OSTEOARTHRITIS : A REVIEW

Review Article

Osteoarthritis: A Review

Abstract

           Osteoarthritis (OA) is a common musculoskeletal disease affecting millions of population all over the world and developing countries are also severely affected by this painful disease of joint stiffness and dysfunction. This review promises to provide adequate knowledge regarding OA, its risk factors and the prevalent medical imaging equipments provided under clinical settings. Basically, knee and hip joints in elderly populations and obese patients are mostly affected by OA. Although OA has multiple causes of etiology, female sex and obesity are considered the well-established factors. Leptin protein has been stated as a systemic linking factor between obesity and sex with OA. Radiograph is the gold standard tool, and MRI is used to assess the accurate visualization of joint structures, cartilage and bone volumes. High Resolution Peripheral Quantitative Computed Tomography (HRpQCT) can also depict the bone microarchitectures, patterns of trabeculae and cortex. Despite immense development in OA imaging, there is still not a single reliable test for early diagnosis. However, this review attempts to describe present imaging modalities.

Introduction

OA is a very much common type of arthritis and a major cause of musculoskeletal disability and dysfunction in most developed countries, but is also prevalent in least developed countries like Nepal.¹ OA is a slowly progressive disease characterized by gradual loss of articular cartilage with a multifactorial cause, mostly in knee and hip joints. ^1-6 The knee is one of the most frequently affected joints, with a prevalence of 30% in people older than 65 years and high resultant disability.^2,3 While its etiology and pathogenesis remain poorly understand, knee OA has been strongly associated with several environmental factors, including obesity, previous injury, vitamin D intake, and menisectomy.^7-12 The financial management of OA are high for individuals and families of the patient must adapt their lives to the disease, and those due to lost work productivity.^13,14 The increase in  prevalence of OA are likely due to aging of the population and the rising prevalence of obesity.⁶

Risk Factors of OA

OA has a multi-factorial etiology, with different sets of factors associated with its incidence. ^5,15 Factors associated with OA has been broadly categorized into person-level factors and joint-level factors.⁶ Person-level factors include age, sex, obesity, genetics, rare/ethinicity and diet. Joint-level factors refer to factors that are unique to a particular joint such as injury, activity, type of occupation, and muscle strength.⁶ Factors associated with OA have also been classified as those that relate to OA development and those relating to disease progression. Regarding knee OA, Doherty reports factors such as age, sex, occupation, weight status and recreational activity are related to the progression of OA, and weight status and dietary factors also represent a crucial role in its progression.¹⁵ Non-modifiable factors such as age and sex are the strongest predictors. For example, women are at greater risk for developing knee and hip OA  in comparison to their male counterparts.^15-17 Hormonal factors, reduced volume of cartilage in the knee and the fact that women are more likely to self-report have been considered as explanatory factors.^15,17,18 Age is considered a major contributor to the sex differences in prevalence of OA, where females are at considerable risk of knee and hand OA than men, particularly after menopausal age.^5,18 Age is one of the strongest non-modifiable factors for OA, where this relationship is likely related to a combination of changes in the capacity for joint tissues to adapt to biomechanical stresses.^5,6,15

Obesity is a strong modifiable risk for the development of knee OA but less so for hip OA.^5,6,19 In a meta-analysis, obese or overweight were approximately three times as likely to present knee OA. ¹⁸ Obesity affects both mechanical and systemic mechanisms. Obesity can impose significant increased load as a result of increased body weight, however, there may be differential systemic consequences varying on the degree of fat versus lean mass involving the activity of adipocytokines.^6,19,20

Other modifiable factors of OA include occupation, dietary factors and physical activity.^6,15 For example, repetitive joint loading through kneeling or squatting have been shown to be associated with an increased risk of knee OA, and this risk is even greater for those who are overweight.^6,21 Furthermore, occupational lifting and prolonged standing have also been most strongly associated with hip OA.^6,22

A number of studies have examined the role of vitamins (such as vitamins D and C) in OA.^6,22,23 It is assumed that vitamin C may serve to decelerate cartilage loss in the joints while low vitamin D intake and reduced circulating serum vitamin D may increase risk of knee.²⁴ The benefits of physical activity for OA are well-established, including walking for individuals with OA.²⁴ However, people with knee OA do not meet standard physical activity guidelines.²⁵ Findings from a current study has stated people with knee OA are capable of walking at the recommended pace required to meet physical activity guidelines, and their knee pain has nominal influence on the status of physical activity.²⁶

For example, healthy lifestyle behaviors may reduce the age-related onset of OA, and there can also be additional multifaceted associations between factors associated with OA. Presuming the increased prevalence of OA, identifying modifiable factors associated with OA are important to guide the development of effective interventions. Currently, it seems to be a scarce of data, particularly for Canada.²⁷

It is well established that female sex and obesity are risk factors for knee OA, however, the underlying mechanism remains obscure but may involve biomechanical processes or variations in sex hormones.^2-4 Although there is a trivial documentation to show a metabolic link between obesity and knee OA, recent theoretical discussions recommend that leptin may represent a systemic element associating sex, obesity and knee OA.^28,29 Leptin ,a 16 kDa protein encoded by an obese gene (ob), is a hormone produced abundantly by adipocytes as well as osteoblasts and chondrocytes. Leptin has been found in the synovial fluid of patients with OA and its concentration or mRNA expression in cartilage has been correlated with BMI and female sex.^30-33 However, it is still not clear whether increased production of leptin is good or bad for cartilage health with recent evidence suggesting that leptin may act in a biphasic manner, i.e., leptin physiologically may have a beneficial effect on cartilage synthesis, but an excess of leptin may lead to detrimental effects on cartilage.^32-34

Imaging Considerations

In addition, a modest but significant genetic effect in radiographic OA (ROA) of the knee has been demonstrated in most studies.^{34, 35} However, radiographs provide only a wide range view of joint pathology. Magnetic resonance imaging (MRI) can allow direct visualization of joint structures and provide precise and reproducible quantitative estimates of cartilage volume and bone area/volume, and the MRI result thus has the potential for linkage analysis.^36,37 MRI can connect cartilage injury to regions where there are the so called bone marrow edema like (BMEL) injuries, which are areas of high signal on T2WI.³⁸ In these places, in addition to edema, necrosis of adipocytes, increase of fibrous tissue and an accelerated bone metabolism can be depicted. However, MR is unable to determine which changes in bone microarchitecture how they relate to disease.

High resolution peripheral quantitative computed tomography (HRpQCT)

HRpQCT is a new technology that permits performing in vivo assessment of bone parameters. HRpQCT assesses the trabecular thickness, trabecular separation, trabecular number and connection density, cortical bone density, porosity and thickness and total bone volume and density, which furthermore allows obtaining digital constructs of bone microarchitecture. The application of mathematics to captured data, a method called finite element analysis, allows the estimation of the physical properties of the tissue in a non-invasive way. In osteoarthritis, it is possible to characterize the bone marrow edema like areas that show a correlation with cartilage breakdown. Given its high cost, HRpQCT is still a research tool, but the high resolution and efficiency of this equipment reveal advantages over the methods currently used for bone assessment, with a potential to become an important tool in clinical practice.³⁹

Conclusion

To sum up, OA is a major public health problem. Despite the remarkable contribution to understand the risk factors of OA and the future of imaging in OA over the past few years, there is still no reliable test to predict or diagnosis early disease. This review attempts to provide the basic insights of OA and the promises of present imaging modalities.

Conflict of Interest: The author has competing interest to disclose.

Abbreviations:

OA                  Osteoarthritis

MRI                Magnetic Resonance Imaging

HRpQCT        High Resolution Peripheral Quantitative Computed Tomography

BMEL             Bone Marrow Edema Like

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