Muscle weakness of the tibialis anterior muscle from a herniated disc can cause the foot to drag when walking. The tibialis anterior picks the ankle up and pulls the foot toward the face. Nerves in the lumbar spine control function of this muscle. Pressure from the disc on the spinal nerve root can lead to loss of nerve supply to the muscle. The result is muscle weakness that can be severe enough to result in a foot drop.
It’s a fairly rare condition. Some studies have been done but no one has really explained exactly what happens and why. Could it be prevented? Is surgery needed? How soon should surgery be done?
The reason the mechanism behind a loss of tibialis anterior strength is difficult to determine is because there isn’t just one nerve that goes to this muscle. It appears from other studies that most patients have footdrop when the L5 nerve root is affected. But there are a fair number of people with L4 nerve root irritation or compression who also develop foot drop. And sometimes the S-1 nerve root is affected, too.
In a recent study from Japan, a group of patients with footdrop were analyzed after surgery. Most of the patients with herniated discs were affected at the L5-S1 level. Some (but not as many) patients had disc herniation at the L3-4 or L4-5 levels. More than half of the disc group had compression of multiple nerve roots (not just one). They also had a free floating piece of disc called a sequestrated fragment pressing on the nerves contributing to this multi-level phenomenon.
Most of the patients recovered strength of the tibialis anterior after surgery. They scored a four or five on the manual muscle test (out of a total of five points), indicating near normal or normal function. For those who still had foot drop, there was no apparent predictive factor before surgery. In other words, there was no way to tell before surgery who would recover and who wouldn’t.
Most surgeons do review all of the possible complications from any surgery. The most common concerns are for infection, delayed wound healing, and blood clots. Specific complications from the planned surgery are usually pointed out as well. Patients don’t always hear everything that’s said — the stress of the situation can make it seem like they never heard any warnings before surgery.
You most likely signed a waiver notifying you of any and all possible complications. Your signature indicated at the time that you had read and understood everything on the page.
Preventing permanent foot drop and restoring full function requires careful attention and early intervention. Since the majority of patients having this surgery have a good outcome, even without knowing who will (or won’t) recover, surgery is carried out as early as possible to prevent long-term consequences of nerve impingement. It’s possible that further treatment may help you. Be sure and make a follow-up appointment with your surgeon and find out what else (if anything) can be done for your condition.