L5-S1 Disc Lesion Neurological Effects

Neuroanatomical Basis of L5-S1 Disc Lesion

L5-S1 disc lesions typically affect the L5 nerve root as it exits the neural foramen, causing compression that leads to specific neurological deficits 1
The L5 nerve root innervates the dorsal aspect of the foot, including the big toe, making sensory loss in this area a characteristic finding 1

Lost sensation in the big toe and dorsal aspect of the foot is a hallmark finding of L5 nerve root compression 1
L5 nerve root compression typically affects foot dorsiflexion and great toe extension rather than plantar flexion 1
Plantar flexion is primarily controlled by the S1 nerve root, not L5, and would not be the primary deficit in an L5-S1 disc lesion 1
The knee jerk reflex is primarily mediated by the L3-L4 nerve roots, not L5-S1 1
L5-S1 disc lesions typically affect the ankle jerk reflex rather than the knee jerk reflex 1

MRI is the mainstay of imaging for lumbosacral plexus and nerve root pathology, providing superior definition of intraneural anatomy and pathologic lesions 2
Clinical diagnosis should be confirmed by electrodiagnostic studies to differentiate radiculopathy from plexopathy 2