Spondylolisthesis

A 19-year-old ballerina comes to the office because of lower back pain during physical activity. She reports first feeling the pain 3 months ago as a dull ache, but states that her symptoms suddenly worsened 2 weeks ago. Musculoskeletal examination reveals an abnormally prominent spinous process of the 5th lumbar vertebra, and sharp pain in the lower lumbar region that radiates to both thighs during lumbar extension. The patient rates the pain as a 7 on a 10-point scale. Neurological examination reveals paresthesia over the lumbosacral area that also radiates to both thighs. An X-ray of the lateral lumbar spine is ordered and the following radiograph is obtained:

Which of the following conditions is the most appropriate diagnosis of the patient based on presentation and imaging results?