Dorsiflexion deficit, also known as foot drop, is a potential neurological effect of spinal nerve root compression in the lower back, but can also be the result of several other causative mechanisms. Foot drop is an objective finding that demonstrates actual pathology in nerve functionality, unlike many highly subjective diagnostic criteria. Patients who express foot drop are often herded quickly towards surgical intervention, which can be either an indicated and appropriate treatment or a complete waste of time, depending on how accurately the source process is identified preoperatively.
We have written much about foot drop over the years, but the questions on this important condition continue to come in. Therefore, we will take this opportunity to expand on our previous coverage of dorsiflexion deficit by explaining lesser known aspects of a dropped foot disorder. If you want to get a primer on the condition first, please read the other articles on the topic throughout our website catalog.
This essay concentrates on investigating alternative causes of foot drop, as well as explaining the usual theorized cause of lumbar nerve root compression.
Dorsiflexion Deficit Theory of Causation
Dropped foot is usually theorized to be caused by compression of the L5 nerve root. Due to slight differences in neurological mapping from person to person, rare cases might include the compression of the L4 or S1 nerve roots with similar effect. This compression occurs in the lumbar spine and can occur due to spinal stenosis compressing one or more of the nerve roots of the cauda equina within the central canal space in some instances. However, far more commonly diagnosed is the existence of foraminal stenosis leading to nerve compression of the L5 nerve.
Either way, both types of stenosis can occur from many possible causative processes, often including a combination of factors, such as herniated discs, degenerated discs, osteoarthritis, atypical lordosis, lumbar scoliosis, spondylolisthesis and ligamentous hypertrophy or ossification, working together to decrease overall patency of the neurological space.
Neurological testing can evaluate the viability of the L5 nerve root and help confirm it as the source of symptomology in most patients.
Alternative Structural Foot Drop Explanations
There are other conditions that can enact foot drop without suffering compression of the L5 nerve root in the lower back. These circumstances can pose diagnostic concerns, since lumbar central and foraminal stenosis are so commonplace and typically not present to such degrees as to enact symptoms. However, when dropped foot exists, many assumptions will be made about the severity of lumbar stenosis, often resulting in unsatisfying surgical treatment. While the stenosis might be resolved in the lower back, the true causative process remains untreated and symptoms therefore persist:
Cervical spinal stenosis can compress tracts within the spinal cord that eventually form the L5 nerve root. Rarely, cervical stenosis can create foot drop as a primary or secondary symptom.
Pseudo-sciatica problems can also cause foot drop in very rare circumstances. Sciatic nerve compression by the piriformis muscle or compression of one of its branches locally in the leg anatomy can cause foot drop.
Nonstructural Dorsiflexion Deficit Causation
Besides lumbar spinal and alternative nonspinal structural causation, there are other circumstances that might result in foot drop through nonstructural processes and scenarios. Some of the conditions are easily diagnosed as the source of symptoms, while other may defy detection and therefore avoid successful treatment for a lifetime of suffering:
Diabetes can degrade the performance and health of some nerves. Foot drop is not common, but is a possible result of extreme diabetic neuropathy conditions, especially in morbidly obese patients.
Some neuromuscular diseases can cause foot drop as a primary manifestation. In undiagnosed patients, this might be one of the earliest signs of the disorder, if indeed it is positively identified.
Ischemia can create foot drop in many patients. We have seen this symptom in TMS patients and those suffering from mindbody pain that was simply never diagnosed as tension myositis syndrome. Ischemia will deprive the nerve oxygen and will therefore degrade its functional viability over time. Ischemia can act on the cauda equina en masse, on the individual L5 root in the lumbar spine, or on the entire sciatic nerve. Ischemia can also act on the piriformis muscle, causing it to clamp down on the sciatic nerve creating piriformis syndrome-related foot drop.