The genetic contribution to muscle strength, knee pain, cartilage volume, bone size, and radiographic osteoarthritis: A sibpair study

Association of polymorphisms rs2303729, rs10880, and rs1131620 of LTBP4 with sarcopenia in elderly patients with type 2 diabetes mellitus

BACKGROUND

Latent TGFβ binding protein 4 (LTBP4) modifies skeletal muscle function, and polymorphisms in this gene have been associated with a longer ambulation time in patients with Duchenne muscular dystrophy. However, no studies associate these polymorphisms with an acquired muscle condition.

AIM

The study aims to determine whether three functional variants within the LTBP4 were associated with sarcopenia in patients with type 2 diabetes mellitus (T2DM).

SUBJECTS AND METHODS

We performed an analysis with 144 elderly individuals with T2DM, including 101 without sarcopenia and 43 with sarcopenia. Polymorphism frequency was determined by real-time PCR allelic discrimination TaqMan assay.

RESULTS

Under different genetic models, the univariant analysis did not show a significant association of any polymorphism with sarcopenia. But the multivariate model analysis showed that variant rs1131620 (OR 7.852, 95% CI 1.854-33.257, p = 0.005) was significantly associated with sarcopenia under a dominant model. Under the same analysis, the variants rs2303729 and rs10880 had a more discrete association (OR 3.537 95% CI 1.078-11.607, p = 0.037; OR 5.008, 95% CI 1.120-22.399, p = 0.035, respectively).

CONCLUSIONS

Our study highlights the importance of studying LTBP4 polymorphisms associated with sarcopenia. These findings suggest that the rs1131620 polymorphism of the LTBP4 may be part of the observed sarcopenia process in patients with T2DM.

Study protocol for a randomised controlled trial of diacerein versus placebo to treat knee osteoarthritis with effusion-synovitis (DICKENS)

Background

There is an unmet need for treatments for knee osteoarthritis (OA). Effusion-synovitis is a common inflammatory phenotype of knee OA and predicts knee pain and structural degradation. Anti-inflammatory therapies, such as diacerein, may be effective for this phenotype. While diacerein is recommended for alleviating pain in OA patients, evidence for its effectiveness is inconsistent, possibly because studies have not targeted patients with an inflammatory phenotype. Therefore, we will conduct a multi-centre, randomised, placebo-controlled double-blind trial to determine the effect of diacerein on changes in knee pain and effusion-synovitis over 24 weeks in patients with knee OA and magnetic resonance imaging (MRI)-defined effusion-synovitis.

Methods

We will recruit 260 patients with clinical knee OA, significant knee pain, and MRI-detected effusion-synovitis in Hobart, Melbourne, Adelaide, and Perth, Australia. They will be randomly allocated to receive either diacerein (50mg twice daily) or identical placebo for 24 weeks. MRI of the study knee will be performed at screening and after 24 weeks of intervention. The primary outcome is improvement in knee pain at 24 weeks as assessed by a 100-mm visual analogue scale (VAS). Secondary outcomes include improvement in volumetric (ml) and semi-quantitative (Whole-Organ Magnetic Resonance Imaging Score, 0–3) measurements of effusion-synovitis using MRI over 24 weeks, and improvement in knee pain (VAS) at 4, 8, 12, 16, and 20 weeks. Intention-to-treat analyses of primary and secondary outcomes will be performed as the primary analyses. Per protocol analyses will be performed as the secondary analyses.

Discussion

This study will provide high-quality evidence to determine whether diacerein improves pain, changes disease trajectory, and slows disease progression in OA patients with effusion-synovitis. If diacerein proves effective, this has the potential to significantly benefit the substantial proportion (up to 60%) of knee OA patients with an inflammatory phenotype.

Trial registration

Australian and New Zealand Clinical Trial Registry ACTRN12618001656224. Registered on 08 October 2018.

The association between change in bone marrow lesion size and change in tibiofemoral cartilage volume and knee symptoms

OBJECTIVE

To describe the association between change in subchondral bone marrow lesions (BMLs) and change in tibiofemoral cartilage volume and knee symptoms in patients with symptomatic knee OA.

METHODS

In total, 251 participants (mean 61.7 years, 51% female) were included. Tibiofemoral cartilage volume was measured at baseline and 24 months, and BML size at baseline, 6 and 24 months. Knee pain and function scores were evaluated at baseline, 6 and 24 months. Change in total and compartment-specific BML size was categorized according to the Least Significance Criterion. Linear mixed-effects models were used to evaluate the associations of change in BMLs over 6 and 24 months with change in cartilage volume over 24 months and knee symptoms over 6 and 24 months.

RESULTS

Total BML size enlarged in 26% of participants, regressed in 31% and remained stable in 43% over 24 months. Compared with stable BMLs in the same compartment, enlarging BMLs over 24 months were associated with greater cartilage loss (difference: -53.0mm3, 95% CI: -100.0, -6.0), and regressing BMLs were not significantly associated with reduced cartilage loss (difference: 32.4mm3, 95% CI: -8.6, 73.3) over 24 months. Neither enlargement nor regression of total BML size over 6 and 24 months was associated with change in knee pain and function over the same time intervals.

CONCLUSIONS

In subjects with symptomatic knee osteoarthritis and BMLs, enlarging BMLs may lead to greater cartilage loss but regressing lesions are not associated with reduced cartilage loss while neither is associated with change in knee symptoms.

Nature vs nurture in knee osteoarthritis - the importance of age, sex and body mass index

OBJECTIVE

(1) To estimate the life-time genetic contribution for knee osteoarthritis (OA) surgery and (2) to explore any differences in the genetic contribution across age, sex and body mass index (BMI).

METHODS

We studied the sex-specific genetic contribution to knee OA surgery in a prospective cohort study of 62,490 twins aged 35 years or older with a follow-up period of up to 47 years (10,092 identical and 21,153 non-identical twin pairs, 54% women). To study interactions with age, we graphed the heritabilities over the lifespan for men and women. We also studied the sex-specific heritability across strata of the median BMI to explore any interactions with BMI.

RESULTS

The overall heritability of knee OA surgery was 0.53 (95% confidence intervals [CI] = 0.31-0.75), with higher heritability among women (H² = 0.80 (95% CI = 0.73-0.87)) than men (H² = 0.39 (95% CI = 0.10-0.69)). For men, the heritability started to rise after age 68. The genetic contribution was particularly low in men above median BMI (H²_{≥23.7 kg/m2} = 0.08, 95% CI = -0.32-0.48). For women, the heritability was consistently high from age 50 to death, independently of BMI (H²_{≥22.5 kg/m2} = 0.77, 95% CI = 0.66-0.87).

CONCLUSION

There is a higher and more consistent genetic contribution for knee OA surgery in women than men. In men the genetic contribution was relatively low and varied with age and BMI.

Bone shape mediates the relationship between sex and incident knee osteoarthritis

Background

Knee bone shape differs between men and women and the incidence of knee osteoarthritis (OA) is higher in women than in men. Therefore, the purpose of the present study was to determine whether the observed difference in the incidence of knee radiographic OA (ROA) between men and women is mediated by bone shape.

Methods

We randomly sampled 304 knees from the OAI with incident ROA (i.e., development of Kellgren/Lawrence grade ≥ 2 by month 48) and 304 knees without incident ROA. We characterized distal femur and proximal tibia shape on baseline radiographs using Statistical Shape Modeling. If a specific bone shape was associated with the risk of incident ROA, marginal structural models were generated to assess the mediation effect of that bone shape on the relation of sex and risk of incident knee ROA adjusting for baseline covariates.

Results

Case and control participants were similar by age, sex and race, but case knees were from higher body mass index (BMI) participants (29.4 vs. 27.0; p < 0.001). Women had 49% increased odds of incident knee ROA compared with men (adjusted odds ratio (OR) = 1.49, 95% Confidence Interval (C.I.): 1.04, 2.12). There was an inconsistent mediation effect for tibial mode 2 between sex and incident knee ROA, with an indirect effect OR of 0.96 (95% C.I.: 0.91–1.00) and a direct effect OR of 1.56 (95% C.I.: 1.08–2.27), suggesting a protective effect for this mode. Similar findings were also observed for the mediation effect of tibia mode 10 and femur mode 4. These shape modes primarily involved differences in the angular relation of the heads to the shafts of the femur and tibia.

Conclusions

Distal femur and proximal tibia bone shapes partially and inconsistently mediated the relationship between sex and incident knee OA. Women had a higher risk of incident ROA, and specific bone shapes modestly protected them from even higher risk of ROA. The clinical significance of these findings warrant further investigation.

A protocol for a multicentre, randomised, double-blind, placebo-controlled trial to compare the effect of annual infusions of zoledronic acid to placebo on knee structural change and knee pain over 24 months in knee osteoarthritis patients - ZAP2

BACKGROUND

Bisphosphonates are a class of drugs that slow bone loss and are a promising candidate to treat knee osteoarthritis (OA) patients. In a pilot study, we demonstrated that zoledronic acid reduced knee pain and size of subchondral bone marrow lesions (BMLs) over 6 months in knee OA patients with significant knee pain and BMLs. A longer, larger study is required to assess whether decreases in BML size will translate to reductions in cartilage loss over time. We are currently conducting a multicentre, randomised, double-blind, placebo-controlled trial over 24 months that aims to compare the effect of annual infusions of zoledronic acid to placebo on knee structural change (assessed using magnetic resonance imaging (MRI)) and knee pain in knee OA patients.

METHODS

Two hundred sixty-four patients with clinical knee OA, significant knee pain and subchondral BMLs present on MRI will be recruited in Hobart, Melbourne, Sydney and Adelaide. They will be randomly allocated to the two arms of the study, receiving an annual identical intravenous infusion of either 100 mL of fluid containing zoledronic acid (5 mg/100 mL) or placebo (0.9% NaCl 100 mL), at baseline and 1 year later. MRI of the study knee will be performed at screening, month 6 and 24. Knee structure, symptoms and function will be assessed using validated methods. The primary outcome is absolute change in tibiofemoral cartilage volume (mm3) over 24 months. Secondary outcomes include improvement in knee pain over 3, 6, 12, 18, and 24 months and reductions in BML size over 6 and 24 months. The primary analyses will be intention-to-treat analyses of primary and secondary outcomes. Per protocol analyses will be performed as the secondary analyses.

DISCUSSION

This study will provide high-quality evidence to assess whether zoledronic acid has a novel disease modifying effect in OA by slowing cartilage loss and reducing pain. If zoledronic acid proves effective, it suggests great potential for cost savings through a delay or reduced need for joint replacement surgery, and potential for great improvements in quality of life for OA suffers.

TRIAL REGISTRATION

Australian New Zealand Clinical Trials Registry: ACTRN12613000039785 , registered on 14 January 2013.

Heritability estimates of muscle strength-related phenotypes: A systematic review and meta-analysis

The purpose of this study was to clarify the heritability estimates of human muscle strength-related phenotypes (H² -msp). A systematic literature search was conducted using PubMed (through August 22, 2016). Studies reporting the H² -msp for healthy subjects in a sedentary state were included. Random-effects models were used to calculate the weighted mean heritability estimates. Moreover, subgroup analyses were performed based on phenotypic categories (eg, grip strength, isotonic strength, jumping ability). Sensitivity analyses were also conducted to investigate potential sources of heterogeneity of H² -msp, which included age and sex. Twenty-four articles including 58 measurements were included in the meta-analysis. The weighted mean H² -msp for all 58 measurements was 0.52 (95% confidence intervals [CI]: 0.48-0.56), with high heterogeneity (I² =91.0%, P<.001). Subgroup analysis showed that the heritability of isometric grip strength, other isometric strength, isotonic strength, isokinetic strength, jumping ability, and other power measurements was 0.56 (95% CI: 0.46-0.67), 0.49 (0.47-0.52), 0.49 (0.32-0.67), 0.49 (0.37-0.61), 0.55 (0.45-0.65), and 0.51 (0.31-0.70), respectively. The H² -msp decreased with age (P<.05). In conclusion, our results indicate that the influence of genetic and environmental factors on muscle strength-related phenotypes is comparable. Moreover, the role of environmental factors increased with age. These findings may contribute toward an understanding of muscle strength-related phenotypes.

Emerging roles for histone deacetylases in age-related muscle atrophy

BACKGROUND: Skeletal muscle atrophy during aging, a process known as sarcopenia, is associated with muscle weakness, frailty, and the loss of independence in older adults. The mechanisms contributing to sarcopenia are not totally understood, but muscle fiber loss due to apoptosis, reduced stimulation of anabolic pathways, activation of catabolic pathways, denervation, and altered metabolism have been observed in muscle from old rodents and humans.

OBJECTIVE: Recently, histone deacetylases (HDACs) have been implicated in muscle atrophy and dysfunction due to denervation, muscular dystrophy, and disuse, and HDACs play key roles in regulating metabolism in skeletal muscle. In this review, we will discuss the role of HDACs in muscle atrophy and the potential of HDAC inhibitors for the treatment of sarcopenia.

CONCLUSIONS: Several HDAC isoforms are potential targets for intervention in sarcopenia. Inhibition of HDAC1 prevents muscle atrophy due to nutrient deprivation. HDAC3 regulates metabolism in skeletal muscle and may inhibit oxidative metabolism during aging. HDAC4 and HDAC5 have been implicated in muscle atrophy due to denervation, a process implicated in sarcopenia. HDAC inhibitors are already in use in the clinic, and there is promise in targeting HDACs for the treatment of sarcopenia.

Osteoarthritis

Osteoarthritis (OA) is the most common joint disorder, is associated with an increasing socioeconomic impact owing to the ageing population and mainly affects the diarthrodial joints. Primary OA results from a combination of risk factors, with increasing age and obesity being the most prominent. The concept of the pathophysiology is still evolving, from being viewed as cartilage-limited to a multifactorial disease that affects the whole joint. An intricate relationship between local and systemic factors modulates its clinical and structural presentations, leading to a common final pathway of joint destruction. Pharmacological treatments are mostly related to relief of symptoms and there is no disease-modifying OA drug (that is, treatment that will reduce symptoms in addition to slowing or stopping the disease progression) yet approved by the regulatory agencies. Identifying phenotypes of patients will enable the detection of the disease in its early stages as well as distinguish individuals who are at higher risk of progression, which in turn could be used to guide clinical decision making and allow more effective and specific therapeutic interventions to be designed. This Primer is an update on the progress made in the field of OA epidemiology, quality of life, pathophysiological mechanisms, diagnosis, screening, prevention and disease management.

Familial effects on structural changes relevant to knee osteoarthritis: a prospective cohort study

OBJECTIVE

Genetic factors play an important role in the pathogenesis of knee osteoarthritis (OA), but which knee structural changes mediate this is unclear. This study aimed to describe the differences in knee structural changes over 8-10 years between offspring having at least one parent with total knee replacement (TKR) for severe primary knee OA and controls with no family history of knee OA.

DESIGN

115 offspring (mean age 45 years) with a family history of TKR for severe knee OA were compared with 104 (mean age 46 years) controls. T1 or T2-weighted fat saturated magnetic resonance imaging (MRI) was performed respectively to evaluate knee cartilage defects, bone marrow lesions (BMLs), meniscal extrusion and tears at baseline and 10 years. Multivariate logistic regression model was used to adjust for potential confounders.

RESULTS

Offspring had a greater increase in cartilage defect score (1.03 vs 0.52, P = 0.007) and meniscal extrusion score (0.28 vs 0.10, P = 0.027) over 10 years, and a greater increase in meniscal tear score (0.40 vs 0.10, P = 0.012) over 8 years in the medial but not the lateral tibiofemoral compartment. Changes in BMLs over 8-years were not different between the two groups. These associations were independent of potential confounders, and strengthened after further adjustment for each other.

CONCLUSION

With the exception of BMLs, offspring with a family history of knee OA have a greater risk of increases in multiple knee structural abnormalities in the medial tibiofemoral compartment suggesting pleiotropic familial effects.

A family history of knee joint replacement increases the progression of knee radiographic osteoarthritis and medial tibial cartilage volume loss over 10 years

OBJECTIVES

Osteoarthritis (OA) has a genetic component but it is uncertain if the offspring of those with knee OA are at a greater risk. The aim of this study was to describe radiographic OA (ROA) progression and cartilage loss over 10 years in a midlife cohort with some having a family history of OA and some community based controls.

METHODS

220 participants [mean-age 45 (26-61); 57% female] were studied at baseline and 10 years. Half were adult offspring of subjects who underwent knee replacement for OA and the remainder were randomly selected controls. Joint space narrowing (JSN) and osteophytes were assessed on radiographs and cartilage volume (tibial, femoral and patellar), cartilage defects, bone marrow lesions (BMLs) and meniscal tears were assessed on Magnetic resonance imaging (MRI).

RESULTS

For ROA, there was a significant difference between offspring and controls in unadjusted analysis for change in total ROA, medial JSN, total medial, total lateral and total osteophyte scores. This difference persisted for medial JSN (difference in ratios = +1.93 (+1.04, +3.51)) only, after adjustment for confounders and baseline differences. In unadjusted analysis for cartilage loss, offspring lost more cartilage at the medial tibial (difference in means = -79.13 (-161.92, +3.71)) site only. This difference became of borderline significance after adjustment for baseline differences (P = 0.055).

CONCLUSION

The offspring of subjects having a total knee replacement have a greater worsening of ROA (both JSN and osteophytes) and higher medial tibial cartilage volume loss over 10 years. Most of these changes are mediated by differences in baseline characteristics of offspring and controls except for increase in medial JSN.

The clinical significance, natural history and predictors of bone marrow lesion change over eight years

Introduction

There is increasing evidence to suggest that bone marrow lesions (BMLs) play a key role in the pathogenesis of osteoarthritis (OA). However, there is a lack of long term data. The aim of this study was to describe the natural history of knee BMLs, their association with knee pain and examine predictors of BML change over eight years.

Methods

A total of 198 subjects (109 adult offspring of subjects who had a knee replacement and 89 community-based controls) were studied. Knee pain and BML size were assessed at two and ten year visits.

Results

At the two year visit, 64% of participants (n = 127) had 229 BMLs (34% patella, 26% femoral and 40% tibial). Over eight years, 24% (55/229) increased in size, 55% (125/229) remained stable and 21% (49/229) decreased in size or resolved completely. Of the participants without BMLs at baseline, 52% (37/71) developed incident BMLs.

After adjusting for confounders, eight year change in total BML size was associated with change in knee pain in offspring (β = 2.50, 95% confidence interval (CI) 0.96 to 4.05) but not controls. This association was stronger in males. Incident BMLs were associated with increase in pain (β = 3.60, 95% CI 1.14 to 6.05). Body mass index (BMI) and strenuous activity (but not radiographic osteoarthritis or smoking) were associated with an increase in BML size.

Conclusion

In this midlife cohort, the proportion of BMLs increasing in size was similar to those decreasing in size with the majority remaining stable. Change in BMLs was predicted by BMI and strenuous activity. An increase in BML size or a new BML resulted in an increase in pain especially in males and those with a family history of OA.

Focal knee lesions in knee pairs of asymptomatic and symptomatic subjects with OA risk factors--data from the Osteoarthritis Initiative

OBJECTIVE

To better understand the relationship between knee pain and bilateral knee lesions, we compared focal knee lesions in knee pairs of subjects with no, unilateral, and bilateral knee pain, and risk factors for knee osteoarthritis (OA), but no radiographic knee OA.

MATERIALS AND METHODS

We examined both knees of 120 subjects from the Osteoarthritis Initiative database. We randomly selected 60 subjects aged 45-55 years with OA risk factors, no knee pain (WOMAC pain score=0) and no radiographic OA (KL-score ≤1) in both knees. We also selected two comparison groups with OA risk factors and no radiographic OA in both knees, but with knee pain (WOMAC pain score ≥5): 30 subjects with right only knee pain and 30 subjects with bilateral knee pain. All subjects underwent 3T MRI of both knees and focal knee lesions were assessed.

RESULTS

Statistically significant associations between prevalence of focal lesions in the right and left knee with odds ratios up to 13.5 were found in all three subject groups. Focal knee lesions were generally not associated with pain in analyses comparing knee pairs of subjects with unilateral knee pain (p>0.05). The prevalence and severity of focal knee lesions were not significantly different in knee pairs of subjects with no knee pain and those with bilateral knee pain (p>0.05).

CONCLUSION

Focal knee lesions in the right and left knee of subjects with OA risk factors were positively associated with each other independent of knee pain status, and were not statistically significant different between knees in subjects with unilateral knee pain.

Knee Structural Alteration and BMI: A Cross-sectional Study

OBJECTIVE

To describe the associations among BMI, knee cartilage morphology, and bone size in adults.

RESEARCH METHODS AND PROCEDURES

A cross-sectional convenience sample of 372 male and female subjects (mean age, 45 years; range, 26 to 61 years) was studied. Knee articular cartilage defect score (0 to 4) and prevalence (defect score of >/=2), volume, and thickness, as well as bone surface area and/or volume, were determined at the patellar, tibial, and femoral sites using T1-weighted fat-saturation magnetic resonance imaging. Height, weight, BMI, and radiographic osteoarthritis were measured by standard protocols.

RESULTS

In multivariate analysis in the whole group, BMI was significantly associated with knee cartilage defect scores (beta: +0.016/kg/m(2) to +0.083/kg/m(2), all p < 0.05) and prevalence (odds ratio: 1.05 to 1.12/kg/m(2), all p < 0.05 except for the lateral tibiofemoral compartment). In addition, BMI was negatively associated with patellar cartilage thickness only (beta = -0.021 mm/kg/m(2); p = 0.039) and was positively associated with tibial bone area (medial: beta = +7.1 mm(2)/kg/m(2), p = 0.001; lateral: beta = +3.2 mm(2)/kg/m(2), p = 0.037). Those who were obese also had higher knee cartilage defect severity and prevalence and larger medial tibial bone area but no significant change in cartilage volume or thickness compared with those of normal weight.

DISCUSSION

This study suggests that knee cartilage defects and tibial bone enlargement are the main structural changes associated with increasing BMI particularly in women. Preventing these changes may prevent knee osteoarthritis in overweight and obese subjects.

Genetic inheritance effects on endurance and muscle strength: an update

Top-level sport seems to play a natural Darwinian stage. The most outstanding athletes appear to emerge as a result of exogenous influences of nature and/or coincidence, namely, the contingency of practicing certain sport for which their talents best fit. This coincidence arises because certain individuals possess anatomical, metabolic, functional and behavioural characteristics that are precisely those required to excel in a given sport. Apart from the effects of training, there is strong evidence of genetic influence upon athletic performance. This article reviews the current state of knowledge regarding heritable genetic effects upon endurance and muscle strength, as reported by several twin and family studies. Due, probably, to the inaccuracy of the measurement procedures and sampling error, heritability estimates differ widely between studies. Even so, the genetic inheritence effects seem incontrovertible in most physical traits: ~40-70% for peak oxygen uptake and cardiac mass and structure, and ~30-90% for anaerobic power and capacity, ranging according to the metabolic category. Studies in development by several researchers at this present time seem to guarantee that future reviews will include twins and family studies concerning genes associated with the adaptive processes against hormetic agents, such as exercise, heat and oxidative stress.

Genetic aspects of skeletal muscle strength and mass with relevance to sarcopenia

Skeletal muscle is a highly heritable quantitative trait, with heritability estimates ranging 30-85% for muscle strength and 50-80% for lean mass. That strong genetic contribution indicates the possibility of using genetic information to individualize treatments for sarcopenia or even aid in prevention strategies through the use of genetic screening prior to the functional limitations. Though these possibilities provide the rationale for genetic studies of skeletal muscle traits, few genes have been identified that appear to contribute to variation in either skeletal muscle strength or mass phenotypes, and sarcopenia per se is remarkably understudied as a trait in this regard. This review examines the heritability of skeletal muscle traits, findings of linkage and genome-wide association analyses and impact of specific genes and gene-sequence variants on these traits as relevant to sarcopenia. Despite considerable work in the area, the genetic underpinnings of skeletal muscle traits remain largely unknown and the genetic aspects of sarcopenia are even less clear. Large-scale longitudinal clinical studies relying on advanced genome-wide association and other techniques are needed to provide further insights into the genes and gene variants that contribute to skeletal muscle strength and mass, and ultimately to susceptibility to sarcopenia.

A role for PACE4 in osteoarthritis pain: evidence from human genetic association and null mutant phenotype

OBJECTIVES

The aim of this study was to assess if genetic variation in the PACE4 (paired amino acid converting enzyme 4) gene Pcsk6 influences the risk for symptomatic knee osteoarthritis (OA).

METHODS

Ten PCSK6 single nucleotide polymorphisms were tested for association in a discovery cohort of radiographic knee OA (n=156 asymptomatic and 600 symptomatic cases). Meta-analysis of the minor allele at rs900414 was performed in three additional independent cohorts (total n=674 asymptomatic and 2068 symptomatic). Pcsk6 knockout mice and wild-type C57BL/6 mice were compared in a battery of algesiometric assays, including hypersensitivity in response to intraplantar substance P, pain behaviours in response to intrathecal substance P and pain behaviour in the abdominal constriction test.

RESULTS

In the discovery cohort of radiographic knee OA, an intronic single nucleotide polymorphism at rs900414 was significantly associated with symptomatic OA. Replication in three additional cohorts confirmed that the minor allele at rs900414 was consistently increased among asymptomatic compared to symptomatic radiographic knee OA cases in all four cohorts. A fixed-effects meta-analysis yielded an OR=1.35 (95% CI 1.17 to 1.56; p=4.3×10(-5) and no significant between-study heterogeneity). Studies in mice revealed that Pcsk6 knockout mice were significantly protected against pain in a battery of algesiometric assays.

CONCLUSIONS

These results suggest that a variant in PCSK6 is strongly associated with protection against pain in knee OA, offering some insight as to why, in the presence of the same structural damage, some individuals develop chronic pain and others are protected. Studies in Pcsk6 null mutant mice further implicate PACE4 in pain.

Molecular genetic studies of gene identification for sarcopenia

Sarcopenia, which is characterized by a progressive decrease of skeletal muscle mass and function with aging, is closely related to several common diseases (such as cardiovascular and airway diseases) and functional impairment/disability. Strong genetic determination has been reported for muscle mass and muscle strength, two most commonly recognized and studied risk phenotypes for sarcopenia, with heritability ranging from 30 to 85% for muscle strength and 45-90% for muscle mass. Sarcopenia has been the subject of increasing genetic research over the past decade. This review is designed to comprehensively summarize the most important and representative molecular genetic studies designed to identify genetic factors associated with sarcopenia. We have methodically reviewed whole-genome linkage studies in humans, quantitative trait loci mapping in animal models, candidate gene association studies, newly reported genome-wide association studies, DNA microarrays and microRNA studies of sarcopenia or related skeletal muscle phenotypes. The major results of each study are tabulated for easy comparison and reference. The findings of representative studies are discussed with respect to their influence on our present understanding of the genetics of sarcopenia. This is a comprehensive review of molecular genetic studies of gene identification for sarcopenia, and an overarching theme for this review is that the currently accumulating results are tentative and occasionally inconsistent and should be interpreted with caution pending further investigation. Consequently, this overview should enhance recognition of the need to validate/replicate the genetic variants underlying sarcopenia in large human cohorts and animal. We believe that further progress in understanding the genetic etiology of sarcopenia will provide valuable insights into important fundamental biological mechanisms underlying muscle physiology that will ultimately lead to improved ability to recognize individuals at risk for developing sarcopenia and our ability to treat this debilitating condition.

Allometric relationships between knee cartilage volume, thickness, surface area and body dimensions

OBJECTIVE

To determine if anthropometric factors obtainable on routine examination can be used to estimate premorbid knee total subchondral bone area (tAB), cartilage surface area (AC), cartilage thickness (ThC), and cartilage volume (VC).

METHOD

Young individuals (21-39 years old) without history of knee joint pain, injury or disease were studied. Magnetic resonance imaging of the right knee was used to determine tAB, AC, ThC and VC for knee cartilage. Multilinear regression and curve fitting by variance minimization were used to model the data.

RESULTS

VC and AC closely depended on tAB(1.5) in both men and women. This relationship subsumed all dependency on sex, height, weight and body mass index. In females, VC depended on height cubed and tAB on height squared. The relationship was much weaker in males. ThC was poorly related to tAB and VC. Confidence limits for VC standardized to tAB(1.5) were narrower than standardization to tAB or height.

CONCLUSION

The absence of a tight relationship of VC and tAB with height in males suggests that the factors stimulating bone and cartilage growth may be different between sexes. The high correlation between tAB and VC across both sexes suggests, however, that (opposite to measures from routine clinical examination) tAB(1.5) can provide individual reference values for VC, against which changes with age and disease can be estimated with high confidence.

Tibial subchondral bone size and knee cartilage defects: relevance to knee osteoarthritis

Unlike knee plain radiography which can only detect joint space narrowing and osteophytes, magnetic resonance imaging can directly visualize and analyse the whole knee structure, including bone size, cartilage defects and loss of cartilage volume. Tibial subchondral bone area expansion may be primary and is associated with risk factors such as age, body mass index (BMI), genetics and/or limb malalignment. It can lead to the development of knee defects, which may also be caused by demographic, anthropometric and environmental factors such as age, female sex, BMI and smoking as well as structural changes such as osteophytes, bone marrow lesions, meniscal tears, meniscal extrusion and ligament abnormalities. Once knee cartilage defects develop, they have a variable natural history but are associated with subsequent cartilage loss in a dose-response manner. Both tibial subchondral bone area and knee cartilage defects are quantitatively related to the severity of knee osteoarthritis (OA), and predictive of the need for knee joint replacement in subjects with knee OA independent of radiographic change. Taken as a whole, these studies suggest that tibial subchondral bone expansion and cartilage defect development represent important targets for the prevention of cartilage loss and joint replacement.

Familial, structural, and environmental correlates of MRI-defined bone marrow lesions: a sibpair study

The aim of this study was to estimate the heritability and describe the correlates of bone marrow lesions in knee subchondral bone. A sibpair design was used. T2- and T1-weighted MRI scans were performed on the right knee to assess bone marrow lesions at lateral tibia and femora and medial tibia and femora, as well as chondral defects. A radiograph was taken on the same knee and scored for individual features of osteoarthritis (radiographic osteoarthritis; ROA) and alignment. Other variables measured included height, weight, knee pain, and lower-limb muscle strength. Heritability was estimated with the program SOLAR (Sequential Oligogenetic Linkage Analysis Routines). A total of 115 siblings (60 females and 55 males) from 48 families, representing 95 sib pairs, took part. The adjusted heritability estimates were 53 +/- 28% (mean +/- SEM; p = 0.03) and 65 +/- 32% (p = 0.03) for severity of bone marrow lesions at lateral and medial compartments, respectively. The estimates were reduced by 8 to 9% after adjustment for chondral defects and ROA (but not alignment). The adjusted heritability estimate was 99% for prevalent bone marrow lesions at both lateral and medial compartments. Both lateral and medial bone marrow lesions were significantly correlated with age, chondral defects, and ROA of the knee (all p < 0.05). Medial bone marrow lesions were also more common in males and were correlated with body mass index (BMI). Thus, bone marrow lesions have a significant genetic component. They commonly coexist with chondral defects and ROA but only share common genetic mechanisms to a limited degree. They are also more common with increasing age, male sex, and increasing BMI.

Genetic mechanisms of knee osteoarthritis: a population-based longitudinal study

To describe the differences in knee structure and non-knee structural factors between offspring having at least one parent with a total knee replacement for severe primary knee osteoarthritis and age- and sex-matched controls with no family history of knee osteoarthritis, a population-based longitudinal study of 163 matched pairs (mean age 45 years, range 26 to 61) was performed at baseline and about 2 years later. Knee cartilage defect score (0 to 4), cartilage volume and bone size were determined with T1-weighted fat saturation magnetic resonance imaging. Body mass index (BMI), lower-limb muscle strength, knee pain, physical work capacity at 170 beats/minute (PWC170) and radiographic osteoarthritis were measured by standard protocols. In comparison with controls, offspring had higher annual knee cartilage loss (-3.1% versus -2.0% at medial tibial site, -1.9% versus -1.1% at lateral tibial site and -4.7% versus -3.7% at patellar site, all P < 0.05), a greater increase in medial cartilage defect score (+0.15 versus -0.01, P < 0.05) and a greater decline in PWC170 (-0.7 watts/kg versus -0.4 watts/kg, P < 0.01). There were no significant differences in change in BMI, lower-limb muscle strength, knee pain or tibial bone area between these two groups; however, the differences in knee cartilage loss and cartilage defect change decreased in magnitude and became non-significant after adjustment for baseline cartilage volume, tibial bone area, BMI and knee pain. This longitudinal study suggests that knee cartilage loss, change in cartilage defects and decrease in physical fitness all have roles in the development of knee osteoarthritis, which is most probably polygenic but may reflect a shared environment. Importantly, the cartilage changes are largely dependent on baseline differences in cartilage volume, tibial bone area, BMI and knee pain, suggesting that these factors might have a role in their initiation.

Quantitative MRI of cartilage and bone: degenerative changes in osteoarthritis

Magnetic resonance imaging (MRI) and quantitative image analysis technology has recently started to generate a great wealth of quantitative information on articular cartilage and bone physiology, pathophysiology and degenerative changes in osteoarthritis. This paper reviews semiquantitative scoring of changes of articular tissues (e.g. WORMS = whole-organ MRI scoring or KOSS = knee osteoarthritis scoring system), quantification of cartilage morphology (e.g. volume and thickness), quantitative measurements of cartilage composition (e.g. T2, T1rho, T1Gd = dGEMRIC index) and quantitative measurement of bone structure (e.g. app. BV/TV, app. TbTh, app. Tb.N, app. Tb.Sp) in osteoarthritis. For each of these fields we describe the hardware and MRI sequences available, the image analysis systems and techniques used to derive semiquantitative and quantitative parameters, the technical accuracy and precision of the measurements reported to date and current results from cross-sectional and longitudinal studies in osteoarthritis. Moreover, the paper summarizes studies that have compared MRI-based measurements with radiography and discusses future perspectives of quantitative MRI in osteoarthritis. In summary, the above methodologies show great promise for elucidating the pathophysiology of various tissues and identifying risk factors of osteoarthritis, for developing structure modifying drugs (DMOADs) and for combating osteoarthritis with new and better therapy.

The effects of exercise on human articular cartilage

The effects of exercise on articular hyaline articular cartilage have traditionally been examined in animal models, but until recently little information has been available on human cartilage. Magnetic resonance imaging now permits cartilage morphology and composition to be analysed quantitatively in vivo. This review briefly describes the methodological background of quantitative cartilage imaging and summarizes work on short-term (deformational behaviour) and long-term (functional adaptation) effects of exercise on human articular cartilage. Current findings suggest that human cartilage deforms very little in vivo during physiological activities and recovers from deformation within 90 min after loading. Whereas cartilage deformation appears to become less with increasing age, sex and physical training status do not seem to affect in vivo deformational behaviour. There is now good evidence that cartilage undergoes some type of atrophy (thinning) under reduced loading conditions, such as with postoperative immobilization and paraplegia. However, increased loading (as encountered by elite athletes) does not appear to be associated with increased average cartilage thickness. Findings in twins, however, suggest a strong genetic contribution to cartilage morphology. Potential reasons for the inability of cartilage to adapt to mechanical stimuli include a lack of evolutionary pressure and a decoupling of mechanical competence and tissue mass.

Musculoskeletal disorders associated with obesity: a biomechanical perspective

Despite the multifactorial nature of musculoskeletal disease, obesity consistently emerges as a key and potentially modifiable risk factor in the onset and progression of musculoskeletal conditions of the hip, knee, ankle, foot and shoulder. To date, the majority of research has focused on the impact of obesity on bone and joint disorders, such as the risk of fracture and osteoarthritis. However, emerging evidence indicates that obesity may also have a profound effect on soft-tissue structures, such as tendon, fascia and cartilage. Although the mechanism remains unclear, the functional and structural limitations imposed by the additional loading of the locomotor system in obesity have been almost universally accepted to produce aberrant mechanics during locomotor tasks, thereby unduly raising stress within connective-tissue structures and the potential for musculoskeletal injury. While such mechanical theories abound, there is surprisingly little scientific evidence directly linking musculoskeletal injury to altered biomechanics in the obese. For the most part, even the biomechanical effects of obesity on the locomotor system remain unknown. Given the global increase in obesity and the rapid rise in musculoskeletal disorders, there is a need to determine the physical consequences of continued repetitive loading of major structures of the locomotor system in the obese and to establish how obesity may interact with other factors to potentially increase the risk of musculoskeletal disease.

Magnetic resonance imaging (MRI) of articular cartilage in knee osteoarthritis (OA): morphological assessment

OBJECTIVE

Magnetic resonance imaging (MRI) is a three-dimensional imaging technique with unparalleled ability to evaluate articular cartilage. This report reviews the current status of morphological assessment of cartilage with quantitative MRI (qMRI), and its relevance for identifying disease status, and monitoring progression and treatment response in knee osteoarthritis (OA).

METHOD

An international panel of experts in MRI of knee OA, with direct experience in the analysis of cartilage morphology with qMRI, reviewed the existing published and unpublished data on the subject, and debated the findings at the OMERACT-OARSI Workshop on Imaging technologies (December 2002, Bethesda, MA) with scientists and clinicians from academia, the pharmaceutical industry and the regulatory agencies. This report reviews (1) MRI pulse sequence considerations for morphological analysis of articular cartilage; (2) techniques for segmenting cartilage; (3) semi-quantitative scoring of cartilage status; and (4) technical validity (accuracy), precision (reproducibility) and sensitivity to change of quantitative measures of cartilage morphology.

RESULTS

Semi-quantitative scores of cartilage status have been shown to display adequate reliability, specificity and sensitivity, and to detect lesion progression at reasonable observation periods (1-2 years). Quantitative assessment of cartilage morphology (qMRI), with fat-suppressed gradient echo sequences, and appropriate image analysis techniques, displays high accuracy and adequate precision (e.g., root-mean-square standard deviation medial tibia=61 microl) for cross-sectional and longitudinal studies in OA patients. Longitudinal studies suggest that changes of cartilage volume of the order of -4% to -6% occur per annum in OA in most knee compartments (e.g., -90 microl in medial tibia). Annual changes in cartilage volume exceed the precision errors and appear to be associated with clinical symptoms as well as with time to knee arthroplasty.

CONCLUSIONS

MRI provides reliable and quantitative data on cartilage status throughout most compartments of the knee, with robust acquisition protocols for multi-center trials now being available. MRI of cartilage has tremendous potential for large scale epidemiological studies of OA progression, and for clinical trials of treatment response to structure modifying OA drugs.

Exercise as a treatment for osteoarthritis

PURPOSE OF REVIEW

This review highlights recent important research, future directions, and clinical applications for exercise and osteoarthritis. It focuses on knee osteoarthritis because of its prevalence and the dearth of research involving other joint osteoarthritis. The review covers exercise prescription for symptomatic relief, and its potential role in reducing development and slowing progression of osteoarthritis.

RECENT FINDINGS

Meta-analyses support recommendations that exercise is important in osteoarthritis management. Benefits appear to be additive when exercise is delivered with other interventions such as weight loss. Mode of exercise delivery has cost implications and may influence overall outcome. It appears that supervised exercise sessions are superior to home exercises for pain reduction. The challenge remains to increase the proportion of patients exercising. Areas of emerging interest are exercise to prevent disease or slow its progression and recognition of patient subgroups that may respond differently to treatment. Based on studies showing a relation between weaker quadriceps strength and increased risk of developing knee osteoarthritis, particularly in women, strength training may be able to prevent knee osteoarthritis. Novel exercise programs that strengthen hip muscles or alter impairments in knee neuromuscular control may also influence disease progression.

SUMMARY

Future studies must identify cost-effective exercise modes, strategies to maximize exercise compliance and optimal treatment combinations. The role of muscle strength and altered neuromuscular control in the prevention and development of osteoarthritis must be evaluated with the view to devising and testing novel exercise interventions.

Optimal sampling of MRI slices for the assessment of knee cartilage volume for cross-sectional and longitudinal studies

Background

MRI slices of 1.5 mm thickness have been used in both cross sectional and longitudinal studies of osteoarthritis, but is difficult to apply to large studies as most techniques used in measuring knee cartilage volumes require substantial post-image processing. The aim of this study was to determine the optimal sampling of 1.5 mm thick slices of MRI scans to estimate knee cartilage volume in males and females for cross-sectional and longitudinal studies.

Methods

A total of 150 subjects had a sagittal T1-weighted fat-suppressed MRI scan of the right knee at a partition thickness of 1.5 mm to determine their cartilage volume. Fifty subjects had both baseline and 2-year follow up MRI scans. Lateral, medial tibial and patellar cartilage volumes were calculated with different samples from 1.5 mm thick slices by extracting one in two, one in three, and one in four to compare to cartilage volume and its rate of change. Agreement was assessed by means of intraclass correlation coefficient (ICC) and Bland & Altman plots.

Results

Compared to the whole sample of 1.5 mm thick slices, measuring every second to fourth slice led to very little under or over estimation in cartilage volume and its annual change. At all sites and subgroups, measuring every second slice had less than 1% mean difference in cartilage volume and its annual rate of change with all ICCs ≥ 0.98.

Conclusion

Sampling alternate 1.5 mm thick MRI slices is sufficient for knee cartilage volume measurement in cross-sectional and longitudinal epidemiological studies with little increase in measurement error. This approach will lead to a substantial decrease in post-scan processing time.

The genetic contribution to longitudinal changes in knee structure and muscle strength: A sibpair study

OBJECTIVE

To estimate the heritability of longitudinal changes in knee cartilage volume, chondral defects, subchondral bone size, and lower limb muscle strength.

METHODS

A sibpair design was used. Longitudinal changes in lateral and medial tibial cartilage volume and bone size, as well as progression of chondral defects, were determined on serial magnetic resonance images. Radiographs were obtained and scored for individual features of radiographic osteoarthritis (OA) at baseline. Lower limb muscle strength was measured by dynamometry. Heritability was estimated using the SOLAR software package.

RESULTS

A total of 115 subjects (55 men and 60 women, mean age 45 years) from 48 families representing 95 sibling pairs were successfully followed up for a mean of 2.4 years. The adjusted heritability estimates for changes in cartilage volume were 73% for the medial compartment (P < 0.01) and 40% for the lateral compartment (P = 0.10). The adjusted heritability estimates for changes in bone size were 62% for the lateral compartment (P = 0.03) and 20% for the medial compartment (P = 0.22). The adjusted heritability estimate for changes in muscle strength was 64% (P = 0.01). The adjusted heritability estimates for progression of chondral defects were 80% for the lateral compartment (P = 0.06) and 98% for the medial compartment (P = 0.03). These estimates changed little after adjusting for each other and for the predominantly mild radiographic OA, with the exception of progression of chondral defects in the lateral compartment.

CONCLUSION

Early longitudinal changes in knee structures of relevance to later OA, such as changes in medial tibial cartilage volume, lateral tibial bone size, progression of chondral defects, and muscle strength, have high heritability, most likely reflecting a strong genetic component and suggesting their potential to be studied in quantitative trait linkage and association analysis.

Genetic mechanisms of knee osteoarthritis: a population based case-control study

OBJECTIVE

To compare subjects who had at least one parent with a total knee replacement for severe primary knee osteoarthritis with age and sex matched controls who had no family history of knee osteoarthritis

DESIGN

Population based case-control study of 188 matched pairs (mean age 45 years, range 26 to 60).

METHODS

Articular cartilage volume and bone size were determined at the patella and at the medial tibial and lateral tibial compartments by processing images acquired using T1 weighted, fat saturated magnetic resonance imaging. Radiographic osteoarthritis (ROA) was assessed from a standing semiflexed radiograph scored for joint space narrowing and osteophytosis. Knee pain was assessed by questionnaire. Height, weight, body mass index (BMI), lower limb muscle strength, and endurance fitness were measured by standard protocols.

RESULTS

Compared with the controls, index offspring had higher BMI (27.8 v 26.0 kg/m(2), p = 0.02), weaker lower limb muscles (127 v 135 kg, p = 0.006), more knee pain (47% v 22%, p<0.001), and greater medial tibial bone area (17.6 v 17.1 cm(2), p = 0.01). With the exception of BMI, these differences persisted in multivariate analysis. There was a non-significant trend to higher cartilage volume at tibial sites and increased ROA in the offspring in the total and subgroup analyses, but no difference in height and endurance fitness.

CONCLUSIONS

BMI, muscle strength, knee pain, and medial tibial bone area, but not cartilage volume, appear to play a role in the genetic regulation and development of knee osteoarthritis.