Backrest elevation for a patient with a sacral-coccygeal pressure ulcer is necessary in certain situations, particularly to enable the patient to take meals. Deep pressure ulcers with undermining formations affect patients and create challenges for caregivers. The procedure of backrest elevation potentially worsens the pre-existing sacral-coccygeal pressure ulcers with undermining formations. Here, we report a Case of the clinical care of a patient using a simple approach for backrest elevation that minimizes additional injury to the existing sacral pressure ulcer covered with granulation tissue. In this case, we performed the backrest elevation in the semi-lateral position. After the backrest elevation, the patient was repositioned to the supine position to take a meal. The supine position was allowed at any time except during backrest elevation. The pressure ulcer of the patient improved rapidly using the combined treatment of our positioning approach and appropriate topical ointments. This practical approach may be effective for some patients as it potentially decreases the effect of shear force. The rationale for this approach can be explained by the mechanism of the undermining formation outlined in our experimental study using a pressure ulcer model mounted to a phantom. Although we used this position for patients with sacral-coccygeal pressure ulcers, this simple approach may also be considered for other patients based on our proposed pathogenesis of undermining formations.