Relation between biological markers and quadriceps muscle strength in patients with osteoarthritis

Objective: It was aimed to evaluate the relation between quadriceps muscle strength and primarily biological markers, along with the variables such as anthropometric data, bone mineral density, radiologic grade, pain and functional state in patients with knee osteoarthritis (OA). Material and Method: One hundred and fifty-two patients diagnosed with primary knee OA and aged between 40-70 years were included in the study. Knee radiographs of the patients were graded according to the Kellgren-Lawrence and medial tibiofemoral joint space width measurement grading. Biological markers belonging to the adipose tissue, cartilage and bone such as leptin, C-telopeptide of type II collagen, osteocalcin, C-telopeptide of type I collagen, 25-hydroxyvitamin D were evaluated by enzyme-linked immunosorbent assay (ELISA) method. Quadriceps muscle strength was measured both manually (by MicroFET3 device) and computerized isokinetic dynamometer. Pain and functional status of the patients were evaluated by using Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC). Results: Of the patients, 77% was obese. Among the biological markers, there was a moderate-strong correlation between leptin levels and body weight, body mass index and waist circumference (r=0.52, r=0.61 ve r=0.43, respectively). Weak negative correlation was found between leptin levels and quadriceps muscle strength (manual microFET3 and isometric extensor muscle strength). Weak negative correlations were detected between muscle strength parameters and visual analog scale, WOMAC pain, function subscales and total scores. WOMAC pain subscale was revealing a weak negative correlation with isometric extensor and flexor, isokinetic 60°/s and 120°/s extensor, isokinetic 60°/s and 120°/s flexor muscle strengths. Conclusion: Independent factors predicting the quadriceps muscle strength in patients with knee OA were not identified in our study. It was found that pain and functional status of the patients might have an influence on predicting quadriceps muscle strength, in other words, muscle strength might be reduced in relation to OA related pain. Key Words: Knee osteoarthritis, leptin, quadriceps muscle strength, isokinetic test