Fig. 8

Entrapment of the deep and superficial peroneal nerves is illustrated: a–c Anterior tarsal tunnel syndrome in a 78-year-old who presented with persistent ankle and foot pain post talonavicular capsule and extensor retinacular sprain. The fat plane around the deep peroneal nerve is effaced as it courses through the anterior tarsal tunnel. Subfigures (a) and (b) are sequential axial PD slices showing the normal fat planes around the deep peroneal nerve (a—white circle) at proximal tunnel, before being surrounded and engulfed by the scar tissue more distally (b—yellow circle). On ultrasound (c), the longitudinal segment of the deep peroneal nerve is over 8 mm in diameter which is thickened (1.5 mm) and hypoechoic due to entrapment at the level of the anterior tarsal tunnel. Dorsal marginal osteophytes from midfoot osteoarthritis impinge on the anterior tarsal tunnel and cause deep peroneal nerve entrapment or irritation (blue arrows). d Targeted ultrasound of the superficial peroneal nerve. There is longitudinal thickening of the nerve (red arrow) as it passes through the crural fascia. This is 15 cm above the level of the ankle joint. This patient had a positive Tinel’s tap at the site of the nerve enlargement