Postoperative peroneal nerve palsy after ENT surgery: A case report

Abstract Postoperative peroneal nerve palsy mostly occurs under general anesthesia. Here, we report a rare case of an 11-year-old girl with peroneal nerve palsy following ENT surgery in the supine position under general anesthesia. Further, we describe the etiology and pathogenesis of peroneal nerve palsy post-operation in the supine position. Finally, it was concluded that clinicians need knowledge to prevent postoperative peroneal nerve palsy following surgery.


Introduction
While a patient loses sensation and consciousness under general anesthesia, we must not only ensure its safety, but also pay attention to its potential complications [1].Common postoperative neurological complications include delirium, postoperative cognitive dysfunction, stroke, spinal cord ischemia, and postoperative visual loss [2].The prevalence of peroneal nerve paralysis following anesthesia is estimated to be .02%[3], especially following head and neck surgery.Postoperative peroneal nerve palsy usually occurs spontaneously.The absence of timely detection, a standardized diagnosis, and treatment may lead to physical disabilities [4].The recovery of peroneal nerve function may be very slow, and potentially incurable, making it a potential adverse event [5].All doctors, nurses, patients, and caregivers should be educated on how to prevent postoperative peroneal nerve palsy [6].

Case report
An 11-year-old girl diagnosed with congenital cholesteatoma underwent postauricular mastoidectomy via a microscopic approach under general anesthesia to clear the cholesteatoma.There were no intraoperative difficulties or excessive bleeding.Anesthesia monitoring data were as follows: temperature: 36.2-36.4°C, respiratory rate: 21/min, heart rate: 107/min, blood pressure: 87/54 mmHg, oxygen saturation: 99%.The operation lasted for more than four hours in the supine position.During the operation, the operating table was tilted to the left by roughly 15 degrees for approximately 30 min due to the exposure of the surgical field.The patient had no history of diabetes, tumors, or immune system and nervous system diseases.She was admitted to the hospital on foot, with a body mass index (BMI) of 17 kg/m 2 , with no abnormalities found in her routine preoperative tests.On the first day after the operation, the patient reported numbness in the left lower limb and dorsum of the foot, difficulty in walking, and no pain.Physical examination revealed that the sensation of the anterolateral aspect of the left lower limb and the dorsum of the foot was significantly weakened, the left foot dropped, and a cross-threshold gait was seen (Video 1).We urgently consulted with a neurologist.The power strength of the foot was 1 according to the Medical Research Council grading, and the patient was diagnosed with postoperative peroneal nerve palsy.Oral mecobalamine at a dosage of .5 mg (specification: .5 mg/tablet, batch number: 2220648) was prescribed thrice a day for 3 months.Peroneal nerve block was confirmed by electromyography 6 days after the operation.Nerve conduction study showed conduction block with a decrease in amplitude and prolonged latency on proximal stimulation of the peroneal nerve while distal conduction parameters are normal.
It suggested that there was a conduction abnormality in the proximal part of the nerve around the fibular head (Figure 1).The patient and her parents refused acupuncture, limb physiotherapy, and foot orthotics.The patient had fully recovered 5 months after the operation and the peroneal nerve conduction parameters became normal (Figure 2 and Video 2).In this case, risk factors for the development of postoperative peroneal nerve palsy may have been the inclination of the operating table, the long operation time, hypothermia, and a low BMI.

Discussion
Postoperative peroneal nerve palsy is more common following spinal and lower extremity surgeries.Since it mostly occurs in the lithotomy position, it occasionally occurs after colorectal and gynecological surgery and is rare in other surgeries [7].Postoperative peroneal nerve palsy is the most common lower extremity position-related peripheral neuropathy, mainly manifesting as decreased or lost sensation in the anterolateral and dorsum of the lower extremity, foot drop, and gait disturbance [8].The lithotomy position is a non-physiological position.However, both lower limbs are in a neutral position (physiological position) in the supine position.If the lower limbs are not immobilized properly, there may be a pathological position in which the lower limbs are excessively abducted or one leg compresses the other leg.The peroneal nerve is prone to compression and traction.
Ischemia caused by entrapment or traction is believed to be the primary mechanism of peripheral nerve palsy under general anesthesia [9].The peroneal nerve runs superficially on the surface of the fibular head and is the most commonly prone to injury.Under general anesthesia, patients lose consciousness with their lower limbs in a pathological position for a long time.Further, reduced muscle tone, blood flow due to compression of blood vessels feeding the peroneal nerve, nutrient and oxygen supply, and demyelination or even damage to the axon of peroneal nerve is seen in postoperative peroneal nerve palsy [10].
In addition, hypothermia promotes the growth of peroneal nerve vasospasm, ischemia and hypoxia, and leads to peroneal nerve paralysis [11].Low BMI causes a lack of necessary muscle protection to the peroneal nerve which may lead to peroneal nerve paralysis [12].To avoid similar complications following surgery, sponges can be placed on both sides of  the knee to place the patient in a more physiological position, warm fluids can be administered to prohibit hypothermia, and the nerves can be monitored for evidence of a decrease in amplitudes, latencies, and nerve conduction velocities in the fibular capitulum up-down.

Conclusions
In conclusion, postoperative peroneal nerve palsy is a recognized perioperative complication.It is not related to the surgical method being used and the technique of the surgeon.It may be caused by entrapment or compression of the peroneal nerve.Therefore, clinicians need to be educated on how to prevent postoperative peroneal nerve palsy.

Figure 1 .
Figure 1.nerve conduction graphs showing conduction block with decrease in amplitude and prolonged latency on proximal stimulation of peroneal nerve while distal conduction parameters are normal.

Figure 2 .
Figure 2. nerve conduction graphs of the peroneal nerve stimulation showing the amplitudes, latencies, and nerve conduction velocities which returned to normal values.