Foot Drop In Obstetrics

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Continuing Education Activity

Obstetric vaginal delivery is not necessarily a benign process. Foot drop is a serious consequence of vaginal delivery. Neurological lesions occurring during delivery can lead to a foot drop. Foot drop can occur due to lesions of the following: L5 lumbar root due to a herniated lumbar disc, lesion of the lumbosacral plexus, lesion of the lumbosacral trunk, and lesion of the common fibular nerve or its branch, the deep fibular nerve. This activity highlights the role of the interprofessional team in diagnosing and treating patients with foot drop In obstetrics.

Objectives:

  • Describe the different lesions that lead to a foot drop in an obstetric patient.
  • Identify the anatomical basis of the different lesions that can lead to an obstetric foot drop.
  • Review the symptoms characteristic of each of the different lesions that can lead to a foot drop.
  • Explain the process that leads to the diagnosis of the cause of a foot drop.

Introduction

While there may be a tendency to associate anesthetic intervention with neurological pathology in the practice of obstetrics, the events surrounding pregnancy and labor are most commonly responsible for such neuropathies. Obstetric palsies are estimated to be more common than neurological injuries caused by regional anesthesia.[1][2] Thus, understanding the spatial relationship between nerves and surrounding anatomical structures is paramount to properly identify the site of obstetrical palsy, its presentation relative to neurological dysfunction, and subsequent treatment options.

Foot drop is one type of obstetrical palsy. First described in 1838, a foot drop can have pronounced adverse effects on quality of life if not recognized, diagnosed, and treated appropriately.[3][4] It can be caused by three separate but similar etiologies: lumbar radiculopathy, lumbosacral (LS) plexopathy, or common fibular (CF) neuropathy. The location of the neural injury should be assessed by a combination of careful neurological examination, MRI imaging, and electrophysiological studies.  

Foot drop manifests primarily as a loss of dorsiflexion and eversion of the foot at the ankle. This can produce a slapping sound when the foot hits the ground. To avoid scraping the foot on the ground, the patient learns to elevate it higher than normal, leading to the classic steppage gait. Patients suffering from foot drop can also present symptoms including but not limited to paresthesia, hypoesthesia, numbness, weakness, atrophy, and diminished or absent deep tendon reflexes.

The presentation of foot drop is most commonly described as unilateral, except for the case of common fibular neuropathy, which may be bilateral. This paper aims to elucidate the individual mechanisms underlying each etiology of obstetric foot drop and to use relevant clinical anatomy to guide clinicians in the appropriate diagnosis and management of such nerve palsies.

Anatomy of the Roots of the Lumbosacral Plexus

The lumbosacral (LS) plexus is located in the psoas muscles and is formed by the L1-S4 nerve roots, which provide motor and sensory innervation to the pelvis, thigh, leg, and foot. Its dorsal (sensory) and ventral (motor) roots emerge from the spinal cord and stream down in the cauda equina to exit the intervertebral foramina to join to form the mixed spinal nerves.

Each mixed spinal nerve then divides into a ventral primary ramus and a dorsal primary ramus. The muscles of the pelvis and lower limbs are innervated by the ventral primary rami of the lumbosacral plexus. Damage to one or more of the dorsal nerve roots before the fibers join causes a loss of sensation in a dermatomal distribution. Meanwhile, damage to the ventral roots will result in paresis of all muscles innervated by that root level. Regarding obstetrical neural lesions, the L5 and S1 ventral rami of the plexus are the most important.

Anatomy of the Lumbosacral Trunk Component of the Lumbosacral Plexus

The nerve roots of L1-L4 form the upper portion of the plexus, while the roots of the L4-S4 constitute the lower portion of the lumbosacral plexus. Between these two portions of the lumbosacral plexus, the L4 and L5 rami unite to form the lumbosacral trunk. The lumbosacral trunk must pass inferiorly on the anterior surface of the sacral ala, where it is liable to injury by the head of the descending fetus.

The lumbosacral trunk is part of the lumbosacral plexus but is considered separately in this paper, as its exposed position renders it especially liable to injury. Damage to the L5 component of the lumbosacral trunk is sufficient to cause foot drop. 

Anatomy of the Peripheral Nerves formed from the Lumbosacral Plexus

Branches of each portion of the lumbosacral plexus divide to form the distinct peripheral nerves associated with the lower limbs. The upper portion of the plexus gives rise to the iliohypogastric nerve (T12-L1), the ilioinguinal nerve (L1), genitofemoral nerve (L1-L2), lateral femoral cutaneous nerve (L2-L3), the femoral nerve (L2-L4), and obturator nerve (L2-L4).

The lower part of the plexus gives rise to the superior gluteal nerve (L4-S1), inferior gluteal nerve (L5-S2), posterior femoral cutaneous nerve (S1-S3), the pudendal nerve (S1-S4), and the large sciatic nerve (L4-S3).  

Anatomy of the Common Fibular Nerve 

The common fibular nerve arises from the sciatic nerve above the popliteal fossa. It passes over the head of the fibula to curve around the posterior aspect of the fibula. It divides into the superficial fibular nerve and the deep fibular nerve.

The superficial fibular nerve supplies the fibularis longus and brevis and the skin over the lateral side of the leg and dorsum of the foot. The fibularis longus and brevis are the evertors of the foot at the ankle.

The deep fibular nerve then enters the anterior compartment of the leg, where it innervates the tibialis anterior, extensor hallucis longus, and extensor digitorum longus muscles. These muscles are extensors of the foot at the ankle (the dorsiflexors in clinical terminology). Lesion of the common fibular nerve or the deep fibular nerve will produce foot drop.

Etiology

All of the lesions causing foot drop involve compression of various neurological structures by the baby, by the mother's or the attending's hand on the patient's thighs during delivery, by use of the dorsolateral lithotomy position, as a result of herniation of a lumbar disc (especially L4/L5), by the use of forceps during delivery, or similar compressive factors.[2]

Radiculopathy

One of the least common but relevant causes of foot drop in parous women involves damage to the roots of the lumbosacral plexus. Such radiculopathies occur secondary to compression by a herniated disc. These injuries are rare in the obstetric literature and are limited to the postpartum period.[5] 

L5 radiculopathy can manifest as neuropathic pain corresponding to the L5 dermatome. This dermatome is located on the lateral aspect of the leg, the dorsum of the foot, the medial half of the dorsum of the big toe, and the middle three toes. Weakness is present involving the tibialis anterior, extensor hallucis longus, and extensor digitorum longus. Patients with radiculopathy may exhibit a diminished or absent ankle jerk, which demonstrates the involvement of the S1 nerve root.[7]  Thus, the presentation with an absent ankle jerk reflex in a patient with foot drop would suggest the involvement of S1. Therefore, the presence or absence of a deep tendon reflex may be used as part of a differential diagnosis.

Radicular pain can be elicited by the hyper flexibility and relaxation of joints occurring secondary to hormonal changes in pregnancy. Lumbosacral joints may loosen substantially during pregnancy, increasing the likelihood of developing a bulging or herniated lumbar disc. It should also be noted that the onset of all neurologic symptoms in these cases occurred days to months after giving birth.

Currently, the standard of care dictates that to confirm the presence of radiculopathy, magnetic resonance imaging (MRI) showing radicular compression and electromyography (EMG) showing nerve conduction abnormalities should be performed in addition to examining the patient's motor and sensory functions.

Lumbosacral Plexopathy

The lumbosacral trunk is affected by the baby's head as it moves down into the pelvis during delivery. Typically the head compresses the L5 lumbar root to cause a foot drop. Lesions of the lumbosacral plexus will often involve L2, L3, and L4 as well, giving rise to symptoms that resemble a lesion of the femoral or obturator nerves in addition to the foot drop from L5. The presence of such a constellation of symptoms is characteristic of a lesion of the lumbosacral trunk.   

Lesions of the Lumbosacral Trunk (Part of the Lumbosacral Plexus)

The lumbosacral trunk is formed primarily from L5, with a contributing branch from L4. It appears at the medial margin of the psoas major and descends over the pelvic brim, anterior to the sacroiliac joint. Here it is vulnerable to injury by the head of the baby as it descends into the pelvis.

It may be difficult to confirm the involvement of the L5 nerve root since the L5 ventral ramus is present in the lumbosacral trunk, in the sciatic nerve, and in its derivative, the common fibular nerve. Electromyography helps make the diagnosis of a lesion of the lumbosacral trunk. Voluntary motor unit action potentials (MUAPs) of obstetric patients exhibiting foot droop have been shown to be significantly reduced in all the muscles below the knee that contain the L5 segment:  tibialis anterior, extensor hallucis longus, extensor digitorum brevis, fibularis longus, tibialis posterior, and flexor digitorum longus.

Note that the tibialis anterior, extensor digitorum brevis and fibularis longus are all supplied by the common fibular nerve, whereas the tibialis posterior and flexor digitorum longus are supplied by the tibial nerve. Thus, patients who have involvement of the tibialis posterior and flexor digitorum longus could not be suffering from a common fibular neuropathy, an important diagnostic distinction.[6]

Common Fibular Neuropathy

The common fibular nerve (L4-S2) arises from the sciatic nerve above the popliteal fossa. It then passes over the head of the fibula to curve around the posterior aspect of the neck of the fibula. It then divides into the superficial fibular nerve, which innervates the lateral compartment of the leg, and the deep fibular nerve, which passes through the anterior compartment of the leg to supply the tibialis anterior and the extensor digitorum longus and the extensor digitorum brevis.

These muscles are the dorsiflexors and are innervated by the deep fibular nerve (L4-L5). The tibialis anterior is the most powerful dorsiflexor of the foot at the ankle. It can be tested by asking the patient to dorsiflex the foot against resistance and compare the results with the other foot.[7]

As the common fibular nerve wraps around the neck of the fibula, it is susceptible to compression. Lesion of the common fibular nerve can lead to peripheral neuropathy with motor and sensory deficits. The superficial fibular nerve (L4-S1) and deep fibular nerve (L4-L5) are branches of the common fibular nerve at risk of damage in common fibular neuropathy.

The superficial fibular nerve provides motor function to fibularis longus and fibularis brevis, allowing for foot eversion and weak plantar flexion. Sensory innervation of the distal portion of the leg and dorsum of the foot, excluding the webbing between the first and second digits, is supplied by the superficial fibular nerve.

The deep fibular nerve provides motor function to the tibialis anterior, extensor digitorum longus, extensor hallucis longus, and fibularis tertius, allowing for dorsiflexion of the ankle and extension of the toes. Sensory innervation to the webbing between the first and second toes is supplied by the deep fibular nerve, which is particularly useful in diagnosing fibular neuropathies because this space is innervated entirely by the deep fibular nerve. Moreover, the L5 dermatome serves the medial aspect of the first digit, second, third, and fourth toes allowing one to distinguish this from a deep or common fibular neuropathy.          

The main source of common fibular neuropathy cited in the obstetrics literature is nerve compression. Lateral manual compression of the common fibular nerve by the patient's hand at the knee during prolonged labor may be a cause of neuropathy. For instance, when the patient is lying on a gurney holding her legs to her chest, this position compresses the common fibular nerve. The patient could also be in a semi-sitting position with the legs being forcefully compressed by the patient or birth attendants.[8] 

It has also been suggested that the deep fibular nerve can be stretched due to its anchored position as it branches from the common fibular nerve and travels through the fibular tunnel deep to a fibrous sheath, resulting in neuropathy.[9] There have also been a few cited cases where delivery in the squatting position with the knees bent resulted in the compression of the common fibular nerve between the rectus femoris tendon and the fibular head.

As giving birth in this position is uncommon in hospitals, it has not been seen frequently in the medical literature. Other cited causes include the use of forceps during delivery and cephalopelvic disproportion. A particularly unusual case of bilateral fibular neuropathy was noted involving a patient who had an uncomplicated cesarean section following a prolonged second stage of labor.[10]

All cases of common fibular neuropathy in the literature presented with weakness in the anterior and lateral compartment muscles of the leg, including tibialis anterior, fibularis longus, and brevis.[9] Patients with a common fibular neuropathy often experience weakness in dorsiflexion and plantar flexion, with the strength of dorsiflexion being weaker than that of plantar flexion.[11] 

Although most plantar flexion is due to innervation from the tibial nerve, the mild weakness in plantar flexion seen in common fibular neuropathy is due to the weak activity of the fibularis longus in plantar flexion. Foot drop was also seen in several of the patients in the literature.[11] 

The sensory deficits experienced by patients with a common fibular neuropathy varied, but paresthesia on the dorsum of the foot and loss of fine touch and pinprick sensation along the distribution of the deep and superficial fibular nerves on the lateral leg were the most common deficits.[9]

Most diagnoses for a common fibular neuropathy were made based on clinical presentation.[12] In addition, an X-ray or MRI was performed in many of the cited cases, though none of these tests provided positive results leading to a diagnosis.[8] In more recent studies, electrodiagnostic analyses were performed to confirm the diagnosis.[12]

Prolonged squatting, as in some forms of natural childbirth, can cause traction on the common fibular nerve at the neck of the fibula. Lithotomy positioning can cause a similar effect, as can direct pressure on the nerve by the patient's or an assistant's hands to keep the knees forcibly flexed. Hence the name "pushing palsy." [6]

Epidemiology

Obstetrical foot drop involves women in their reproductive years. Obstetrical foot drop has been estimated to occur in 0.92% of deliveries.[2]

Risk Factors For Obstetrical Neural Injury

Prolonged labor, especially in the second stage, is a recognized risk factor for neurological injury in pregnancy.[13] Lesions of the lumbosacral trunk are seen primarily in short women (5 feet or less) in which the baby is relatively large compared to the size of the pelvis (cephalopelvic disproportion).[6] Fetal macrosomia and malpresentation are risk factors for lumbosacral plexopathy.[2] 

For common fibular neuropathy, risk factors are squatting (as in some forms of natural childbirth), knee hyperflexion, and external compression by the patient’s or the attendant’s hand.[9] Unilateral cases of common fibular neuropathy can be correlated with the side of the patient’s dominant hand.[12]

Pathophysiology

Mechanism of Obstetrical Compression Neuropathy

All the lesions discussed in this paper belong to the category of compression neuropathy. The pressure exerted by the fetus compresses the axons of the nerve, damaging them and cutting off their blood supply. This mechanism of injury is classified as Wallerian degeneration.[14] 

This process generally involves the death of the axon distal to the lesion. Descriptions of the mechanism have been published.[13][15] Common findings include foot drop, other motor losses, sensory losses, pain, and loss of the patellar tendon reflex.

History and Physical

The patient’s vital signs - blood pressure, pulse rate, oxygen saturation, respiratory rate, height, and weight- are part of the routine physical examination. The more important concern is the presence of foot drop, which is a consequence of weakening or denervation of the muscles of the anterior crural compartment:  tibialis anterior (the most important one), extensor hallucis longus, and extensor digitorum longus.[16][17] 

The severity of weakness can be assessed by having the patient sit on the examining table with the foot off the edge. The examiner then holds the ankle with one hand and the foot with the other. The examiner then pushes the foot downwards into plantar flexion and notes the resistance the patient’s foot offers to this maneuver. The other foot is tested for comparison purposes. 

One should also observe the patient’s gait, being careful to support her as she attempts to walk, so she doesn’t fall. If a foot drop is present, the patient will scuff the toes of the affected foot and will have to lift the foot off the floor higher than normal so as not to scuff the toes (steppage gait, as in a Tennessee walking horse).[7] 

Another indication of foot drop occurs when the patient places the heel on the ground when walking and the foot slaps the floor (slap foot). Patients with a foot drop have difficulty walking on the heels because this requires active dorsiflexion of the foot.

The patient should be examined for other motor losses. In true foot drop, these should be limited to the dorsiflexors (but see the description of tests because the tibialis posterior is not involved in a common fibular nerve lesion but will be involved in the lesion involves the L5 nerve root, as in a herniated lumbar disc, lesion of the lumbosacral plexus or lumbosacral trunk).[17] The sensory losses and pain should be carefully mapped.[16]

The course of the common fibular nerve should be examined. Tinel’s sign performed by tapping over the lateral part of the neck of the fibula to stimulate the common fibular nerve can elicit a sense of tingling that radiates from the site of the tapping.[18] This may be useful in case of a lesion of the common fibular nerve.

If positive, the Lasegue straight-leg raising test indicates a proximal lesion such as a herniated lumbar disc.[19] For the foot drop, the appropriate disc would be the L4/L5 disc. If there is a herniated L4/L5 lumbar disc, the pain pattern will follow the L5 dermatome (area of skin innervated by a single dorsal root). If the test is positive, examine the patient for paralumbar muscle spasm, which will probably accompany the herniated lumbar disc.

The presence of a herniated lumbar disc can be confirmed by an MRI.[20] MR neurography can be especially helpful in localizing the lesion.[21]

The Achilles tendon reflex should be normal (unless the lesion also involves the S1 nerve root).[3]

One should then obtain a neurological consultation to determine the precise localization of the patient’s lesion.

It is important to reassure the patient that she did nothing wrong and that an obstetrical foot drop should respond well to treatment if she follows the treatment plan.

Evaluation

Lasegue Straight Leg Raising Test for Radicular Pain Due to a Herniated Lumbar Disc

The patient lies supine. The examiner raises the lower limb with the leg extended at the knee. If there is irritation of a spinal root (due to a herniated lumbar disc), pain is appreciated along the appropriate dermatome. The pain should be felt at less than 60 degrees of elevation.[22]

For disc L4/L5, the spinal root is L5, and the pain is appreciated along the L5 dermatome. The L5 dermatome passes down the lateral leg over the dorsum of the foot to cover the big toe and second and third toes (Foerster dermatome pattern).

For disc L5/S1, the S1 dermatome covers the heel and posterior side of the foot and both anterior and posterior sides of the fourth and fifth toes (Foerster). The S1 nerve root is associated with the Achilles tendon reflex.[3] Damage to this root will cause loss of the Achilles tendon reflex.

Test for the Severity of Foot Drop

The condition is usually obvious. The patient scuffs the toes of her foot or shoe when walking and has to lift the foot higher than normal to clear the ground.[7] When wearing slippers, the patient cannot keep them on her foot. The patient has difficulty walking on her heels.

To test the severity of foot drop, the patient is seated at the edge of the examination table with the foot hanging off the edge. The examiner grasps the ankle to stabilize it and then uses the other hand to force the foot into plantar flexion (testing dorsiflexion against resistance). The test is then performed on the other side for comparison purposes. This is the same test used for the common fibular and deep fibular nerves since a lesion of either of them will cause a foot drop.

Test for Femoral Neuropathy (reverse Lasegue test; Femoral nerve Lasegue test)

The patient lies prone. The leg is flexed at the knee. The examiner holds the patient’s ankle with his left hand and then raises the patient’s thigh with his right hand. This maneuver places tension on the femoral nerve and L2-L4 nerve roots. If this test causes pain in the presence of a foot drop, this result suggests a lumbosacral plexus lesion.

One can test the motor function of the femoral nerve by having the patient lie supine and flex the thigh at the hip against resistance. One can also have the patient lie on the side with the leg flexed. The examiner then holds the patient’s ankle with one hand and the knee with the other. The examiner then has the patient extend the leg at the knee against resistance.

The same test is performed on the other side for comparison purposes. The presence of what appears to be femoral nerve signs in the presence of foot drop indicates that the lesion involves the L2, L3, and L4 nerve roots with a diagnosis of lumbar plexopathy.

Tests for Obturator Internus Neuropathy

The patient lies supine with the thigh flexed at the hip and the leg flexed at the knee. The examiner has one hand on the medial side of the knee and the other on the ankle. The patient then adducts the thigh against resistance to determine weakness or pain due to what appears to be an obturator neuropathy. The other side is tested for comparison purposes.

The presence of what appears to be an obturator internus neuropathy in combination with a foot drop indicates that the patient has a lumbosacral plexopathy (L2, L3, and L4) rather than an obturator internus neuropathy. If pain or numbness is present on the anterior and medial thigh and medial leg (L2, L3, and L4 dermatomes – Foerster) in conjunction with a foot drop (resembling a femoral neuropathy), this is consistent with a lumbosacral plexopathy.

By contrast, a lesion of the obturator nerve would produce weakness in adduction of the thigh combined with pain or numbness in the medial thigh in a much smaller pattern. No foot drop would be present.

Test for lesion of the Common Fibular Nerve

The patient is seated at the edge of the examination table with the foot hanging off the edge. The examiner grasps the patient’s foot with one hand and the ankle with the other. He then forces the foot into plantar flexion against resistance. The examiner then tests the other foot for comparison purposes. Pain or numbness should be present on the lateral leg, dorsum of the foot, and over the toes, including the space between the big and second toes. Foot drop is present.

Test for the Deep Fibular Nerve

The test is the same as for the common fibular nerve. The presence of foot drop with pain or numbness between the big and second toes is consistent with a lesion of the deep fibular nerve. 

For radiculopathy, an MRI of the appropriate area of the lumbar spine should provide evidence of a herniated lumbar disc at L4/L5. Absent this finding, one should search for other causes delineated in this paper. 

Confirmation of the lesion by electrophysiological analysis is very important in obtaining an accurate diagnosis.[6]

Treatment / Management

Treatment for Obstetrical Neural Injury

Successful results in the treatment of the compression neuropathies discussed in this paper depend first of all on an accurate diagnosis by a neurologist. This begins with the history and results of the physical examination by a neurologist. Special tests such as imaging (especially important in the case of radiculopathies) and electrophysiological examination to localize the lesion accurately are essential in helping to establish the diagnosis.[6] 

In terms of treatment in the absence of other underlying pathology of a non-obstetrical origin, an important aspect of treatment is to use non-invasive treatment modalities.[23]

Lumbosacral Radiculopathy: For non-surgical treatment, patient education, exercise, manual therapy, and non-steroidal anti-inflammatory drugs are all part of the treatment regimen. Oral corticosteroids may also be employed to reduce inflammation in the acute phase. The next step may include pain injections with a glucocorticoid and bupivacaine into the area generating pain.[20]

For lumbosacral radiculopathy, pain may be alleviated with transcutaneous electrical nerve stimulation and lidocaine patches.[16] Neurosurgery is an option if the patient’s condition proves refractive to treatment.[24]

Lumbosacral plexopathy: Treatment with analgesics and muscle relaxing drugs may be employed. Other drugs that may be used include amitriptyline, duloxetine, gabapentin, pregabalin, and opioids.[25]  Physical therapy should be an important modality of treatment.

Common Fibular Neuropathy: In addition to the pharmacological agents discussed for lumbosacral plexopathy, physical therapy and gait retraining can be helpful. Ankle foot orthoses may be employed to treat the foot drop to enable the patient to walk better. In more severe cases of common fibular neuropathy, surgical operations can be performed to improve nerve function. Surgery may be especially important in farm workers whose livelihood depends on the ability to work in a squatting position.[26]

In terms of prognosis, full mobility was seen in 6 months following a common fibular nerve injury, with rapid improvement often occurring in the first two months. Occasionally some symptoms persist for a year. Total recovery should occur even in prolonged symptoms by two years.[3]  Regardless of the presentation, the outcome for intrapartum and postpartum LS plexopathy was generally good, with the resolution of symptoms ranging from days to months.[3][27] 

Only a few of the reported patients still presented with deficits as of their last visit. These deficits were generally benign and were not reported to negatively impact the quality of life. For L5 radiculopathy causing foot drop, the symptoms had almost disappeared by six months after delivery.[27]

Regarding physical therapy, the most important aspect is to stretch the plantar flexors and inverters to remove resistance to dorsiflexion.[16] Then the dorsiflexors are exercised against resistance to strengthen them. 

The nerve damage in foot drop is usually not so severe as to cause severe muscle atrophy if the physical therapy regimen is carried out, but if this is a concern, electrical stimulation to promote muscle contraction to prevent atrophy is a possible therapeutic option.

Differential Diagnosis

Various obstetrical injuries during delivery can lead to foot drop in the patient. Injury to the roots of the lumbosacral plexus can lead to foot drop, often due to softening of the ligaments during late pregnancy. Injuries to the lumbosacral plexus itself can lead to a foot drop.

One of the hallmarks of this type of foot drop is that it may be accompanied by a lesion that appears as femoral neuropathy, or an obturator neuropathy, as these nerves share the L2-L4 segments with the lumbosacral plexus. A different injury is a lesion of the lumbosacral trunk. This structure passes on the anterior surface of the sacral ala, where it can be compressed by the baby’s head during the delivery process.

A somewhat different lesion that can lead to foot drop involves the common fibular nerve or its branch, the deep fibular nerve. As noted above, this is commonly due to the patient or the attending holding the patient’s legs flexed at the hip and flexed at the knee during the pushing or bearing down process increasing intra-abdominal pressure to facilitate movement of the baby into the birth canal. Placing the patient in the dorsal lithotomy position can also result in this type of foot drop.

Thus, a variety of different lesions can produce a foot drop. The art of differential diagnosis consists of being able to tease out the other aspects that can indicate exactly where the lesion occurred that resulted in the foot drop. Factors to be considered include motor losses, sensory losses, and pain. Tests will be needed. For L5 lumbar radiculopathy, an MRI may be helpful.

If the foot drop is caused by L5 lumbar radiculopathy, there should be evidence of damage to the ligaments and nucleus pulposus at the L4/L5 level. In addition to a careful and precise neurological examination, electrophysiological studies can be used to document precisely the extent of the lesion. These offer more precise information than physical examination. For example, mapping sensory losses and pain depends on the cooperation of the patient, who may be scared or distracted by her condition.

The following details form the basis for the differential diagnosis of foot drop.[3]

Radiculopathy

Sensory Criteria for Radiculopathy

Lumbar pain radiating down into the lower limb is characteristic. The pain should follow a dermatomal pattern. For the L4 dermatome, the pain would involve the anterior and medial thigh and the medial leg. For the L5  dermatome, the pain will occur on the lateral thigh, leg, and dorsum of the foot. For the S1 dermatome, the pain will involve the posterior thigh, leg, and heel.

Motor criteria for radiculopathy: The weakness and loss of motor function will occur in a myotomal pattern involving a ventral root. For the L4 myotome, the quadriceps femoris will be involved. For the L5 myotome, the tibialis anterior, extensor digitorum longus, and extensor hallucis longus are involved, as these cause the foot drop. However, the L5 myotome also involves the fibularis longus and the tibialis posterior. For the S1 myotome, the gastrocnemius and gluteus maximus will be involved.

Other criteria for radiculopathy include a positive Lasegue’s sign. In addition, there will be the abolition of the deep tendon reflexes. For the L4 myotome, the patellar tendon reflex will be lost. For S1, the Achilles tendon reflex will be lost. There is no reflex for L5.

For radiculopathy, electromyographic abnormalities will occur in a radicular pattern. The L4 myotome will involve the quadriceps femoris. For the L5 myotome, they will involve the tibialis anterior, the extensor hallucis longus, and the extensor digitorum longus. These cause the foot drop. But in addition, they will involve the fibularis longus and tibialis posterior. The S1 myotome will affect the gastrocnemius muscle and the gluteus maximus.[3]

In addition, the MRI of the lumbar spine should show a lesion such as a herniated lumbar disc.

Identifying a Lumbosacral Plexopathy

A lumbosacral plexopathy should be suspected if a dermatomal pattern of sensory loss is not present and there is a global palsy of the lower extremity. If there is no global palsy of the lower extremities, but there is still involvement of the hip flexors and adductors, this indicates a lumbosacral plexopathy. Patient presentation of a sensory deficit over the foot strongly indicates a lumbosacral plexopathy. If a sensory deficit over the dorsum of the foot is not present, it is still likely to be a lumbosacral plexopathy based on the motor symptoms. However, additional factors and patient history should be considered before confirming a diagnosis.[3] 

Sensory Criteria for Lumbar Plexopathy

A sensory deficit will be present in the territories of the obturator (medial thigh) and femoral nerves (anterior and medial thigh, medial leg;  medial malleolus through its saphenous nerve branch).

Motor criteria include weakness in the obturator nerve (which innervates the adductor muscles of the thigh) and the femoral nerve (which innervates the psoas and quadriceps femoris muscles). The patellar deep tendon reflex will also be abolished.

Criteria for sacral plexopathy:  palsy and a sensory deficit in the sciatic (hamstrings included) and sacral territories

Lesions of the Lumbosacral Trunk (Part of the Lumbosacral Plexus)

The lumbosacral trunk is formed primarily from L5, with a contributing branch from L4. It appears at the medial margin of the psoas major and descends over the pelvic brim, anterior to the sacroiliac joint. Here it is vulnerable to injury by the head of the baby as it descends into the pelvis. It may be difficult to confirm the involvement of the L5 nerve root since the L5 ventral ramus is present in the lumbosacral trunk, in the sciatic nerve, and its derivative, the common fibular nerve.

Electromyography helps make the diagnosis of a lesion of the lumbosacral trunk. Voluntary motor unit action potentials (MUAPs) of obstetric patients exhibiting foot droop have been shown to be significantly reduced in all the muscles below the knee that contain the L5 segment:  tibialis anterior, extensor hallucis, extensor digitorum brevis, fibularis longus, tibialis posterior, and flexor digitorum longus.

The tibialis anterior, extensor digitorum brevis and fibularis longus are all supplied by the common fibular nerve. In contrast, the tibialis posterior and flexor digitorum longus are supplied by the tibial nerve. Thus, these patients could not be suffering from a common fibular neuropathy.[6]

Identifying a Common Fibular Neuropathy

In the absence of involvement of the hip flexors or hip adductors, then the lesion is suspected to involve a common fibular neuropathy. A common fibular neuropathy will likely present as weakness in foot eversion, plantar flexion, dorsiflexion of the ankle, and/or extension of the toes. Loss of sensation over the lateral leg and dorsum of the foot may occur.

If the patient presentation aligns with these characteristics, conducting an EMG can aid in confirming a diagnosis of common fibular neuropathy. Electromyographic changes should be limited to the tibialis anterior, extensor digitorum longus, and extensor hallucis longus for the deep fibular nerve, the fibularis longus, and brevis for the superficial fibular nerve, and both for the common fibular nerve.

If there is more extensive involvement (such as the tibialis posterior for lumbosacral plexopathy), then the common fibular nerve is ruled out, and one should seek a lumbosacral trunk lesion other than lumbosacral plexopathy, or L5 radiculopathy.

Prognosis

The prognosis for obstetrical foot drop is generally good in those patients who are properly treated.[2] For L5 radiculopathy causing foot drop, the symptoms had almost disappeared by six months after delivery.[5] 

The outcome for intrapartum and postpartum lumbosacral plexus plexopathy was generally good, with the resolution of symptoms ranging from days to months.[27] Only a few reported patients still presented with deficits as of their last visit. These deficits were generally benign and were not reported as negatively impacting the quality of life.[3] 

Full mobility was seen in 6 months following a common fibular nerve injury, with rapid improvement often occurring in the first two months. Occasionally some symptoms persisted for a year. Total recovery should occur even in prolonged symptoms by two years.[2][10]

Complications

The recovery process is generally relatively straightforward if the diagnosis is correct, the treatment plan is followed, and patient compliance is not an issue.

The worst complication is that the patient may fall while trying to walk. The use of orthotics can help, but in severe cases, using a walker might be well-advised to help the patient walk safely while learning to ambulate with her condition.

One possible complication is the possibility of a similar problem occurring in a subsequent pregnancy. In general, the risk of complications is worst in the first pregnancy. However, the short mother/big baby pattern has a genetic basis, so this is possible. Thus, while this is not a genetic condition per se, the anatomical substrate involved in foot drop can be hereditary.

Patient counseling should include diet, especially for obese patients. Trying to walk safely with a foot drop is a serious problem, without obesity complicating the process.

Instructing the patient not to sit with the legs crossed is crucial, as this could exacerbate a foot drop, especially one due to compression of the common fibular nerve. Indeed, chronic leg-crossing over the years can result in a foot drop.[17]

Deterrence and Patient Education

Deterrence begins with awareness of the risk factors for obstetrical foot drop. Dealing with a short, obese patient with diabetes of pregnancy and a large baby should raise a concern about whether the delivery should be by cesarean section rather than vaginal delivery. 

Patient education should be focused first of all on reassuring the patient that her condition is likely to have a good prognosis if she follows the treatment protocol. Psychological counseling should be made available to help the patient cope with this most distressing development in her delivery.

The patient should be informed of the nature of her condition. Some discussion of the mechanisms that produced her foot drop can be provided if the patient desires it, but care should be taken to reassure her that her condition is NOT her fault.

On a practical note, the patient should be counseled NEVER to sit with her legs crossed, as this may exacerbate her condition.[17] If the patient is obese, dietary counseling should be part of her education. She should be made aware of the possibility that she might have another incident of foot drop in the delivery of a subsequent pregnancy.

Pearls and Other Issues

The key to proper recovery from obstetrical foot drop involves obtaining an accurate neurological diagnosis supplemented as necessary by an MRI and accurate documentation of the injury by electrophysiological analysis. MR neurography can be helpful in cases in which the diagnosis is in doubt.

The role of the L5 nerve root and its dermatome/myotome is a key to understanding foot drop. This can be injured by a herniated L4/L5 lumbar disc, a lesion of the lumbosacral plexus, the lumbosacral trunk, the common fibular nerve, and the deep fibular nerve, all of which carry the L5 nerve root.

Learning to walk with an obstetrical foot drop is a skill not easily mastered. Falling while trying to walk with a foot drop is an important concern in the recovery process. Physical therapy teaching the patient how to walk with her condition is essential. Orthotics and possibly the use of a walker can be helpful.

Physical therapy should be directed towards lengthening the plantar flexor muscles, so they do not worsen the foot drop because they are now much stronger relative to the dorsiflexors.

Make sure that the patient never again sits with her legs crossed. Sitting with the legs crossed for a number of years can cause a foot drop.[17]

Reassure the patient that if she follows the treatment protocol and avoids falling, she should recover within a year or so.

Patients with a foot drop will have difficulty walking on their heels.

Enhancing Healthcare Team Outcomes

Foot drop resulting from vaginal delivery is a catastrophic event regarding the patient's feelings. It converts what should be the happiest moment of the patient's life into a shocking event that takes away from the joy of the mother holding her newborn baby and may cast doubt in her mind that she will be able to care for her precious infant. An interprofessional team approach is the best result in treating obstetric foot drop.[28] 

The differential diagnosis and treatment of the patient's condition begins with her obstetrician, who will then want a consultation with a neurologist who can provide an accurate diagnosis. This process may involve a radiologist if an MRI is needed. The services of an electrophysiologist will be required to help provide a diagnosis based on accurate data concerning the location of the lesion that has caused the patient's foot drop.

Once a diagnosis has been obtained, the services of a physiotherapist will become essential. Nurses are a critical component of the team, as they monitor the patient's vital signs and help educate the patient and her family concerning the patient's condition and, indeed, her future. Nurses are in a position to offer support and encouragement as they interact with the patient from day to day.[29] 

The services of a prosthetist may be needed to provide the proper orthotic to help her walk and correct the foot drop. Thus the management of obstetrical neural injuries requires a carefully chosen interprofessional team. Careful coordination between the team members will ensure a successful outcome for the patient. Adding a psychiatrist to the interprofessional team may be appropriate for the occasional patient whose symptoms are inconsistent with the anatomical findings.[6]


Article Details

Article Author

Asa C. Black

Article Author

Shanna E. Williams

Article Author

Julie A. Holt

Article Author

Mason Jackson

Article Author

Karen Hawks

Article Editor:

Sunil Munakomi

Updated:

8/9/2022 11:58:01 PM

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