We report the case of a patient who, after posterior lumbar fixation for lumbar spinal canal stenosis, presented with difficulty in reaching the gluteal cleft with the right upper limb from the dorsal side while wiping after excretion and inevitably used the left upper limb. Through observation of a simulated wiping motion with the right upper limb, a decrease in the ability to perform the following movements was suspected: moving the pelvis from a posterior to an anterior inclination with flexion, internally rotating the left hip joint, extending the trunk, elevating the right pelvis and flexing the trunk to the right side, and rotating the trunk to the right. Examination based on these observations identified decreased tonus of the bilateral internal oblique muscles of the abdomen and multifidus and longissimus muscles, and increased tonus of the bilateral iliocostal muscles to be the primary causes. Therefore, surface electromyography was performed, and electromyographic waveform patterns of the aforementioned trunk muscles during simulated wiping motion with the right upper limb were compared with those of healthy subjects. No activity was detected in the bilateral internal oblique muscles of the abdomen. The patterns of the other muscles were similar, albeit with decreased activity. During physical therapy, the patient retained the physiological curvature of the spine, with the pelvis in the center of the anterior and posterior inclinations and the trunk extended in a sitting position. Furthermore, right pelvic elevation and right rotation of the trunk accompanied by right-sided flexion were promoted while shifting the body weight in the left anterior direction. Satisfactory wiping motion with the right upper limb was acquired through this therapy. This case report suggests that when examining the wiping motion after excretion, it is necessary to evaluate the ability to elevate the pelvis and flex and rotate the trunk to the required side while retaining the physiological curvature of the spine.