What symptom is associated with a herniated disc at the S1 level?

A herniated disc at the S1 level is primarily associated with symptoms affecting the lower extremities, particularly the foot and ankle. One of the hallmark symptoms is weakness in plantar flexion, which is the movement of pointing the toes downward. This muscle strength is predominantly controlled by the S1 nerve root, and a herniation at this level can impinge on the nerve, leading to difficulty in standing on one's toes or performing activities that require this motion, such as pushing off while walking.

In addition to weakness in plantar flexion, patients may also experience sensory changes along the posterior and lateral aspects of the leg and the sole of the foot. While other reflex or muscle weaknesses may occur, the specific weakness in plantar flexion is a direct result of an S1 nerve root involvement.

In contrast, ankle dorsiflexion weakness is mainly associated with the L4-L5 levels, as that is where the primary nerve roots for this motion originate. Knee jerk reflex loss tends to be linked to L3-L4 levels, while anterior thigh weakness is related to L2-L3 innervations. Therefore, the association of plantar flexion weakness with an S1 herniated disc is the most direct and characteristic symptom.