Andrew J. Teichtahl

Relationship between body adiposity measures and risk of primary knee and hip replacement for osteoarthritis: a prospective cohort study

IntroductionTotal joint replacement is considered a surrogate measure for symptomatic end-stage osteoarthritis. It is unknown whether the adipose mass and the distribution of adipose mass are associated with the risk of primary knee and hip replacement for osteoarthritis. The aim of the present investigation was to examine this in a cohort study.MethodsA total of 39,023 healthy volunteers from Melbourne, Australia were recruited for a prospective cohort study during 1990 to 1994. Their body mass index, waist circumference, and waist-to-hip ratio were obtained from direct anthropometric measurements. The fat mass and percentage fat were estimated from bioelectrical impedance analysis. Primary knee and hip replacements for osteoarthritis between 1 January 2001 and 31 December 2005 were determined by data linkage to the Australian Orthopaedic Association National Joint Replacement Registry. Cox proportional hazards regression models were used to estimate the hazard ratios (HRs) for primary joint replacement associated with each adiposity measure.ResultsComparing the fourth quartile with the first, there was a threefold to fourfold increased risk of primary joint replacement associated with body weight (HR = 3.44, 95% confidence interval (CI) = 2.83 to 4.18), body mass index (HR = 3.44, 95% CI = 2.80 to 4.22), fat mass (HR = 3.51, 95% CI = 2.87 to 4.30), and percentage fat (HR = 2.99, 95% CI = 2.46 to 3.63). The waist circumference (HR = 2.77, 95% CI = 2.26 to 3.39) and waist-to-hip ratio (HR = 1.46, 95% CI = 1.21 to 1.76) were less strongly associated with the risk. Except for the waist-to-hip ratio, which was not significantly associated with hip replacement risk, all adiposity measures were associated with the risk of both knee and hip joint replacement, and were significantly stronger risk factors for knee.ConclusionsRisk of primary knee and hip joint replacement for osteoarthritis relates to both adipose mass and central adiposity. This relationship suggests both biomechanical and metabolic mechanisms associated with adiposity contribute to the risk of joint replacement, with stronger evidence at the knee rather than the hip.

Reviewing knee osteoarthritis — a biomechanical perspective

Osteoarthritis (OA) is the most common form of arthritis and is a major cause of disability in people aged over 65. Despite the major socioeconomic burden imposed by OA, the aetiology of this condition remains unclear. Although controversial, several metabolic factors have been implicated in the disease pathogenesis. Nevertheless, no unequivocal systemic risk factors for the onset or progression of OA have been identified. Recently, there has been a growing interest in the biomechanical factors associated with the pathogenesis of OA. This review aims to discuss several of the more pertinent biomechanical and neuromuscular factors, such as the knee adduction moment and muscle strength, that are becoming increasingly accepted as factors that contribute toward the pathogenesis of knee OA.

Women have increased rates of cartilage loss and progression of cartilage defects at the knee than men: a gender study of adults without clinical knee osteoarthritis.

Objective:Women have an increased risk of knee osteoarthritis (OA). However, little is known about gender differences in cartilage health before the onset of clinical knee OA. The aim of this study was to examine whether there are longitudinal gender differences in knee cartilage in a cohort of healthy, asymptomatic adults with no clinical knee disease. Methods:Two hundred seventy-one participants (169 women) aged between 50 and 79 years with no clinical history of knee pain or pathology were examined using magnetic resonance imaging at baseline and 2.3 years later. From these images, changes in tibial and patella cartilage volume and progression of cartilage defects were determined. Results:In multivariate analyses, after adjustment for potential confounders, the average annual percentage loss of total tibial cartilage volume was significantly greater in women (1.6% [95% CI, 1.1-2.2]) than in men (0.4% [95% CI, −0.4 to 1.2]) (P = 0.05 for difference). Likewise, the female gender was also associated with an increased risk for the progression of tibiofemoral cartilage defects (odds ratio, 3.0; 95% CI, 1.1-8.1; P = 0.03). At the patella, the average annual percentage loss of cartilage volume was significantly greater in women (2.3% [95% CI, 1.7-2.8]) than in men (0.8% [95% CI, 0.1-1.6]) (P = 0.02 for difference). Conclusions:The female predisposition toward knee OA may, at least in part, be due to gender differences in cartilage health, even before the onset of clinical knee disease. Understanding the mechanism for these gender differences may provide a means to reduce the risk of knee OA in women.

Body composition and knee cartilage properties in healthy, community-based adults

Background: Although obesity is widely accepted as a risk factor for knee osteoarthritis, whether weight per se or the specific components of body composition are the major determinants of properties of articular knee cartilage is unclear. Objective: To examine associations between anthropometric and body composition measures and knee cartilage properties in healthy adults. Methods: 297 healthy adults with no clinical knee osteoarthritis were recruited from an existing community-based cohort. Anthropometric measures and body composition, including fat-free mass and fat mass assessed using bioelectrical impedance analysis, were measured at baseline (1990–4) and current follow-up (2003–4). Tibial cartilage volume and tibiofemoral cartilage defects were assessed using MRI at follow-up. Results: After adjustment for potential confounders, baseline and current fat-free mass, independent of fat mass, were positively associated with tibial cartilage volume (all p<0.001). Increased fat-free mass over the time period was positively associated with tibial cartilage volume (p<0.001). Current fat mass was negatively associated with tibial cartilage volume (p = 0.004). Baseline and current fat mass were weakly associated with increased tibiofemoral cartilage defects (p = 0.06 and p = 0.07, respectively), independent of fat-free mass. Conclusion: The findings suggest a beneficial effect of fat-free mass, but a deleterious effect of fat mass, on knee cartilage properties in healthy adults. This suggests that weight-loss programmes aimed at reducing fat mass but maintaining muscle mass may be important in preventing the onset and/or progression of knee osteoarthritis.

Is Physical Activity a Risk Factor for Primary Knee or Hip Replacement Due to Osteoarthritis? A Prospective Cohort Study

Objective. To estimate prospectively any association between measures of physical activity and the risk of either primary knee or hip replacement due to osteoarthritis (OA). Methods. Eligible subjects (n = 39,023) were selected from participants in a prospective cohort study recruited 1990–1994. Primary knee and hip replacement for OA during 2001–2005 was determined by linking the cohort records to the National Joint Replacement Registry. A total physical activity level was computed, incorporating both intensity and frequency for different forms of physical activity obtained by questionnaire at baseline attendance. Results. There was a dose-response relationship between total physical activity level and the risk of primary knee replacement [hazards ratio (HR) 1.04, 95% CI 1.01–1.07 for an increase of 1 level in total physical activity]. Although vigorous activity frequency was associated with an increased risk of primary knee replacement (HR 1.42, 95% CI 1.08–1.86) for 1–2 times/week and HR 1.24 (95% CI 0.90–1.71) for ≥ 3 times/week), the p for trend was marginal (continuous HR 1.08, 95% CI 1.00–1.16, p = 0.05). The frequency of less vigorous activity or walking was not associated with the risk of primary knee replacement, nor was any measure of physical activity associated with the risk of primary hip replacement. Conclusion. Increasing levels of total physical activity are positively associated with the risk of primary knee but not hip replacement due to OA. Physical activity might affect the knee and hip joints differently depending on the preexisting health status and anatomy of the joint, as well as the sort of physical activity performed.

Obesity and Knee Osteoarthritis: New Insights Provided by Body Composition Studies

disability-adjusted life years, in the developed world and is predicted to increase over the coming decades (1). In addition to being a painful and disabling condition, OA incurs substantial costs to the community in terms of work absences, contacts with health professionals, drug treatment, and surgical procedures (2). In the Unites States in 2003, the cost of arthritis and other rheumatic conditions was estimated at 1.2% of gross domestic product (3). In similar to that, in Australia in 2004, the cost of arthritis was estimated at 1.4% of gross domestic product (4). Of the spectrum of the arthropathies, OA was by far the major contributor to the direct and indirect costs of arthritis and other rheumatic conditions (3,4). Obesity is arguably the most important modifiable risk factor for the onset, progression, and symptoms of knee OA (5–11). Maintaining an ideal body weight has been shown to reduce the risk for the onset of knee OA (8), and reducing the BMI helps reduce pain and increase function in people with established disease (12,13). Despite these findings, the association between obesity and joint disease is not mechanistically well understood. Measures of central adiposity, such as waist circumference and waist-tohip ratio, are better predictors of major public health problems such as diabetes and cardiovascular diseases than the BMI (14). In contrast, most available data have suggested that fat distribution does not affect the risk of developing knee OA (15–17). Studies that have examined the obesity–OA relationship have predominantly used either the BMI (kg/m2) or weight (kg) as a surrogate measure of obesity (8–11,18,19). However, a limitation of either weight or BMI is that these measures do not discriminate adipose from non-adipose mass (20). Therefore, it is only possible to determine whether added mass relative to height effects the risk for the onset, progression, and symptoms of knee OA. It is unclear whether it is weight per se, or the specific components of body composition, such as fat mass or fat-free mass, which are associated with knee OA. Determining which components of body composition are associated with knee OA may provide potential pathways to understanding the pathogenesis of the disease, as well as more focused management strategies for the prevention and treatment of knee OA. Recently, several studies have examined the relationship between knee joint structure and body composition measures in both healthy and arthritic states. This discussion reviews the available evidence regarding obesity and the development of knee OA. Furthermore, new perspectives into the obesity–OA relationship are discussed in the context of recent findings from body composition studies.

Fat infiltration of paraspinal muscles is associated with low back pain, disability, and structural abnormalities in community-based adults.

BACKGROUND CONTEXT Low back pain and disability are major public health problems and may be related to paraspinal muscle abnormalities, such as a reduction in muscle size and muscle fat content. PURPOSE The aim of this study was to examine the associations between paraspinal muscle size and fat content with lumbar spine symptoms and structure. STUDY DESIGN/SETTING This was a community-based magnetic resonance imaging (MRI) cohort study. PATIENT SAMPLE A total of 72 adults not selected on the basis of low back pain were included in the study. OUTCOME MEASURES The outcomes measured were lumbar modic change and intervertebral disc height. Pain intensity and disability were measured from the Chronic Pain Grade Questionnaire at the time of MRI. METHODS The cross-sectional area (CSA) and amount of fat in multifidus and erector spinae (high percentage defined by >50% of muscle) were measured, and their association with outcome was assessed. RESULTS Muscle CSA was not associated with low back pain/disability or structure. High percentage of fat in multifidus was associated with an increased risk of high-intensity pain/disability (odds ratio [OR], 12.6; 95% confidence interval [CI], 2.0-78.3; p=.007) and modic change (OR, 4.3; 95% CI, 1.1-17.3; p=.04). High fat replacement of erector spinae was associated with reduced intervertebral disc height (β=-0.9 mm; 95% CI, -1.4 to -0.3; p=.002) and modic change (OR, 4.9; 95% CI, 1.1-21.9; p=.04). CONCLUSIONS Paraspinal fat infiltration, but not muscle CSA, was associated with high-intensity pain/disability and structural abnormalities in the lumbar spine. Although cause and effect cannot be determined from this cross-sectional study, longitudinal data will help to determine whether disabling low back pain and structural abnormalities of the spine are a cause or result of fat replacement of paraspinal muscles.

Change in knee angle influences the rate of medial tibial cartilage volume loss in knee osteoarthritis

OBJECTIVES Identifying factors that influence the rate of cartilage loss at the knee may help to prevent or delay the progression of knee osteoarthritis (OA). Changes in knee alignment alter knee joint load and may affect the rate of cartilage loss. The aim of this study was to determine whether change in knee alignment between baseline and 2 years is associated with a change in knee cartilage volume in knee OA in the subsequent 2.5 years. METHODS Seventy-eight adults with symptomatic knee OA were recruited using a combined strategy. Radiographs were performed at time 0 and 2 years to determine change in knee alignment, measured on a continuous scale. Magnetic Resonance Imaging was performed at 2 and 4.5 years to determine annual percentage change in medial and lateral tibial cartilage volumes. RESULTS In multivariate analyses, for every 1 degrees change toward genu valgum, there is an associated 0.44% reduction in the rate of annual medial tibial cartilage volume loss (95% CI: -0.85%, -0.04%, P=0.03). Similarly, because our measures of change in alignment and cartilage volume were continuous, these results also implied that for every 1 degrees change toward genu varum, there was an associated 0.44% increase in the rate of annual medial tibial cartilage volume loss. Change in knee angle did not significantly affect the rate of loss of the lateral tibial cartilage volume (P=0.95). CONCLUSION Our results have demonstrated that progressive change toward genu valgum reduced the annual rate of medial tibial cartilage volume loss in people with knee OA, without expediting the rate of lateral tibial cartilage volume loss. These findings suggest that methods to reduce varus alignment may delay the progression of medial tibiofemoral OA and warrant further investigation.

Factors that may mediate the relationship between physical activity and the risk for developing knee osteoarthritis

Studies investigating the effect of physical activity on risk for developing osteoarthritis at weight-bearing joints have reported conflicting results. We examine evidence to suggest that this may be due to the existence of subgroups of individuals who differ in their response to physical activity, as well as methodological issues associated with the assessment of knee joint structure and physical activity. Recommendations for future studies of physical activity and the development of knee osteoarthritis are discussed.

Obesity and adiposity are associated with the rate of patella cartilage volume loss over 2 years in adults without knee osteoarthritis

Objectives: The aim of this study was to determine whether measures of obesity and adiposity are associated with the rate of patella cartilage volume loss in healthy adults. Methods: 297 community-based adults aged 50–79 years with no clinical knee osteoarthritis were recruited at baseline (2003–4). 271 (62% female) subjects were re-examined at follow-up (2006–7). Measures of obesity (body mass index (BMI) and weight) and adiposity (fat mass and percentage fat mass), as well as patella cartilage volume, were determined by established protocols. Results: Patella cartilage volume was lost at an annual rate of 1.8% (95% CI 1.4% to 2.1%). Increased baseline BMI, weight, fat mass and percentage fat mass were all associated with an increased rate of patella cartilage volume loss after adjustment for confounders (all p⩽0.04). The direction and magnitude of the effects were similar for both sexes but the number of men examined was considerably smaller and the associations were not statistically significant. There were no significant associations observed between change in any of the obesity and adiposity measures and the rate of patella cartilage volume loss. Conclusion: This study demonstrated that increased levels of obesity and adiposity are associated with an increased annual rate of patella cartilage volume loss in healthy adults. Weight-loss interventions that reduce body mass, or specifically target a reduction in fat mass, may help to reduce the rate at which patella cartilage volume is lost, and subsequently the risk of patellofemoral osteoarthritis.