Safety and efficacy of ultrasound-guided percutaneous flexor retinaculum release of the ankle: an anatomical study

Abstract

Background: Tarsal tunnel syndrome (TTS) is a condition in which the tibial nerve (TN) (or its terminal branches) is compressed by the flexor retinaculum (FR) and the deep fascia of the abductor hallucis muscle at the tarsal tunnel, causing symptoms that negatively impact the patient's quality of life, including numbness, a sensation of a foreign object, coldness, and pain. FR release via microtrauma using needle-knife has proven to be effective in China and is widely used by clinicians. The traditional acupotomy, however, is the "blind knife" treatment, which cannot guarantee patient safety due to risk of injury to important structures, particularly the neurovascular bundle. Compared with the conventional treatments, ultrasound-guided percutaneous FR release possesses noteworthy advantages including high efficacy and safety.

Methods: Percutaneous release of the FR was performed on 51 formalin-fixed specimens. The specimens were divided into two groups: an ultrasound-guided acupotomy pushing group comprising 20 legs (group U) and a nonultrasound-guided acupotomy pushing group comprising 31 legs (group N). After high-frequency ultrasound exploration, those with clear vascular imaging were included in group U; otherwise, they were included in group N. The FR was released percutaneously, soft tissue was dissected layer by layer, and anatomical data were recorded.

Results: There no cases of injury in group U (0%) and four in group N (12.9%). Among the different intervention methods, there were no significant differences in tissue injury types (χ²=2.80; P=0.09). The percentage of released FR in group U was 80.00% while that in group N was 61.29% (χ²=1.977; P=0.16), which did not represent a significant difference between the two groups. However, group U had a significantly greater release length than that in the group N (t=3.359; P=0.002), indicating that the flexor release length guided by ultrasound is significantly greater than the unguided one.

Conclusions: Ultrasound-guided percutaneous release of the FR using a needle-knife can provide greater length and percentage of released FR while maintaining a comparable safety rate to the unguided procedure.

Keywords: Acupotome; anatomy; percutaneous release; tarsal tunnel syndrome (TTS); ultrasound-guided technique.

Figure 1

Images of the acupuncture needle, injector needle, and acupotome needle.

Figure 2

Actual anatomical diagram of the anatomical landmarks points, including three imaginary reference lines and the needle entry point. Group U, ultrasound-guided small needle-knife pushing group; DML, Dellon-McKinnon malleolar-calcaneal line; DML-P, a line beginning 10 mm proximal to the Dellon-McKinnon malleolar-calcaneal line; DML-D, a line which started 10 mm distal to the DML; A, the tip of the medial malleolus; B, the calcaneus’ center, a calcaneal tubercle’s tip located at the greatest distance from the medial malleolus.

Figure 3

Ultrasound image of needle knife operation in group U (original figure). The shaded blue area is the flexor retinaculum. △: the cylindrical needle body of the needle-knife. Group U, ultrasound-guided small needle-knife pushing group; PTA, posterior tibial artery; MI, mechanical index; TIS, thermal index of soft tissue; OM, Omni; C, the third of all nine maps (A-I); H, high frequency; TV, TeraVision; Gn, gain; DR, dynamic range.

Figure 4

The image of the needle-knife operation of group N. ① The flexor retinaculum, ② the high-frequency ultrasound probe, ③ the needle knife, ④ the skin, and ⑤ the needle tip. Group N, nonultrasound-guided small needle-knife pushing group. A, the tip of the medial malleolus; B, center of the calcaneus; D, the distal end of the flexor retinaculum; L, the length of the flexor retinaculum; P, the proximal end of the flexor retinaculum; W, the width of the flexor retinaculum; S, skin; ∠_S-Z, the angle of the needle to the skin; ∠_AB-Z, the angle of the needle-knife and the line of the DML; D_A-N, the shortest distance between the point A and the point N; DML-P, a line beginning 10 mm proximal to the Dellon-McKinnon malleolar-calcaneal line; DML-D, a line which started 10 mm distal to the DML; D_N-DML-P, the shortest distance between point N to the line 10 mm proximal to the Dellon-McKinnon malleolar-calcaneal line.

Figure 5

The short-axis ultrasound image and schematic diagram of the tarsal tunnel. AN, ankle; TP, tibialis posterior tendon; FDL, flexor digitorum longus tendon; TN, tibial nerve; PTV, posterior tibial vein; PTA, posterior tibial artery; FR, flexor retinaculum; FHL, flexor hallucis long tendon; P, pelma; MI, mechanical index; TIS, thermal index of soft tissue; OM, Omni; C, the third of all nine maps (A-I); H, high frequency; TV, TeraVision; Gn, gain; DR, dynamic range.

Figure 6

The long-axis ultrasound image of the tarsal tunnel. TP, tibialis posterior tendon; FDL, flexor digitorum longus tendon; FHL, flexor hallucis long tendon; TN, tibial nerve; PTV, posterior tibial vein; PTA, posterior tibial artery; MI, mechanical index; TIS, thermal index of soft tissue; OM, Omni; C, the third of all nine maps (A-I); H, high frequency; TV, TeraVision; Gn, gain; DR, dynamic range.

Figure 7

Schematic diagram of the flexor retinaculum release via microtrauma with the needle-knife. (A) Schematic diagram of desirable needle knife operation; (B) the different types of release. FR, flexor retinaculum.

Figure 8

Percutaneous release distribution in group U and group N. Group U, ultrasound-guided small needle-knife pushing group; Group N, nonultrasound-guided small needle-knife pushing group.