Journal of Foot and Ankle Surgery (Asia Pacific)

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VOLUME 10 , ISSUE 3 ( July-September, 2023 ) > List of Articles


Identification of the Superficial Peroneal Nerve: Is the Ankle Plantar Flexion Fourth Toe Flexion Sign Useful in a South-East Asian Population?

Yuet Peng Khor, Manu J Abraham, Audrey WC Tan, Christopher J Pearce

Keywords : Fourth toe flexion sign, Observational study, Superficial peroneal nerve

Citation Information : Khor YP, Abraham MJ, Tan AW, Pearce CJ. Identification of the Superficial Peroneal Nerve: Is the Ankle Plantar Flexion Fourth Toe Flexion Sign Useful in a South-East Asian Population?. J Foot Ankle Surg Asia-Pacific 2023; 10 (3):119-122.

DOI: 10.5005/jp-journals-10040-1302

License: CC BY-NC 4.0

Published Online: 07-07-2023

Copyright Statement:  Copyright © 2023; The Author(s).


Aim and background: Iatrogenic injury to the superficial peroneal nerve (SPN) can occur during surgery on the foot or ankle. The purpose of the study was to evaluate the prevalence of the SPN clinically when using the ankle plantar flexion fourth toe flexion sign in our local population. Materials and methods: Between August and November 2020, all new patients between 21 and 70 years of age who attended our foot and ankle specialist clinic were invited to participate in the study. Participation was voluntary, and individuals with a history of surgery to the foot were excluded from the study. Volunteers were provided with a patient information leaflet and asked to complete an anonymous questionnaire with details of their age, sex, weight, height, race, shoe size, and weekly sports participation. Their feet were then examined by a consultant foot and ankle surgeon to record the presence of the SPN. The SPN can be identified by flexing the fourth toe with the ankle in plantar flexion and inversion (Fig. 1). This was recorded as either visible, not visible but palpable, or absent. Results: A total of 154 volunteers were recruited for the study (male = 93, female = 61). The SPN was visible in 35% (n = 54) of patients. In those patients where the nerve was not visible, another 14 patients had the nerve identified by means of palpation. In total, the nerve was identifiable 44% of the time on clinical examination. Body mass index (BMI) (p = 0.01) and sports participation (p = 0.011) were significant determinants of whether the nerve was clinically identifiable. Age, sex, shoe size, and race did not differ between the groups where the SPN was identifiable clinically. Conclusion and clinical significance: The ankle plantar flexion fourth toe flexion sign is a useful clinical sign to identify the SPN when planning incisions over the foot or ankle during surgery to reduce the chance of iatrogenic injury. This sign can aid in identifying the nerve in 44% of our local population. A lower BMI and the population who participated in sports were factors associated with identifying the nerve.

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