A 28-year-old woman is evaluated for a 2-week history of left hip pain that occurs at night and with walking. She has a 1-year history of systemic lupus erythematosus with class IV nephritis. Treatment has included prednisone as high as 60 mg/d and cyclophosphamide. Current medications are mycophenolate mofetil, hydroxychloroquine, prednisone, furosemide, lisinopril, calcium, and vitamin D.

On physical examination, vital signs are normal. BMI is 26. She has a cushingoid appearance. There is pain on internal rotation of the left hip. There is no pain on hip adduction or with pressure over the lateral hip. The remainder of the examination is normal.

Laboratory studies reveal an erythrocyte sedimentation rate of 18 mm/h, normal complement (C3 and C4) levels, and stable anti–double-stranded DNA antibodies.

Anterior-posterior pelvis and lateral left hip radiographs are normal.

Which of the following is the most appropriate diagnostic test to perform next?