When a patient develops foot drop following back surgery, it is natural to assume that the problem originates in the lumbar spine. However, not every case of foot drop after spinal surgery is necessarily caused by ongoing compression or damage to a spinal nerve.
In some patients, the source of the weakness may be farther down the leg—a condition known as peripheral nerve entrapment.
Our clinic recently evaluated a patient who had undergone back surgery but did not experience the significant pain relief that had been hoped for. Over the following months, the patient’s overall condition gradually improved with physical therapy. Unfortunately, another problem had developed following the operation: foot drop.
What is foot drop?
Foot drop describes difficulty lifting the front of the foot and toes toward the shin. This weakness can cause the toes to drag while walking, increasing the risk of tripping and falling. Some patients compensate by lifting the knee higher than normal with each step.
Foot drop is a symptom rather than a diagnosis.
Lumbar nerve root problems, particularly involving the L4-L5 region and L5 nerve root, are important potential causes. However, peripheral nerves outside the spine can also be responsible. The common peroneal (fibular) nerve is a particularly important consideration, although other peripheral nerve injuries can contribute depending on the patient’s pattern of weakness and sensory loss.
For this reason, determining exactly where nerve dysfunction is occurring can be critical before assuming that additional spinal treatment is necessary.
Could surgical positioning contribute to nerve injury?
Patients undergoing surgery may remain in one position for an extended period. Depending on the procedure, positioning, padding, duration of surgery, and individual anatomy, peripheral nerves can potentially be subjected to compression or stretching.
This is somewhat analogous to waking up with an arm that has “fallen asleep” after lying on it. Pressure on a nerve can temporarily interfere with normal nerve signaling. With greater pressure or prolonged compression, however, the nerve injury can be more significant and recovery may take considerably longer.
Postoperative peripheral nerve injuries are recognized complications of surgery and may occur even when the operation itself is being performed in a completely different part of the body.
Therefore, when a patient develops new weakness following surgery, the evaluation should not necessarily stop at the surgical site.
Finding the source of the patient’s foot drop
When this patient came to our clinic, the assumption was that the foot drop represented nerve damage associated with the previous back surgery.
A detailed physical examination raised the possibility of a peripheral nerve problem.
Musculoskeletal ultrasound was then used to evaluate the nerve dynamically. Unlike a static image, ultrasound allows the physician to examine certain peripheral nerves in real time, follow their course through the extremity, and look for changes in size, shape, movement, or surrounding tissues that may suggest entrapment.
The examination identified an area where the nerve appeared compressed.
This finding changed the treatment strategy. Instead of automatically attributing the patient’s weakness to the lumbar spine, there was now a specific peripheral location that could be addressed.
What happens when a peripheral nerve is compressed?
A healthy peripheral nerve contains bundles of nerve fibers surrounded and supported by specialized tissues, including Schwann cells and myelin.
When a nerve becomes compressed, its normal structure and ability to transmit electrical signals may be affected. Depending on the nerve and severity of compression, patients may experience:
- Numbness or altered sensation
- Tingling or “pins and needles”
- Burning or nerve pain
- Muscle weakness
- Loss of coordination or motor control
With foot drop, weakness of the muscles responsible for dorsiflexion—the movement that pulls the foot and toes upward—becomes particularly noticeable.
The longer significant nerve dysfunction persists, the more important it becomes to determine precisely where along the nerve pathway the problem is occurring.
Ultrasound-guided nerve hydrodissection
Once the suspected site of peripheral nerve entrapment was identified, the patient underwent ultrasound-guided nerve hydrodissection.
Hydrodissection is an image-guided procedure in which fluid is carefully introduced around a peripheral nerve with the goal of separating the nerve from surrounding tissues that may be restricting or compressing it.
Ultrasound guidance is especially important because the physician can visualize the nerve, needle, surrounding blood vessels, muscles, fascia, and other structures during the procedure.
Rather than simply injecting medication into the general area of symptoms, the goal is to identify the nerve and address the tissue interface surrounding the suspected entrapment.
In this patient’s case, improvement became noticeable within approximately one to two weeks, including a return of some strength in the affected limb.
While an individual patient’s response cannot predict how another person will respond, the case illustrates an important diagnostic lesson: foot drop following back surgery does not automatically mean that another back procedure is necessary.
Peripheral nerve entrapment can occur throughout the body
Peripheral nerve entrapment is not limited to the leg.
One of the best-known examples is carpal tunnel syndrome, in which the median nerve becomes compressed as it travels through the carpal tunnel at the wrist.
Similar problems can occur at many locations where nerves travel through relatively confined anatomical spaces or pass between muscles, fascia, ligaments, and bones.
The specific symptoms depend on which nerve is affected, but the diagnostic principle remains the same: identify the involved nerve, determine where the dysfunction is occurring, and then consider treatment directed at the actual source of the problem.
A comprehensive evaluation may include the neurological and musculoskeletal examination
A patient with foot drop after spinal surgery may understandably fear that the operation damaged a nerve or that another spinal procedure will be required.
Sometimes the lumbar spine is indeed responsible. In other cases, however, peripheral nerve entrapment may be contributing to the patient’s symptoms.
A comprehensive evaluation may include the neurological and musculoskeletal examination, review of spinal imaging, electrodiagnostic testing such as EMG and nerve-conduction studies when appropriate, and diagnostic ultrasound of accessible peripheral nerves.
For selected patients, dynamic musculoskeletal ultrasound can provide another piece of the diagnostic puzzle by allowing the physician to examine a peripheral nerve directly and evaluate potential sites of entrapment.
The central lesson from this case is simple: before treating foot drop, determine where the nerve problem is actually occurring.
When the true source can be identified, treatment can be directed toward that structure rather than assuming persistent symptoms necessarily require additional spinal intervention.