Sensory Potentials and Ultrasonography in Common Peroneal Mononeuropathy
Sensory Potentials and Ultrasonography in Common Peroneal Mononeuropathy
Common peroneal mononeuropathy at the fibular neck (CPN) is one of the most frequent
 mononeuropathies of the lower extremities.

 The common peroneal nerve sub serves sensation to the dorsum of the foot and toes. In CPN
 motor fibers of the deep peroneal nerve are more frequently affected than those of the
 superficial peroneal nerve. Fascicles of the deep branch of the common peroneal nerve are
 more anteriorly located and more vulnerable to injury than those of the superficial peroneal
 branch. The clinical and electrodiagnostic findings in CPN resemble the anatomical structure
 of the common peroneal nerve, indeed fibers for the deep peroneal nerve and the superficial
 peroneal nerve are bounded in separate fascicles along the course of the nerve.

 Superficial peroneal nerve sensory potential (SPSP) should be performed to localize the site
 of injury.

 Electrodiagnostic testing is used widely to evaluate the function of the common peroneal
 nerve. SPSP have been examined in CPN with conflicting results. A loss in amplitude of this
 response implies some axonal loss affecting either the common peroneal nerve or its
 superficial branch. Prominent axonal loss is the hallmark of most CPN lesions and suggested
 that abnormalities in sensory nerves mirror those in motor nerves.

 Moreover, assessment of the structure of the common peroneal nerve is likely to improve the
 diagnostic yield" by using high-resolution ultrasonography. Ultrasound imaging is painless,
 does not expose the patient to radiation, and has several advantages compared with magnetic
 resonance imaging in the laboratory setting, including reduced cost, accessibility, ability
 to image the entire length of the nerve in a single study, and the ability to image both
 statically and dynamically.

 This study was conducted to evaluate the superficial peroneal sensory potential and
 high-resolution ultrasonography role in confirmation of common peroneal mononeuropathy at the
 fibular neck.
The current study is a case control study that was done in the period from January 2015 to
 January 2016. The study included 70 participants presented with clinical and
 electrophysiological evidence of common peroneal neuropathy at the fibular neck (CPN)
 attending to Zagazig University Hospitals (Neurology, Rheumatology& Rehabilitation, and
 Orthopedic departments) and insurance hospitals of Sharkia governorate (47 male and 23
 female). Their age (mean ± SD/years) was 40.4± 12.9, the duration between the onset of
 symptom and enrollment in the study ranged between 21 days to 6 months. Seventy (45 males and
 25 females) apparently healthy volunteers were included as controls, and their age (mean ±
 SD/ years) was 41.3 ± 11.8. They were selected from the persons attending to blood bank for
 blood donation.

 All participants included in the present study are subjected to:

 1. Full history taking.

 2. Thorough clinical and neurological examination.

 3. Routine laboratories tests for exclusion of other systemic affection like diabetes
 mellitus, renal or hepatic failure.

 4. Electrodiagnostic studies

 All tests were done in the same room, at the time of clinical diagnosis using a Nicolet
 Viking Quest cart electrodiagnostic system. Lower extremity temperature was maintained
 at or above 30º C at time of examination. The electrophysiological studies included the
 following:

 A-Motor nerve conduction studies:

 Motor conduction study of the common peroneal nerve (ankle-fibular neck -popliteal
 fossa), tibial motor nerve conduction study were performed with surface disc recording
 electrodes for the affected limb and the contralateral limb in all subjects. Evaluations
 of both upper limbs were added to exclude more wide lesions if suspected.

 Common peroneal CMAPs were recorded over extensor digitorum brevis and tibialis
 anterior.

 Investigators considered that the lesion is axonal via axonal loss estimation:

 Axonal loss of the motor branch of the common peroneal nerve was estimated by comparing
 the CMAP amplitude recorded from the extensor digitorum brevis on the affected and
 contralateral sides.

 An estimate of EDB axonal loss was obtained from the formula (U -A)/U ×100 U : (extensor
 digitorum brevis response amplitude from the unaffected side).

 A : (extensor digitorum brevis response amplitude from the affected side).

 Categorization based on the motor estimated axonal loss as follow:

 No loss: (<50%). Mild to moderate loss: (50-75%). Severe loss: (>75%).

 B- Sensory nerve conduction studies:

 Antidromic evaluation of the superficial peroneal nerve sensory potential (SPSP) at the
 ankle was studied with surface stimulating and recording electrodes on the affected limb
 and the contralateral limb in all subjects. The site of stimulation was just anterior to
 the edge of the shaft of the fibula and 14 cm proximal to the active ankle electrode.
 The active recording electrode was placed midway between the edge of the tibia and the
 tip of the lateral malleolus or 3 cm proximal to the bimalleolar line. The reference
 recording electrode was placed 3 cm distal to the active electrode.

 SPSP was considered affected when any one of the following is detected :

 -  No constant wave forms could be detected.

 -  SPSP amplitudes < 5 μv or < 50% of the contra lateral side.

 -  Increased peak latency ≥ 4.4 ms (based on standard distance of 14 cm).

 C-Electromyographic study (EMG) was carried out using concentric needle in the following
 muscles: extensor digitorum brevis (EDB), tibialis anterior, peroneus longus, tibialis
 posterior, extensor halucis longus, short head of biceps femoris, vastus lateralis,
 medial head of gastrocnemius, iliacus, gluteus medius, tensor fascia lata and Paraspinal
 muscles. Concentric needle EMG was performed in all patients. Spontaneous and voluntary
 motor unit activity was assessed.

 5. Radiological examination:

 A) Ultrasonographic assessment of participants:

 Ultrasonographic examination by radiologist was conducted with a General Electric Logiq 7 Pro
 machine (GE Healthcare, Chalfont St Giles, England), using a 5- to 12-MHz linear array
 transducer. The cross sectional area (CSA) of the common peroneal nerve was determined within
 the echogenic rim surrounding the nerve at the level of the fibular neck with the probe
 perpendicular to the main nerve course in the transverse and longitudinal plane. The
 sonographic measurements were done on the same day or within 1 week after the
 electrodiagnostic studies.

 The radiologist was blinded to the participants' electrophysiological study data. However,
 the radiologist was aware of the clinical and electrophysiological suspicion for common
 peroneal neuropathy.

 Authors of the present study considered that common peroneal nerve is affected by the
 sonographic measurements if the value of CSA of the common peroneal nerve at the fibular neck
 was >11 mm2 according to the study control group.

 B) Plain radiographs were done to detect the underlying traumatic injuries, such as a
 proximal fibular head fracture or osseous tumors, or in assessing the severity of angular
 deformities about the knee. Lumbosacral plain X ray or MRI were done only if needed to rule
 lumbosacral affection.
Inclusion Criteria:

 -  Participants were eligible for inclusion in the study if they had clinical and motor
 electrophysiological evidence suggesting common peroneal mononeuropathy at the fibular
 neck

 Clinical evidence of common peroneal mononeuropathy at the fibular neck:

 -  Numbness of the antero lateral aspect of the lower limb from about midway between the
 knee and the ankle, most of the dorsal aspect of the foot and toes and the web space
 between the first and second toes.

 -  Weakness of the leg muscles innervated by the peroneal nerve. The strength of the
 tibialis anterior (TA), extensor hallucislongus (EHL), and peroneius longus muscles
 was tested using the Medical Research Council (MRC) rating scale.

 Electrophysiological Motor localizing evidence of common peroneal mononeuropathy at the
 fibular neck:

 Peroneal motor nerve conduction velocity decrement ≥10 m/s across the fibular neck segment;
 or focal conduction block, defined as compound motor action potential (CMAP) amplitude and
 area reduction ≥ 50% across the fibular neck segment.

 Exclusion Criteria:

 -  Participants were excluded if any of the following was detected:

 -  Historical or clinical signs suggesting coexisting neurological conditions (e.g.
 polyneuropathy and motor neuropathy).

 -  Foot drop with symptoms, signs or radiological findings of L5 radiculopathy in
 association with CPN.

 -  Symptoms or signs suggesting systemic clinical illness like diabetes mellitus,
 renal failure, and hepatic failure.

 -  Previous surgery for peroneal nerve.