Magnetic resonance imaging (MRI) has identified features of osteoarthritis (OA) in more than a third of all asymptomatic adults above age 40 worldwide, according to a recent systematic review and meta-analysis.  While knee OA is detected in a mere 1% of all individuals between ages 25 and 34, it is prevalent in almost 50% by age 75 and older. Compared with a prevalence of approximately 19 % among 45-year-old adults, almost 44% of those in the 80 plus category showed radiographic evidence of knee OA.
In a meta-analysis of 63 studies comprising 5,397 knees belonging to 4,751 adults, cartilage defects were detected in almost a quarter of them, and meniscal tears found in 10%. The prevalence of symptoms increased with age, suggesting that eldelry patients were at a higher risk of osteoarthritis. Additional features apparent on MRI, such as bone marrow lesions (BMLs) and bony outgrowths (or osteophytes), also correlated with increased age. However, these findings should be considered in conjunction with clinical presentation for appropriate intervention.1
The tell-tale symptoms of pain, joint stiffness, and progressive inability to perform activities of daily living resulting from osteoarthritis are triggered by an imbalance between bone breakdown and bone reconstruction.2 The degenerative disease leads to joint cartilage loss, remodeling of bone beneath the cartilage, loose ligaments, meniscal damage, osteophytes, occasional fluid accumulation ( effusion), and joint inflammation (synovitis). Among the elderly specifically, a weak musculature, diminished proprioception, friable cartilage, and poor cellular response to joint stress are significant risk factors.
While imaging with 7.0 T scanners may be of research interest, 3.0 T scanners are most widely used clinically. In cases of knee OA, morphological MRI with intermediate-weighted (IW) 2D fast spin-echo (FSE) sequences is most appropriate for clinical practice.
Structural defects have been scored using Whole-Organ Magnetic Resonance Imaging Score (WORMS), Knee Osteoarthritis Scoring System (KOSS), the Boston Leeds Osteoarthritis Knee Score (BLOKS), and the MRI Osteoarthritis Knee Score (MOAKS).3 Changes in joint composition have been detected using delayed Gadolinium Enhanced Magnetic Resonance Imaging of Cartilage (dGEMRIC), T1 rho, and T2 mapping.
Early detection of biochemical changes along with analysis of wear and tear is critical to successful reversal of the degenerative changes associated with OA. Techniques such as diffusion-weighted imaging, Dixon technique, dynamic contrast enhanced (DCE)-MRI, and T2 mapping have been used to elucidate the pathophysiology of OA. Prompt detection of cartilage defects obviously results in better treatment outcomes in patients compared with those manifesting advanced OA.
Dynamic Contrast-Enhanced-MRI (DCE) offers insights into the pathophysiology of inflammation, based on a high-resolution 3D gradient echo sequence using a scan speed higher than 4 s per dynamic. OA displays higher semi-quantitative rate of early enhancement (REE) and quantitative measures (Ktrans and Kep) compared with control patients.5,7 Ktrans is a constant representing the volume transfer between blood plasma and extravascular extracellular space (EES). The Kep refers to the rate correlating EES and blood plasma. These quantitative values are lower than in rheumatoid arthritis (RA), probably because of a lower angiogenic potential and synovial permeability in OA patients.6
3.0T DCE-MRI has been used to delineate the temporal changes in intensity of synovial inflammation observed in erosive osteoarthritis involving the interphalangeal joints, suggesting its role in therapeutic monitoring of patients. In addition, 3.0T DCE-MRI has been shown to demonstrate a lower angiogenic potential and diminished synovial permeability in OA. It helps with the detection of erosions, bone marrow edema, and synovitis.
Furthermore, 3.0-T MRI was effectively utilized to elucidate abnormal cartilage and labral defects involving hip joints. Based on hip arthroscopy as a reference standard, scoring hip osteoarthritis with MRI (SHOMRI) has recently been validated as an acceptable tool for diagnosis of chondrolabral hip joint abnormalities in a retrospective study of femoroacetabular impingement (FAI) refractory to conventional approaches.8
Multiplanar MRI techniques
MRI of joints needs to be performed in several planes using multiple fat-suppression sequences, which extends the total scan time. The chemical shift imaging (CSI) and Dixon techniques may be used to reduce the scan time via different phases using interleaved water‐fat (IWF) sequences. The findings from these techniques suggested accurate and rapid evaluation of subchondral bone thickness in OA. IWF is touted as a promising technique for arthritis diagnosis and treatment for its potential in elucidating the pathophysiology of joint disease. CSI is based on gradient-echo and leverages the differences in times of echo (TE) associated with fat and water. An in-phase CSI image entails addition of fat and water signals, whereas the opposed-phase images involve subtraction of fat signal from that of water. Dixon technique involves acquisition of several TEs simultaneously which are merged to obtain MRI maps with "fat" or "water" alone, in addition to imaging in or out of phase.5
T2 mapping facilitates the detection of areas with increased T2 values within a field of apparently normal hyaline cartilage based on morphological sequences.  In OA, cartilage degeneration usually occurs at points exposed to increased stress, in contrast to RA and other types of inflammatory arthritis. Indeed, T2 mapping MRI has been shown to reveal the presence of bony outgrowths in the medial tibia of patients in their initial stages of OA, which are closely related to extrusion of the medial meniscus, confirming degenerative OA of the knee.
In conclusion, the choice of MRI technique depends on the severity and intensity of the disease. Aside from determining focal cartilage abnormalities and improving tissue contrast, recent advances have focused on assessment of the whole organ for the identification of joint lesions, enhanced reliability, specificity, and sensitivity of the diagnosis for appropriate clinical decision-making. Advances in MRI may also facilitate drug development aside from reliable therapeutic monitoring of patients based on imaging biomarkers.
 Prevalence of knee osteoarthritis features on magnetic resonance imaging in asymptomatic uninjured adults: a systematic review and meta-analysis. British Journal of Sports Medicine. doi: 10.1136/bjsports-2018-099257. Accessed July 23, 2018.
 Epidemiology and burden of osteoarthritis.British Medical Bulletin.https://doi.org/10.1093/bmb/lds038. Accessed July 23, 2018.
 Imaging of Osteoarthritis in Geriatric Patients. Current Radiology Reports.https://link.springer.com/article/10.1007/s40134-015-0133-9. Accessed July 23, 2018.
 Delayed gadolinium-enhanced MRI of cartilage (dGEMRIC) shows no change in cartilage structural composition after viscosupplementation in patients with early-stage knee osteoarthritis. PLoS One. 2013;8(11):e79785.
 Clinical applications of advanced magnetic resonance imaging techniques for arthritis evaluation.World Journal of Orthopedics.https://www.wjgnet.com/2218-5836/full/v8/i9/660.htm#B62.
doi: 10.5312/wjo.v8.i9.660. Accessed July 23, 2018.
 Value of T2-mapping and DWI in the diagnosis of early knee cartilage injury. http://www.radiologycases.com/index.php/radiologycases/article/view/515. https://dx.doi.org/10.3941/jrcr.v5i2.515. Accessed July 23, 2018.
 Dynamic Contrast-Enhanced Magnetic Resonance Imaging Using Pharmacokinetic Modeling: Initial Experience in Patients With Early Arthritis. Arthritis & Rheumatology. https://dx.doi.org/10.1002/art.39469. Accessed July 23, 2018.
 3 T DCE-MRI assessment of synovitis of the interphalangeal joints in patients with erosive osteoarthritis for treatment response monitoring. Skeletal Radiology. https://link.springer.com/article/10.1007%2Fs00256-012-1453-y. doi: 10.1007/s00256-012-1453-y. Accessed July 23, 2018.
 Validation of scoring hip osteoarthritis with MRI (SHOMRI) scores using hip arthroscopy as a standard of reference. European Radiology.https://link.springer.com/article/10.1007/s00330-018-5623-8. Accessed July 23, 2018.
 High-resolution interleaved water-fat MR imaging of finger joints with chemical-shift elimination. Journal of Magnetic Resonance Imaging. https://dx.doi.org/10.1002/jmri.22427. Accessed July 23, 2018.
 Knee cartilage T2 characteristics and evolution in relation to morphologic abnormalities detected at 3-T MR imaging: a longitudinal study of the normal control cohort from the Osteoarthritis Initiative. Radiology.https://pubs.rsna.org/doi/10.1148/radiol.11102234. Accessed July 23, 2018.
 Cartilage and meniscal T2 relaxation time as non-invasive biomarker for knee osteoarthritis and cartilage repair procedures. Osteoarthritis Cartilage. https://www.oarsijournal.com/article/S1063-4584(13)00898-4/fulltext.DOI: https://doi.org/10.1016/j.joca.2013.07.012. Accessed July 23, 2018.
 MRI of articular cartilage in OA: novel pulse sequences and compositional/functional markers. Osteoarthritis Cartilage. https://www.oarsijournal.com/article/S1063-4584(06)00066-5/fulltext.DOI: https://doi.org/10.1016/j.joca.2006.03.010. Accessed July 23, 2018.
 Association of medial meniscal extrusion with medial tibial osteophyte distance detected by T2 mapping MRI in patients with early-stage knee osteoarthritis. Arthritis Research & Therapy. https://doi.org/10.1186/s13075-017-1411-0.Accessed July 23, 2018.