The current study is a case-control study that was done in the period from January 2015 to January 2016. The study included 70 patients presented with clinical and electrophysiological evidence of common peroneal neuropathy at the fibular neck (CPN) attending to Zagazig University Hospitals (Neurology, Rheumatology and 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, and 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.
Ethical consideration
A written consent was taken from all of the participants. The study was approved from the institutional ethics committee of the faculty of medicine, Zagazig University (ZU-IRB#4729\ 24-6-2016).
Inclusion criteria
Patients were eligible for inclusion in the study if they had clinical and motor electrophysiological evidence suggesting CPN according to [3].
Clinical evidence of CPN
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Numbness of the anterolateral 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
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Weakness of the leg muscles innervated by the peroneal nerve. The strength of the tibialis anterior (TA), extensor hallucis longus (EHL), and peroneus longus muscles was tested using the [10]
Electrophysiological motor localizing evidence of CPN [3]
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
Patients were excluded if any of the following was detected:
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Historical or clinical signs suggesting coexisting neurological conditions (e.g., polyneuropathy and motor neuropathy)
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Foot drop with symptoms, signs, or radiological findings of L5 radiculopathy in association with CPN
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Symptoms or signs suggesting systemic clinical illness like diabetes mellitus, renal failure, and hepatic failure
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Previous surgery for peroneal nerve
All patients included in the present study are subjected to:
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1-
Full history taking
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2-
Thorough clinical and neurological examination
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3-
Routine laboratories tests for exclusion of other systemic affection like diabetes mellitus, renal, or hepatic failure
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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 30 °C at the time of examination. The electrophysiological studies included the following:
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A-
Motor nerve conduction studies
Motor conduction study of the common peroneal nerve (ankle-fibular neck-popliteal fossa) and 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 (EDB). If the common peroneal CMAP was not evoked with EDB recording, CMAP was recorded over tibialis anterior (TA).
We considered that the lesion is axonal via axonal loss estimation [3]:
Axonal loss of the motor branch of the common peroneal nerve was estimated by comparing the CMAP amplitude recorded from the EDB on the affected and contralateral sides.
An estimate of EDB axonal loss was obtained from the formula (U -A)/U × 100
U: EDB response amplitude from the unaffected side.
A: (EDB response amplitude from the affected side.
Categorization based on the motor estimated axonal loss as follows:
No loss, < 50%.
Mild to moderate loss, 50–75%
Severe loss, > 75%
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B-
Sensory nerve conduction studies [11, 12]
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 [3]:
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No constant waveforms could be detected
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SPSP amplitudes < 5 μv or < 50% of the contralateral side
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Increased peak latency ≥ 4.4 ms (based on the standard distance of 14 cm)
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C-
Electromyographic study (EMG) was carried out using a concentric needle in the following muscles: extensor digitorum brevis (EDB), tibialis anterior, peroneus longus, tibialis posterior, extensor hallucis 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.
Radiological examination
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A)
Ultrasonographic assessment of patients and controls [13, 14]
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 patients’ 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 (Fig. 1).
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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 was done only if needed to rule lumbosacral affection.
Statistical analysis
Descriptive statistical methods were used to calculate means and standard deviation (SD). For comparisons with the continuous variables, Student’s t test was used. Comparison of categorical data was performed using the χ2 test and the Fisher exact test. Logistic regression analysis was used to calculate odds ratios (OR) and 95% confidence intervals (CI) for risk estimation. A p value of less than 0.05 was considered statistically significant. Intra-observer agreement was assessed using the kappa coefficient. Kappa value for intra-observer reproducibility was 0.73 indicating high reproducibility. From the measurements in our control group, we found the following cutoff value for an abnormally large peroneal nerve CSA at the fibular neck: 11 mm2. The sensitivity and specificity of sensory potentials and sonography were also assessed by a receiver operating characteristic (ROC) curve. Data were analyzed using statistical package of social science, version 14.0.0 software package (SPSS Inc., Chicago, Illinois, USA) [15].