Axial views of the patella are standard in the investigation of anterior Knee symptoms, and many investigators use congruence angles and patellar tilt in determining the diagnosis and appropriate treatment. A variety of different methods are used to obtain axial radiographs of the patella, but they are static representations of a dynamic phenomenon. The effect of quadriceps contraction on these indices has not been well defined. The purpose of this study was to compare the 30° axial view of the patella with the 45° axial view of the patella and to study the effect of quadriceps contraction on the 30° axial radiograph of the patella. Forty knees with normal patellofemoral joints and 20 knees with patellar subluxation were radiographed using 30° axial views of the patella with the quadriceps relaxed and contracted and with 45° axial views with the quadriceps relaxed. There was no significant difference in the sulcus or congruence angles between the 30 and 45° axial view in either the control or the patellar subluxation group. Contraction of the quadriceps did not cause a significant or consistent alteration in the congruence angles in either group. With quadriceps contraction, 55% of patients will centralize the patella, whereas 40% will actually increase lateral tracking or subluxation. In conclusion. the 30° axial view of the patella is equivalent to the 45° axial view in the assessment of patellar subluxation. Quadriceps contraction does not alter the congruence angles obtained in these axial views in a significant or consistent manner. Therefore, indices obtained from radiographs taken in a static mode with a relaxed quadriceps may not relate with the clinical situation and may be of limited value.