After lifting a load, a 36-year-old male patient has experienced a severe pain in the lumbar region, which spread to the right leg and was getting worse when he moved his foot or coughed. Objectively: the long back muscles on the right are strained. Achilles jerk is reduced on the right. There is a pronounced tenderness of paravertebral points in the lumbar region. The straight leg raise (Lasegue's sign) is positive on the right. What additional tests should be performed in the first place?