Introduction: Adult-acquired flatfoot is a common disorder affecting mostly middle-aged females. Causes of adult-acquired flatfoot include posterior tibialis tendon (PTT) degeneration, trauma, neuroarthropathy, neuromuscular disease, and inflammatory arthritis. Out of all these, PTT degeneration is by far the most common. We present a case with iatrogenic rupture of this tendon due to the passage of screws, particularly in minimally invasive ankle fracture fixation, eventually leading to pes planus. Case description: A 61-year-old female presented to us with pain and difficulty in walking over the left ankle for 4 years. She underwent minimally invasive ankle fixation 4 years ago. On ultrasound evaluation, the malleolar screw was found to be passing through the tibialis posterior tendon, causing its rupture. The patient was managed with implant removal, tibialis posterior exploration, corrective osteotomy, and medial arch restoration. Postoperatively, the patient started weight-bearing at 12 weeks and had a good outcome. American Orthopedic Foot and Ankle Society (AOFAS) score increased from 41 preoperatively to 87 at 1 year following surgery. Conclusion: Adult-acquired flatfoot can range from an asymptomatic problem to a disabling illness. The tibialis posterior tendon plays an important role in maintaining the medial arch of the foot, while its damage is one of the most important causes of adult-acquired flatfoot. Minimally invasive fixation of the medial malleolus can injure this tendon, which can further result in disastrous complications like flatfoot, and its early recognition is of utmost importance.