Individuals with high bone mass have increased progression of radiographic and clinical features of knee osteoarthritis

Relationship between knee pain and depth-specific measures of proximal tibial subchondral bone density

BACKGROUND

Altered subchondral bone mineral density (BMD) may be a possible contributor to osteoarthritis (OA) pain. We evaluated the relation of compartment-specific proximal tibial BMD, at varying depths beneath the subchondral surface, to knee pain.

METHODS

Multicenter Osteoarthritis (MOST) study participants with knee CTs were included. A 3D imaging tool measuring BMD in relation to depth from the subchondral surface was used to assess proximal tibial subchondral BMD at depths of 0-2.5, 2.5-5.0, and 5-10 mm. Knee pain in the past 30 days was scored on a numeric rating scale (range 0-100), dichotomized at 40/100 to define the presence of at least moderate pain. We cross-sectionally evaluated the relation of subchondral BMD to the presence of knee pain using binomial regression with generalized estimating equations (to account for correlations between two knees per individual) for each compartment and depth in separate models and adjusted for age, sex, and body mass index (BMI).

RESULTS

We included 2082 participants (mean age: 61 years, 56.5% female, mean BMI: 29 kg/m2). The prevalence of moderate pain was significantly lower for each SD unit increase in average subchondral BMD, after confounder adjustment, in each compartment. The magnitude of association did not differ for increasing depths beneath the subchondral surface or between compartments.

CONCLUSION

Lower subchondral proximal tibial BMD measures were associated with the prevalence of moderate knee pain in individuals with or at risk for knee OA, without differences by depth or compartment. These findings suggest bone remodeling responses throughout subchondral bone contribute to the knee pain experience.

Revealing the mediating mechanisms between BMI and osteoarthritis: a Mendelian randomization and mediation analysis

BACKGROUND

Despite well-documented associations between Body mass index (BMI) and Osteoarthritis (OA), the specific biological pathways and mediators involved remain poorly understood. This study aims to explore mediators through which BMI influences OA risk, particularly knee osteoarthritis (KOA), using Mendelian Randomization (MR) and mediation analysis.

METHODS

We used a two-step MR approach with data from the IEU OpenGWAS and FinnGen version 7 databases. BMI (N = 322,154) was the primary exposure, with knee disorders (KD), total bone mineral density (TBMD), metabolic disorders (MD), and anxiety disorders (AD) as potential mediators. Outcomes included KOA (N = 22,347), hip OA (HOA) (N = 11,989), and all OA (AllOA) (N = 50,508). Univariate MR evaluated causal relationships, followed by multivariate MR to quantify mediation effects. Multiple sensitivity analyses were conducted to validate robustness, while horizontal pleiotropy and heterogeneity were assessed using MR-Egger intercept and Cochran's Q statistic.

RESULTS

BMI significantly increased the risk of KOA (odds ratio [OR]: 2.00, 95% confidence interval [CI]: 1.56-2.56), HOA (OR: 2.05, 95% CI: 1.40-2.98), and AllOA (OR: 1.66, 95% CI: 1.41-1.95). KD and TBMD significantly mediated the effect on KOA, with mediation proportions of 20.89% and 3.59%, respectively. MD and AD showed no significant effects. Sensitivity analyses supported the robustness of these findings. Horizontal pleiotropy and heterogeneity tests indicated minimal evidence of bias, supporting the reliability of our results.

CONCLUSIONS

BMI increases OA risk, with KD and TBMD partially mediating the effect, particularly for KOA. The direct impact of BMI remains predominant, emphasizing the importance of weight reduction, joint protection, and physical activity as preventive measures.

Associations between Bone Mineral Density and WOMAC Scores in Healthy Individuals: Insights from the Qatar Biobank

BACKGROUND

Bone mineral density (BMD) is an indicator of bone health that predicts future bone fractures. The Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) is used to assess the severity of symptoms related to pain, stiffness, and function in diseased hip and knee joints. Here we assessed whether BMD measured at specific sites predicts WOMAC scores in healthy individuals whilst controlling for sociodemographic variables.

METHODOLOGY

BMD, sociodemographic, and WOMAC data were collected from 1764 healthy adult individuals attending the Qatar Biobank (QBB). Multiple linear regression was used to examine associations between sociodemographic factors, total body BMD and BMD related to specific skeletal sites (including femoral (femoral neck and trochanter), trunk, pelvis and total spine), and the three WOMAC subscales (pain, stiffness, and physical function).

RESULTS

After controlling for sociodemographic variables, total body and specific BMD measures did not predict pain. However, BMD measures significantly contributed to predicting stiffness after controlling for sociodemographic variables (R2 = 0.065, ΔF(7, 1724) = 3.34, p = 0.002), with a higher total body BMD associated with increased stiffness and a higher trunk BMD associated with decreased stiffness. Total body BMD measures also significantly contributed to predicting compromised physical function (R2 = 0.091, ΔF(7, 1724) = 3.762, p < 0.001) after controlling for sociodemographic variables, with a higher total body BMD associated with an increase in compromised physical function.

CONCLUSION

Total body BMD seems to be a more important predictor of stiffness and physical function than specific skeletal sites BMD measures. Monitoring BMD may have important implications for osteoarthritis patients.

Subchondral Bone Degeneration and Pathology 3-15 Years Following Ankle Sprain Injury in Adolescent Sport

BACKGROUND

Sport-related ankle sprains (SASs) are prevalent in adolescents (ages 10-19), increasing the risk of developing posttraumatic osteoarthritis (PTOA). Although early ankle osteoarthritis (OA) is not well defined, OA eventually includes alterations in bone mineral density (BMD), structural changes, and soft tissue pathology. This study examined the impact of SAS sustained in adolescent sport on bone and soft tissue structural outcomes 3-15 years postinjury.

METHODS

Participants (n = 10) with prior unilateral SAS in adolescent sport (HxAI) were compared to age- and sex-matched controls. To assess injury-related pathologies and BMD, 1.5-tesla (T) extremity magnetic resonance imaging (MRI) and computed tomography scans were used. Semiquantitative scores for injury patterns and OA features from MRI scans were summed and compared between groups. The talus, calcaneus, navicular, and 5% distal tibia were segmented, and BMD was measured for each bone.

RESULTS

All HxAI participants exhibited MRI injury pathology (median 2; IQR 1-6), whereas only 1 of 10 controls showed pathology (median 0; IQR 0-0), χ2(1, n = 20) = 16.36, P < .001. Both the injured and uninjured ankles in HxAI displayed injury pattern pathology. Additionally, 3 of 10 injured ankles and 2 of 10 uninjured ankles in the HxAI group (median 0; IQR 0-3), but none of the controls (median 0; IQR 0-0), exhibited OA features. In the HxAI group, talus BMD was lower in the injured ankle (502.4 ± 67.9 g/cm3) compared with the uninjured ankle (515.6 ± 70.1 g/cm3) (F = 13.33, P = .002), with no significant BMD differences at the calcaneus, navicular, or 5% distal tibia. No differences were observed between the ankles of the control group.

CONCLUSION

The presence of injury pattern pathology, structural changes, and reduced talus BMD suggest that degenerative changes may occur in individuals as early as 3-15 years following ankle injury.

Short-term prediction of clinical and radiographic contralateral hip osteoarthritis after index total hip arthroplasty

INTRODUCTION

Patients with primary hip osteoarthritis undergoing unilateral total hip arthroplasty (THA) often face uncertainty about the future need for arthroplasty in the contralateral hip. We aimed to identify parameters that have predictive value with regard to the necessity for contralateral THA or the development of contralateral radiographic osteoarthritis (OA) phenotypes following index surgery.

MATERIALS AND METHODS

In this retrospective study, we analyzed 220 patients undergoing THA. Of these, 24.1% required contralateral THA at a mean follow-up of 18.3months. Our assessments included preoperative and follow-up pelvis radiographs as well as bone mineral density (BMD) measurement by dual-energy X-ray absorptiometry prior to index THA. Comprehensive radiological measurements such as the Kellgren-Lawrence OA grade, osteophyte evaluation as well as joint shape and alignment (including alpha and CE angles) were performed.

RESULTS

We identified three indicators at the initial assessment for predicting the need for contralateral THA: higher BMI (odds ratio (OR) 1.1 [95%-CI 1.0-1.2], p = 0.033), higher alpha angles (> 61.5°) (OR 2.5 [95%-CI 1.0-6.3], p = 0.045) and the presence of multiple osteophytes (OR 2.6 [95%-CI 1.4-4.9], p = 0.004). Moreover, higher alpha angles were linked to more severe radiographic OA, especially osteophytosis. Higher BMD T-scores were also associated with progressive formation of multiple and large osteophytes but not joint space narrowing.

CONCLUSION

Three factors - BMI, alpha angle, and osteophyte number - are key short-term predictors for contralateral THA after index THA. We also identified BMD as a surrogate for osteophyte formation. These findings provide novel and valuable insights for patients and surgeons regarding risks and counseling for contralateral OA and THA.

Causal inference in health and disease: a review of the principles and applications of Mendelian randomization

Mendelian randomization (MR) is a genetic epidemiological technique that uses genetic variation to infer causal relationships between modifiable exposures and outcome variables. Conventional observational epidemiological studies are subject to bias from a range of sources; MR analyses can offer an advantage in that they are less prone to bias as they use genetic variants inherited at conception as "instrumental variables", which are proxies of an exposure. However, as with all research tools, MR studies must be carefully designed to yield valuable insights into causal relationships between exposures and outcomes, and to avoid biased or misleading results that undermine the validity of the causal inferences drawn from the study. In this review, we outline Mendel's laws of inheritance, the assumptions and principles that underlie MR, MR study designs and methods, and how MR analyses can be applied and reported. Using the example of serum phosphate concentrations on liability to kidney stone disease we illustrate how MR estimates may be visualized and, finally, we contextualize MR in bone and mineral research including exemplifying how this technique could be employed to inform clinical studies and future guidelines concerning BMD and fracture risk. This review provides a framework to enhance understanding of how MR may be used to triangulate evidence and progress research in bone and mineral metabolism as we strive to infer causal effects in health and disease.

PTH treatment before cyclic joint loading improves cartilage health and attenuates load-induced osteoarthritis development in mice

Osteoarthritis (OA) treatment is limited by the lack of effective nonsurgical interventions to slow disease progression. Here, we examined the contributions of the subchondral bone properties to OA development. We used parathyroid hormone (PTH) to modulate bone mass before OA initiation and alendronate (ALN) to inhibit bone remodeling during OA progression. We examined the spatiotemporal progression of joint damage by combining histopathological and transcriptomic analyses across joint tissues. The additive effect of PTH pretreatment before OA initiation and ALN treatment during OA progression most effectively attenuated load-induced OA pathology. Individually, PTH directly improved cartilage health and slowed the development of cartilage damage, whereas ALN primarily attenuated subchondral bone changes associated with OA progression. Joint damage reflected early transcriptomic changes. With both treatments, the structural changes were associated with early modulation of immunoregulation and immunoresponse pathways that may contribute to disease mechanisms. Overall, our results demonstrate the potential of subchondral bone-modifying therapies to slow the progression of OA.

Osteoporosis, Osteoarthritis, and Subchondral Insufficiency Fracture: Recent Insights

The increased incidence of osteoarthritis (OA), particularly knee and hip OA, and osteoporosis (OP), owing to population aging, have escalated the medical expense burden. Osteoarthritis is more prevalent in older women, and the involvement of subchondral bone fragility spotlights its association with OP. Notably, subchondral insufficiency fracture (SIF) may represent a more pronounced condition of OA pathophysiology. This review summarizes the relationship between OA and OP, incorporating recent insights into SIF. Progressive SIF leads to joint collapse and secondary OA and is associated with OP. Furthermore, the thinning and fragility of subchondral bone in early-stage OA suggest that SIF may be a subtype of OA (osteoporosis-related OA, OPOA) characterized by significant subchondral bone damage. The high bone mineral density observed in OA may be overestimated due to osteophytes and sclerosis and can potentially contribute to OPOA. The incidence of OPOA is expected to increase along with population aging. Therefore, prioritizing OP screening, early interventions for patients with early-stage OA, and fracture prevention measures such as rehabilitation, fracture liaison services, nutritional management, and medication guidance are essential.

Rare and Common Variants in GALNT3 May Affect Bone Mass Independently of Phosphate Metabolism

Anabolic treatment options for osteoporosis remain limited. One approach to discovering novel anabolic drug targets is to identify genetic causes of extreme high bone mass (HBM). We investigated a pedigree with unexplained HBM within the UK HBM study, a national cohort of probands with HBM and their relatives. Whole exome sequencing (WES) in a family with HBM identified a rare heterozygous missense variant (NM_004482.4:c.1657C > T, p.Arg553Trp) in GALNT3, segregating appropriately. Interrogation of data from the UK HBM study and the Anglo-Australasian Osteoporosis Genetics Consortium (AOGC) revealed an unrelated individual with HBM with another rare heterozygous variant (NM_004482.4:c.831 T > A, p.Asp277Glu) within the same gene. In silico protein modeling predicted that p.Arg553Trp would disrupt salt-bridge interactions, causing instability of GALNT3, and that p.Asp277Glu would disrupt manganese binding and consequently GALNT3 catalytic function. Bi-allelic loss-of-function GALNT3 mutations alter FGF23 metabolism, resulting in hyperphosphatemia and causing familial tumoral calcinosis (FTC). However, bone mineral density (BMD) in FTC cases, when reported, has been either normal or low. Common variants in the GALNT3 locus show genome-wide significant associations with lumbar, femoral neck, and total body BMD. However, no significant associations with BMD are observed at loci coding for FGF23, its receptor FGFR1, or coreceptor klotho. Mendelian randomization analysis, using expression quantitative trait loci (eQTL) data from primary human osteoblasts and genome-wide association studies data from UK Biobank, suggested increased expression of GALNT3 reduces total body, lumbar spine, and femoral neck BMD but has no effect on phosphate concentrations. In conclusion, rare heterozygous loss-of-function variants in GALNT3 may cause HBM without altering phosphate concentration. These findings suggest that GALNT3 may affect BMD through pathways other than FGF23 regulation, the identification of which may yield novel anabolic drug targets for osteoporosis. © 2023 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

High bone mass and cam morphology are independently related to hip osteoarthritis: findings from the High Bone Mass cohort

BACKGROUND

High bone mass (HBM, BMD Z-score ≥  + 3.2) and cam morphology (bulging of lateral femoral head) are associated with greater odds of prevalent radiographic hip osteoarthritis (rHOA). As cam morphology is itself a manifestation of increased bone deposition around the femoral head, it is conceivable that cam morphology may mediate the relationship between HBM and rHOA. We therefore aimed to determine if individuals with HBM have increased odds of prevalent cam morphology. In addition, we investigated whether the relationship between cam and prevalent and incident osteoarthritis was preserved in a HBM population.

METHODS

In the HBM study, a UK based cohort of adults with unexplained HBM and their relatives and spouses (controls), we determined the presence of cam morphology using semi-automatic methods of alpha angle derivation from pelvic radiographs. Associations between HBM status and presence of cam morphology, and between cam morphology and presence of rHOA (or its subphenotypes: osteophytes, joint space narrowing, cysts, and subchondral sclerosis) were determined using multivariable logistic regression, adjusting for age, sex, height, weight, and adolescent physical activity levels. The association between cam at baseline and incidence of rHOA after an average of 8 years was determined. Generalised estimating equations accounted for individual-level clustering.

RESULTS

The study included 352 individuals, of whom 235 (66.7%) were female and 234 (66.5%) had HBM. Included individuals contributed 694 hips, of which 143 had a cam deformity (20.6%). There was no evidence of an association between HBM and cam morphology (OR = 0.97 [95% CI: 0.63-1.51], p = 0.90) but a strong relationship was observed between cam morphology and rHOA (OR = 3.96 [2.63-5.98], p = 5.46 × 10-11) and rHOA subphenotypes joint space narrowing (OR = 3.70 [2.48-5.54], p = 1.76 × 10-10), subchondral sclerosis (OR = 3.28 [1.60-6.60], p = 9.57 × 10-4) and osteophytes (OR = 3.01 [1.87-4.87], p = 6.37 × 10-6). Cam morphology was not associated with incident osteoarthritis (OR = 0.76 [0.16-3.49], p = 0.72).

CONCLUSIONS

The relationship between cam morphology and rHOA seen in other studies is preserved in a HBM population. This study suggests that the risk of OA conferred by high BMD and by cam morphology are mediated via distinct pathways.

OA foundations - experimental models of osteoarthritis

Osteoarthritis (OA) is increasingly recognised as a disease of diverse phenotypes with variable clinical presentation, progression, and response to therapeutic intervention. This same diversity is readily apparent in the many animal models of OA. However, model selection, study design, and interpretation of resultant findings, are not routinely done in the context of the target human (or veterinary) patient OA sub-population or phenotype. This review discusses the selection and use of animal models of OA in discovery and therapeutic-development research. Beyond evaluation of the different animal models on offer, this review suggests focussing the approach to OA-animal model selection on study objective(s), alignment of available models with OA-patient sub-types, and the resources available to achieve valid and translatable results. How this approach impacts model selection is discussed and an experimental design checklist for selecting the optimal model(s) is proposed. This approach should act as a guide to new researchers and a reminder to those already in the field, as to issues that need to be considered before embarking on in vivo pre-clinical research. The ultimate purpose of using an OA animal model is to provide the best possible evidence if, how, when and where a molecule, pathway, cell or process is important in clinical disease. By definition this requires both model and study outcomes to align with and be predictive of outcomes in patients. Keeping this at the forefront of research using pre-clinical OA models, will go a long way to improving the quality of evidence and its translational value.

Epidemiology of osteoarthritis

OBJECTIVE

To summarize the current state of the evidence regarding osteoarthritis (OA) prevalence, incidence and risk factors at the person-level and joint-level.

DESIGN

This was a narrative review that took a comprehensive approach regarding inclusion of potential risk factors. The review complements prior reviews of OA epidemiology, with a focus on new research and emerging topics since 2017, as well as seminal studies.

RESULTS

Studies continue to illustrate the high prevalence of OA worldwide, with a greater burden among older individuals, women, some racial and ethnic groups, and individuals with lower socioeconomic status. Modifiable risk factors for OA with the strongest evidence are obesity and joint injury. Topics of high interest or emerging evidence for a potential association with OA risk or progression include specific vitamins and diets, high blood pressure, genetic factors, metformin use, bone mineral density, abnormal joint shape and malalignment, and lower muscle strength/quality. Studies also continue to highlight the heterogenous nature of OA, with strong interest in understanding and defining OA phenotypes.

CONCLUSIONS

OA is an increasingly prevalent condition with worldwide impacts on many health outcomes. The strong evidence for obesity and joint injury as OA risk factors calls for heightened efforts to mitigate these risks at clinical and public health levels. There is also a need for continued research regarding how potential person- and joint-level risk factors may interact to influence the development and progression of OA.

Hemodynamic stress shapes subchondral bone in osteoarthritis: An emerging hypothesis

Osteoarthritis (OA) is no longer regarded as a simple wear-and-tear problem of articular cartilage. Instead, OA is a whole joint disorder involving both cartilaginous and non-cartilaginous tissues such as subchondral bone and synovium. Among them, subchondral bone undergoes constant remodeling in response to the changes of mechanical environment. Current understanding of subchondral bone disturbance in OA is limited to its link with an altered local mechanical loading as a result of ligament or meniscus injury. Very recently, hypertension, the most common vascular morbidity, has been emerged as an independent risk factor of OA. It might suggest a plausible role of systemic hemodynamic mechanical stress in subchondral bone remodeling and the pathogenesis of OA. However, their relationship remains not fully understood. Based on our preliminary clinical observation on the association of hemodynamic parameters with subchondral bone mass and microstructure in late-stage knee OA patients, we formulate a vascular etiology hypothesis of OA from a mechanobiology perspective. Noteworthily, hemodynamic stress associated with subchondral bone mineral density; yet compressive mechanical loading does not. Furthermore, hemodynamic parameters positively correlated with subchondral plate-like trabecular bone volume but negatively associated with rod-like trabecular bone volume. In contrast, compressive mechanical loading tends to increase both plate-like and rod-like trabecular bone volume. Taken together, it warrants further investigations into the distinct role of hemodynamic or compressive stress in shaping subchondral bone in the pathophysiology of OA.

The Translational potential of this article

This work provides a new insight, from the angle of biomechanics, into the emerging role of vascular pathologies, such as hypertension, in the pathogenesis of OA. It might open up a new avenue for the development of a mechanism-based discovery of novel diagnostics and therapeutics.

Using multivariable Mendelian randomization to estimate the causal effect of bone mineral density on osteoarthritis risk, independently of body mass index

OBJECTIVES

Observational analyses suggest that high bone mineral density (BMD) is a risk factor for osteoarthritis (OA); it is unclear whether this represents a causal effect or shared aetiology and whether these relationships are body mass index (BMI)-independent. We performed bidirectional Mendelian randomization (MR) to uncover the causal pathways between BMD, BMI and OA.

METHODS

One-sample (1S)MR estimates were generated by two-stage least-squares regression. Unweighted allele scores instrumented each exposure. Two-sample (2S)MR estimates were generated using inverse-variance weighted random-effects meta-analysis. Multivariable MR (MVMR), including BMD and BMI instruments in the same model, determined the BMI-independent causal pathway from BMD to OA. Latent causal variable (LCV) analysis, using weight-adjusted femoral neck (FN)-BMD and hip/knee OA summary statistics, determined whether genetic correlation explained the causal effect of BMD on OA.

RESULTS

1SMR provided strong evidence for a causal effect of BMD estimated from heel ultrasound (eBMD) on hip and knee OA {odds ratio [OR]hip = 1.28 [95% confidence interval (CI) = 1.05, 1.57], p = 0.02, ORknee = 1.40 [95% CI = 1.20, 1.63], p = 3 × 10-5, OR per standard deviation [SD] increase}. 2SMR effect sizes were consistent in direction. Results suggested that the causal pathways between eBMD and OA were bidirectional (βhip = 1.10 [95% CI = 0.36, 1.84], p = 0.003, βknee = 4.16 [95% CI = 2.74, 5.57], p = 8 × 10-9, β = SD increase per doubling in risk). MVMR identified a BMI-independent causal pathway between eBMD and hip/knee OA. LCV suggested that genetic correlation (i.e. shared genetic aetiology) did not fully explain the causal effects of BMD on hip/knee OA.

CONCLUSIONS

These results provide evidence for a BMI-independent causal effect of eBMD on OA. Despite evidence of bidirectional effects, the effect of BMD on OA did not appear to be fully explained by shared genetic aetiology, suggesting a direct action of bone on joint deterioration.

Osteophyte size and location on hip DXA scans are associated with hip pain: Findings from a cross sectional study in UK Biobank

OBJECTIVE

It remains unclear how the different features of radiographic hip osteoarthritis (rHOA) contribute to hip pain. We examined the relationship between rHOA, including its individual components, and hip pain using a novel dual-energy x-ray absorptiometry (DXA)-based method.

METHODS

Hip DXAs were obtained from UK Biobank. A novel automated method obtained minimum joint space width (mJSW) from points placed around the femoral head and acetabulum. Osteophyte areas at the lateral acetabulum, superior and inferior femoral head were derived manually. Semi-quantitative measures of osteophytes and joint space narrowing (JSN) were combined to define rHOA. Logistic regression was used to examine the relationships between these variables and hip pain, obtained via questionnaires.

RESULTS

6807 hip DXAs were examined. rHOA was present in 353 (5.2%) individuals and was associated with hip pain [OR 2.42 (1.78-3.29)] and hospital diagnosed OA [6.01 (2.98-12.16)]. Total osteophyte area but not mJSW was associated with hip pain in mutually adjusted models [1.31 (1.23-1.39), 0.95 (0.87-1.04) respectively]. On the other hand, JSN as a categorical variable showed weak associations between grade ≥ 1 and grade ≥ 2 JSN with hip pain [1.30 (1.06-1.60), 1.80 (1.34-2.42) respectively]. Acetabular, superior and inferior femoral osteophyte areas were all independently associated with hip pain [1.13 (1.06-1.20), 1.13 (1.05-1.24), 1.10 (1.03-1.17) respectively].

CONCLUSION

In this cohort, the relationship between rHOA and prevalent hip pain was explained by 2-dimensional osteophyte area, but not by the apparent mJSW. Osteophytes at different locations showed important, potentially independent, associations with hip pain, possibly reflecting the contribution of distinct biomechanical pathways.

Cam morphology but neither acetabular dysplasia nor pincer morphology is associated with osteophytosis throughout the hip: findings from a cross-sectional study in UK Biobank

OBJECTIVES

To examine whether acetabular dysplasia (AD), cam and/or pincer morphology are associated with radiographic hip osteoarthritis (rHOA) and hip pain in UK Biobank (UKB) and, if so, what distribution of osteophytes is observed.

DESIGN

Participants from UKB with a left hip dual-energy X-ray absorptiometry (DXA) scan had alpha angle (AA), lateral centre-edge angle (LCEA) and joint space narrowing (JSN) derived automatically. Cam and pincer morphology, and AD were defined using AA and LCEA. Osteophytes were measured manually and rHOA grades were calculated from JSN and osteophyte measures. Logistic regression was used to examine the relationships between these hip morphologies and rHOA, osteophytes, JSN, and hip pain.

RESULTS

6,807 individuals were selected (mean age: 62.7; 3382/3425 males/females). Cam morphology was more prevalent in males than females (15.4% and 1.8% respectively). In males, cam morphology was associated with rHOA [OR 3.20 (95% CI 2.41-4.25)], JSN [1.53 (1.24-1.88)], and acetabular [1.87 (1.48-2.36)], superior [1.94 (1.45-2.57)] and inferior [4.75 (3.44-6.57)] femoral osteophytes, and hip pain [1.48 (1.05-2.09)]. Broadly similar associations were seen in females, but with weaker statistical evidence. Neither pincer morphology nor AD showed any associations with rHOA or hip pain.

CONCLUSIONS

Cam morphology was predominantly seen in males in whom it was associated with rHOA and hip pain. In males and females, cam morphology was associated with inferior femoral head osteophytes more strongly than those at the superior femoral head and acetabulum. Further studies are justified to characterise the biomechanical disturbances associated with cam morphology, underlying the observed osteophyte distribution.

Kniearthrose bei Patienten mit hoher Knochendichte

Bei Kniegelenksarthrose treten häufig Osteophyten und Gelenkspaltverschmälerung auf. Außerdem besteht ein Zusammenspiel mit der Knochendichte. Studien weisen auf eine inverse Beziehung zwischen Osteoporose und Arthrose hin. Die Autoren erforschen den Zusammenhang zwischen Knochendichte und Kniearthrose näher. Dazu untersuchten sie eine Kohorte mit generalisierter hoher Knochendichte und deren gesunde Verwandte hinsichtlich Kniegelenksarthrose.

Osteoarthritis: Insights Offered by the Study of Bone Mass Genetics

PURPOSE OF REVIEW

This paper reviews how bone genetics has contributed to our understanding of the pathogenesis of osteoarthritis. As well as identifying specific genetic mechanisms involved in osteoporosis which also contribute to osteoarthritis, we review whether bone mineral density (BMD) plays a causal role in OA development.

RECENT FINDINGS

We examined whether those genetically predisposed to elevated BMD are at increased risk of developing OA, using our high bone mass (HBM) cohort. HBM individuals were found to have a greater prevalence of OA compared with family controls and greater development of radiographic features of OA over 8 years, with predominantly osteophytic OA. Initial Mendelian randomisation analysis provided additional support for a causal effect of increased BMD on increased OA risk. In contrast, more recent investigation estimates this relationship to be bi-directional. However, both these findings could be explained instead by shared biological pathways. Pathways which contribute to BMD appear to play an important role in OA development, likely reflecting shared common mechanisms as opposed to a causal effect of raised BMD on OA. Studies in HBM individuals suggest this reflects an important role of mechanisms involved in bone formation in OA development; however further work is required to establish whether the same applies to more common forms of OA within the general population.

Identifying Robust Risk Factors for Knee Osteoarthritis Progression: An Evolutionary Machine Learning Approach

Knee osteoarthritis (KOA) is a multifactorial disease which is responsible for more than 80% of the osteoarthritis disease's total burden. KOA is heterogeneous in terms of rates of progression with several different phenotypes and a large number of risk factors, which often interact with each other. A number of modifiable and non-modifiable systemic and mechanical parameters along with comorbidities as well as pain-related factors contribute to the development of KOA. Although models exist to predict the onset of the disease or discriminate between asymptotic and OA patients, there are just a few studies in the recent literature that focused on the identification of risk factors associated with KOA progression. This paper contributes to the identification of risk factors for KOA progression via a robust feature selection (FS) methodology that overcomes two crucial challenges: (i) the observed high dimensionality and heterogeneity of the available data that are obtained from the Osteoarthritis Initiative (OAI) database and (ii) a severe class imbalance problem posed by the fact that the KOA progressors class is significantly smaller than the non-progressors' class. The proposed feature selection methodology relies on a combination of evolutionary algorithms and machine learning (ML) models, leading to the selection of a relatively small feature subset of 35 risk factors that generalizes well on the whole dataset (mean accuracy of 71.25%). We investigated the effectiveness of the proposed approach in a comparative analysis with well-known FS techniques with respect to metrics related to both prediction accuracy and generalization capability. The impact of the selected risk factors on the prediction output was further investigated using SHapley Additive exPlanations (SHAP). The proposed FS methodology may contribute to the development of new, efficient risk stratification strategies and identification of risk phenotypes of each KOA patient to enable appropriate interventions.

The Genetic Architecture of High Bone Mass

The phenotypic trait of high bone mass (HBM) is an excellent example of the nexus between common and rare disease genetics. HBM may arise from carriage of many 'high bone mineral density [BMD]'-associated alleles, and certainly the genetic architecture of individuals with HBM is enriched with high BMD variants identified through genome-wide association studies of BMD. HBM may also arise as a monogenic skeletal disorder, due to abnormalities in bone formation, bone resorption, and/or bone turnover. Individuals with monogenic disorders of HBM usually, though not invariably, have other skeletal abnormalities (such as mandible enlargement) and thus are best regarded as having a skeletal dysplasia rather than just isolated high BMD. A binary etiological division of HBM into polygenic vs. monogenic, however, would be excessively simplistic: the phenotype of individuals carrying rare variants of large effect can still be modified by their common variant polygenic background, and by the environment. HBM disorders-whether predominantly polygenic or monogenic in origin-are not only interesting clinically and genetically: they provide insights into bone processes that can be exploited therapeutically, with benefits both for individuals with these rare bone disorders and importantly for the many people affected by the commonest bone disease worldwide-i.e., osteoporosis. In this review we detail the genetic architecture of HBM; we provide a conceptual framework for considering HBM in the clinical context; and we discuss monogenic and polygenic causes of HBM with particular emphasis on anabolic causes of HBM.