In what direction did the herniated disk move to cause the patient's symptoms, including foot drop?

Posterolateral Disc Herniation Causes Foot Drop

In this patient with right foot drop after bending and lifting a heavy object, the herniated disc has moved in a posterolateral direction (option A). 1, 2, 3

Pathophysiology of Disc Herniation and Foot Drop

When a disc herniates, the nucleus pulposus typically moves in a posterolateral direction through a weakened or torn annulus fibrosus. This direction of herniation is most common due to:

1. Anatomical factors: The posterior longitudinal ligament is strongest in the midline and weaker laterally, creating a path of least resistance 4

2. Nerve root compression: Posterolateral herniations compress the traversing nerve root in the lateral recess or as it exits the neural foramen 1

3. L5 nerve root involvement: In this patient with foot drop, the L5 nerve root is most likely compressed, as it innervates the anterior tibialis muscle responsible for dorsiflexion of the foot 2

Clinical Correlation with Imaging Findings

MRI is the gold standard for diagnosing disc herniation and would show:

• Posterolateral disc material extending into the lateral recess or neural foramen
• Compression of the L5 nerve root (most commonly) causing foot drop
• Possible associated findings like nerve root edema or displacement 4

Why Other Options Are Incorrect

• B. Anterior direction - Anterior disc herniations are extremely rare and would not typically cause foot drop. These unusual herniations can be mistaken for retroperitoneal tumors 5

• C. Inferioromedial direction - This direction would not typically compress nerve roots to cause radiculopathy or foot drop

• D. Central posterior direction - While central posterior herniations do occur, they typically cause cauda equina syndrome with bilateral symptoms rather than unilateral foot drop 4

Clinical Implications

Foot drop due to lumbar disc herniation represents an urgent surgical indication, as delayed treatment can lead to permanent neurological deficit 1. The posterolateral direction of herniation explains the unilateral nature of the symptoms and the specific nerve root involvement.

In patients with foot drop from disc herniation, urgent surgical decompression is typically recommended to relieve pressure on the affected nerve root and maximize chances of neurological recovery 1, 2.