To investigate the sagittal alignment, proper and consistent radiographic evaluation is needed. We sought to use an alternative method of obtaining the same view, a direct lateral view and compare it with the conventional method. Conventional lateral long bone radiography and direct lateral long bone radiography were undertaken by 74 consecutive patients undergoing total knee arthroplasty (TKA), preoperatively and postoperatively. Angles between sagittal axes and the mechanical axis (MA), and the visible hip joint area were measured. Postoperative angles between the MA and femoral implant were also significantly different between the two radiologic methods of conventional and direct lateral long bone radiography (92.1 ± 2.1 degrees vs. 94.4 ± 2.6 degrees, p = 0.034). Hip joint visibility was significantly inferior using the direct lateral method (p < 0.001). The angles on the sagittal axes on conventional radiography of the lower extremities were different from those on direct lateral long bone radiography. The direct lateral long bone radiographs show the true lateral view, and surgeons may consider using the direct lateral method when evaluating relevant alignments before and after TKAs. For obese patients, however, conventional or combined methods should be considered because of inferior visibility of the hip joint using the direct method.