We sought to evaluate the effects of diabetes on the physical properties of the patellar and quadriceps tendons using radiological techniques. Twenty-seven diabetic and 34 nondiabetic patients with primary osteoarthritis of the right knee were studied. All patients had anteroposterior and lateral knee radiographs. The lengths of the patella and the patellar tendon were measured. The width and thickness of the patellar tendon were determined by ultrasound (US) examination at midpoint. The increase in the thickness of the patellar tendon sheath was graded qualitatively. The length of the quadriceps and patellar tendons, and the thickness and width of tendons in mid-length were measured by magnetic resonance imaging (MRI). Buckling of tendons and increase in intensities were also evaluated. The mean age in the diabetic group was 57.6 +/- 10.1 years, and the mean age in the control group was 52.6 +/- 9.1 years. The mean duration of diabetes was 104.1 +/- 67.1 months. X-ray, US, and MRI measurements did not reveal any differences between the two groups. Quadriceps buckling was more prevalent in diabetic patients (P=.025). In both groups, the width of the patellar tendon was greater in men than in women (P=.001). In conclusion, we found no significant structural changes in the patellar and quadriceps tendons in diabetic patients in midterm. On MRI examination, the quadriceps tendons had more buckling in diabetic patients.