Extended-Duration High-Voltage Pulsed Current Stimulation for Persistent Lateral Ankle Pain With Local Hypersensitivity After Talonavicular Coalition Resection: A Case Report.

Persistent lateral ankle pain after talonavicular coalition resection can be difficult to manage when mechanical factors alone do not explain the symptoms. This case highlights the clinical relevance of reassessing localized mechanical pain hypersensitivity at the sinus tarsi and adjusting electrical stimulation parameters based on the patient's clinical response. We describe a 22-year-old woman with persistent right lateral ankle pain during gait 14 months after resection of a talonavicular coalition. Analgesic medication had provided insufficient relief, and medication use remained unchanged throughout the treatment period. Initial assessment showed tenderness around the anterior talofibular and calcaneofibular ligaments, positive anterior drawer and inversion stress tests, restricted ankle range of motion, early heel-off during the right stance phase, and increased hip and knee flexion during gait. Walking pain was 5/10 on the numerical rating scale (NRS). Taping was applied for four weeks to reduce mechanical stress associated with lateral instability, but walking pain persisted at NRS 5/10. Reassessment identified the sinus tarsi as the primary pain site, with tactile hypersensitivity and a markedly reduced pressure pain threshold (PPT) on the affected side. High-voltage pulsed current (HVPC) stimulation was applied to the sinus tarsi for 10 minutes per session, four to five times weekly for five weeks. Pain transiently decreased to NRS 4/10 immediately after sessions, but sustained improvement was not achieved, and walking pain subsequently worsened to NRS 6/10. The stimulation duration was then extended to 30 minutes per session while the same electrode placement and intensity range were maintained. After this sequential change, walking pain decreased to NRS 2/10, and the affected-side PPT, gait findings, and affected forefoot loading improved. At the four-week follow-up, walking pain remained at NRS 0-1/10, with no adverse events. This case suggests that localized mechanical pain hypersensitivity at the sinus tarsi should be considered when persistent lateral ankle pain after talonavicular coalition resection cannot be explained by mechanical factors alone. The clinical improvement observed after extending the stimulation duration represents a temporal association and should be interpreted as a hypothesis-generating observation. Because this was a sequential single-case design without a control condition, washout period, or repeated baseline, the improvement cannot be attributed solely to the longer stimulation duration. Alternative explanations, including cumulative treatment effects, natural recovery, placebo response, and regression to the mean, cannot be excluded.