST cohorts. Radiographs were automatically segmented to determine 16 regions of interest. Patients with an early stage of OA risk, with Kellgren and Lawrence (KL) grade of 1 < KL < 4, were selected. The definition of OA progression was an increase in the OARSI medial joint space narrowing (mJSN) grades over 48 months in OAI and 60 months in MOST. The performance of the TBT-CNN model was evaluated and compared to well-known prediction models using logistic regression.

Results

The TBT-CNN model was predictive of the JSN progression with an area under the curve (AUC) up to 0.75 in OAI and 0.81 in MOST. The predictive ability of the TBT-CNN model was invariant with respect to the acquisition modality or image quality. The prediction models performed significantly better with estimated KL (KLprob) grades than those provided by radiologists. TBT-based models significantly outperformed KLprob-based models in MOST and provided similar performances in OAI. In addition, the combined model, when trained in one cohort, was able to predict OA progression in the other cohort.

Conclusion

The proposed combined model provides a good performance in the prediction of mJSN over 4 to 6 years in patients with relevant KOA. Furthermore, the current study presents an important contribution in showing that TBT-based OA prediction models can work with different databases.

Post-traumatic osteoarthritis progression is diminished by early mechanical unloading and anti-inflammatory treatment in mice

OBJECTIVE

Post-traumatic osteoarthritis (PTOA) is a degenerative joint disease initiated by injury. Early phase (0-7 days) treatments often include rest (unloading) and anti-inflammatory medications, but how those early interventions impact PTOA progression is unknown. We hypothesized that early unloading and anti-inflammatory treatment would diminish joint inflammation and slow PTOA progression.

DESIGN

Mice were injured with non-invasive ACL rupture followed by hindlimb unloading (HLU) or normal cage activity (ground control: GC) for 7 days, after which all mice were allowed normal cage activity. HLU and GC mice were treated with daily celecoxib (CXB; 10 mg/kg IP) or vehicle. Protease activity was evaluated using in vivo fluorescence imaging, osteophyte formation and epiphyseal trabecular bone were quantified using micro-computed tomography, and synovitis and articular cartilage were evaluated using whole-joint histology at 7, 14, 21, and 28 days post-injury.

RESULTS

HLU significantly reduced protease activity (-22-30% compared to GC) and synovitis (-24-50% relative to GC) at day 7 post-injury (during unloading), but these differences were not maintained at later timepoints. Similarly, trabecular bone volume was partially preserved in HLU mice at during unloading (-14-15% BV/TV for HLU mice, -21-22% for GC mice relative to uninjured), but these differences were not maintained during reloading. Osteophyte volume was reduced by both HLU and CXB, but there was not an additive effect of these treatments (HLU: -46%, CXB: -30%, HLU + CXB: -35% relative to vehicle GC at day 28).

CONCLUSIONS

These data suggest that early unloading following joint injury can reduce inflammation and potentially slow PTOA progression.

Trabecular bone texture analysis of conventional radiographs in the assessment of knee osteoarthritis: review and viewpoint

BACKGROUND

Trabecular bone texture analysis (TBTA) has been identified as an imaging biomarker that provides information on trabecular bone changes due to knee osteoarthritis (KOA). Consequently, it is important to conduct a comprehensive review that would permit a better understanding of this unfamiliar image analysis technique in the area of KOA research. We examined how TBTA, conducted on knee radiographs, is associated to (i) KOA incidence and progression, (ii) total knee arthroplasty, and (iii) KOA treatment responses. The primary aims of this study are twofold: to provide (i) a narrative review of the studies conducted on radiographic KOA using TBTA, and (ii) a viewpoint on future research priorities.

METHOD

Literature searches were performed in the PubMed electronic database. Studies published between June 1991 and March 2020 and related to traditional and fractal image analysis of trabecular bone texture (TBT) on knee radiographs were identified.

RESULTS

The search resulted in 219 papers. After title and abstract scanning, 39 studies were found eligible and then classified in accordance to six criteria: cross-sectional evaluation of osteoarthritis and non-osteoarthritis knees, understanding of bone microarchitecture, prediction of KOA progression, KOA incidence, and total knee arthroplasty and association with treatment response. Numerous studies have reported the relevance of TBTA as a potential bioimaging marker in the prediction of KOA incidence and progression. However, only a few studies have focused on the association of TBTA with both OA treatment responses and the prediction of knee joint replacement.

CONCLUSION

Clear evidence of biological plausibility for TBTA in KOA is already established. The review confirms the consistent association between TBT and important KOA endpoints such as KOA radiographic incidence and progression. TBTA could provide markers for enrichment of clinical trials enhancing the screening of KOA progressors. Major advances were made towards a fully automated assessment of KOA.

Macro, Micro, and Molecular. Changes of the Osteochondral Interface in Osteoarthritis Development

Osteoarthritis (OA) is a long-term condition that causes joint pain and reduced movement. Notably, the same pathways governing cell growth, death, and differentiation during the growth and development of the body are also common drivers of OA. The osteochondral interface is a vital structure located between hyaline cartilage and subchondral bone. It plays a critical role in maintaining the physical and biological function, conveying joint mechanical stress, maintaining chondral microenvironment, as well as crosstalk and substance exchange through the osteochondral unit. In this review, we summarized the progress in research concerning the area of osteochondral junction, including its pathophysiological changes, molecular interactions, and signaling pathways that are related to the ultrastructure change. Multiple potential treatment options were also discussed in this review. A thorough understanding of these biological changes and molecular mechanisms in the pathologic process will advance our understanding of OA progression, and inform the development of effective therapeutics targeting OA.

A machine learning approach to distinguish between knees without and with osteoarthritis using MRI-based radiomic features from tibial bone

Objectives

Our aim was to assess the ability of semi-automatically extracted magnetic resonance imaging (MRI)–based radiomic features from tibial subchondral bone to distinguish between knees without and with osteoarthritis.

Methods

The right knees of 665 females from the population-based Rotterdam Study scanned with 1.5T MRI were analyzed. A fast imaging employing steady-state acquisition sequence was used for the quantitative bone analyses. Tibial bone was segmented using a method that combines multi-atlas and appearance models. Radiomic features related to the shape and texture were calculated from six volumes of interests (VOIs) in the proximal tibia. Machine learning–based Elastic Net models with 10-fold cross-validation were used to distinguish between knees without and with MRI Osteoarthritis Knee Score (MOAKS)–based tibiofemoral osteoarthritis. Performance of the covariate (age and body mass index), image features, and combined covariate + image features models were assessed using the area under the receiver operating characteristic curve (ROC AUC).

Results

Of 665 analyzed knees, 76 (11.4%) had osteoarthritis. An ROC AUC of 0.68 (95% confidence interval (CI): 0.60–0.75) was obtained using the covariate model. The image features model yielded an ROC AUC of 0.80 (CI: 0.73–0.87). The model that combined image features from all VOIs and covariates yielded an ROC AUC of 0.80 (CI: 0.73–0.87).

Conclusion

Our results suggest that radiomic features are useful imaging biomarkers of subchondral bone for the diagnosis of osteoarthritis. An advantage of assessing bone on MRI instead of on radiographs is that other tissues can be assessed simultaneously.

Key Points

• Subchondral bone plays a role in the osteoarthritis disease processes.

• MRI radiomics is a potential method for quantifying changes in subchondral bone.

• Semi-automatically extracted radiomic features of tibia differ between subjects without and with osteoarthritis.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00330-021-07951-5.

Evaluation and Management of Subchondral Calcium Phosphate Injection Technique to Treat Bone Marrow Lesion

PURPOSE

This study aimed to compile available data in medical literature about subchondral calcium phosphate injection, comparing results obtained with this technique, as well as indications, complications, and other important factors in treatment of bone marrow lesions.

DESIGNS

A literature review using PubMed and Medline database in order to identify works with terms "subchondral calcium phosphate injection," " subchondroplasty®," "bone marrow lesion," and "knee." Eight relevant articles were found.

RESULTS

A total of 164 patients with bone marrow lesion mainly on femoral condyle and tibial plateau recovered with significant functional improvement of knee after subchondral calcium phosphate treatment. Although 25% of them still had some type of pain complaint, they also showed improvement. There were few complications reported and return to activities occurred after 3 months on average.

CONCLUSIONS

Few studies evaluate the result of using subchondral calcium phosphate injection technique. However, all presented favorable results regarding pain and improvement of knee function. In addition, within 2 years, there was a 70% reduction in conversion to total knee arthroplasty in patients with previous surgical indication who choose calcium phosphate treatment.

Short-Term Outcomes for the Biologic Treatment of Bone Marrow Edema of the Knee Using Bone Marrow Aspirate Concentrate and Injectable Demineralized Bone Matrix

Purpose

To evaluate short-term outcomes for the biologic treatment of bone marrow edema (BME) of the knee using bone marrow aspirate concentrate (BMAC) and injectable demineralized bone matrix (iDBM).

Methods

We performed a review of prospectively collected data from patients who underwent treatment for bone marrow lesions (BMLs) of the knee using BMAC and iDBM (IntraOsseous BioPlasty; Arthrex, Naples, FL) between May 2017 and December 2018. Inclusion criteria included patients aged 18 to 65 years with the presence of BME on T2-weighted magnetic resonance imaging in the subchondral weightbearing region of the tibia or femoral condyle, with pain corresponding to the same compartment. The International Knee Documentation Committee (IKDC), pain visual analog scale (VAS), and 12-Item Short Form Health Survey (SF-12) scores were used to evaluate clinical outcomes.

Results

We evaluated 20 patients who were treated at a single academic medical institution over a mean 14.5-month follow-up (median, 14 months; range, 6-25 months). The average patient age was 51.7 years (range 38-62 years). Compared with preoperative values, the visual analog scale decreased from 7.0 to 1.3 (P = .008). The mean International Knee Documentation Committee scores improved from 29.2 to 66.1 (P = .063). Both the Physical and Mental Component Scores of the 12-Item Short Form Health Survey also showed improvement (Physical Component Score, P = .438; Mental Component Score, P = .563). Based on postoperative magnetic resonance imaging, 75% (3 of 4) of the BMLs demonstrated complete healing. The survival rate was 93% at 1-year follow-up.

Conclusion

Biologic treatment of BME of the knee using BMAC and iDBM is an effective adjunct to arthroscopy that provides short-term pain relief for BMLs associated with degenerative conditions of the knee. This procedure is associated with clinically significant improvements in knee pain and function at a short-term follow-up.

Level of Evidence

Level IV, therapeutic case series.

Bone texture analysis for prediction of incident radiographic hip osteoarthritis using machine learning: data from the Cohort Hip and Cohort Knee (CHECK) study

OBJECTIVE

To assess the ability of radiography-based bone texture variables in proximal femur and acetabulum to predict incident radiographic hip osteoarthritis (rHOA) over a 10 years period.

DESIGN

Pelvic radiographs from CHECK at baseline (987 hips) were analyzed for bone texture using fractal signature analysis (FSA) in proximal femur and acetabulum. Elastic net (machine learning) was used to predict the incidence of rHOA (including Kellgren-Lawrence grade (KL) ≥ 2 or total hip replacement (THR)), joint space narrowing score (JSN, range 0-3), and osteophyte score (OST, range 0-3) after 10 years. Performance of prediction models was assessed using the area under the receiver operating characteristic curve (ROC AUC).

RESULTS

Of the 987 hips without rHOA at baseline, 435 (44%) had rHOA at 10-year follow-up. Of the 667 hips with JSN grade 0 at baseline, 471 (71%) had JSN grade ≥ 1 at 10-year follow-up. Of the 613 hips with OST grade 0 at baseline, 526 (86%) had OST grade ≥ 1 at 10-year follow-up. AUCs for the models including age, gender, and body mass index (BMI) to predict incident rHOA, JSN, and OST were 0.59, 0.54, and 0.51, respectively. The inclusion of bone texture variables in the models improved the prediction of incident rHOA (ROC AUC 0.68 and 0.71 when baseline KL was also included in the model) and JSN (ROC AUC 0.62), but not incident OST (ROC AUC 0.52).

CONCLUSION

Bone texture analysis provides additional information for predicting incident rHOA or THR over 10 years.

Bone Density and Texture from Minimally Post-Processed Knee Radiographs in Subjects with Knee Osteoarthritis

Plain radiography is the most common modality to assess the stage of osteoarthritis. Our aims were to assess the relationship of radiography-based bone density and texture between radiographs with minimal and clinical post-processing, and to compare the differences in bone characteristics between controls and subjects with knee osteoarthritis or medial tibial bone marrow lesions (BMLs). Tibial bone density and texture was evaluated from radiographs with both minimal and clinical post-processing in 109 subjects with and without osteoarthritis. Bone texture was evaluated using fractal signature analysis. Significant correlations (p < 0.001) were found in all regions (between 0.94 and 0.97) for calibrated bone density between radiographs with minimal and clinical post-processing. Correlations varied between 0.51 and 0.97 (p < 0.001) for FD_Ver texture parameter and between − 0.10 and 0.97 for FD_Hor. Bone density and texture were different (p < 0.05) between controls and subjects with osteoarthritis or BMLs mainly in medial tibial regions. When classifying healthy and osteoarthritic subjects using a machine learning-based elastic net model with bone characteristics, area under the receiver operating characteristics (ROCAUC) curve was 0.77. For classifying controls and subjects with BMLs, ROCAUC was 0.85. In conclusion, differences in bone density and texture can be assessed from knee radiographs when using minimal post-processing.

Subchondral trabecular bone integrity changes following ACL injury and reconstruction: a cohort study with a nested, matched case-control analysis

OBJECTIVE

There is limited information regarding changes in bone architecture following anterior cruciate ligament (ACL) injury. The objective of this study was to evaluate differences in tibial fractal signature in the medial and lateral compartments following ACL injury and describe how these values change following ACL-reconstruction and return to activity.

DESIGN

This was a prospective cohort study with a nested case-control analysis. ACL-injured subjects and matched controls were evaluated at pre-surgical baseline and post ACL reconstruction follow-up at a mean of 46 months. Serial Fractal Dimensions (FD) of tibial subchondral bone architecture were calculated in medial and lateral regions of interest in the horizontal and vertical dimensions.

RESULTS

In the medial and lateral compartments, there were significant differences in the vertical FD signature for ACL-injured subjects at final follow-up, when compared to the contralateral healthy tibia (medial P < 0.0001; lateral P < 0.0001) and the control group (medial P = 0.01; lateral P < 0.0001). Similarly, in the lateral compartment, there were significant differences in the horizontal FD profile for ACL-injured subjects at final follow-up, when compared to the contralateral healthy tibia (P = 0.003) and the controls (P < 0.0001). There were no significant side-to-side differences in FDs among healthy control subjects in the medial or lateral compartments at baseline or final follow-up.

CONCLUSION

At 46-month follow-up, FD profiles are significantly different, and show an overall lower FD signature, for ACL-injured knees when compared to the contralateral healthy knee and uninjured controls. Additionally, this study provided the first side-to-side symmetry data of medial and lateral FD values in healthy controls.

Association of subchondral bone texture on magnetic resonance imaging with radiographic knee osteoarthritis progression: data from the Osteoarthritis Initiative Bone Ancillary Study

Objectives

To assess whether initial or 12–18-month change in magnetic resonance imaging (MRI) subchondral bone texture is predictive of radiographic knee osteoarthritis (OA) progression over 36 months.

Methods

This was a nested case-control study including 122 knees/122 participants in the Osteoarthritis Initiative (OAI) Bone Ancillary Study, who underwent MRI optimised for subchondral bone assessment at either the 30- or 36-month and 48-month OAI visits. Case knees (n = 61) had radiographic OA progression between the 36- and 72-month OAI visits, defined as ≥ 0.7 mm minimum medial tibiofemoral radiographic joint space (minJSW) loss. Control knees (n = 61) without radiographic OA progression were matched (1:1) to cases for age, sex, body mass index and initial medial minJSW. Texture analysis was performed on the medial femoral and tibial subchondral bone. We assessed the association of texture features with radiographic progression by creating a composite texture score using penalised logistic regression and calculating odds ratios. We evaluated the predictive performance of texture features for predicting radiographic progression using c-statistics.

Results

Initial (odds ratio [95% confidence interval] = 2.13 [1.41–3.40]) and 12– 18-month change (3.76 [2.04–7.82]) texture scores were significantly associated with radiographic OA progression. Combinations of texture features were significant predictors of radiographic progression using initial (c-statistic [95% confidence interval] = 0.65 [0.64–0.65], p = 0.003) and 12–18-month change (0.68 [0.68-0.68], p < 0.001) data.

Conclusions

Initial and 12–18-month changes in MRI subchondral bone texture score were significantly associated with radiographic progression at 36 months, with better predictive performance for 12–18-month change in texture. These results suggest that texture analysis may be a useful biomarker of subchondral bone in OA.

Key Points

• Subchondral bone MRI texture analysis is a promising knee osteoarthritis imaging biomarker.

• In this study, subchondral bone texture was associated with knee osteoarthritis progression.

• This demonstrates predictive and concurrent validity of MRI subchondral bone texture analysis.

• This method may be useful in clinical trials with interventions targeting bone.

Electronic supplementary material

The online version of this article (10.1007/s00330-018-5444-9) contains supplementary material, which is available to authorized users.

Periarticular bone predicts knee osteoarthritis progression: Data from the Osteoarthritis Initiative

OBJECTIVE

Osteoarthritis (OA) is a disease with a substantial public health burden. Quantitative assessments of periarticular bone may be a biomarker capable of monitoring early disease progression. The purpose of this study was to evaluate whether measures of periarticular bone associate with longitudinal structural progression.

METHODS

We conducted a 12-18 months longitudinal study using the Osteoarthritis Initiative (OAI). Participants received knee dual-energy x-ray absorptiometry (DXA), trabecular magnetic resonance (MR) imaging, and x-rays. Knee DXAs generated proximal tibial medial:lateral periarticular bone mineral density (paBMD) measures. Proximal tibial trabecular MR images were assessed for trabecular morphometry: apparent bone volume fraction (BVF), trabecular number, thickness, and spacing. Weight-bearing x-rays were assessed for medial tibiofemoral joint space narrowing (JSN). Chi-squared analyses assessed whether periarticular bone measures were predictive of worsening medial tibiofemoral JSN, adjusted for age, sex, and BMI.

RESULTS

In all, 444 participants, mean age 64.2 ± 9.2 years, BMI 29.5 ± 4.6kg/m², and 52% male at baseline. Medial JSN (radiographic progression) occurred in 40 participants (9%). Higher baseline medial:lateral paBMD, apparent BVF, trabecular number and thickness, and lower baseline and decreased trabecular spacing were all associated with more progression of JSN in the medial compartment. From lowest to highest baseline medial:lateral paBMD quartile groups, 2%, 5%, 11%, and 18% had medial JSN progression, respectively, between the 36- and 48-month visits, p-values = 0.001 and 0.002 unadjusted and adjusted. The rate of change in medial:lateral paBMD, apparent BVF, and spacing were associated with more medial JSN. For rate of medial:lateral paBMD change from lowest to highest quartile, the proportion of each group that experienced medial JSN progression were 5%, 5%, 11%, and 18%, with an unadjusted and adjusted p-value of 0.005.

CONCLUSION

Baseline and most rates of periarticular bone change associate with knee OA structural progression, highlighting the close relationship between subchondral bone and JSN. Future studies should focus on developing these measures as predictive and pathophysiological biomarkers, and evaluating their deployment in clinical trials testing bone-targeted therapeutics.

Predictive Validity of Radiographic Trabecular Bone Texture in Knee Osteoarthritis: The Osteoarthritis Research Society International/Foundation for the National Institutes of Health Osteoarthritis Biomarkers Consortium

OBJECTIVE

To evaluate radiographic subchondral trabecular bone texture (TBT) as a predictor of clinically relevant osteoarthritis (OA) progression (combination of symptom and structural worsening).

METHODS

The Foundation for the National Institutes of Health (FNIH) OA Biomarkers Consortium undertook a study of progressive knee OA cases (n = 194 knees with both radiographic and pain progression over 24-48 months) and comparators (n = 406 OA knees not meeting the case definition). TBT parameters were extracted from a medial subchondral tibial region of interest by fractal signature analysis of radiographs using validated semiautomated software. Baseline TBT and time-integrated values over 12 and 24 months were evaluated for association with case status and separately with radiographic and pain progression status, adjusted for age, sex, body mass index, race, baseline Kellgren/Lawrence grade, baseline joint space width, Western Ontario and McMaster Universities Osteoarthritis Index pain score, and pain medication use. C statistics were generated from receiver operating characteristic curves.

RESULTS

Relative to comparators, cases were characterized by thinner vertical and thicker horizontal trabeculae. The summed composite of 3 TBT parameters at baseline and over 12 and 24 months best predicted case status (odds ratios 1.24-1.43). The C statistic for predicting case status using the TBT composite score (0.633-0.649) was improved modestly but statistically significantly over the use of covariates alone (0.608). One TBT parameter, reflecting thickened horizontal trabeculae in cases, at baseline and over 12 and 24 months, predicted risk of any progression (radiographic and/or pain progression).

CONCLUSION

Although associations are modest, TBT could be an attractive means of enriching OA trials for progressors since it can be generated from screening knee radiographs already standard in knee OA clinical trials.

Association between radiography-based subchondral bone structure and MRI-based cartilage composition in postmenopausal women with mild osteoarthritis

OBJECTIVE

Our aim was to investigate the relation between radiograph-based subchondral bone structure and cartilage composition assessed with delayed gadolinium enhanced magnetic resonance imaging of cartilage (dGEMRIC) and T₂ relaxation time.

DESIGN

Ninety-three postmenopausal women (Kellgren-Lawrence grade 0: n = 13, 1: n = 26, 2: n = 54) were included. Radiograph-based bone structure was assessed using entropy of the Laplacian-based image (E_Lap) and local binary patterns (E_LBP), homogeneity indices of the local angles (HI_Angles,mean, HI_Angles,Perp, HI_Angles,Paral), and horizontal (FD_Hor) and vertical fractal dimensions (FD_Ver). Mean dGEMRIC index and T₂ relaxation time of tibial cartilage were calculated to estimate cartilage composition.

RESULTS

HI_Angles,mean (r_s = -0.22) and HI_Angles,Paral (r_s = -0.24) in medial subchondral bone were related (P < 0.05) to dGEMRIC index of the medial tibial cartilage. E_Lap (r_s = -0.23), FD_Hor,0.34 mm (r = 0.21) and FD_Ver,0.68 mm (r = 0.24) in medial subchondral bone were related (P < 0.05) to T₂ relaxation time values of the medial tibial cartilage. FD_Hor at different scales in lateral subchondral bone were related (P < 0.01) to dGEMRIC index (r = 0.29-0.41) and T₂ values of lateral tibial cartilage (r = -0.28 to -0.36). FD_Ver at larger scales were related (P < 0.05) to dGEMRIC index (r = 0.24-0.25) and T₂ values of lateral tibial cartilage (r = -0.21). HI_Angles,Paral (r = -0.25) and FD_Ver,0.68 mm (r_s = 0.22) in the lateral tibial trabecular bone were related (P < 0.05) to dGEMRIC index of the lateral tibial cartilage.

CONCLUSION

Our results support the presumption that several tissues are affected in the early osteoarthritis (OA). Furthermore, they indicate that the detailed analysis of radiographs may serve as a complementary imaging tool for OA studies.

Subchondral tibial bone texture predicts the incidence of radiographic knee osteoarthritis: data from the Osteoarthritis Initiative

OBJECTIVES

To evaluate whether trabecular bone texture (TBT) parameters measured on computed radiographs (CR) could predict the onset of radiographic knee osteoarthritis (OA).

MATERIALS AND METHODS

Subjects from the Osteoarthritis Initiative (OAI) with no sign of radiographic OA at baseline were included. Cases that developed either a global radiographic OA defined by the Kellgren-Lawrence (KL) scale, a joint space narrowing (JSN) or tibial osteophytes (TOS) were compared with the controls with no changes after 48 months of follow-up. Baseline bilateral fixed flexion CR were analyzed using a fractal method to characterize the local variations. The prediction was explored using logistic regression models evaluated by the area under the receiver operating characteristic curves (AUC).

RESULTS

From the 344 knees, 79 (23%) developed radiographic OA after 48 months, 44 (13%) developed progressive JSN and 59 (17%) developed osteophytes. Neither age, gender and BMI, nor their combination predicted poorer KL (AUC 0.57), JSN or TOS (AUC 0.59) scores. The inclusion of the TBT parameters in the models improved the global prediction results for KL (AUC 0.69), JSN (AUC 0.73) and TOS (AUC 0.71) scores.

CONCLUSIONS

Several differences were found between the models predictive of three different outcomes (KL, JSN and TOS), indicating different underlying mechanisms. These results suggest that TBT parameters assessed when radiographic signs are not yet apparent on radiographs may be useful in predicting the onset of radiological tibiofemoral OA as well as identifying at-risk patients for future clinical trials.

Association Between Biochemical Markers of Bone Turnover and Bone Changes on Imaging: Data From the Osteoarthritis Initiative

OBJECTIVE

To determine the relationship between biochemical markers involved in bone turnover and bone features on imaging in knees with osteoarthritis (OA).

METHODS

We analyzed data from the Foundation for the National Institutes of Health OA Biomarkers Consortium within the Osteoarthritis Initiative (n = 600). Bone marrow lesions (BMLs), osteophytes, and subchondral bone area (mm² ) and shape (position on 3-D vector) were assessed on magnetic resonance images, and bone trabecular integrity (BTI) was assessed on radiographs. Serum and urinary markers (serum C-terminal crosslinked telopeptide of type I collagen [CTX-I], serum crosslinked N-telopeptide of type I collagen [NTX-I], urinary NTX-I, urinary C-terminal crosslinked telopeptide of type II collagen [CTX-II], and urinary CTX-Iα and CTX-Iβ) were measured. The associations between biochemical and imaging markers at baseline and over 24 months were assessed using regression models adjusted for covariates.

RESULTS

At baseline, most biochemical markers were associated with BMLs, with C statistics for the presence/absence of any BML ranging from 0.675 to 0.688. At baseline, urinary CTX-II was the marker most consistently associated with BMLs (with odds of having ≥5 subregions affected compared to no BML increasing by 1.92-fold [95% confidence interval (95% CI) 1.25, 2.96] per 1 SD of urinary CTX-II), large osteophytes (odds ratio 1.39 [95% CI 1.10, 1.77]), bone area and shape (highest partial R²  = 0.032), and changes in bone shape over 24 months (partial R² range 0.008 to 0.024). Overall, biochemical markers were not predictive of changes in BMLs or osteophytes. Serum NTX-I was inversely associated with BTI of the vertical trabeculae (quadratic slope) in all analyses (highest partial R²  = 0.028).

CONCLUSION

We found multiple significant associations, albeit mostly weak ones. The role of systemic biochemical markers as predictors of individual bone anatomic features of single knees is limited based on our findings.

Crystallographic orientation of the c-axis of biological apatite as a new index of the quality of subchondral bone in knee joint osteoarthritis

The aim of the present study was to investigate the preferred orientation of biological apatite (BAp) as a new index of the quality of subchondral bone (SB) in knee joint osteoarthritis (OA). Ten OA and five normal knee joints were obtained. Thickness, quantity and bone mineral density (BMD) of SB were analyzed at the medial condyle of the femur in dry conditions by peripheral quantitative computed tomography. In addition, the preferred crystallographic orientation of the c-axis of BAp was evaluated as bone quality parameter using a microbeam X-ray diffractometer technique. BMD and thickness of SB were significantly increased in OA specimens compared to normal knee specimens (P < 0.01), and the preferred orientation of the c-axis of BAp along the normal direction of SB surface was significantly higher in OA specimens (P < 0.01), reflecting the change in stress of concentration in the pathological portion without cartilage. SB sclerosis in OA results in both proliferation of bone tissues and enhanced degree of preferential alignment of the c-axis of BAp. Our findings could have major implications for the diagnosis of clinical studies, including pathologic elucidation in OA.

Subchondroplasty for treating bone marrow lesions in the knee - initial experience

OBJECTIVE

To evaluate the use of subchondroplasty in the treatment of bone marrow lesions in an initial series of five cases.

METHODS

The study included patients aged between 40 and 75 years old, with pain in the knee for at least six months, associated with high-signal MRI lesion on T2 sequences, on the tibia or femur. Patients were assessed using the visual analog pain scale and the KOOS score, one week before surgery and one, three, six, 12, and 24 weeks after the procedure. Subchondroplasty was performed with a technique developed for filling the area of the bone marrow lesion with a calcium phosphate bone substitute.

RESULTS

The filling was performed on the medial femoral condyle in four patients and medial tibial plateau in one case. The assessment by the KOOS score presented a preoperative average of 38.44 points and 62.7, 58.08, 57.92, 63.34, and 71.26 points with one, three, six, 12, and 24 weeks after surgery, respectively. In the evaluation by the VAS, the average was 7.8 points preoperatively and 2.8, 3, 2.8, 1.8, and 0.6 points over the same periods. All patients were able to ambulate without additional support, on the first day after the procedure. One patient had a minimal graft dislocation to the soft tissue, with local pain, which resolved completely after a week.

CONCLUSION

The subchondroplasty technique provided significant improvements in the parameters of pain and functional capacity in the short-term assessment.

Early Osteoarthritis After Untreated Anterior Meniscal Root Tears: An In Vivo Animal Study

Background:

Meniscal root tears cause menisci and their insertions to inadequately distribute loads and potentially leave underlying articular cartilage unprotected. Untreated meniscal root tears are becoming increasingly recognized to induce joint degradation; however, little information is known about anterior meniscal root tears and how they affect joint tissue.

Purpose:

To observe the early degenerative changes within the synovial fluid, menisci, tibial articular cartilage, and subchondral bone after arthroscopic creation of untreated anterior meniscal root tears.

Study Design:

Controlled laboratory study.

Methods:

Anterolateral meniscal root tears were created in 1 knee joint of 5 adult Flemish Giant rabbits, and anteromedial meniscal root tears were created in 4 additional rabbits. The contralateral limbs were used as nonoperated controls. The animals were euthanized at 8 weeks postoperatively; synovial fluid was aspirated, and tissue samples of menisci and tibial articular cartilage were collected and processed for multiple analyses to detect signs of early degeneration.

Results:

Significant changes were found within the synovial fluid, meniscal tissue, and tibial subchondral bone of the knees with anterior meniscal root tears when compared with controls. There were no significant changes identified in the tibial articular cartilage when comparing the tear groups with controls.

Conclusion:

This study demonstrated early degenerative changes within the synovial fluid, menisci, and tibial subchondral bone when leaving anterior meniscal root tears untreated for 8 weeks. The results suggest that meniscal tissue presents measurable, degenerative changes prior to changes within the articular cartilage after anterior meniscal root tears. Anterior destabilization of the meniscus arthroscopically may lead to measurable degenerative changes and be useful for future in vivo natural history and animal repair studies.

Clinical Relevance:

The present study is the first to investigate various tissue changes after anterior meniscal root tears of both the medial and lateral menisci. The results from this study suggest that degenerative changes occur within the synovial fluid, meniscus, and tibial subchondral bone prior to any measurable changes to the tibial articular cartilage. Further studies should expand on this study to evaluate how these components continue to progress when left untreated for long periods.

Differences in tibial subchondral bone structure evaluated using plain radiographs between knees with and without cartilage damage or bone marrow lesions - the Oulu Knee Osteoarthritis study

Objectives

To investigate whether subchondral bone structure from plain radiographs is different between subjects with and without articular cartilage damage or bone marrow lesions (BMLs).

Methods

Radiography-based bone structure was assessed from 80 subjects with different stages of knee osteoarthritis using entropy of Laplacian-based image (E_Lap) and local binary patterns (E_LBP), homogeneity index of local angles (HI_Angles,mean), and horizontal (FD_Hor) and vertical fractal dimensions (FD_Ver). Medial tibial articular cartilage damage and BMLs were scored using the magnetic resonance imaging osteoarthritis knee score. Level of statistical significance was set to p < 0.05.

Results

Subjects with medial tibial cartilage damage had significantly higher FD_Ver and E_LBP as well as lower E_Lap and HI_Angles,mean in the medial tibial subchondral bone region than subjects without damage. FD_Hor, FD_Ver, and E_LBP were significantly higher, whereas E_Lap and HI_Angles,mean were lower in the medial trabecular bone region. Subjects with medial tibial BMLs had significantly higher FD_Ver and E_LBP as well as lower E_Lap and HI_Angles,mean in medial tibial subchondral bone. FD_Hor, FD_Ver, and E_LBP were higher, whereas E_Lap and HI_Angles,mean were lower in medial trabecular bone.

Conclusions

Our results support the use of bone structural analysis from radiographs when examining subjects with osteoarthritis or at risk of having it.

Key points

• Knee osteoarthritis causes changes in articular cartilage and subchondral bone

• Magnetic resonance imaging is a comprehensive imaging modality for knee osteoarthritis

• Radiography-based bone structure analysis can provide additional information of osteoarthritic subjects

Age-dependent Changes in the Articular Cartilage and Subchondral Bone of C57BL/6 Mice after Surgical Destabilization of Medial Meniscus

Age is the primary risk factor for osteoarthritis (OA), yet surgical OA mouse models such as destabilization of the medial meniscus (DMM) used for evaluating disease-modifying OA targets are frequently performed on young adult mice only. This study investigates how age affects cartilage and subchondral bone changes in mouse joints following DMM. DMM was performed on male C57BL/6 mice at 4 months (4 M), 12 months (12 M) and 19+ months (19 M+) and on females at 12 M and 18 M+. Two months after surgery, operated and unoperated contralateral knees were harvested and evaluated using cartilage histology scores and μCT quantification of subchondral bone plate thickness and osteophyte formation. The 12 M and 19 M+ male mice developed more cartilage erosions and thicker subchondral bone plates after DMM than 4 M males. The size of osteophytes trended up with age, while the bone volume fraction was significantly higher in the 19 M+ group. Furthermore, 12 M females developed milder OA than males as indicated by less cartilage degradation, less subchondral bone plate sclerosis and smaller osteophytes. Our results reveal distinct age/gender-dependent structural changes in joint cartilage and subchondral bone post-DMM, facilitating more thoughtful selection of murine age/gender when using this surgical technique for translational OA research.

Subchondral tibial bone texture analysis predicts knee osteoarthritis progression: data from the Osteoarthritis Initiative: Tibial bone texture & knee OA progression

OBJECTIVES

To examine whether trabecular bone texture (TBT) parameters assessed on computed radiographs could predict knee osteoarthritis (OA) progression.

METHODS

This study was performed using data from the Osteoarthritis Initiative (OAI). 1647 knees in 1124 patients had bilateral fixed flexion radiographs acquired 48 months apart. Images were semi-automatically segmented to extract a patchwork of regions of interest (ROI). A fractal texture analysis was performed using different methods. OA progression was defined as an increase in the joint space narrowing (JSN) over 48 months. The predictive ability of TBT was evaluated using logistic regression and receiver operating characteristic (ROC) curve. An optimization method for features selection was used to reduce the size of models and assess the impact of each ROI.

RESULTS

Fractal dimensions (FD's) were predictive of the JSN progression for each method tested with an area under the ROC curve (AUC) up to 0.71. Baseline JSN grade was not correlated with TBT parameters (R < 0.21) but had the same predictive capacity (AUC 0.71). The most predictive model included the clinical covariates (age, gender, body mass index (BMI)), JSN and TBT parameters (AUC 0.77). From a statistical point of view we found higher differences in TBT parameters computed in medial ROI between progressors and non-progressors. However, the integration of TBT results from the whole patchwork including the lateral ROIs in the model provided the best predictive model.

CONCLUSIONS

Our findings indicate that TBT parameters assessed in different locations in the joint provided a good predictive ability to detect knee OA progression.

Advanced Knee Structure Analysis (AKSA): a comparison of bone mineral density and trabecular texture measurements using computed tomography and high-resolution peripheral quantitative computed tomography of human knee cadavers

Background

A change of loading conditions in the knee causes changes in the subchondral bone and may be a cause of osteoarthritis (OA). However, quantification of trabecular architecture in vivo is difficult due to the limiting spatial resolution of the imaging equipment; one approach is the use of texture parameters. In previous studies, we have used digital models to simulate changes of subchondral bone architecture under OA progression. One major result was that, using computed tomography (CT) images, subchondral bone mineral density (BMD) in combination with anisotropy and global homogeneity could characterize this progression.

The primary goal of this study was a comparison of BMD, entropy, anisotropy, variogram slope, and local and global inhomogeneity measurements between high-resolution peripheral quantitative CT (HR-pQCT) and CT using human cadaveric knees. The secondary goal was the verification of the spatial resolution dependence of texture parameters observed in the earlier simulations, two important prerequisites for the interpretation of in vivo measurements in OA patients.

Method

The applicability of texture analysis to characterize bone architecture in clinical CT examinations was investigated and compared to results obtained from HR-pQCT. Fifty-seven human knee cadavers (OA status unknown) were examined with both imaging modalities. Three-dimensional (3D) segmentation and registration processes, together with automatic positioning of 3D analysis volumes of interest (VOIs), ensured the measurement of BMD and texture parameters at the same anatomical locations in CT and HR-pQCT datasets.

Results

According to the calculation of dice ratios (>0.978), the accuracy of VOI locations between methods was excellent. Entropy, anisotropy, and global inhomogeneity showed significant and high linear correlation between both methods (0.68 < R² < 1.00). The resolution dependence of these parameters simulated earlier was confirmed by the in vitro measurements.

Conclusion

The high correlation of HR-pQCT- and CT-based measurements of entropy, global inhomogeneity, and anisotropy suggests interchangeability between devices regarding the quantification of texture. The agreement of the experimentally determined resolution dependence of global inhomogeneity and anisotropy with earlier simulations is an important milestone towards their use to quantify subchondral bone structure. However, an in vivo study is still required to establish their clinical relevance.

Imaging of osteoarthritis (OA): What is new?

In daily clinical practice, conventional radiography is still the most applied imaging technique to supplement clinical examination of patients with suspected osteoarthritis (OA); it may not always be needed for diagnosis. Modern imaging modalities can visualize multiple aspects of the joint, and depending on the diagnostic need, radiography may no longer be the modality of choice. Magnetic resonance imaging (MRI) provides a complete assessment of the joint and has a pivotal role in OA research. Computed tomography (CT) and nuclear medicine offer alternatives in research scenarios, while ultrasound can visualize bony and soft-tissue pathologies and is highly feasible in the clinic. In this chapter, we overview the recent literature on established and newer imaging modalities, summarizing their ability to detect and quantify the range of OA pathologies and determining how they may contribute to early OA diagnosis. This accurate imaging-based detection of pathologies will underpin true understanding of much needed structure-modifying therapies.

Baseline trabecular bone and its relation to incident radiographic knee osteoarthritis and increase in joint space narrowing score: directional fractal signature analysis in the MOST study

PURPOSE

To explore the association of baseline trabecular bone structure with incident tibiofemoral (TF) osteoarthritis (OA) and with increase in joint space narrowing (JSN) score.

METHODS

The Multicenter Osteoarthritis Study (MOST) includes subjects with or at risk for knee OA. Knee radiographs were scored for Kellgren-Lawrence (KL) grade and JSN at baseline, 30, 60 and 84 months. Knees (KL ≤ 1) at baseline were assessed for incident OA (KL ≥ 2) and increases in JSN score. For each knee image at baseline, a variance orientation transform method (VOT) was applied to subchondral tibial bone regions of medial and lateral compartments. Seventeen fractal parameters were calculated per region. Associations of each parameter with OA incidence and with medial and lateral JSN increases were explored using logistic regression. Analyses were stratified by digitized film (DF) vs computer radiography (CR) and adjusted for confounders.

RESULTS

Of 894 knees with CR and 1158 knees with DF, 195 (22%) and 303 (26%) developed incident OA. Higher medial bone roughness was associated with increased odds of OA incidence at 60 and 84 months and also, medial and lateral JSN increases (primarily vertical). Lower medial and lateral anisotropy was associated with increased odds of medial and lateral JSN increase. Compared to DF, CR had more associations and also, similar results at overlapping scales.

CONCLUSION

Baseline trabecular bone texture was associated with incident radiographic OA and increase of JSN scores independently of risk factors for knee OA. Higher roughness and lower anisotropy were associated with increased odds for radiographic OA change.

Early osteoarthritis of the knee

There is an increasing awareness on the importance in identifying early phases of the degenerative processes in knee osteoarthritis (OA), the crucial period of the disease when there might still be the possibility to initiate treatments preventing its progression. Early OA may show a diffuse and ill-defined involvement, but also originate in the cartilage surrounding a focal lesion, thus necessitating a separate assessment of these two entities. Early OA can be considered to include a maximal involvement of 50 % of the cartilage thickness based on the macroscopic ICRS classification, reflecting an OARSI grade 4. The purpose of this paper was to provide an updated review of the current status of the diagnosis and definition of early knee OA, including the clinical, radiographical, histological, MRI, and arthroscopic definitions and biomarkers. Based on current evidence, practical classification criteria are presented. As new insights and technologies become available, they will further evolve to better define and treat early knee OA.

Subchondral bone and osteoarthritis

PURPOSE OF REVIEW

Increasing evidence show that bone is a key factor in the development of osteoarthritis. This article reviews the latest results of basic and clinical research on the role of the subchondral bone in osteoarthritis.

RECENT FINDINGS

Early changes in the subchondral bone can predict subsequent symptoms or disease structural progression. New tools may help clinicians to stratify different osteoarthritis phenotypes with regards to bone remodeling status.

SUMMARY

The involvement of bone in osteoarthritis has long been thought to be secondary to cartilage damage as an adaptation of the joint. Recent clinical studies with MRI have demonstrated that bone changes could be observed in early stages of the disease, even preceding cartilage lesions. Moreover, there is clear evidence of an association between subchondral bone mineral density and osteoarthritis. The level of bone remodeling plays a critical role under mechanical loading conditions as demonstrated by consistent experimental studies. Yet new clinical biomarkers are being developed to assess the bone phenotype of osteoarthritic patients. This stratification strategy is likely to better identify groups of patients who would benefit from bone-acting drugs to decrease disease progression and improve pain and disability.

MRI texture analysis of subchondral bone at the tibial plateau

OBJECTIVES

To determine the feasibility of MRI texture analysis as a method of quantifying subchondral bone architecture in knee osteoarthritis (OA).

METHODS

Asymptomatic subjects aged 20-30 (group 1, n = 10), symptomatic patients aged 40-50 (group 2, n = 10) and patients scheduled for knee replacement aged 55-85 (group 3, n = 10) underwent high spatial resolution T1-weighted coronal 3T knee MRI. Regions of interest were created in the medial (MT) and lateral (LT) tibial subchondral bone from which 20 texture parameters were calculated. T2 mapping of the tibial cartilage was performed in groups 1 and 2. Mean parameter values were compared between groups using ANOVA. Linear discriminant analysis (LDA) was used to evaluate the ability of texture analysis to classify subjects correctly.

RESULTS

Significant differences in 18/20 and 12/20 subchondral bone texture parameters were demonstrated between groups at the MT and LT respectively. There was no significant difference in mean MT or LT cartilage T2 values between group 1 and group 2. LDA demonstrated subject classification accuracy of 97 % (95 % CI 91-100 %).

CONCLUSION

MRI texture analysis of tibial subchondral bone may allow detection of alteration in subchondral bone architecture in OA. This has potential applications in understanding OA pathogenesis and assessing response to treatment.

KEY POINTS

• Improved techniques to monitor OA disease progression and treatment response are desirable • Subchondral bone (SB) may play significant role in the development of OA • MRI texture analysis is a method of quantifying changes in SB architecture • Pilot study showed that this technique is feasible and reliable • Significant differences in SB texture were demonstrated between individuals with/without OA.

Conventional and novel imaging modalities in osteoarthritis: current state of the evidence

PURPOSE OF REVIEW

Imaging modalities are currently an inseparable part of osteoarthritis diagnosis. In this review, we describe the current state of evidence regarding conventional and novel imaging modalities in evaluation of osteoarthritis. Modalities including radiography (qualitative and semi-quantitative assessments), ultrasonography, computed tomography [CT; conventional multidetector CT (MDCT), cone-beam CT (CBCT) and four-dimensional CT (4DCT)], MRI (MRI; semi-quantitative, quantitative and compositional) and PET and their applications are reviewed.

RECENT FINDINGS

Radiography is the modality of choice for initial assessment of osteoarthritis. However, due to its low sensitivity and specificity, numerous recent investigations have proposed MRI as a powerful addition to detect and grade osteoarthritis features, which are not apparent in radiography. Semi-quantitative MRI measurements are feasible to perform in routine clinical practice. Quantitative and compositional MRI measurements have extended the amount of information an MRI examination can provide regarding the three-dimensional shape and tissue composition of articular cartilage. 4DCT and CBCT are introduced as imaging examinations that may reveal biomechanical cartilage abnormalities in osteoarthritis joint by dynamic and weight-bearing evaluations, respectively. Recent PET studies may unveil the underlying metabolic activities that can be associated with osteoarthritis.

SUMMARY

In addition to the established role of radiographs, MRI is the advanced modality of choice for detection and quantification of various osteoarthritis features. 4DCT and CBCT may have specified applications when diagnosis of underlying motion abnormality or dynamic changes in weight-bearing situation is suspected. Future studies should elucidate the specific clinical applications of ultrasonography and PET.

Gene therapy for human osteoarthritis: principles and clinical translation

INTRODUCTION

Osteoarthritis (OA) is the most prevalent chronic joint disease. Its key feature is a progressive articular cartilage loss. Gene therapy for OA aims at delivering gene-based therapeutic agents to the osteoarthritic cartilage, resulting in a controlled, site-specific, long-term presence to rebuild the damaged cartilage.

AREAS COVERED

An overview is provided of the principles of gene therapy for OA based on a PubMed literature search. Gene transfer to normal and osteoarthritic cartilage in vitro and in animal models in vivo is reviewed. Results from recent clinical gene therapy trials for OA are discussed and placed into perspective.

EXPERT OPINION

Recombinant adeno-associated viral (rAAV) vectors enable to directly transfer candidate sequences in human articular chondrocytes in situ, providing a potent tool to modulate the structure of osteoarthritic cartilage. However, few preclinical animal studies in OA models have been performed thus far. Noteworthy, several gene therapy clinical trials have been carried out in patients with end-stage knee OA based on the intraarticular injection of human juvenile allogeneic chondrocytes overexpressing a cDNA encoding transforming growth factor-beta-1 via retroviral vectors. In a recent placebo-controlled randomized trial, clinical scores were improved compared with placebo. These translational results provide sufficient reason to proceed with further clinical testing of gene transfer protocols for the treatment of OA.

Longitudinal validation of periarticular bone area and 3D shape as biomarkers for knee OA progression? Data from the FNIH OA Biomarkers Consortium

OBJECTIVE

To perform a longitudinal validation study of imaging bone biomarkers of knee osteoarthritis (OA) progression.

METHODS

We undertook a nested case-control study within the Osteoarthritis Initiative in knees (one knee per subject) with a Kellgren and Lawrence grade of 1-3. Cases were defined as knees having the combination of medial tibiofemoral radiographic progression and pain progression at the 24-month, 36-month or 48-month follow-up compared with baseline. Controls (n=406) were eligible knees that did not meet both endpoint criteria and included 200 with neither radiographic nor pain progression, 103 with radiographic progression only and 103 with pain progression only. Bone surfaces in medial and lateral femur, tibia and patella compartments were segmented from MR images using active appearance models. Independent variables of primary interest included change from baseline to 24 months in (1) total area of bone and (2) position on three-dimensional (3D) bone shape vectors that discriminate OA versus non-OA shapes. We assessed the association of bone markers changes over 24 months with progression using logistic regression.

RESULTS

24-month changes in bone area and shape in all compartments were greater in cases than controls, with ORs of being a case per 1 SD increase in bone area ranging from 1.28 to 1.71 across compartments, and per 1 SD greater change in 3D shape vectors ranging from 1.22 to 1.64. Bone markers were associated most strongly with radiographic progression and only weakly with pain progression.

CONCLUSIONS

In knees with mild-to-moderate radiographic OA, changes in bone area and shape over 24 months are associated with the combination of radiographic and pain progression over 48 months. This finding of association with longer term clinical outcome underscores their potential for being an efficacy of intervention biomarker in clinical trials.

Correlation of Subchondral Bone Density and Structure from Plain Radiographs with Micro Computed Tomography Ex Vivo

Osteoarthritis causes changes in the subchondral bone structure and composition. Plain radiography is a cheap, fast, and widely available imaging method. Bone tissue can be well seen from plain radiograph, which however is only a 2D projection of the actual 3D structure. Therefore, the aim was to investigate the relationship between bone density- and structure-related parameters from 2D plain radiograph and 3D bone parameters assessed from micro computed tomography (µCT) ex vivo. Right tibiae from eleven cadavers without any diagnosed joint disease were imaged using radiography and with µCT. Bone density- and structure-related parameters were calculated from four different locations from the radiographs of proximal tibia and compared with the volumetric bone microarchitecture from the corresponding regions. Bone density from the plain radiograph was significantly related with the bone volume fraction (r = 0.86; n = 44; p < 0.01). Mean homogeneity index for orientation of local binary patterns (HI_angle,mean) and fractal dimension of vertical structures (FD_Ver) were related (p < 0.01) with connectivity density (HI_angle,mean: r = −0.73, FD_Ver: r = 0.69) and trabecular separation (HI_angle,mean: r = 0.73, FD_Ver: r = −0.70) when all ROIs were pooled together (n = 44). Bone density and structure in tibia from standard clinically available 2D radiographs are significantly correlated with true 3D microstructure of bone.

Wolff's law in action: a mechanism for early knee osteoarthritis

There is growing interest in the role of bone in knee osteoarthritis. Bone is a dynamic organ, tightly regulated by a multitude of homeostatic controls, including genetic and environmental factors. One such key environmental regulator of periarticular bone is mechanical stimulation, which, according to Wolff’s law, is a key determinant of bone properties. Wolff’s law theorizes that repetitive loading of bone will cause adaptive responses enabling the bone to better cope with these loads. Despite being an adaptive response of bone, the remodeling process may inadvertently trigger maladaptive responses in other articular structures. Accumulating evidence at the knee suggests that expanding articular bone surface area is driven by mechanical stimulation and is a strong predictor of articular cartilage loss. Similarly, fractal analysis of bone architecture provides further clues that bone adaptation may have untoward consequences for joint health. This review hypothesizes that adaptations of periarticular bone in response to mechanical stimulation cause maladaptive responses in other articular structures that mediate the development of knee osteoarthritis. A potential disease paradigm to account for such a hypothesis is also proposed, and novel therapeutic targets that may have a bone-modifying effect, and therefore potentially a disease-modifying effect, are also explored.

OA phenotypes, rather than disease stage, drive structural progression--identification of structural progressors from 2 phase III randomized clinical studies with symptomatic knee OA

BACKGROUND/PURPOSE

The aim of this study was to identify key characteristics of disease progression through investigation of the association of radiographic progression over two years with baseline Joint Space Width (JSW), Kellgren-Lawrence (KL) grade, Western Ontario and McMaster Universities Arthritis Index (WOMAC) pain, Joint Space Narrowing (JSN), and BMI.

METHODS

Data from 2206 subjects (4390 knees) were combined for this post-hoc analysis of two randomized, double-blind, multi-center, placebo-controlled phase III trials (NCT00486434 and NCT00704847) that evaluated the efficacy and safety of 2-years treatment with oral salmon calcitonin of subjects with painful knee osteoarthritis (OA).

RESULTS

There was a clear positive and significant correlation between KL grade and WOMAC pain and total WOMAC, albeit the variance in pain measures was from min-to-max for all KL categories, emphasizing the heterogeneity of this patient population and pain perception. 32% of target knees did not progress, and only 51% had changes over minimum significant change (MSC). BMI, KL-Score and WOMAC pain was diagnostic, but only KL-score and pain had prognostic value, albeit pain in a non-linear manner.

CONCLUSION

These data clearly describe significant associations between KL grade, JSW, pain and BMI in patients with symptomatic knee OA. KL grade, BMI and WOMAC pain were diagnostically associated with OA based on JSW but only KL-score and pain in a non-linier fashion was prognostic. 50% of patients did not progress more than MSC, highlighting the importance for identification of structural progressors and the phenotypes associated with these. These results suggest that disease phenotypes, rather than disease status, are responsible for disease progression.

Joint unloading implant modifies subchondral bone trabecular structure in medial knee osteoarthritis: 2-year outcomes of a pilot study using fractal signature analysis

Background

Knee osteoarthritis (OA) is largely attributable to chronic excessive and aberrant joint loading. The purpose of this pilot study was to quantify radiographic changes in subchondral bone after treatment with a minimally invasive joint unloading implant (KineSpring^® Knee Implant System).

Methods

Nine patients with unilateral medial knee OA resistant to nonsurgical therapy were treated with the KineSpring System and followed for 2 years. Main outcomes included Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) pain, function, and stiffness subscores and independent core laboratory determinations of joint space width and fractal signature of the tibial cortex.

Results

WOMAC scores, on average, improved by 92% for pain, 91% for function, and 79% for stiffness over the 2-year follow-up period. Joint space width in the medial compartment of the treated knee significantly increased from 0.9 mm at baseline to 3.1 mm at 2 years; joint space width in the medial compartment of the untreated knee was unchanged. Fractal signatures of the vertically oriented trabeculae in the medial compartment decreased by 2.8% in the treated knee and increased by 2.1% in the untreated knee over 2 years. No statistically significant fractal signature changes were observed in the horizontally oriented trabeculae in the medial compartment or in the horizontal or vertical trabeculae of the lateral compartment in the treated knee.

Conclusion

Preliminary evidence suggests that the KineSpring System may modify knee OA disease progression by increasing joint space width and improving subchondral bone trabecular integrity, thereby reducing pain and improving joint function.

Characterization of knee osteoarthritis-related changes in trabecular bone using texture parameters at various levels of spatial resolution-a simulation study

Articular cartilage and subchondral bone are the key tissues in osteoarthritis (OA). The role of the cancellous bone increasingly attracts attention in OA research. Because of its fast adaptation to changes in the loading distribution across joints, its quantification is expected to improve the diagnosis and monitoring of OA. In this study, we simulated OA progression-related changes of trabecular structure in a series of digital bone models and then characterized the potential of texture parameters and bone mineral density (BMD) as surrogate measures to quantify trabecular bone structure. Five texture parameters were studied: entropy, global and local inhomogeneity, anisotropy and variogram slope. Their dependence on OA relevant structural changes was investigated for three spatial resolutions typically used in micro computed tomography (CT; 10 μm), high-resolution peripheral quantitative CT (HR-pQCT) (90 μm) and clinical whole-body CT equipment (250 μm). At all resolutions, OA-related changes in trabecular bone architecture can be quantified using a specific (resolution dependent) combination of three texture parameters. BMD alone is inadequate for this purpose but if available reduces the required texture parameter combination to anisotropy and global inhomogeneity. The results are summarized in a comprehensive analysis guide for the detection of structural changes in OA knees. In conclusion, texture parameters can be used to characterize trabecular bone architecture even at spatial resolutions below the dimensions of a single trabecula and are essential for a detailed classification of relevant OA changes that cannot be achieved with a measurement of BMD alone.

Osteoarthritis year in review 2014: imaging

PURPOSE

This narrative review covers original publications related to imaging in osteoarthritis (OA) published in English between April 2013 and March 2014. In vitro data, animal studies and studies with less than 20 observations were not included.

METHODS

To extract relevant studies, an extensive PubMed database search was performed based on, but not limited to the query terms "Osteoarthritis" in combination with "MRI", "Imaging", "Radiography", "Ultrasound", "Computed Tomography" and "Nuclear Medicine". Publications were sorted according to relevance based on potential impact to the OA research community with the overarching goal of a balanced overview covering all aspects of imaging. Focus was on publications in high impact special interest journals. The literature will be presented in a methodological fashion covering radiography, ultrasound, compositional and morphologic Magnetic resonance imaging (MRI), and from an anatomic perspective including bone, muscle, meniscus and synovitis.

RESULTS AND CONCLUSIONS

Imaging research in OA in the last year was characterized by a strong focus on MRI-based studies dealing with epidemiological and methodological aspects of the disease. Ultrastructural tissue assessment specifically of cartilage and meniscus using compositional MRI is evolving further. Additional subsets of the large publicly available Osteoarthritis Initiative (OAI) MRI dataset are being analyzed at present and have been published with muscle analyses coming increasingly into the focus of the community. Bone parameters were evaluated using varying technology and a persistent interest in inflammatory disease manifestations has been noted. Other modalities than MRI have been less explored. To date most OA imaging research is still focused on the knee joint.

MRI signal-based quantification of subchondral bone at the tibial plateau: a population study

OBJECTIVE

To determine whether differences in subchondral sclerosis at the tibial plateau could be detected with magnetic resonance (MR) imaging in two different age groups.

MATERIALS AND METHODS

This was a retrospective hypothesis-testing study. Thirty-two knees in group A (25-30 year olds) and 32 knees in group B (45-50 years old) were included. Participants had no MR features of osteoarthritis (OA). On coronal images, tibial articular cartilage thickness was measured, and regions of interest were created in the medial and lateral tibial plateau subchondral bone and in the tibial metaphysis. The measure of heterogeneity at the tibial plateaux was the ratio of the standard deviation of the signal in the medial/lateral compartment to the standard deviation of the signal in the metaphysis (ratio of standard deviations--RSS(medial)/RSS(lateral)). Differences between groups were assessed using unpaired Student's t-tests.

RESULTS

Mean RSS(medial) was 2.61 (standard deviation, SD = 0.77) in group A and 2.97 (SD = 0.59) in group B. Mean RSS(lateral) in group A was 1.86 (SD = 0.63) and 1.89 (SD = 0.43) in group B. Mean total cartilage thickness (in mm) in group A was 3.38 (SD = 0.90) for the medial and 3.90 (SD = 1.09) for the lateral compartment and 3.44 (SD = 0.74) for the medial and 3.96 (SD = 0.96) for the lateral compartment in group B. The only parameter to show a statistically significant difference between groups was RSS(medial) (p = 0.04).

CONCLUSION

A difference in medial subchondral bone sclerosis between two age groups was demonstrated in the absence of MR features of OA. This may represent the earliest OA change detectable on MR imaging.

Alpha C-telopeptide of type I collagen is associated with subchondral bone turnover and predicts progression of joint space narrowing and osteophytes in osteoarthritis

OBJECTIVE

To evaluate joint tissue remodeling using the urinary collagen biomarkers urinary α-C-telopeptide of type I collagen (α-CTX) and urinary C-telopeptide of type II collagen (CTX-II) and to determine the association of these biomarkers with osteoarthritis (OA) severity, progression, and localized knee bone turnover.

METHODS

Participants (n = 149) with symptomatic and radiographic knee OA underwent fixed-flexion knee radiography at baseline and 3 years, and late-phase bone scintigraphy of both knees at baseline, which were scored semiquantitatively for osteophyte and joint space narrowing (JSN) severity and uptake intensity, with scores summed across knees. Urinary concentrations of α-CTX and CTX-II were determined by enzyme-linked immunosorbent assay. Immunohistochemical analysis of human OA knees was performed to localize the joint tissue origin of the biomarker epitopes.

RESULTS

Urinary α-CTX concentrations correlated strongly with the intensity of bone scintigraphic uptake and with JSN progression (risk ratio 13.2) and osteophyte progression (risk ratio 3). Urinary CTX-II concentrations were strongly associated with intensity of bone scintigraphic uptake, with JSN and osteophyte severity, and with OA progression based on osteophyte score. Urinary α-CTX localized primarily to high bone turnover areas in subchondral bone. CTX-II localized to the bone-cartilage interface, the tidemark, and damaged articular cartilage.

CONCLUSION

Baseline urinary α-CTX, which was localized to high turnover areas of subchondral bone, was associated with dynamic bone turnover of knees, as signified by scintigraphy, and progression of both osteophytes and JSN. Urinary CTX-II correlated with JSN and osteophyte severity and progression of osteophytes. To our knowledge, this represents the first report of serologic markers reflecting subchondral bone turnover. These collagen markers may be useful for noninvasive detection and quantification of active subchondral bone turnover and joint remodeling in knee OA.