A  previously healthy 48-year-old man presents to his primary care office  with severe low back pain that began the previous day after he helped  his daughter move into her college dorm. He denies any trauma or  previous back injury. He describes the pain as generally “achy” and  sometimes characterized as being “sharp” when he moves suddenly. The  pain is located in his lower back and radiates down the back of both  legs to the middle of his posterior thighs. He denies any bladder or  bowel incontinence or weakness in his legs. He denies fever, chills,  weight loss, or malaise. He finds it very difficult to stand for  prolonged periods of time because he cannot find a comfortable position.  He states that this is the worst back pain he has ever experienced. It  has not been relieved with acetaminophen or ibuprofen. His past medical  history is significant for hypertension, and his only medication is  lisinopril daily. He does not smoke or use illicit drugs and only drinks  alcohol on occasion. On physical examination, he is well developed,  overweight, and in moderate discomfort. His vitals are within normal  limits. On neuromuscular examination, he has moderate tenderness  bilaterally in his lumbar paraspinous muscles, and his lumbar flexion  and extension are limited by pain. Strength and sensation are within  normal limits and are symmetrical bilaterally. He has normal and  symmetric knee and ankle deep tendon reflexes. Straight leg raise  testing is negative bilaterally, and gait is within normal limits.
Questions
What is the most likely diagnosis?
What is the most appropriate workup?
What is the best treatment plan?