A 65 year-old female presents to your clinic with a chief complaint of difficulty walking. She states that she has had low back pain and balance difficulties for the last 2 years, but over the last few months new bilateral posterior thigh and buttock pain has prevented her from walking more than 100 feet. She states the only place she can walk comfortably is in the grocery store.
On physical exam she is unable to preform a tandem gait, and she has 5/5 strength with hip flexion, knee flexion/extension, ankle dorsiflexion/plantar flexion and great toe extension. Her sensation is intact in L2-S2, and she has equal and symmetric 3+ achilles and patellar reflexes. She has 8 beats of clonus, and a down-going Babinski reflex bilaterally.
Radiographs of her lumbar spine are seen in figures A and B. What is the next step.