Giant Ganglion Cyst of the Tibialis Anterior Tendon Presenting with Adult-Acquired Flatfoot Deformity: A Case Report.

INTRODUCTION

Ganglion cysts of the tibialis anterior tendon (ATT) are exceedingly rare. We report a case of a giant ATT ganglion cyst associated with adult-acquired flatfoot deformity and underlying degenerative tendinopathy and describe a systematic multimodal surgical technique for its management.

CASE REPORT: A 55-year-old male construction worker presented with a 4-month history of a progressively enlarging left ankle swelling that prevented him from wearing protective footwear. Magnetic resonance imaging (MRI) demonstrated a lobulated cyst measuring 4.4 × 3.9 × 11.7 cm with internal septations and extensive underlying ATT degenerative change. Surgical management comprised an anterior elliptical incision, cyst decompression, tendon debridement, tubularization with Vicryl 4-0 sutures, platelet-rich plasma injection, and sheath marsupialization. Approximately 4 weeks postoperatively, the patient developed infective tenosynovitis, confirmed on repeat MRI, with a subcentimeter susceptibility focus raising suspicion for a retained foreign body.

CONCLUSION

Giant ATT ganglion cysts may harbor significant underlying degenerative tendinopathy requiring active surgical management beyond simple excision. A systematic approach combining cyst excision, debridement, tubularization, and biologic augmentation is described. Surgeons should maintain a low threshold for repeat MRI when post-operative infective tenosynovitis is suspected following ATT surgery.