Abstract
Background: High frequency ultrasound (US) is widely used as the modality of choice when examining nerves in the human body. It is an inexpensive imaging modality with a flexible field of view through which a nerve can be easily traced. Tarsal tunnel syndrome (TTS) is a rare and sometimes underdiagnosed disease affecting the posterior tibial nerve (PTN) at the medial aspect of the ankle causing debilitating pain when left untreated. Currently, there exists no protocol, backed by a research determined cut-off cross sectional area reference value, for diagnosing TTS. Previous studies across several countries with different ethnical groups have shown that an ultrasound cross-sectional area reference (CSA) of 0.06 cm2, 0.07 cm2, 0.10 cm2 and 0.12 cm2 respectively be suggested as a cut-off value in diagnosing TTS. The aim of this study was to test the specific cut of value for a normal posterior tibial nerve to diagnose TTS amongst people of different race in Pretoria, South Africa.
Methods: In a multi-ethnic population of 60.14 million people in South Africa (Black African - 76.4%, Coloured - 8.9%, Indian - 2.5% and White - 9.1% respectively), detailed ultrasound measurements of both ankles on 112 participants were performed and ethnic age, gender and body mass index (BMI) were assessed. The posterior tibial nerve was measured along its course and a mean measurement was recorded.
Results: It is evident that the primary variables (age, gender and BMI) of this study are considered to affect the CSA measurement of the PTN which will aid in the early diagnosis of TTS. Inferential statistics demonstrated that there is a correlation between age and the PTN with a p-value < 0.05. From the data obtained it could be expected that the higher the age, the higher the PTN measurement. A similar appearance occurred with the correlation between BMI and the PTN with a p-value < 0.05. It seems that with an increase in BMI, a larger PTN measurement will occur. In this study, a mean CSA measurement of 0.10 cm2 across all racial groups could be used as a cut-off value for a normal PTN at the ankle. Conclusion: The results obtained revealed that, with increase in age and BMI, a greater PTN measurement would occur. Race appeared to be a contributing factor, but further research is needed as the sample sizes for the different racial groups differed substantially. The reference (cut-off) CSA value for normal PTN for consideration during a basic musculoskeletal ultrasound exam protocol in South Africa, should be 0.10 cm2.