An Unusual Case of Hip Flexion Failure Caused by Bone Metastasis from Hepatocellular Carcinoma Infiltrating the Psoas Muscle.

When malignant tumors infiltrate the psoas muscle, they can result in what is referred to as malignant psoas syndrome (MPS). We are reporting this case as the malignant tumor had invaded the psoas muscle, and the clinical course of the patient differed from that of typical MPS. A 75-year-old male patient with liver cancer presented with pain around the right hip joint and difficulty in flexing the right hip joint, resulting in gait disturbance. There was no painful immobilization of the right hip, and the patient was able to extend the lower extremity. A CT scan revealed multiple liver tumors, multiple bone metastases, and swelling of the psoas muscle contiguous with the tumor at the lesser trochanter of the right femur. There were no apparent intracranial or spinal cord lesions, and no obvious abnormalities were detected around the psoas muscle in the abdominal cavity. Palliative radiation therapy was administered at a dose of 20 Gy in five fractions for pain relief. One month later, a follow-up CT scan presented no change in the shape of the tumor; however, the swelling of the right psoas muscle had improved. Unfortunately, the patient passed away 1 month after irradiation because of progressive liver and renal failure. When a patient with a malignant tumor presents with periprosthetic hip pain and hip flexion failure, one should consider the possibility of a malignant tumor in the lesser trochanter.