Are you or some you know, suffering from the most common leg neuropathy?
Most common entrapment neuropathy in the legs is the Common Fibular Nerve (CFN) aka "Drop Foot."
· At the bottom of this blog is a small "Definitions" section for reference.
Disclaimer: In no, way, shape or form am I looking to create a diagnosis or counter a rendered diagnosis in your case. Please keep in mind that all information presented is only a small amount of accessible information to creating the true clinical picture for your unique case. You should always consult with your attending physician about your condition.
-Dr. Ryan Revels
Anatomy & Function
The Common Fibular Nerve & Its Function
Before we discuss what CFN neuropathy is, let's explore more about the CFN. The old naming of the CFN is recognized as the "Common Peroneal Nerve." The Federative Committee on Anatomic Terminology has renamed the peroneal nerve as the fibular nerve to prevent confusion between the peroneal and perineal nerves and to align the name with its counterpart, the tibial nerve. [9], as these are used interchangeably throughout many books, articles and teachings.
As the lateral column of the sciatic nerve, the CFN plays a huge role in the function of the lower extremities. The CFN branches off the sciatic nerve just above the popliteal fossa (back of the knee) (Figure 1). It courses laterally from the division to give it's only muscle innervation which is above the knee. This innervation supplies the short head of the biceps femoris muscle. All other innervation in the lower extremities occur below the knees and in the feet. As the remaining biceps muscles of the thigh are innervated by the medial branch of the sciatic nerve-the tibial nerve.
Figure 1. Common fibular nerve as it courses and produces the deep fibular nerve: Common Entrapment Neuropathies; Hobson-Webb Lisa D. M.D. and Juel, Vern C. M.D., FAAN. 2017.
As the CFN proceeds to the foot, it produces a few more branches. It commonly branches just below the fibular head-this bony prominence can be located by touching the lateral side of the knee and approximately 2" back from the kneecap (patella), and running your fingers approximately 2.5-3.5 inches below the knee cap.
The CFN wraps around the fibular shaft just below the fibular head (Figure 1). It's here the CFN is most vulnerable to impact trauma or chronic pressure/entrapment i.e., habitual leg crossing. [6] The nerve is most superficial at this point and is susceptible to compression. This is partly why the CFN is the most common lower extremity mononeuropathy. [6]
The CFN then dives back into the leg splitting which yields the superficial fibular nerve (SFN) and the deep fibular nerve (DFN).
The Deep Fibular Nerve
It's important to know that the lower region of the leg is divided into three separate compartments. [6]
These are the:
· Anterior
· Posterior
· Lateral
The deep branch of the fibular nerve produces motor (movement) innervation to the following muscles of the anterior compartment (Figure 1):
· Anterior tibialis
· Extensor digitorum longus
· Extensor halicus longus
· Peroneus tertius
· Extensor digitorum brevis
· First dorsal interossi [6]
The DFN has a single cutaneous (skin sensation) innervation this is the webbing of the first and second digits (toes) of the foot (Figure 1). This comes from the muscular branch of the deep fibular nerve to yield the cutaneous branch of the deep fibular nerve. Any physician reading this, it's unique in its own right, and it's important to acknowledge this for proper diagnostic criteria when differentiating neuropathies of the DFN, SFN and an L5 radiculopathy.
The Superficial Fibular Nerve
Contrast to the DFN, the SFN provides minimal motor innervation to the muscles of the leg and is highly sensory based (Figure 2).
Figure 2. The superficial fibular nerve provides motor innervation to the fibularis longus and brevis-annotated by yellow; cutaneous innervation of the dorsolateral surface of the leg, and the dorsal surface of the foot-annotated in purple. Common Entrapment Neuropathies; Hobson-Webb Lisa D. M.D. and Juel, Vern C. M.D., FAAN. 2017.
The superficial branch of the fibular nerve produces motor (movement) innervation to the following muscles of the lateral compartment (Figure 2):
· Fibularis longus
· Fibularis brevis
The superficial branch of the fibular nerve produces cutaneous innervation to the lower lateral region of the leg and the majority of surface of the foot (Figure 2).
How to identify if you may be currently experiencing or have experienced CFN neuropathy symptoms?
Symptoms of CFN neuropathy may include:
• Lateral lower leg pain
• Aching
• Burning
• Weakness
• Inability/decreased ability to lift foot up
• Inability/decreased ability to point sole of your foot out
• Numbness
• Tingling/Pins & Needles
This nerve branches off the sciatic nerve and is more commonly damaged due to how taut it is, and its superficial location in the leg.
Causes for CFN injury:
• Easily entrapped or damaged by
• Trauma/impact
• Endocrine/metabolic disorders [1]
• Alcoholism [1]
• Diabetes [1]
• Vitamin B deficiencies [1]
• High Ankle Sprains [2,3]
• Habitual Leg Crossing [4]
. . . just to name a few!
Fibular nerve disease may be misdiagnosed as L5 (nerve root) radiculopathy leading to inappropriate conservative care, unnecessary prescription or back/spinal surgery. [5]
Studies & Case Reports
The purpose of these following studies is to give depth to the understanding of how CFN neuropathy manifests, ways it's treated, and diagnostic processes and therapeutics used in case management.
Article 1: Peroneal Neuropathy Misdiagnosed as L5 Radiculopathy: A Case Report.[5]
Summary:
53-year-old registered nurse who was referred to a chiropractic office in August 2003 by her primary care physician with a chief complaint of leg pain. MRI findings revealed degenerative disc disease, posterior disc bulging facet arthropathy at L5-S1 resulting in moderate left foraminal stenosis (narrowing). X-ray findings revealed mild hip osteoarthritis. Following conservative care did not mitigate symptoms, as the patient followed-up with a neurosurgeon in Jan 2003.
Neurosurgeon diagnosed the patient with L5 radiculopathy. She continued with physical therapy, anti-inflammatory medications and received three epidural injections which provided mild relief. Symptoms persisted as she underwent elective left L5-S1 hemilaminectomy (definition provided) [7] with discectomy [definition provided, (video provided)].
The patient reported no improvement post-surgical intervention.
Follow-up MRI revealed a large fluid collection that extended from the spinal canal through the laminectomy defect, and into the spinal canal through the defect and into the subcutaneous tissue. She underwent a second surgery three weeks after the first surgery to repair a cerebral spinal fluid leak, and recurrent extruded disc at L5-S1.
Patient returned for follow-up chiropractic examination where she was observed crossing her legs throughout process. She was instructed to stop crossing her legs, and six days later she reported less pain along her left lateral leg and was sleeping better. She was followed for two months and discharged at that time symptom free.
The importance of this case study is differential diagnosis between a L5 radiculopathy and fibular neuropathy. The patient's sensory complaints, exam findings and imaging mimicked a L5 radiculopathy. There are indications however, pointing to a fibular neuropathy which included weakness with foot eversion along with dorsiflexion and toe extension. More so, tenderness over the fibular neck and peroneal tunnel with a history of increased pain upon ankle inversion and relief upon eversion.
Ideally, electrodiagnostic testing would have been performed prior to the second surgery and would have essentially ruled out lumbar spine involvement. Additionally, an EMG/NCV may have provided a more conclusive diagnosis of peroneal neuropathy.
Article 2: Compressive Peroneal Neuropathy During Harvesting Season in Indian Farmers [3]
Summary: The common peroneal nerve is susceptible to compression at its entrance into the fibular tunnel under the fibrous fibular arch, and as it courses superficially around the fibular neck. Most peroneal palsies are unilateral (one-sided). Causes of compression include prolonged squatting, compression by cast, bony callus, fracture, anorexia nervosa. The deep peroneal nerve is more severely affected than the superficial branch because of its topographic location.
Although these lesions (injuries) maintain a male predilection (male: female, 2.8:1), this predominance was not evident in this study. Also, this neuropathy was noted more prevalent in those with slim frames. The unique habit for these Indian farmers to squat more than 5-hours a day, they would propel themselves forward with their right leg--this is the belief behind the dominance of CPN neuropathy to manifest in the majority of the left lower extremities of the Indian farmers.
Most lesions recovered completely within 3-6 weeks. Two more lesions recovered after 9 weeks; two patients had incomplete recovery at the end of 3 months, they were offered surgical decompression, but refused as the had partially recovered. These two had complete recovery in 16-20 weeks. Vastamaki reported that spontaneous recovery could take 18-24 months. [8]
All our patients recovered completely on conservative treatment, and we feel these cases of 'harvesting palsy' should be managed non-surgically, except when the electrophysiological studies show total axonal lesions or when recovery has not started 12 weeks' time.
Article 3: Foot Drop [9]
Summary:
Definition: foot drop is defined as severe weakness of ankle dorsiflexion (extension) with intact plantar flexion. It should be distinguished from a flail foot in which there is no or minimal ankle or foot movement in all directions, including severe weakness of ankle dorsiflexion, plantar flexion, and intrinsic foot muscles. In contrast to a flail foot, voluntary movement at or distal to the ankle occurs in foot drop due to intact plantar flexion and intrinsic foot muscles.
Etiology (cause): foot drop is a direct effect of tibialis anterior muscle weakness. It is often associated with weakness of toe extension due to weakness of the extensor hallucis and extensors digitorum longus and brevis.
Fibular (Peroneal) Neuropathy (Table 1): Fibular neuropathy is a common cause of foot drop and is the most common compressive neuropathy in the lower extremity. The most common site of fibular nerve compression is at or near the fibular neck. However, more distal lesions affecting the deep and superficial fibular nerves as well as proximal common fibular nerve lesions do occur less commonly
L5 radiculopathy (Table 1): is the most common lower extremity radiculopathy. This is partially due to long course of the L5 root within the cauda equina rendering it (along with the S1 root) susceptible to compression at multiple spinal levels. Although ankle and toe dorsiflexor weakness is common in patients with L5 radiculopathy, overt foot drop may be the presenting complaint in patients with severe L5 radiculopathy, associated with significant motor axon loss or segmental demyelination. With L5 root lesions, there is additional weakness of foot inversion and toe flexion that is not present in fibular nerve lesions.
Sciatic Neuropathy (Table 1): Partial sciatic nerve lesions usually affect the lateral division (fibular nerve) more than the adjacent medial division (tibial nerve), due to greater vulnerability of the fibular division of the sciatic nerve to physical injury. This often presents a diagnostic challenge because they imitate a distal selective fibular nerve injury due to compression at the fibular head. Although the neurological history is useful such as with a history of a gluteal injection or gunshot wound, the examiner should look for signs caused by tibial nerve involvement. Common manifestations of sciatic nerve involvement, which are inconsistent with a fibular neuropathy at the fibular head, include severe foot pain, a unilaterally absent or depressed ankle jerk, weak ankle inversion, or sensory loss in the sole.
*Foot Drop B Katirji, Case Western Reserve University, Cleveland, OH, USA; and University Hospitals Case Medical Center, Cleveland, OH, USA r 2014 Elsevier Inc.
Table 1. Differential diagnosis of common causes of foot drop. Foot Drop B Katirji, Case Western Reserve University, Cleveland, OH, USA; and University Hospitals Case Medical Center, Cleveland, OH, USA r 2014 Elsevier Inc.
Conservative Care or Surgery?
I've given you a lot of information to read through, study and even watch. It's my full intentions to empower you the patient or doctor brushing up on the subject, with information that will allow you to make sense of what your experiencing or aid a doc having difficulties making a diagnosis, and what to chose next in the care of your patient(s). If you're a patient or a curious reader, hopefully this gives you insight for an initial exam or the next visit.
What does all the information from the above articles tell? In short, describing a neuropathy isn't as straight-forward, and the accompanying symptoms of CFN neuropathy has many layers which need to be systematically uncovered to isolate the true cause. Some key points to acknowledge is that it's important to have the correct diagnosis established to render proper care.
Article 1:
We see the misfortune of a hemilaminectomy followed by a discectomy in the first article where the final diagnosis and care was conservative care for CFN mononeuropathy. The complexity in that case involved the belief of an L5 radiculopathy. It's important for the doctor to evaluate all aspects of their MRS (muscle/reflex/sensory) findings to differentiate between an L5 radiculopathy or a CFN mononeuropathy. As the care protocols may heavily vary.
Article 2:
In the second article we see that chronic habits, and sometimes something as simple as squatting or crossing of the legs can have some very unwanted outcomes. We also learn that the recovery time for this specific cause, is relatively short, and provided 100% recovery through conservative care.
Article 3:
Summarizes the anatomy and the clinical correlations between the CFN, L5 radiculopathy and sciatic neuropathy. This article is geared toward the physicians reading through this blog, and gives a great reference with the table provided for an algorithm which may aid in proper diagnosis. The table provides profound historical information to correlate with onset, pain presentation and other symptoms which will provide for identification of what type of neuropathy your patient presents with.
It's important to note that conservative care may not be the answer for your case as a current patient or potential patient suffering from CFN neuropathy. In the event EMG findings indicate axonal loss, vice a demyelinating (definition provided) neuropathy, surgical intervention may be highly considered or recommended by your attending physician.
Proper Diagnosis IS The Difference
• Ideally electrodiagnostic (EMG) testing would essentially rule out lumbar spine involvement. [5]
• EMG can establish relevance, location, causes and timing of nerve injury. [5]
• EMG should be used in the event a patient does not improve with treatment. [5]
I'd love to hear your thoughts and answer any questions! Thank you for reading and check back for future blogs.
If you have any topics, you'd like for me to cover, please email me at info@syn-ndx.com, or find me on Facebook at @SynapseNDx
Best wishes in mind, body and soul,
Ryan Revels DC, DIBE
Definitions
Discectomy
· A discectomy (or diskectomy) is performed on the discs of the spine. The procedure removes the herniated portion of a vertebral disc. The vertebral discs are the spongy tissue between the vertebrae that function as shock absorbers for the spine.
Demyelination
· A demyelinating disease is any condition that results in damage to the protective covering (myelin sheath) that surrounds nerve fibers in your brain, optic nerves and spinal cord. When the myelin sheath is damaged, nerve impulses slow or even stop, causing neurological problems.
Hemilaminectomy
· A hemilaminectomy is a spine surgery that involves removing part of one of the two laiminae on a vertebra to relieve excess pressure on the spinal nerve(s) in the lumbar spine, or lower back. A hemilaminectomy can be performed to relieve symptoms such as back pain and radiating leg pain.
Neuropathy
· Disease or dysfunction of one or more peripheral nerves, typically causing numbness or weakness.
Radiculopathy
· Irritation of or injury to a nerve root (as from being compressed) that typically causes pain, numbness, or weakness in the part of the body which is supplied with nerves from that root.
Videos
N/A
References
1. Focal Peripheral Neuropathies: doi.org/10.1002/ana.410250123
2. Peroneal nerve Palsy due to rare reasons: https://www.researchgate.net/publication/8647507_Peroneal_nerve_palsy_due_to_rare_reasons_a_report_of_three_cases
3. Compressive peroneal neuropathy during harvesting season in Indian farmers: doi.org/10.1177/004947550403400424
4. Peroneal mononeuropathy: https://emedicine.medscape.com/article/1141734-overview
5. Peroneal Neuropathy misdiagnosed as L5 radiculopathy: a case report: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3662609/pdf/2045-709X-21-12.pdf
6. Hobson-Webb, Lisa D. MD., Juel, Vern C. MD., FAAN. Common entrapment neuropathies: Review Article, Continuum. Department of Neurology, Duke University Medical Center. 2017, American Academy of Neurology. Pgs. 502-505. https://renaissance.stonybrookmedicine.edu/sites/default/files/Common_Entrapment_Neuropathies_12.pdf
8. Vastamaki, Martti. Decompression for peroneal nerve entrapment: Acta Orthop Scan 1986;57:551-4. https://www.tandfonline.com/doi/pdf/10.3109/17453678609014792
9. B Katirji. Foot Drop. Western Reserve University, Cleveland, OH, USA; and University Hospitals Case Medical Center, Cleveland, OH, USA r 2014 Elsevier Inc. https://www.researchgate.net/publication/323813432_Foot_Drop
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