PURPOSE
The goal of the present study was to compare the patellar tendon cross-sectional area with the patellar tendon thickness and to determine the intra-observer compliance level in the cross-sectional area and thickness measurements. This comparison was used to describe the effects of playing volleyball on the patellar tendon.

MATERIALS AND METHODS
The patellar tendons of 60 volleyball players and 60 non-player female students, who were 11–16 years of age with similar physical characteristics, were examined using Doppler ultrasonography (US). Cross-sectional area and thickness measurements were conducted.

RESULTS
The proximal and distal thicknesses of the patellar tendon were similar, but the area was smaller for the distal portion. A correlation was observed between age and tendon thickness and between the thickness and area of the tendon. All of the measurements in the subjects with tendinosis were larger than those in the healthy controls. There were no pathological findings in the non-players. The intra-observer compliance was high.

CONCLUSION
The transverse plane area measurement was as reliable as the thickness measurement and exhibited a high level of intraobserver compliance. This measurement can be conducted during routine examinations. The patellar tendons in the athletes were observed to be widened and thickened, most likely because of overuse. Patellar tendinosis and Osgood-Schlatter Syndrome may be asymptomatic and incidentally detected. Therefore, routine US examinations may help prevent further injuries. Although the tendon thicknesses were observed to be the same in both extremities, any observed difference in the tendon areas may alert the physician to a risk factor for the development of tendinosis.