Foot drop, sometimes called drop foot, is a muscle weakness of the tibialis anterior muscle which can cause the foot to drag when walking. Degenerative conditions of the lumbar spine such as disc herniation or spinal stenosis (narrowing of the spinal canal) have been linked with foot drop.
It’s a fairly rare condition that is not well understood in etiology or treatment. A medical journal article reports on a study of 28 patients with foot drop from disc herniation or spinal stenosis seen over a period of 10 years. Everyone in the study had spine surgery to correct the problem.
Patients with herniated discs had an MRI done before surgery to determine the level of disc affected and the amount of damage done. The surgeon also recorded observations made during the operation. The number of nerve roots (and which ones) compressed by the herniated disc was reported. For patients with stenosis, the same process was done to discover how much the canal size was reduced by and at what levels.
Among other factors, they measured muscle strength tested before surgery and any weakness observed after surgery. 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 foot drop 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.
Most of the patients with herniated discs were affected at the L5-S1 level but some at 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 disc patients recovered some strength of the tibialis anterior after surgery. There was no way to tell before surgery who would recover better.
As far as the group with stenosis goes, the upper lumbar levels were affected most often (L2-3, L3-4). Most often, multiple levels were involved. Far fewer patients in this group recovered their tibialis anterior strength after surgery.
Workers comp patients get foot drop. The authors sorted through all the data and concluded that foot drop in patients with a herniated disc occurs most often when a piece of the disc breaks off and ends up putting pressure on more than one nerve root. But disc patients were much more likely to recover muscle strength after surgery than stenosis patients.
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