Ortho Dx: What are the grade and type of this spondylolisthesis?

A 55-year-old woman presents with a 2-year history of lower back pain. Over the last 6 months, she has begun to have bilateral lower extremity pain and weakness. She has also noticed numbness in both feet and has felt unsteady while walking because of lower extremity weakness. There is no history of trauma, and the patient ...