What are the symptoms of S1 (first sacral) radiculopathy?

S1 radiculopathy typically presents with pain that radiates from the lower back down the posterior thigh and calf to the lateral aspect of the foot, often affecting the little toe. Patients commonly experience numbness or tingling along this same distribution, particularly on the lateral foot and heel. Weakness may be present in plantar flexion of the foot (difficulty standing on tiptoes), which is controlled by the gastrocnemius and soleus muscles. Diminished or absent ankle reflex is a classic finding in S1 radiculopathy. Patients may also report difficulty walking, especially on uneven surfaces, and may develop an antalgic gait to avoid pain. The symptoms are often exacerbated by activities that increase pressure on the nerve root, such as sitting, coughing, sneezing, or straining. The underlying cause is typically compression or irritation of the S1 nerve root, commonly due to a herniated lumbar disc, spinal stenosis, or foraminal narrowing. The pain and neurological symptoms occur because compression of the nerve root leads to inflammation, edema, and impaired nerve conduction, affecting both motor and sensory functions in the S1 distribution.