Lumbar spine pain, unilateral or bilateral leg pain, urinary retention, and saddle anesthesia indicate Cauda Equina Syndrome, a neurosurgical emergency.  Emergent MRI is required.  Often caused by a large central herniated disc that obliterates the spinal canal distal to the conus medullaris.  Other causes include anticoagulation-related epidural hematoma, post-surgical epidural hematoma, spinal epidural abscess, burst fractures, migrating hardware, tumors, and Pott’s disease, to name a few.  Lower motor neurons signs predominate which include hypo-reflexic or areflexic deep tendon reflexes, flaccid–as opposed to spastic–leg weakness, and no resistance to passive muscle stretch (no clasped-knife tendency).  Treatment is immediate surgical decompression.