J Rheum Dis 2020; 27(1): 51-60  
Clinical Usefulness of Uric Acid as a Biomarker for Knee Osteoarthritis: A Comparative Analysis With Plain Radiography and Musculoskeletal Ultrasound
Seong-Kyu Kim, M.D., Ph.D., Ui Hong Jung, M.D., Jung-Yoon Choe, M.D., Ph.D.
Division of Rheumatology, Department of Internal Medicine, Daegu Catholic University School of Medicine, Daegu, Korea
Correspondence to: Seong-Kyu Kim http://orcid.org/0000-0002-7780-0167
Division of Rheumatology, Department of Internal Medicine, Daegu Catholic University School of Medicine, 33 Duryugongwon-ro 17-gil, Nam-gu, Daegu 42472, Korea. E-mail:kimsk714@cu.ac.kr
Received: September 25, 2019; Revised: October 16, 2019; Accepted: November 7, 2019; Published online: January 1, 2020.
© Korean College of Rheumatology. All rights reserved.

This is a open Access article, which permits unrestricted non-commerical use, distribution, and reproduction in any medium, provided the original work is properly cited.
Abstract
Objective. The aim of this study was to determine the relationships of serum and urine uric acid with severity or activity in knee osteoarthritis (OA). Methods. A total of 42 patients with knee OA was enrolled, together with 58 healthy controls. Serum uric acid and spot urine uric acid levels were assessed for all patients. The severity and activity of knee OA were assessed by musculoskeletal ultrasound (MSUS) and plain radiography of the knee joint. Ultrasonographic abnormalities in knee OA included synovial hypertrophy, suprapatellar effusion, cartilage degradation, and osteophyte formation. Kellgren-Lawrence (K-L) grade was used to evaluate radiological progression of knee OA. Results. Patients with K-L grade III had a higher urine uric acid/creatinine ratio compared to those with K-L grade I (p=0.043). Patients with synovial hypertrophy had higher serum uric acid level compared to those without synovial hypertrophy (p=0.016). The urine uric acid/creatinine ratio was higher in patients with cartilage degradation compared to those without cartilage degradation (p=0.022). Serum uric acid was significantly associated with synovial hypertrophy thickness (r=0.375, p=0.018) but not with cartilage thickness after adjusting for age and body mass index. Lower urine uric acid was related with knee OA compared to healthy controls (odds ratio=0.974, 95% confidence interval 0.954∼0.994, p=0.013). Conclusion. The results of our study suggest that serum and urine uric acid reflects synovial inflammation based on MSUS and radiographic progression and then is associated with the pathogenesis of knee OA.
Keywords: Osteoarthritis, Uric acid, Knee, Radiography, Ultrasound


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