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

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 (χ=2.80; P=0.09). The percentage of released FR in group U was 80.00% while that in group N was 61.29% (χ=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 (=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.