PMC7372091_01
Clinical findings of the right foot. (a) Paresthesia and sensory disturbance in the lateral and calcaneal parts of the sole (shaded area). (b) Tinel sign (arrow) was recognized over the swelling (dotted line) posterior to the medial malleolus.
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Paresthesia and sensory disturbance were recognized on the lateral and calcaneal parts of the right sole (Fig. 1a). There was a positive Tinel sign over the swollen tarsal tunnel (Fig. 1b).
Ultrasound images of the right medial ankle visualized by the probe with a short axis view. (a) At the site over the swelling posterior to the medial malleolus, a hypoechoic space occupying lesion (SOL) was observed. (b) At the site just proximal to the SOL. N (arrow): tibial nerve, A: posterior tibial artery, V: posterior tibial vein. Dashed arrow: planned route for insertion of the needle. The needle was to be inserted toward the tibial nerve without penetrating the SOL and vessels. The depth, from the tip of the needle to the target nerve, was measured as 7 mm based on the ultrasound image.
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TTS. The ultrasound image demonstrated a hypoechoic SOL posterior to the medial malleolus (Fig. 2a). A hypoechoic, clear cystic SOL was identified (Fig. 2a). Ultrasound imaging visualized the posterior tibial nerve, along with the posterior tibial artery and the two posterior tibial veins (Fig. 2b). At the same time, the distance between the insertion site and the nerve was measured (Fig. 2b).
Needle insertion using the ultrasound-assisted near nerve method. The needle electrode was inserted at the site chosen from the ultrasound image. The scale on the side of the probe gave information regarding the depth of the inserted needle.
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A scale was attached on the side of the ultrasound probe, so that we could recognize how far the tip of the needle was moved under the skin (Fig. 3).
Nerve conduction study using ultrasound-assisted near nerve method. Dis: distance (mm), CV: conduction velocity (m/sec) Upper trace: mixed nerve conduction study of the medial plantar nerve with stimulation of the medial sole. Middle trace: mixed nerve conduction study of the lateral plantar nerve with stimulation of the lateral sole. The compound nerve action potential of the nerve on the affected side (Right) was absent. Lower trace: sensory nerve conduction study of the medial plantar nerve with stimulation of the big toe. Temporal dispersion of the sensory nerve action potential was apparent on the affected side. Dispersion of the potential was recognized only on the right side (Fig. 4, lower trace). The amplitude of the potential on the affected side was not lower than that on the normal side.
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In the mixed NCS of the medial plantar nerve on the affected side (Right), the conduction velocity and the amplitude showed no significant differences compared with those on the healthy side (Left) (Fig. 4, upper trace). On the contrary, in the mixed NCS of the lateral plantar nerve, the nerve action potential was absent (Fig. 4, middle trace). In the sensory NCS, dispersion of the potential was recognized only on the right side (Fig. 4, lower trace).