内側腓腹筋へのボツリヌス毒素A型注射による難治性足底筋膜炎の治療：症例シリーズ

Plantar fasciitis is the most common cause of pain on the plantar aspect of the hindfoot and may become refractory even after months of conservative care. It is common not only in athletes engaged in activities involving repeated microtrauma to the heel, such as running, walking, basketball or tennis, but also in middle-aged non-athletes with risk factors such as prolonged standing, excessive body weight, foot posture abnormalities and gastrocnemius tightness. Surgical options such as partial plantar fasciotomy or surgical release of the medial gastrocnemius aim to reduce tension in the Achilles-plantar fascia complex, but carry perioperative risks. We report a single-center three-patient case series evaluating a minimally invasive alternative: ultrasound-guided botulinum toxin type A (BoNT-A) injections into the medial gastrocnemius to reduce calf tone and offload the plantar fascia. Patients included in this study had a clinical diagnosis of chronic plantar fasciitis lasting >12 months and were refractory to multimodal conservative care, including supervised physical therapy, extracorporeal shockwave therapy, orthoses or prior corticosteroid injections. These patients were selected for the injection of two motor-point targets within the medial gastrocnemius with 50 U of BoNT-A under ultrasound guidance. A standardized post-injection program emphasized calf and plantar-fascia stretching, progressive eccentric calf strengthening, intrinsic foot activation and gradual return to activity. Outcomes were the Numeric Rating Scale (NRS) for pain, the Foot and Ankle Disability Index - Activities of Daily Living Subscale (FADI-ADL) and the Maryland Foot Score (MFS) at baseline and follow-up at four weeks post-injection. The index patient (male, 66 years) improved from NRS 7/10, FADI-ADL 76, MFS 78 to NRS 3/10, FADI-ADL 99, MFS 88 at four weeks. Case 2 (female, 57 years) improved from NRS 9/10, FADI-ADL 39, MFS 33 to NRS 4/10, FADI-ADL 60, MFS 74 at four weeks. Case 3 (female, 45 years; bilateral symptoms) improved from NRS 9/10, FADI-ADL 77, MFS 76 to NRS 7/10, FADI-ADL 81, MFS 80 at four weeks. No complications occurred, including no detectable plantar flexion weakness. These cases suggest that targeted BoNT-A injection into the medial gastrocnemius may reduce pain and improve function in refractory plantar fasciitis while avoiding surgery. Controlled studies are warranted to define optimal dosing, injection sites and rehabilitation protocols, and also to compare gastrocnemius-targeted injection with corticosteroid and local anesthetic injection, extracorporeal shockwave therapy and surgery.