Acquired flatfoot deformity after injury is usually due to partial or complete tearing of the tendon of tibialis posterior, with secondary failure of the other structures which maintain the medial longitudinal arch. We describe a patient in whom the rupture of the plantar calcaneonavicular (spring) ligament resulted in a clinical picture similar to that of rupture of the tendon of tibialis posterior. Operative repair of the ligament and transfer of the tendon of flexor digitorum gave an excellent result at four years with the patient returning to full sporting activities.