Ultrasound-guided transverse myofascial acupotomy for the tibialis posterior muscle in type II painful accessory navicular: a retrospective cohort study with 1-year follow-up.

BACKGROUND: Type II painful accessory navicular (PAN II) commonly causes medial foot pain and functional limitation, and symptoms may persist when conservative care fails to reduce posterior tibial tendon traction on the accessory navicular synchondrosis. This study evaluated whether Ultrasound-Guided Transverse Myofascial Acupotomy for Tibialis Posterior (UG-MA-TP) is associated with better 1-year clinical and biomechanical outcomes than conventional conservative therapy. METHODS: This retrospective cohort study included 70 patients with PAN II treated between February 2022 and May 2024 at a single tertiary center. Patients were stratified according to treatment modality into the UG-MA-TP group (n=35) and the conventional therapy group (n=35). Outcomes included the 12-month clinical response rate and magnetic resonance imaging (MRI)-defined bone marrow edema resolution, serial Visual Analog Scale (VAS) pain scores and tibialis posterior/medial gastrocnemius muscle tone, American Orthopaedic Foot & Ankle Society (AOFAS) midfoot scores, surface electromyography-derived normalized root mean square relative values (nRMS-RV), Meary's angle, and adverse events. RESULTS: The UG-MA-TP group showed significant improvements in VAS and AOFAS scores and a sustained reduction in tibialis posterior muscle tone after intervention (all P<0.05). In contrast, the control group showed transient improvement only at 1 month, followed by a return toward baseline. At 12 months, the UG-MA-TP group had a higher clinical response rate, lower VAS score, higher AOFAS score, higher MRI-defined bone marrow edema resolution rate (82.86% vs. 25.71%), and lower tibialis posterior muscle tone than the control group (all P<0.05). Medial gastrocnemius muscle tone and Meary's angle remained stable in both groups (P>0.05). Tibialis anterior nRMS-RV was lower, whereas lateral gastrocnemius nRMS-RV was higher, in the UG-MA-TP group than in both the control group and baseline values (all P<0.05). CONCLUSIONS: For PAN II, UG-MA-TP was associated with favorable mid-term (1-year) clinical and biomechanical outcomes compared with conventional therapy. It was associated with greater pain reduction, functional improvement, and tibialis posterior muscle tone regulation, with no recorded serious adverse events in this retrospective cohort. This treatment may be associated with favorable neuromuscular adaptations and may represent a minimally invasive option for selected patients with PAN II.