Distinct subtypes of knee osteoarthritis: data from the Osteoarthritis Initiative

Clinical phenotypes and associated factors in knee osteoarthritis in an African black population

Objective

Our objective was to study the clinical phenotypes of knee osteoarthritis in rheumatology in a black sub-Saharan African population.

Methods

This study took place from October 1, 2022, to September 30, 2023, in the rheumatology department. It involved adult patients with knee osteoarthritis. The researchers used K-means clustering analysis to identify different phenotypes and logistic regression to determine associated factors.

Results

A total of 321 patients were included in the study. The mean age was 58.7 years (ranging from 21 to 92 years), with a sex ratio of 0.23 (M/F). The study identified five clinical phenotypes through clustering: 152 patients (47.3 ​%) exhibited the "osteoporotic" phenotype, 113 patients (35.2 ​%) exhibited the "metabolic" phenotype, 17 patients (5.3 ​%) exhibited the "genetic" phenotype, 24 patients (7.4 ​%) exhibited the "biomechanical" phenotype, and 15 patients (4.6 ​%) exhibited the "post-traumatic" phenotype. The "osteoporotic" phenotype was significantly more frequent in patients aged 60 years or older (OR ​= ​1.13 [1.10; 1.16], p ​< ​0.0001) and in women (OR ​= ​2.44 [1.20; 4.94], p ​< ​0.0001). On the other hand, the "post-traumatic" phenotype was significantly more frequent in patients younger than 60 years (OR ​= ​1.93 [1.91; 1.96], p ​< ​0.0001) and in those with tibiofemoral osteoarthritis (OR ​= ​0.44 [0.21; 0.94], p ​= ​0.034).

Conclusion

The osteoporotic and metabolic phenotypes were the most frequently observed. The osteoporotic phenotype was more common in women and patients over 60 years while the post-traumatic phenotype was more prevalent in tibiofemoral osteoarthritis under 60 years.

Computational Translation of Mouse Models of Osteoarthritis Predicts Human Disease

Objective

Translation of biological insights from preclinical studies to human disease is a pressing challenge in biomedical research, including in osteoarthritis. Translatable Components Regression (TransComp-R) is a computational framework that has previously been used to synthesize preclinical and human OA data to identify biological pathways predictive of human disease conditions. We aimed to evaluate the translatability of two common murine models of post-traumatic osteoarthritis - surgical destabilization of the medial meniscus (DMM) and noninvasive anterior cruciate ligament rupture (ACLR) - to transcriptomics cartilage data from human OA outcomes.

Design

Transcriptomics cartilage data of DMM and ACLR mouse and human data was acquired from Gene Expression Omnibus. TransComp-R was used to project human OA data into a mouse model (DMM or ACLR) principal component analysis space. The principal components (PCs) were regressed against human OA conditions using increasing complexity of linear regression models incorporating human demographic covariates of OA, sex, and age. Biological pathways of the mouse PCs that significantly stratified human OA and control groups were then interpreted using Gene Set Enrichment Analysis.

Results

From the TransComp-R model, we identified different enriched biological pathways across DMM and ACLR models. While PCs among the DMM models revealed pathways associated with cell signaling and metabolism, ACLR PCs represented immune function and cellular pathways associated with OA condition. The immune pathways presented in the ACLR further highlighted the potential relevance of the OA pathways observed in human conditions.

Conclusions

The ACLR mouse model more successfully predicted human OA conditions, particularly with the human control groups without a history of joint injury or disease. Cross-species translational approaches support the selection of preclinical models intended for therapeutic discovery and pathway analysis in humans.

Advances in the pathology and treatment of osteoarthritis

BACKGROUND

Osteoarthritis (OA), a widespread degenerative joint disease, predominantly affects individuals from middle age onwards, exhibiting non-inflammatory characteristics. OA leads to the gradual deterioration of articular cartilage and subchondral bone, causing pain and reduced mobility. The risk of OA increases with age, making it a critical health concern for seniors. Despite significant research efforts and various therapeutic approaches, the precise causes of OA remain unclear.

AIM OF REVIEW

This paper provides a thorough examination of OA characteristics, pathogenic mechanisms at various levels, and personalized treatment strategies for different OA stages. The review aims to enhance understanding of disease mechanisms and establish a theoretical framework for developing more effective therapeutic interventions.

KEY SCIENTIFIC CONCEPTS OF REVIEW

This review systematically examines OA through multiple perspectives, integrating current knowledge of clinical presentation, pathological mechanisms, and associated signaling pathways. It assesses diagnostic methods and reviews both pharmacological and surgical treatments for OA, as well as emerging tissue engineering approaches to manage the disease. While therapeutic strategies such as exercise, anti-inflammatory drugs, and surgical interventions are employed to manage symptoms and modify joint structure, none have been able to effectively halt OA's advancement or achieve long-lasting symptom relief. Tissue engineering strategies, such as cell-seeded scaffolds, supportive matrices, and growth factor delivery, have emerged as promising approaches for cartilage repair and OA treatment. To combat the debilitating effects of OA, it is crucial to investigate the molecular basis of its pathogenesis and seek out innovative therapeutic targets for more potent preventive and treatment strategies.

Structural phenotypes of knee osteoarthritis: potential clinical and research relevance

A joint contains many different tissues that can exhibit pathological changes, providing many potential targets for treatment. Researchers are increasingly suggesting that osteoarthritis (OA) comprises several phenotypes or subpopulations. Consequently, a treatment for OA that targets only one pathophysiologic abnormality is unlikely to be similarly efficacious in preventing or delaying the progression of all the different phenotypes of structural OA. Five structural phenotypes have been proposed, namely the inflammatory, meniscus-cartilage, subchondral bone, and atrophic and hypertrophic phenotypes. The inflammatory phenotype is characterized by marked synovitis and/or joint effusion, while the meniscus-cartilage phenotype exhibits severe meniscal and cartilage damage. Large bone marrow lesions characterize the subchondral bone phenotype. The hypertrophic and atrophic OA phenotype are defined based on the presence large osteophytes or absence of any osteophytes, respectively, in the presence of concomitant cartilage damage. Limitations of the concept of structural phenotyping are that they are not mutually exclusive and that more than one phenotype may be present. It must be acknowledged that a wide range of views exist on how best to operationalize the concept of structural OA phenotypes and that the concept of structural phenotypic characterization is still in its infancy. Structural phenotypic stratification, however, may result in more targeted trial populations with successful outcomes and practitioners need to be aware of the heterogeneity of the disease to personalize their treatment recommendations for an individual patient. Radiologists should be able to define a joint at risk for progression based on the predominant phenotype present at different disease stages.

Intra-articular delivery of micronized dehydrated human amnion/chorion membrane reduces degenerative changes after onset of post-traumatic osteoarthritis

Background: Micronized dehydrated human amnion/chorion membrane (mdHACM) has reduced short term post-traumatic osteoarthritis (PTOA) progression in rats when delivered 24 h after medial meniscal transection (MMT) and is being investigated for clinical use as a disease modifying therapy. Much remains to be assessed, including its potential for longer-term therapeutic benefit and treatment effects after onset of joint degeneration. Objectives: Characterize longer-term effects of acute treatment with mdHACM and determine whether treatment administered to joints with established PTOA could slow or reverse degeneration. Hypotheses: Acute treatment effects will be sustained for 6 weeks, and delivery of mdHACM after onset of joint degeneration will attenuate structural osteoarthritic changes. Methods: Rats underwent MMT or sham surgery (left leg). mdHACM was delivered intra-articularly 24 h or 3 weeks post-surgery (n = 5-7 per group). Six weeks post-surgery, animals were euthanized and left tibiae scanned using equilibrium partitioning of an ionic contrast agent microcomputed tomography (EPIC-µCT) to structurally quantify joint degeneration. Histology was performed to examine tibial plateau cartilage. Results: Quantitative 3D µCT showed that cartilage structural metrics (thickness, X-ray attenuation, surface roughness, exposed bone area) for delayed mdHACM treatment limbs were significantly improved over saline treatment and not significantly different from shams. Subchondral bone mineral density and thickness for the delayed treatment group were significantly improved over acute treated, and subchondral bone thickness was not significantly different from sham. Marginal osteophyte degenerative changes were decreased with delayed mdHACM treatment compared to saline. Acute treatment (24 h post-surgery) did not reduce longer-term joint tissue degeneration compared to saline. Histology supported µCT findings and further revealed that while delayed treatment reduced cartilage damage, chondrocytes displayed qualitatively different morphologies and density compared to sham. Conclusion: This study provides insight into effects of intra-articular delivery timing relative to PTOA progression and the duration of therapeutic benefit of mdHACM. Results suggest that mdHACM injection into already osteoarthritic joints can improve joint health, but a single, acute mdHACM injection post-injury does not prevent long term osteoarthritis associated with meniscal instability. Further work is needed to fully characterize the durability of therapeutic benefit in stable osteoarthritic joints and the effects of repeated injections.

Identifying multivariate disease trajectories and potential phenotypes of early knee osteoarthritis in the CHECK cohort

OBJECTIVE

To gain better understanding of osteoarthritis (OA) heterogeneity and its predictors for distinguishing OA phenotypes. This could provide the opportunity to tailor prevention and treatment strategies and thus improve care.

DESIGN

Ten year follow-up data from CHECK (1002 early-OA subjects with first general practitioner visit for complaints ≤6 months before inclusion) was used. Data were collected on WOMAC (pain, function, stiffness), quantitative radiographic tibiofemoral (TF) OA characteristics, and semi-quantitative radiographic patellofemoral (PF) OA characteristics. Using functional data analysis, distinctive sets of trajectories were identified for WOMAC, TF and PF characteristics, based on model fit and clinical interpretation. The probabilities of knee membership to each trajectory were used in hierarchical cluster analyses to derive knee OA phenotypes. The number and composition of potential phenotypes was selected again based on model fit (silhouette score) and clinical interpretation.

RESULTS

Five trajectories representing different constant levels or changing WOMAC scores were identified. For TF and PF OA, eight and six trajectories respectively were identified based on (changes in) joint space narrowing, osteophytes and sclerosis. Combining the probabilities of knees belonging to these different trajectories resulted in six clusters ('phenotypes') of knees with different degrees of functional (WOMAC) and radiographic (PF) parameters; TF parameters were found not to significantly contribute to clustering. Including baseline characteristics as well resulted in eight clusters of knees, dominated by sex, menopausal status and WOMAC scores, with only limited contribution of PF features.

CONCLUSIONS

Several stable and progressive trajectories of OA symptoms and radiographic features were identified, resulting in phenotypes with relatively independent symptomatic and radiographic features. Sex and menopausal status may be especially important when phenotyping knee OA patients, while radiographic features contributed less. Possible phenotypes were identified that, after validation, could aid personalized treatments and patients selection.

Characterization of aberrant glycosylation associated with osteoarthritis based on integrated glycomics methods

BACKGROUND

Osteoarthritis (OA) is the most common form of arthritis, affecting millions of aging people. Investigation of abnormal glycosylation is essential for the understanding of pathological mechanisms of OA.

METHODS

The total protein was isolated from OA (n = 13) and control (n = 11) cartilages. Subsequently, glycosylation alterations of glycoproteins in OA cartilage were investigated by lectin microarrays and intact glycopeptides analysis. Finally, the expression of glycosyltransferases involved in the synthesis of altered glycosylation was assessed by qPCR and GEO database.

RESULTS

Our findings revealed that several glycopatterns, such as α-1,3/6 fucosylation and high-mannose type of N-glycans were altered in OA cartilages. Notably, over 27% of identified glycopeptides (109 glycopeptides derived from 47 glycoproteins mainly located in the extracellular region) disappeared or decreased in OA cartilages, which is related to the cartilage matrix degradation. Interestingly, the microheterogeneity of N-glycans on fibronectin and aggrecan core protein was observed in OA cartilage. Our results combined with GEO data indicated that the pro-inflammatory cytokines altered the expression of glycosyltransferases (ALG3, ALG5, MGAT4C, and MGAT5) which may contribute to the alterations in glycosylation.

CONCLUSION

Our study revealed the abnormal glycopatterns and heterogeneities of site-specific glycosylation associated with OA. To our knowledge, it is the first time that the heterogeneity of site-specific N-glycans was reported in OA cartilage. The results of gene expression analysis suggested that the expression of glycosyltransferases was impacted by pro-inflammatory cytokines, which may facilitate the degradation of protein and accelerate the process of OA. Our findings provide valuable information for the understanding of molecular mechanisms in the pathogenesis of OA.

Patterns of variation among baseline femoral and tibial cartilage thickness and clinical features: Data from the osteoarthritis initiative

Objective

To employ novel methodologies to identify phenotypes in knee OA based on variation among three baseline data blocks: 1) femoral cartilage thickness, 2) tibial cartilage thickness, and 3) participant characteristics and clinical features.

Methods

Baseline data were from 3321 Osteoarthritis Initiative (OAI) participants with available cartilage thickness maps (6265 knees) and 77 clinical features. Cartilage maps were obtained from 3D DESS MR images using a deep-learning based segmentation approach and an atlas-based analysis developed by our group. Angle-based Joint and Individual Variation Explained (AJIVE) was used to capture and quantify variation, both shared among multiple data blocks and individual to each block, and to determine statistical significance.

Results

Three major modes of variation were shared across the three data blocks. Mode 1 reflected overall thicker cartilage among men, those with higher education, and greater knee forces; Mode 2 showed associations between worsening Kellgren-Lawrence Grade, medial cartilage thinning, and worsening symptoms; and Mode 3 contrasted lateral and medial-predominant cartilage loss associated with BMI and malalignment. Each data block also demonstrated individual, independent modes of variation consistent with the known discordance between symptoms and structure in knee OA and reflecting the importance of features such as physical function, symptoms, and comorbid conditions independent of structural damage.

Conclusions

This exploratory analysis, combining the rich OAI dataset with novel methods for determining and visualizing cartilage thickness, reinforces known associations in knee OA while providing insights into the potential for data integration in knee OA phenotyping.

Unsupervised machine-learning algorithms for the identification of clinical phenotypes in the osteoarthritis initiative database

OBJECTIVES

Osteoarthritis (OA) is a complex disease comprising diverse underlying patho-mechanisms. To enable the development of effective therapies, segmentation of the heterogenous patient population is critical. This study aimed at identifying such patient clusters using two different machine learning algorithms.

METHODS

Using the progression and incident cohorts of the Osteoarthritis Initiative (OAI) dataset, deep embedded clustering (DEC) and multiple factor analysis with clustering (MFAC) approaches, including 157 input-variables at baseline, were employed to differentiate specific patient profiles.

RESULTS

DEC resulted in 5 and MFAC in 3 distinct patient phenotypes. Both identified a "comorbid" cluster with higher body mass index (BMI), relevant burden of comorbidity and low levels of physical activity. Both methods also identified a younger and physically more active cluster and an elderly cluster with functional limitations, but low disease impact. The additional two clusters identified with DEC were subgroups of the young/physically active and the elderly/physically inactive clusters. Overall pain trajectories over 9 years were stable, only the numeric rating scale (NRS) for pain showed distinct increase, while physical activity decreased in all clusters. Clusters showed different (though non-significant) trajectories of joint space changes over the follow-up period of 8 years.

CONCLUSION

Two different clustering approaches yielded similar patient allocations primarily separating complex "comorbid" patients from healthier subjects, the latter divided in young/physically active vs elderly/physically inactive subjects. The observed association to clinical (pain/physical activity) and structural progression could be helpful for early trial design as strategy to enrich for patients who may specifically benefit from disease-modifying treatments.

Gait biomechanics phenotypes among total knee arthroplasty candidates by machine learning cluster analysis

Knee osteoarthritis patient phenotyping is relevant to developing targeted treatments and assessing the treatment efficacy of total knee arthroplasty (TKA). This study aimed to identify clusters among TKA candidates based on demographic and knee mechanic features during gait, and compare gait changes between clusters postoperatively. TKA patients underwent 3D gait analysis 1-week pre (n = 134) and 1-year post-TKA (n = 105). Principal component analysis was applied to frontal and sagittal knee angle and moment waveforms, extracting major patterns of variability. Age, sex, body mass index, gait speed, and frontal and sagittal pre-TKA angle and moment PC scores previously identified as relevant to TKA outcomes were standardized (mean = 0, SD = 1, [134 × 15]). Multidimensional scaling and machine learning-based hierarchical clustering were applied. Final clusters were validated by examining intercluster differences pre-TKA and gait feature changes (Post_PCscore  - Pre_PCscore ) by k-way Χ² and ANOVA tests. Four TKA candidate phenotypes yielded optimum clustering metrics, interpreted as higher and lower functioning clusters that were predominantly male and female. Higher functioning clusters pre-TKA (clusters 1 and 4) had more dynamic sagittal flexion moment (p < 0.001) and frontal plane adduction moment (p < 0.001) loading/un-loading patterns during stance. Post-TKA, higher functioning clusters demonstrated less knee mechanic improvements during gait (flexion angle p < 0.001; flexion moment p < 0.001). TKA candidates can be characterized by four clusters, predominately separated by sex and knee joint biomechanics. Post-TKA knee kinematics and kinetics improvements were cluster-specific; lower functioning clusters experienced more improvement. Cluster-based patient profiling may aid in triaging and developing OA management and surgical strategies meeting group-level function needs.

Knee osteoarthritis phenotypes based on synovial fluid immune cells correlate with clinical outcome trajectories

BACKGROUND

Knee osteoarthritis (KOA) is a highly heterogeneous disease encompassing a wide range of clinical phenotypes. Phenotypes based on immune cells and protein pattern in synovial fluid (SF) and their relationship to clinical trajectories have not been described.

OBJECTIVE

To assess phenotypes based on immune cells and protein pattern of SF in KOA.

DESIGN

SF-derived immune cells were investigated in 119 patients with KOA using flow cytometry. Immune-phenotypes (iPhen) were determined by multivariate patient similarity network analysis and related to clinical trajectory (3-6 months post-sampling) along with protein pattern and macrophage chemokine receptors.

RESULTS

Four iPhen were detected based on the distribution of T-lymphocytes, monocyte-macrophage lineage cells and activated CD8+ T-lymphocytes. The 'activated' phenotype (n = 17) had high T-lymphocytes but low monocyte-macrophage lineage cells and neutrophils, all highly activated, and showed improved symptoms in 70% patients. The 'lymphoid progressive' phenotype (n = 31) had high neutrophils, low lymphocytes and monocyte-macrophage lineage cells, low activation and was associated with lower pain levels. The 'myeloid progressive' phenotype (n = 35) had high NK and monocyte-macrophage lineage cells but low T-lymphocytes and activation. The 'aggressive' phenotype (n = 36) had high lymphocytes, macrophages, NK cells and neutrophils and high activation, and only 39% of patients improved during follow-up. Low CXCR4 and CCR7 expression on macrophages and high CXCL10 in SF were linked to improved clinical trajectory.

CONCLUSION

We identified four immune-phenotypes that were associated with different clinical trajectories in KOA patients. How these phenotypes can be targeted therapeutically deserves further investigation.

Defining and predicting radiographic knee osteoarthritis progression: a systematic review of findings from the osteoarthritis initiative

PURPOSE

The purposes of this systematic review were to (1) identify the commonly used definitions of radiographic KOA progression, (2) summarize the important associative risk factors for disease progression based on findings from the OAI study and (3) summarize findings from radiographic KOA progression prediction modeling studies regarding the characterization of progression and outcomes.

METHODS

A systematic review was performed by conducting a literature search of definitions, risk factors and predictive models for radiographic KOA progression that utilized data from the OAI database. Radiographic progression was further characterized into "accelerated KOA" and "typical progression," as defined by included studies.

RESULTS

Of 314 studies identified, 41 studies were included in the present review. Twenty-eight (28) studies analyzed risk factors associated with KOA progression, and 13 studies created or validated prediction models or risk calculators for progression. Kellgren-Lawrence (KL) grade based on radiographs was most commonly used to characterize KOA progression (50%), followed by joint space width (JSW) narrowing (32%) generally over 48 months. Risk factors with the highest odds ratios (OR) for progression included periarticular bone mineral density (OR 10.40), any knee injury within 1 year (OR 9.22) and baseline bone mineral lesions (OR 7.92). Nine prediction modeling studies utilized both clinical and structural risk factors to inform their models, and combined models outperformed purely clinical or structural models.

CONCLUSION

The cumulative evidence suggests that combinations of structural and clinical risk factors may be able to predict radiographic KOA progression, particularly in patients with accelerated progression. Clinically relevant and feasible prediction models and risk calculators may provide valuable decision-making support when caring for patients at risk of KOA progression, although standardization in modeling and variable identification does not yet exist.

Mice Lacking Wnt9a or Wnt4 Are Prone to Develop Spontaneous Osteoarthritis With Age and Display Alteration in Either the Trabecular or Cortical Bone Compartment

Osteoarthritis (OA) is a common degenerative disease of the joint, with a complex multifactorial not yet fully understood etiology. Over the past years, the Wnt signaling pathway has been implicated in osteoarthritis. In a recent genomewide association study (GWAS), the chromosomal location on chromosome 1, linked to the Wnt3a-Wnt9a gene locus, was identified as the most significant locus associated with a thumb osteoarthritis endophenotype. Previously, it was shown that WNT9a is involved in maintaining synovial cell identity in the elbow joint during embryogenesis. Here, we report that the conditional loss of Wnt9a in the Prx1-Cre expressing limb mesenchyme or Prg4-CreER expressing cells predispositions the mice to develop spontaneous OA-like changes with age. In addition, the trabecular bone volume is altered in these mice. Similarly, mice with a conditional loss of Wnt4 in the limb mesenchyme are also more prone to develop spontaneously OA-like joint alterations with age. These mice display additional alterations in their cortical bone. The combined loss of Wnt9a and Wnt4 increased the likelihood of the mice developing osteoarthritis-like changes and enhanced disease severity in the affected mice. © 2022 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

The influence of different hinge position on PTS during HTO: comparison between open-wedge and closed-wedge HTO

PURPOSE

The purpose of this study was to determine the significance of hinge position through comparison between open-wedge and closed-wedge high tibial osteotomy (HTO) and to determine the ideal hinge position to minimize the effect of HTO on the posterior tibial slope (PTS) and medial proximal tibial angle (MPTA).

METHODS

Procedures were performed on 32 cadaveric knees using open-wedge HTO with the standard hinge position or a low hinge position or closed-wedge HTO with the standard hinge position or a low hinge position. To define the standard hinge position in open wedge HTO, we drew a line 3-cm inferior to the medial tibial plateau toward the fibular head and located the intersection of this line with a longitudinal line 1-cm medial to fibular shaft. The low hinge position was then defined as the point 1-cm inferior to the standard position. For the standard hinge position for closed-wedge HTO, we drew a line parallel with joint line from 2-cm inferior to the lateral tibial plateau. The low hinge position was then defined as the point 1-cm inferior to the standard position.

RESULTS

For the open-wedge procedure, osteotomy through the low hinge position resulted in a significantly greater PTS compared to osteotomy through the standard hinge position. MPTA was also significantly greater for the low hinge position compared to standard hinge position. In the closed-wedge HTO, neither the PTS nor MPTA was significantly different for the low and standard hinge positions.

CONCLUSIONS

Hinge position significantly affects changes in the PTS and MPTA following open-wedge but not closed-wedge HTO. Understanding how to hinge position affects the PTS and MPTA is critical for surgeons performing open-wedge HTO procedures. Adopting an accurate hinge position is crucial for preventing complications, especially in open-wedge osteotomy, due to postoperative changes in the PTS and MPTA.

Use of machine learning in osteoarthritis research: a systematic literature review

OBJECTIVE

The aim of this systematic literature review was to provide a comprehensive and exhaustive overview of the use of machine learning (ML) in the clinical care of osteoarthritis (OA).

METHODS

A systematic literature review was performed in July 2021 using MEDLINE PubMed with key words and MeSH terms. For each selected article, the number of patients, ML algorithms used, type of data analysed, validation methods and data availability were collected.

RESULTS

From 1148 screened articles, 46 were selected and analysed; most were published after 2017. Twelve articles were related to diagnosis, 7 to prediction, 4 to phenotyping, 12 to severity and 11 to progression. The number of patients included ranged from 18 to 5749. Overall, 35% of the articles described the use of deep learning And 74% imaging analyses. A total of 85% of the articles involved knee OA and 15% hip OA. No study investigated hand OA. Most of the studies involved the same cohort, with data from the OA initiative described in 46% of the articles and the MOST and Cohort Hip and Cohort Knee cohorts in 11% and 7%. Data and source codes were described as publicly available respectively in 54% and 22% of the articles. External validation was provided in only 7% of the articles.

CONCLUSION

This review proposes an up-to-date overview of ML approaches used in clinical OA research and will help to enhance its application in this field.

AI MSK clinical applications: cartilage and osteoarthritis

The advancements of artificial intelligence (AI) for osteoarthritis (OA) applications have been rapid in recent years, particularly innovations of deep learning for image classification, lesion detection, cartilage segmentation, and prediction modeling of future knee OA development. This review article focuses on AI applications in OA research, first describing machine learning (ML) techniques and workflow, followed by how these algorithms are used for OA classification tasks through imaging and non-imaging-based ML models. Deep learning applications for OA research, including analysis of both radiographs for automatic detection of OA severity, and MR images for detection of cartilage/meniscus lesions and cartilage segmentation for automatic T₂ quantification will be described. In addition, information on ML models that identify individuals at high risk of OA development will be provided. The future vision of machine learning applications in imaging of OA and cartilage hinges on implementation of AI for optimizing imaging protocols, quantitative assessment of cartilage, and automated analysis of disease burden yielding a faster and more efficient workflow for a radiologist with a higher level of reproducibility and precision. It may also provide risk assessment tools for individual patients, which is an integral part of precision medicine.

Pharmaceutical therapeutics for articular regeneration and restoration: state-of-the-art technology for screening small molecular drugs

Articular cartilage damage caused by sports injury or osteoarthritis (OA) has gained increased attention as a worldwide health burden. Pharmaceutical treatments are considered cost-effective means of promoting cartilage regeneration, but are limited by their inability to generate sufficient functional chondrocytes and modify disease progression. Small molecular chemical compounds are an abundant source of new pharmaceutical therapeutics for cartilage regeneration, as they have advantages in design, fabrication, and application, and, when used in combination, act as powerful tools for manipulating cellular fate. In this review, we present current achievements in the development of small molecular drugs for cartilage regeneration, particularly in the fields of chondrocyte generation and reversion of chondrocyte degenerative phenotypes. Several clinically or preclinically available small molecules, which have been shown to facilitate chondrogenesis, chondrocyte dedifferentiation, and cellular reprogramming, and subsequently ameliorate cartilage degeneration by targeting inflammation, matrix degradation, metabolism, and epigenetics, are summarized. Notably, this review introduces essential parameters for high-throughput screening strategies, including models of different chondrogenic cell sources, phenotype readout methodologies, and transferable advanced systems from other fields. Overall, this review provides new insights into future pharmaceutical therapies for cartilage regeneration.

Clinical Manifestations, Histopathological Changes And Quality Of Life In Patients With Advanced Knee Osteoarthritis Caused By Age, Trauma, Obesity And Their Combination

Objective — to reveal and analyze clinical characteristics, knee joint histopathology, and quality of life in patients at late stages of knee osteoarthritis (OA) triggered by age, trauma, metabolic syndrome, or their combination. Material and methods — We studied 120 subjects with knee OA (sensu Altman R.D., 1991) of Kellgren-Lawrence Grades 3-4. They were distributed among 4 groups (30 participants in each) based on the presence of age-related, post-traumatic, metabolic, or combined phenotypes. Clinical examination of patients with pain and their functional status evaluation (via Visual Analogue Scale, WOMAC, Lequesne index), quality of life assessment (MOS SF-36 questionnaire), along with histopathological study of medial tibial plateau cartilage and synovial membrane, were caried out, followed by statistical data processing. Results — Age-related OA phenotype was characterized by the latest clinical onset [59.5 (54-68) years of age] with the largest average patient age [72.5 (63-77) years], moderate to severe pain and knee dysfunction [total WOMAC score of 160 (127-190) points and Lequesne index of 20 (8-21) points], severe degenerative cartilage lesions [8.5 (6-10) points sensu Mankin] with high-grade synovitis [5 (3-8) points sensu Krenn]. Post-traumatic OA phenotype was distinguished by the lowest pain, stiffness and knee functional limitations [total WOMAC score of 129 (100-166), Lequesne index of 15 (14-19)], the highest quality of life in patients [physical component summary of 34.1 (30.5-36.1) points, mental component summary of 40.4 (32.9-43.8) points] against the background of local severe cartilage lesions [8 (6-8) sensu Mankin] with reparative pattern and synovial fibrosis. For metabolic OA phenotype, the typical traits included female-biased sex ratio (87%), high prevalence of clinical synovitis (77%), severe pain and functional knee disorders [total WOMAC score of 188 (162-207) points, Lequesne index of 20 (19-23) points], the worst quality of life [physical component summary of 28.0 (24.3-31.9) points, mental component summary of 30.9 (26.9-35.9) points], vascular invasion of cartilage, and high-grade synovitis [4 (3-5) points sensu Krenn]. Combined OA phenotype was characterized by variable clinical and histopathological features. Conclusion — Comprehensive comparative clinical and morphological analysis of late-stage knee OA of various origin was completed, and age-related, post-traumatic, metabolic and combined OA phenotypes were studied. The methodological basis for differential approach to treating different categories of OA patients was developed.

Identifying the Phenotypic and Temporal Heterogeneity of Knee Osteoarthritis: Data From the Osteoarthritis Initiative

Objective: Previous studies discussing phenotypic and temporal heterogeneity of knee osteoarthritis (KOA) separately have fatal limitations that either clustering patients with similar severity or assuming all knees have a single common progression pattern, which are unreliable. This study tried to uncover more reliable information on phenotypic and temporal heterogeneity of KOA. Design: Data were from Osteoarthritis Initiative database. Six hundred and seventy-eight unilateral knees that have greater Kellgren and Lawrence (KL) grade than the contralateral knees at baseline and in all follow-up 48 months were included. Measurements of biomarkers at baseline were chosen. Subtype and Stage Inference model (SuStaIn) was applied as a subtype-progression model to identify subtypes, subtype biomarker progress sequences and stages of KOA. Results: This study identified three subtypes which account for 15, 61, and 24% of knees, respectively. Each subtype has distinct subtype biomarker progress sequence. For knees with KL grade 0/1, 2, 3, and 4, they have different distributions on stage and 26, 53, 89, and 95% of them are strongly assigned to subtypes. When assessing whether a knee has KL (grade ≥ 2), subtypes and stages from subtypes-progression model (SuStaIn) are significantly better fitting than those from subtypes-only (mixture of Gaussians) (likelihood ratio = 105.59, p = 2.2 × 10^-16) or stages-only (SuStaIn where setting c = 1) (likelihood ratio = 58.04, p = 2.57 × 10^-14) model. Stages in subtypes-progression model has greater β than stages-only model. Subtypes from subtypes-progression model have no statistical significance. Conclusions: For subtypes-progression model, stages contain more complete temporal information and subtypes are closer to real OA subtypes.

A Retrospective Chart Review of 122 Inpatients with Knee Osteoarthritis Treated with Korean Medicine: An Analysis of the Effects of Treatment

Background: Korean medicine treatment was assessed in patients with knee osteoarthritis (OA) according to subgroups of: sex, age, cause of knee OA, body mass index, hospitalization period, history, OA compartment, phenotype, and comorbidity. Methods: A retrospective review was performed of 122 inpatients who were admitted to the Hospital of Korean Medicine for Korean medicine treatment of knee pain, and were diagnosed with knee OA based on magnetic resonance imaging findings. Analysis of patient subgroups (sex, age, cause of knee OA, body mass index, hospitalization period, history, OA compartment, phenotype, and comorbidity) was carried out and treatments including acupuncture, cupping, pharmacopuncture, herbal medicine, chuna therapy, medicinal steaming therapy, manual therapy, and extracorporeal shock wave therapy were listed. The numeric rating scale (NRS), Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), and 5-level EuroQol- 5 Dimension (EQ-5D-5L) scores were measured before and after treatment to assess the effects of treatment on pain and quality of life. Results: Seventeen males and 105 females were included in this study. Most patients were in their 60s. In the total study population, NRS, WOMAC, and EQ-5D-5L scores were improved statistically significant when comparing before and after treatment. The NRS and WOMAC scores improved statistically significant in the medial, patellofemoral, medial + patellofemoral, medial + lateral + patellofemoral compartment. Conclusion: Korean medicine treatment significantly reduced pain, stiffness, and physical dysfunction, and improved the quality of life of patients with knee OA, suggesting that it may be an effective alternative to the current conservative treatments.

Identification and characterization of two consistent osteoarthritis subtypes by transcriptome and clinical data integration

OBJECTIVE

To identify OA subtypes based on cartilage transcriptomic data in cartilage tissue and characterize their underlying pathophysiological processes and/or clinically relevant characteristics.

METHODS

This study includes n = 66 primary OA patients (41 knees and 25 hips), who underwent a joint replacement surgery, from which macroscopically unaffected (preserved, n = 56) and lesioned (n = 45) OA articular cartilage were collected [Research Arthritis and Articular Cartilage (RAAK) study]. Unsupervised hierarchical clustering analysis on preserved cartilage transcriptome followed by clinical data integration was performed. Protein-protein interaction (PPI) followed by pathway enrichment analysis were done for genes significant differentially expressed between subgroups with interactions in the PPI network.

RESULTS

Analysis of preserved samples (n = 56) resulted in two OA subtypes with n = 41 (cluster A) and n = 15 (cluster B) patients. The transcriptomic profile of cluster B cartilage, relative to cluster A (DE-AB genes) showed among others a pronounced upregulation of multiple genes involved in chemokine pathways. Nevertheless, upon investigating the OA pathophysiology in cluster B patients as reflected by differentially expressed genes between preserved and lesioned OA cartilage (DE-OA-B genes), the chemokine genes were significantly downregulated with OA pathophysiology. Upon integrating radiographic OA data, we showed that the OA phenotype among cluster B patients, relative to cluster A, may be characterized by higher joint space narrowing (JSN) scores and low osteophyte (OP) scores.

CONCLUSION

Based on whole-transcriptome profiling, we identified two robust OA subtypes characterized by unique OA, pathophysiological processes in cartilage as well as a clinical phenotype. We advocate that further characterization, confirmation and clinical data integration is a prerequisite to allow for development of treatments towards personalized care with concurrently more effective treatment response.

Identification of tissue-dependent proteins in knee OA synovial fluid

OBJECTIVE

For many proteins from osteoarthritic synovial fluid, their intra-articular tissue of origin remains unknown. In this study we performed comparative proteomics to identify osteoarthritis-specific and joint tissue-dependent secreted proteins that may serve as candidates for osteoarthritis biomarker development on a tissue-specific basis.

DESIGN

Protein secretomes of cartilage, synovium, Hoffa's fat pad and meniscus from knee osteoarthritis patients were determined using liquid chromatography tandem mass spectrometry, followed by label-free quantification. Validation of tissue-dependent protein species was conducted by ELISA on independent samples. Differential proteomes of osteoarthritic and non-osteoarthritic knee synovial fluids were obtained via similar proteomics approach, followed by ELISA validation.

RESULTS

Proteomics revealed 64 proteins highly secreted from cartilage, 94 from synovium, 37 from Hoffa's fat pad and 21 from meniscus. Proteomic analyses of osteoarthritic vs non-osteoarthritic knee synovial fluid revealed 70 proteins with a relatively higher abundance and 264 proteins with a relatively lower abundance in osteoarthritic synovial fluid. Of the 70 higher abundance proteins, 23 were amongst the most highly expressed in the secretomes of a specific intra-articular tissue measured. Tissue-dependent release was validated for SLPI, C8, CLU, FN1, RARRES2, MATN3, MMP3 and TNC. Abundance in synovial fluid of tissue-dependent proteins was validated for IGF2, AHSG, FN1, CFB, KNG and C8.

CONCLUSIONS

We identified proteins with a tissue-dependent release from intra-articular human knee OA tissues. A number of these proteins also had an osteoarthritis-specific abundance in knee synovial fluid. These proteins may serve as novel candidates for osteoarthritis biomarker development on a tissue-specific basis.

Obesity with radiological changes or depression was associated with worse knee outcome in general population: a cluster analysis in the Nagahama study

Background

In knee osteoarthritis (OA), pain is the most frequent and dominant symptom. However, which factors other than radiological changes contribute to the symptoms is unresolved. The aims of this study were to identify factors affecting knee pain from various variables with radiological changes taken into count and exploratively examine what subgroups or phenotype could be identified by cluster analysis using the identified knee pain factors.

Methods

Patients 60 years or older who underwent radiographic evaluation were included in this cross-sectional study, and those subjects who completed a questionnaire about knee symptoms without missing data were eligible for analysis. Multiple regression analysis was used to examine the associations between selected variables and The Japanese Knee Osteoarthritis Measure (JKOM) pain score. We grouped the subjects by cluster analysis using identified variables.

Results

Two thousand five hundred forty-two subjects were included in the full set of analyses. Age, body mass index (BMI), radiological grade, bone mineral density (BMD), and high-sensitivity C-reactive protein (hs-CRP) showed a statistically significant correlation with radiological showing the strongest value. For dichotomous variable, presence of depression showed a statistically significant result. We used BMI, radiological grade, BMD, hs-CRP, and presence of depression as a variable for cluster analysis and identified six subgroups: (1) minimal joint disease subgroup, (2) male and high BMD subgroup, (3) high CRP subgroup, (4) severe radiological OA subgroup, (5) depressive subgroup, and (6) moderate radiological OA with high BMI subgroup, showing the worst knee outcome.

Conclusion

This study identified the factors affecting knee pain other than radiological changes and identified six subgroups of knee outcome in the general population. The results showed that obesity with radiological changes or depression was associated with worse knee outcome.

Identification of TGFβ signatures in six murine models mimicking different osteoarthritis clinical phenotypes

OBJECTIVE

TGFβ is a key player in cartilage homeostasis and OA pathology. However, few data are available on the role of TGFβ signalling in the different OA phenotypes. Here, we analysed the TGFβ pathway by transcriptomic analysis in six mouse models of OA.

METHOD

We have brought together seven expert laboratories in OA pathophysiology and, used inter-laboratories standard operating procedures and quality controls to increase experimental reproducibility and decrease bias. As none of the available OA models covers the complexity and heterogeneity of the human disease, we used six different murine models of knee OA: from post-traumatic/mechanical models (meniscectomy (MNX), MNX and hypergravity (HG-MNX), MNX and high fat diet (HF-MNX), MNX and seipin knock-out (SP-MNX)) to aging-related OA and inflammatory OA (collagenase-induced OA (CIOA)). Four controls (MNX-sham, young, SP-sham, CIOA-sham) were added. OsteoArthritis Research Society International (OARSI)-based scoring of femoral condyles and ribonucleic acid (RNA) extraction from tibial plateau samples were done by single operators as well as the transcriptomic analysis of the TGFβ family pathway by Custom TaqMan® Array Microfluidic Cards.

RESULTS

The transcriptomic analysis revealed specific gene signatures in each of the six models; however, no gene was deregulated in all six OA models. Of interest, we found that the combinatorial Gdf5-Cd36-Ltbp4 signature might discriminate distinct subgroups of OA: Cd36 upregulation is a hallmark of MNX-related OA while Gdf5 and Ltbp4 upregulation is related to MNX-induced OA and CIOA.

CONCLUSION

These findings stress the OA animal model heterogeneity and the need of caution when extrapolating results from one model to another.

Chondroprotective Actions of Selective COX-2 Inhibitors In Vivo: A Systematic Review

Knee osteoarthritis (OA) is a condition mainly characterized by cartilage degradation. Currently, no effective treatment exists to slow down the progression of OA-related cartilage damage. Selective COX-2 inhibitors may, next to their pain killing properties, act chondroprotective in vivo. To determine whether the route of administration is important for the efficacy of the chondroprotective properties of selective COX-2 inhibitors, a systematic review was performed according to the PRISMA guidelines. Studies investigating OA-related cartilage damage of selective COX-2 inhibitors in vivo were included. Nine of the fourteen preclinical studies demonstrated chondroprotective effects of selective COX-2 inhibitors using systemic administration. Five clinical studies were included and, although in general non-randomized, failed to demonstrate chondroprotective actions of oral selective COX-2 inhibitors. All of the four preclinical studies using bolus intra-articular injections demonstrated chondroprotective actions, while one of the three preclinical studies using a slow release system demonstrated chondroprotective actions. Despite the limited evidence in clinical studies that have used the oral administration route, there seems to be a preclinical basis for considering selective COX-2 inhibitors as disease modifying osteoarthritis drugs when used intra-articularly. Intra-articularly injected selective COX-2 inhibitors may hold the potential to provide chondroprotective effects in vivo in clinical studies.

Arthritis and the role of endogenous glucocorticoids

Rheumatoid arthritis and osteoarthritis, the most common forms of arthritis, are chronic, painful, and disabling conditions. Although both diseases differ in etiology, they manifest in progressive joint destruction characterized by pathological changes in the articular cartilage, bone, and synovium. While the potent anti-inflammatory properties of therapeutic (i.e., exogenous) glucocorticoids have been heavily researched and are widely used in clinical practice, the role of endogenous glucocorticoids in arthritis susceptibility and disease progression remains poorly understood. Current evidence from mouse models suggests that local endogenous glucocorticoid signaling is upregulated by the pro-inflammatory microenvironment in rheumatoid arthritis and by aging-related mechanisms in osteoarthritis. Furthermore, these models indicate that endogenous glucocorticoid signaling in macrophages, mast cells, and chondrocytes has anti-inflammatory effects, while signaling in fibroblast-like synoviocytes, myocytes, osteoblasts, and osteocytes has pro-inflammatory actions in rheumatoid arthritis. Conversely, in osteoarthritis, endogenous glucocorticoid signaling in both osteoblasts and chondrocytes has destructive actions. Together these studies provide insights into the role of endogenous glucocorticoids in the pathogenesis of both inflammatory and degenerative joint disease.

Association between knee alignment, osteoarthritis disease severity, and subchondral trabecular bone microarchitecture in patients with knee osteoarthritis: a cross-sectional study

Background

Knee osteoarthritis (OA) is a common disabling disease involving the entire joint tissue, and its onset and progression are affected by many factors. However, the current number of studies investigating the relationship between subchondral trabecular bone (STB), knee alignment, and OA severity is limited. We aimed to investigate the variation in tibial plateau STB microarchitecture in end-stage knee OA patients and their association with knee alignment (hip-knee-ankle, HKA, angle) and OA severity.

Methods

Seventy-one knee OA patients scheduled for total knee arthroplasty (TKA) underwent preoperative radiography to measure the HKA angle and Kellgren-Lawrence grade. Tibial plateaus collected from TKA were scanned using micro-computed tomography to analyze the STB microarchitecture. Histological sections were used to assess cartilage degeneration (OARSI score). Correlations between the HKA angle, OA severity (OARSI score, Kellgren-Lawrence grade), and STB microarchitecture were evaluated. Differences in STB microstructural parameters between varus and valgus alignment groups based on the HKA angle were examined.

Results

The HKA angle was significantly correlated with all STB microarchitecture parameters (p < 0.01). The HKA angle was more correlated with the medial-to-lateral ratios of the microarchitecture parameters than with the medial or lateral tibia plateaus. The HKA angle and all STB microarchitecture parameters are significantly correlated with both the OARSI score and Kellgren-Lawrence grade (p < 0.01).

Conclusions

The STB microarchitecture is associated with the HKA angle and OA severity. With the increase of the knee alignment deviation and OA severity, the STB of the affected side tibial plateau increased in bone volume, trabecular number, and trabecular thickness and decreased in trabecular separation.

Topographic modeling of early human osteoarthritis in sheep

Articular cartilage damage occurring during early osteoarthritis (OA) is a key event marking the development of the disease. Here, we modeled early human OA by gathering detailed spatiotemporal data from surgically induced knee OA development in sheep. We identified a specific topographical pattern of osteochondral changes instructed by a defined meniscal injury, showing that both cartilage and subchondral bone degeneration are initiated from the region adjacent to the damage. Alterations of the subarticular spongiosa arising locally and progressing globally disturbed the correlations of cartilage with subchondral bone seen at homeostasis and were indicative of disease progression. We validated our quantitative findings against human OA, showing a similar pattern of early OA correlating with regions of meniscal loss and an analogous late critical disturbance within the entire osteochondral unit. This translational model system can be used to elucidate mechanisms of OA development and provides a roadmap for investigating regenerative therapies.

Differential patterns of pathology in and interaction between joint tissues in long-term osteoarthritis with different initiating causes: phenotype matters

OBJECTIVE

To determine if osteoarthritis (OA) progression and joint tissue-pathology associations link specific animal models to different human OA phenotypes.

DESIGN

Male 11-week-old C57BL6 mice had unilateral medial-meniscal-destabilization (DMM) or antigen-induced-arthritis (AIA). Joint tissue histopathology was scored day-3 to week-16. Tissue-pathology associations (corrected for time and at week-16) were determined by partial correlation coefficients, and odds ratios (OR) calculated for likelihood of cartilage damage and joint inflammation by ordinal-logistic-regression.

RESULTS

Despite distinct temporal patterns of progression, by week-16 joint-wide OA pathology in DMM and AIA was equivalent. Significant pathology associations common to both models included: osteophyte size and maturity (r > 0.4); subchondral bone (SCB) sclerosis and osteophyte maturity (r > 0.25); cartilage erosion and chondrocyte hypertrophy/apoptosis (r > 0.4), SCB sclerosis (r > 0.26), osteophyte size (r > 0.3), and maturity (r > 0.32). DMM-specific associations were between cartilage proteoglycan loss and structural damage (r = 0.56), osteophyte maturity (r = 0.49), size (r = 0.45), and SCB sclerosis (r = 0.28). AIA-specific associations were between SCB sclerosis and chondrocyte hypertrophy/apoptosis (r = 0.40) and osteophyte size (r = 0.37); and synovitis with cartilage structural damage (r = 0.18). No tissue-pathology associations were common to both models at week-16. Increased likelihood of cartilage structural damage was associated with: chondrocyte hypertrophy/apoptosis (OR>1.7), and osteophyte size (OR>2.3) in both models; SCB sclerosis (OR = 2.0) and proteoglycan loss (OR = 2.4) in DMM; and synovitis (OR = 1.2) in AIA. Joint inflammation was associated positively with cartilage proteoglycan loss (OR = 1.4) and inversely with osteophyte size (OR = 0.21) in AIA only.

CONCLUSION

This study highlights the importance of defining OA-models by initiating mechanisms and progression, not just end-stage joint-tissue pathology.

Perfusion in bone marrow lesions assessed on DCE-MRI and its association with pain in knee osteoarthritis: a cross-sectional study

OBJECTIVE

To investigate the association between pain and perfusion in bone marrow lesions with and without cysts assessed dynamic contrast-enhanced (DCE)-MRI in patients with knee osteoarthritis.

SUBJECTS AND METHODS

In a cross-sectional setting, perfusion in bone marrow lesions was assessed using 3 Tesla MRI and correlated (Spearman's rank correlation) to pain using the knee injury and osteoarthritis outcome score (KOOS). Bone marrow lesions were assessed across the whole knee with DCE-MRI using heuristic variable and non-contrast-enhanced-MRI using MRI osteoarthritis knee score.

RESULTS

Data were available from 107 participants. The participants had a mean age of 60.8 years, mean BMI of 34.5 kg/m², mean KOOS-pain of 63.7 (0-100 scale), and mean bone marrow lesion sum score of 6.5 (0-45 scale). The bivariate association between KOOS-pain and the heuristic perfusion variable time to peak in bone marrow lesions containing subchondral cysts showed a statistically significant correlation (r = 0.40; p = 0.002). The perfusion variables were not correlated with KOOS-pain in bone marrow lesions without cysts.

CONCLUSION

In this cross-sectional study, the rate of perfusion (TTP) in bone marrow lesions containing subchondral cysts was associated with pain in patients with knee OA. DCE-MRI has a potential to be used for separating subtypes of OA.

Identification of knee osteoarthritis disability phenotypes regarding activity limitation: a cluster analysis

Background

Studies have reported the subtypes of individuals with knee osteoarthritis (OA) attempting to cluster this heterogonous condition. Activity limitations are commonly used to set goals in knee OA management and better identify subgroups based on level of disability in this patient population. Therefore, the objective of this study was to identify those activity limitations which could classify the disability phenotypes of knee OA. The phenotypes were also validated by comparing impairments and participation restrictions.

Methods

Participants comprised individuals with symptomatic knee OA. They were interviewed and undertook physical examination according to a standard evaluation forms based on the International Classification of Functioning, Disability and Health (ICF) model. Cluster analysis was used to determine those activity limitations which could best classify the phenotypes of knee OA. To validate the clustered variables, comparisons and regression analysis were performed for the impairments consisting of pain intensity, passive range of motion and muscle strength, and the participation restrictions included the difficulty level of acquiring goods and services and community life.

Results

In all, 250 participants with symptomatic knee OA were enrolled in the study. Three activity limitations identified from data distribution and literature were used as the cluster variables, included the difficulty level of maintaining a standing position, timed stair climbing and 40-m self-paced walk test. The analysis showed four phenotypes of individuals with knee OA according to the levels of disability from no to severe level of disability. All parameters of impairment and participation restrictions significantly differed among phenotypes. Subgroups with greater disability experienced worse pain intensity, limited range of motion (ROM), muscle power and participation restriction levels. The variance accounted for of the subgroups were also greater than overall participants.

Conclusion

The results of this study emphasized the heterogeneous natures of knee OA. Three activity limitations identified could classify the individuals with symptomatic knee OA to homogeneous subgroups from no to severe level of disability. The management plan, based on these homogeneous subgroups of knee OA, could be designated by considering the levels of impairments and participation restrictions.

Unicompartmental knee arthroplasties in Hong Kong: 15 years of experience in a teaching hospital

INTRODUCTION

Osteoarthritis (OA) of the knee is a growing problem in an aging population. Unicompartmental knee arthroplasties (UKA) have been used for management of isolated OA of the medial tibiofemoral joint. This is the first study on the usage of UKA in Hong Kong.

METHODS

Retrospective analysis of all patients undergoing medial compartment UKA in a tertiary referral center since 2003. Preoperative and postoperative International Knee Society Knee Scores (KSKS) and Knee Societal Functional Assessment (KSFA) scores, range of motion, flexion deformity, and lower limb mechanical alignment were measured. Statistical analysis using paired sample t-tests was performed. Revision operations, rate of revisions, and causes of failure were analyzed. Univariate and multivariate logistic regression analyses of risk factors for revision operation were performed against patient demographics, type of prosthesis, postoperative alignment, and degree of correction.

RESULTS

There were 94 UKA performed with an average follow-up of 4.3 years (range: 0.5-15.2 years). The KSKS and KSFA scores improved from 54.5 and 54.0 to 85.6 and 64.5 ( p < 0.01), respectively. There was no significant improvement in the range of motion ( p = 0.87) and fixed flexion deformity ( p = 0.14). Mechanical alignment improved from 172.1° to 174.9° varus postoperatively ( p < 0.01). Six cases required revision operation with a revision rate of 1.50 per 100 observed component years. Causes of revision included two cases of tibial tray loosening and one case each of progressive OA, mechanical failure, persistent pain, and infection. Logistic regression analysis for risk factors showed no statistical significance.

CONCLUSIONS

UKA offers good functional improvement but further long-term studies are required to evaluate survivorship.

Identifying subgroups of community-dwelling older adults and their prospective associations with long-term knee osteoarthritis outcomes

OBJECTIVES

To identify subgroups of community-dwelling older adults and to assess their longitudinal associations with long-term osteoarthritis (OA) outcomes.

METHODS

1046 older adults aged 50-80 years were studied. At baseline, body mass index (BMI), pedometer-measured ambulatory activity (AA), and Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) determined knee pain and information on comorbidities were obtained. Tibial cartilage volume and bone-marrow lesions (BMLs) were assessed using MRI at baseline and 10 years and total knee replacements (TKR) by data linkage to the Australian Orthopaedic Association National Joint Replacement Registry. Latent class analysis was used to determine participant subgroups, considering baseline BMI, AA, pain and comorbidities, and linear mixed-effects or log-binomial models were used to assess the associations.

RESULTS

Three subgroups/classes were identified: subgroup 1 (43%): Normal/overweight participants with higher AA, lower pain and lower comorbidities; subgroup 2 (32%): Overweight participants with lower AA, mild pain and higher comorbidities; subgroup 3 (25%): Obese participants with lower AA, mild pain and higher comorbidities. Subgroup 3 had greater cartilage volume loss (β - 60.56 mm³, 95% CI - 105.91, - 15.21) and a higher risk of TKR (RR 3.19, 95% CI 1.75, 5.81), compared to subgroup 1. Subgroup 2 was not associated with cartilage volume change (β 13.06 mm³, 95% CI - 30.87, 57.00) or risk of TKR (RR 1.16, 95% CI 0.56, 2.36), compared to subgroup 1. Subgroup membership was not associated with worsening BMLs.

CONCLUSIONS

Our findings suggest the existence of homogeneous subgroups of participants and support the utility of identifying patterns of characteristics/risk factors that may cluster together and using them to identify subgroups of people who may be at a higher risk of developing and/or progressing OA. Key Points • Complex interplay among characteristics/factors leads to conflicting evidence between ambulatory activity and knee osteoarthritis. • Distinct subgroups are identifiable based on ambulatory activity, body mass index, knee pain, and comorbidities. • Identifying subgroups can be used to determine those who are at risk of developing/progressing osteoarthritis.

Phenotypes of osteoarthritis: current state and future implications

In the most recent years, an extraordinary research effort has emerged to disentangle osteoarthritis heterogeneity, opening new avenues for progressing with therapeutic development and unravelling the pathogenesis of this complex condition. Several phenotypes and endotypes have been proposed albeit none has been sufficiently validated for clinical or research use as yet. This review discusses the latest advances in OA phenotyping including how new modern statistical strategies based on machine learning and big data can help advance this field of research.

The role of radiography and MRI for eligibility assessment in DMOAD trials of knee OA

Currently, no disease-modifying osteoarthritis drugs (DMOADs) have been approved. Past clinical trials have failed for several reasons, including the commonly applied definition of eligibility based on radiographic assessment of joint structure. In the context of precision medicine, finding the appropriate patient for a specific treatment approach will be of increasing relevance. Phenotypic stratification by use of imaging at the time of determining eligibility for clinical trials will be paramount and cannot be achieved using radiography alone. Furthermore, identification of joints at high risk of rapid progression of osteoarthritis is needed in order to enable a more efficient DMOAD trial design. In addition, joints at high risk of collapse need to be excluded at screening. The use of MRI might offer advantages over radiography in this context. Technological advances and simplified image assessment address many of the commonly perceived barriers to the application of MRI to assessment of eligibility for DMOAD clinical trials.

Current concepts in joint pain in knee osteoarthritis

Joint pain attributable to osteoarthritis (OA) is complex and influenced by a myriad of factors beyond local joint pathology. Current practice continues to predominantly adopt a biomedical approach to OA despite emerging evidence of the importance of a more holistic approach. This paper will summarise evidence for the presence of multidimensional pain profiles in knee joint pain and the presence of subgroups characterized by systemic features such as psychological distress, high comorbidity load or sensitisation of the nervous system. These factors have the potential to influence patient outcomes making them relevant for clinicians and highlighting the necessity of a broader multifactorial approach to assessment and treatment. This review describes the current state of the evidence for treatments of people with knee OA-related pain, including those receiving strong recommendations from current clinical guidelines, namely exercise, weight loss, self-management advice and pharmacological approaches. Other pain-modulating treatment options are emerging such as sleep and psychological interventions, pain education and multisensory retraining. The evidence and rationale for these newer therapeutic approaches is discussed. Finally, this review will highlight some of the limitations of current international guidelines for the management of OA and make recommendations for future research.

Chondroprotective Factors in Osteoarthritis: a Joint Affair

PURPOSE OF THE REVIEW

Osteoarthritis is widely regarded as a spectrum of conditions that affect all joint tissues, typified by a common entity: cartilage loss. Here, we review recent progress and challenges in chondroprotection and discuss new strategies to prevent cartilage loss in osteoarthritis.

RECENT FINDINGS

Advances in clinical, molecular, and cellular characterization are enabling improved stratification of osteoarthritis subtypes. Integration of next-generation sequencing and "omics" approaches with clinically relevant readouts shows promise in delineating both subtypes of disease and meaningful trial end points. Novel delivery strategies are enabling joint-specific delivery. Chondroprotection requires a whole joint approach, stratification of patient groups, and use of patient-relevant end points. Drug development should continue to explore new targets, while using modern technologies and recent knowledge to re-visit unsuccessful therapeutics from the past. The overarching goal for chondroprotection is to provide the right treatment(s) for the right patient at the right time.

Midfoot osteoarthritis: potential phenotypes and their associations with demographic, symptomatic and clinical characteristics

OBJECTIVE

To investigate the demographic, symptomatic, clinical and structural foot characteristics associated with potential phenotypes of midfoot osteoarthritis (OA).

DESIGN

Cross-sectional study of 533 community-dwelling adults aged ≥50 years with foot pain in the past year. Health questionnaires and clinical assessments of symptoms, foot structure and function were undertaken. Potential midfoot OA phenotypes were defined by the pattern of radiographic joint involvement affecting either the medial midfoot (talonavicular, navicular-1^st cuneiform, or cuneiform-1^st metatarsal joint), central midfoot (2^nd cuneiform-metatarsal joint), or both medial and central midfoot joints. Multivariable regression models with generalised estimating equations were used to investigate the associations between patterns of midfoot joint involvement and symptomatic, clinical and structural characteristics compared to those with no or minimal midfoot OA.

RESULTS

Of 879 eligible feet, 168 had medial midfoot OA, 103 central midfoot OA, 76 both medial and central midfoot OA and 532 no/minimal OA. Having both medial and central midfoot OA was associated with higher pain scores, dorsally-located midfoot pain (OR 2.54, 95%CI 1.45, 4.45), hallux valgus (OR 1.76, 95%CI 1.02, 3.05), flatter foot posture (β 0.44, 95%CI 0.12, 0.77), lower medial arch height (β 0.02, 95%CI 0.01, 0.03) and less subtalar inversion and 1^st MTPJ dorsiflexion. Isolated medial midfoot OA and central midfoot OA had few distinguishing clinical characteristics.

CONCLUSIONS

Distinct phenotypes of midfoot OA appear challenging to identify, with substantial overlap in symptoms and clinical characteristics. Phenotypic differences in symptoms, foot posture and function were apparent in this study only when both the medial and central midfoot were involved.

Zhuang Gu Guan Jie Wan: Reasonable Application Can Alleviate the Liver Injury for Osteoarthritis Treatment

The potential toxicity of herbal drugs, particularly drug-induced liver injury (DILI), has received extensive attention as the use of Chinese herbal medicine has rapidly increased globally. As a classic Chinese patent medicine, Zhuang Gu Guan Jie Wan (ZGGJW) has been brought into focus recently because of its satisfactory therapeutic effects on osteoarthritis (OA) as well as its unanticipated side effects. This study aimed to decipher the puzzling phenomenon of liver injury developing in response to ZGGJW that varies by the subtype of OA. Normal, anterior cruciate ligament transaction (ACLT) and partial medial meniscectomy (MMx) induced OA and ovariectomy combined with ACLT and partial MMx induced rat models were used and treated orally with ZGGJW or distilled water for 30 days. The results from histopathology, biochemistry, and immunohistochemistry showed that ZGGJW induced liver injury, increased the level of malondialdehyde (MDA), and decreased the levels of total antioxidation capability (T-AOC), superoxide dismutase (SOD), interleukin-22 (IL-22), and signal transducer and activator of transcription factor 3 (STAT3) in the liver of normal rats, while liver injury was alleviated and showed different tendencies in the above markers for ACLT and partial MMx induction rats and ovariectomy combined with ACLT and partial MMx induction rats after ZGGJW treatment. In the OA disease states, hepatic injury induced by ZGGJW could be associated with an impairment in antioxidant capacity and the high levels of IL-22 and STAT3 after ZGGJW treatment may be responsible for the slight hepatic injury of ZGGJW based on the subtype of OA. This study provides a novel approach to better understanding of the risks and limitations when using potentially toxic Chinese patent medicine in clinical applications.

Dehydroepiandrosterone: Molecular mechanisms and therapeutic implications in osteoarthritis

Dehydroepiandrosterone (DHEA), a 19-carbon steroid hormone primarily synthesized in the adrenal gland, exerts a chondroprotective effect against osteoarthritis (OA) and has been considered an effective candidate of disease-modifying OA drugs (DMOADs) that slow disease progression. We and others previously demonstrated that DHEA exerted a beneficial effect on osteoarthritic cartilage by positively modulating the balance between anabolic and catabolic factors (e.g., MMPs/TIMP-1, ADAMTS/TIMP-3 and cysteine proteinases/cystatin C), inhibiting catabolic signaling pathways (e.g., Wnt/β-catenin), and suppressing proinflammatory cytokines-mediated low-grade synovial inflammation (e.g., IL-1β). However, the full picture of the pharmacological molecular mechanism(s) underlying the activity of DHEA against OA is still incomplete, and a comprehensive and up-to-date review article in this field is unavailable. In this review, recent findings (apart from the well documented pathogenesis of OA) regarding disease-related mechanisms involving low grade synovial inflammation, cartilage matrix stiffness, chondrocyte autophagy and the roles of a variety of catabolic cellular signaling pathways are discussed. Moreover, the possible relationship between these disease-related mechanisms and DHEA action is discussed. Emerging evidence from in vivo and in vitro studies were scrutinized and are concisely presented to demonstrate the investigational and putative mechanisms underlying the anti-OA potential of DHEA.

Is osteoarthritis one disease or a collection of many?

OA is a multifaceted and heterogeneous syndrome that may be amenable to tailored treatment. There has been an increasing focus within the OA research community on the identification of meaningful OA phenotypes with potential implications for prognosis and treatment. Experimental and clinical data combined with sophisticated statistical approaches have been used to characterize and define phenotypes from the symptomatic and structural perspectives. An improved understanding of the existing phenotypes based on underlying disease mechanisms may shed light on the distinct entities that make up the disease. This narrative review provides an updated summary of the most recent advances in this field as well as limitations from previous approaches that can be addressed in future studies.

A 6-week hip muscle strengthening and lumbopelvic-hip core stabilization program to improve pain, function, and quality of life in persons with patellofemoral osteoarthritis: a feasibility pilot study

Background

Patellofemoral joint (PFJ) osteoarthritis (OA) is prevalent in middle-aged and older adults. Despite this, there are minimal studies which have examined conservative interventions for PFJ OA. Weakness of proximal lower extremity muscles is associated with PFJ OA. It is unknown if a hip muscle strengthening and lumbopelvic-hip core stabilization program will improve symptoms and function in persons with PFJ OA. This study examined the feasibility and impact of a 6-week hip muscle strengthening and core stabilization program on pain, symptoms, physical performance, peak muscle torques, and quality of life in persons with PFJ OA.

Methods

Ten females with PFJ OA and ten age- and sex-matched controls participated in baseline tests. PFJ OA participants attended ten twice-a-week hip strengthening and core stabilization exercise sessions. Outcome measures included questionnaires, the Timed-Up-and-Go, and peak isometric torque of hip and quadriceps muscles. Data were tested for normality; parametric and non-parametric tests were used as appropriate.

Results

At baseline, the PFJ OA group had significantly worse symptoms, slower Timed-Up-and-Go performance, and lower muscle torques than control participants. PFJ OA group adherence to supervised exercise sessions was adequate. All PFJ OA participants attended at least nine exercise sessions. Five PFJ OA participants returned 6-month follow-up questionnaires, which was considered fair retention. The PFJ OA participants' self-reported pain, symptoms, function in daily living, function in sport, and quality of life all improved at 6 weeks (P < 0.05). Timed-Up-and-Go time score improved at 6 weeks (P = 0.005). Peak hip external rotator torque increased (P = 0.01). Improvements in pain and self-reported function were no longer significant 6 months following completion of the intervention.

Conclusions

PFJ OA participants were adherent to the supervised sessions of the intervention. Improvement in symptoms, physical performance, and muscle torque were found after 6 weeks. Participant retention at 6 months was fair, and significant changes were no longer present. Our findings suggest that a hip strengthening and core stabilization program may be beneficial to improve symptoms, function, and physical performance in persons with PFJ OA. Future studies are needed, and additional measures should be taken to improve long-term adherence to exercise.

Trial registration

ClinicalTrials.gov NCT02825238. Registered 6 July 2016 (retrospectively registered).

Relationships between in vivo dynamic knee joint loading, static alignment and tibial subchondral bone microarchitecture in end-stage knee osteoarthritis

OBJECTIVE

To study, in end-stage knee osteoarthritis (OA) patients, relationships between indices of in vivo dynamic knee joint loads obtained pre-operatively using gait analysis, static knee alignment, and the subchondral trabecular bone (STB) microarchitecture of their excised tibial plateau quantified with 3D micro-CT.

DESIGN

Twenty-five knee OA patients scheduled for total knee arthroplasty underwent pre-operative gait analysis. Mechanical axis deviation (MAD) was determined radiographically. Following surgery, excised tibial plateaus were micro-CT-scanned and STB microarchitecture analysed in four subregions (anteromedial, posteromedial, anterolateral, posterolateral). Regional differences in STB microarchitecture and relationships between joint loading and microarchitecture were examined.

RESULTS

STB microarchitecture differed among subregions (P < 0.001), anteromedially exhibiting highest bone volume fraction (BV/TV) and lowest structure model index (SMI). Anteromedial BV/TV and SMI correlated strongest with the peak external rotation moment (ERM; r = -0.74, r = 0.67, P < 0.01), despite ERM being the lowest (by factor of 10) of the moments considered, with majority of ERM measures below accuracy thresholds; medial-to-lateral BV/TV ratios correlated with ERM, MAD, knee adduction moment (KAM) and internal rotation moment (|r|-range: 0.54-0.74). When controlling for walking speed, KAM and MAD, the ERM explained additional 11-30% of the variations in anteromedial BV/TV and medial-to-lateral BV/TV ratio (R² = 0.59, R² = 0.69, P < 0.01).

CONCLUSIONS

This preliminary study suggests significant associations between tibial plateau STB microarchitecture and knee joint loading indices in end-stage knee OA patients. Particularly, anteromedial BV/TV correlates strongest with ERM, whereas medial-to-lateral BV/TV ratio correlates strongest with indicators of medial-to-lateral joint loading (MAD, KAM) and rotational moments. However, associations with ERM should be interpreted with caution.

Stratification of knee osteoarthritis: two major patient subgroups identified by genome-wide expression analysis of articular cartilage

INTRODUCTION

Osteoarthritis (OA) is a heterogeneous and complex disease. We have used a network biology approach based on genome-wide analysis of gene expression in OA knee cartilage to seek evidence for pathogenic mechanisms that may distinguish different patient subgroups.

METHODS

Results from RNA-Sequencing (RNA-Seq) were collected from intact knee cartilage at total knee replacement from 44 patients with OA, from 16 additional patients with OA and 10 control patients with non-OA. Results were analysed to identify patient subsets and compare major active pathways.

RESULTS

The RNA-Seq results showed 2692 differentially expressed genes between OA and non-OA. Analysis by unsupervised clustering identified two distinct OA groups: Group A with 24 patients (55%) and Group B with 18 patients (41%). A 10 gene subgroup classifier was validated by RT-qPCR in 16 further patients with OA. Pathway analysis showed increased protein expression in both groups. PhenomeExpress analysis revealed group differences in complement activation, innate immune responses and altered Wnt and TGFβ signalling, but no activation of inflammatory cytokine expression. Both groups showed suppressed circadian regulators and whereas matrix changes in Group A were chondrogenic, in Group B they were non-chondrogenic with changes in mechanoreceptors, calcium signalling, ion channels and in cytoskeletal organisers. The gene expression changes predicted 478 potential biomarkers for detection in synovial fluid to distinguish patients from the two groups.

CONCLUSIONS

Two subgroups of knee OA were identified by network analysis of RNA-Seq data with evidence for the presence of two major pathogenic pathways. This has potential importance as a new basis for the stratification of patients with OA for drug trials and for the development of new targeted treatments.

Objective assessment of physical activity and sedentary behaviour in knee osteoarthritis patients - beyond daily steps and total sedentary time

BACKGROUND

Knee osteoarthritis patients may become physically inactive due to pain and functional limitations. Whether physical activity exerts a protective or harmful effect depends on the frequency, intensity, time and type (F.I.T.T.). The F.I.T.T. dimensions should therefore be assessed during daily life, which so far has hardly been feasible. Furthermore, physical activity should be assessed within subgroups of patients, as they might experience different activity limitations. Therefore, this study aimed to objectively describe physical activity, by assessing the F.I.T.T. dimensions, and sedentary behaviour of knee osteoarthritis patients during daily life. An additional goal was to determine whether activity events, based on different types and durations of physical activity, were able to discriminate between subgroups of KOA patients based on risk factors.

METHODS

Clinically diagnosed knee osteoarthritis patients (according to American College of Rheumatology criteria) were monitored for 1 week with a tri-axial accelerometer. Furthermore, they performed three functional tests and completed the Knee Osteoarthritis Outcome Score. Physical activity levels were described for knee osteoarthritis patients and compared between subgroups.

RESULTS

Sixty-one patients performed 7303 mean level steps, 319 ascending and 312 descending steps and 601 bicycle crank revolutions per day. Most waking hours were spent sedentary (61%), with 4.6 bouts of long duration (> 30 min). Specific events, particularly ascending and descending stairs/slopes, brief walking and sedentary bouts and prolonged walking bouts, varied between subgroups.

CONCLUSIONS

From this sample of KOA patients, the most common form of activity was level walking, although cycling and stair climbing activities occurred frequently, highlighting the relevance of distinguishing between these types of PA. The total active time encompassed a small portion of their waking hours, as they spent most of their time sedentary, which was exacerbated by frequently occurring prolonged bouts. In this study, event-based parameters, such as stair climbing or short bouts of walking or sedentary time, were found more capable of discriminating between subgroups of KOA patients compared to overall levels of PA and sedentary time. Thereby, subtle limitations in physical behaviour of KOA-subgroups were revealed, which might ultimately be targeted in rehabilitation programs.

TRIAL REGISTRATION

German Clinical Trials Registry under ' DRKS00008735 ' at 02.12.2015.

Alterations of Subchondral Bone Progenitor Cells in Human Knee and Hip Osteoarthritis Lead to a Bone Sclerosis Phenotype

Subchondral bone tissue plays a key role in the initiation and progression of human and experimental osteoarthritis and has received considerable interest as a treatment target. Elevated bone turnover and remodeling leads to subchondral bone sclerosis that is characterized by an increase in bone material that is less mineralized. The aim of this study was to investigate whether perturbations in subchondral bone-resident progenitor cells might play a role in aberrant bone formation in osteoarthritis. Colony formation assays indicated similar clonogenicity of progenitor cells from non-sclerotic and sclerotic subchondral trabecular bone tissues of osteoarthritic knee and hip joints compared with controls from iliac crest bone. However, the osteogenic potential at the clonal level was approximately two-fold higher in osteoarthritis than controls. An osteogenic differentiation assay indicated an efficient induction of alkaline phosphatase activity but blunted in vitro matrix mineralization irrespective of the presence of sclerosis. Micro-computed tomography and histology demonstrated the formation of de novo calcified tissues by osteoblast-like cells in an ectopic implantation model. The expression of bone sialoprotein, a marker for osteoblast maturation and mineralization, was significantly less in sclerotic progenitor cells. Perturbation of resident progenitor cell function is associated with subchondral bone sclerosis and may be a treatment target for osteoarthritis.

Classification of patients with knee osteoarthritis in clinical phenotypes: Data from the osteoarthritis initiative

OBJECTIVES

The existence of phenotypes has been hypothesized to explain the large heterogeneity characterizing the knee osteoarthritis. In a previous systematic review of the literature, six main phenotypes were identified: Minimal Joint Disease (MJD), Malaligned Biomechanical (MB), Chronic Pain (CP), Inflammatory (I), Metabolic Syndrome (MS) and Bone and Cartilage Metabolism (BCM). The purpose of this study was to classify a sample of individuals with knee osteoarthritis (KOA) into pre-defined groups characterized by specific variables that can be linked to different disease mechanisms, and compare these phenotypes for demographic and health outcomes.

METHODS

599 patients were selected from the OAI database FNIH at 24 months' time to conduct the study. For each phenotype, cut offs of key variables were identified matching the results from previous studies in the field and the data available for the sample. The selection process consisted of 3 steps. At the end of each step, the subjects classified were excluded from the further classification stages. Patients meeting the criteria for more than one phenotype were classified separately into a 'complex KOA' group.

RESULTS

Phenotype allocation (including complex KOA) was successful for 84% of cases with an overlap of 20%. Disease duration was shorter in the MJD while the CP phenotype included a larger number of Women (81%). A significant effect of phenotypes on WOMAC pain (F = 16.736 p <0.001) and WOMAC physical function (F = 14.676, p < 0.001) was identified after controlling for disease duration.

CONCLUSION

This study signifies the feasibility of a classification of KOA subjects in distinct phenotypes based on subgroup-specific characteristics.

Knee osteoarthritis phenotypes and their relevance for outcomes: a systematic review

OBJECTIVE

To systematically review the literature for studies investigating knee osteoarthritis (OA) phenotypes to examine what OA characteristics are relevant for phenotyping.

METHODS

A comprehensive search was performed in Medline, EMBASE, Web of Sciences, CINAHL, and Scopus databases from inception to September 2016. Inclusion was limited to observational studies of individuals with symptomatic knee OA that identified phenotypes based on any OA characteristics and assessed their association with clinically important outcomes. A descriptive synthesis of the data was performed.

RESULTS

Of the 2777 citations retrieved, 34 studies were included. Clinical phenotypes were investigated most frequently, followed by laboratory, imaging and aetiologic phenotypes. Eight studies defined subgroups based on outcome trajectories (pain, function and radiographic progression trajectories). Most studies used a single patient or disease characteristic to identify patients subgroups while five included characteristics from multiple domains. We found evidence from multiple studies suggesting that pain sensitization, psychological distress, radiographic severity, body mass index (BMI), muscle strength, inflammation and comorbidities are associated with clinically distinct phenotypes. Gender, obesity and other metabolic abnormalities, the pattern of cartilage damage, and inflammation may be implicated in delineating distinct structural phenotypes. Only a few studies investigated the external validity of the phenotypes or their prospective validity using longitudinal outcomes.

CONCLUSIONS

There is marked heterogeneity in the data selected by the studies investigating knee OA phenotypes. We identified the phenotypic characteristics that can be considered for a comprehensive phenotype classification in future studies. A framework for the investigation of phenotypes could be useful for future studies.

PROTOCOL REGISTRATION

PROSPERO CRD42016036220.