Acquired adult flat foot due to isolated plantar calcaneonavicular (spring) ligament insufficiency with a normal tibialis posterior tendon

BackgroundWe present nine cases of acquired flat foot deformity (AFFD) in adults caused by isolated spring ligament insufficiency.MethodsWe present the clinical sign that allows differentiation of this diagnosis from posterior tibialis tendon (PTT) dysfunction namely the ability to single leg tiptoe, but with persistent forefoot abduction and heel valgus. In addition we illustrate the unique radiological features which allow confirmation of the diagnosis. Only a solitary previous case report has documented this alternative aetiology of AFFD; in that case, diagnosis was made intra-operatively.ResultsSix patients have been managed with orthoses. Three patients underwent surgery; one patient who presented early had isolated repair of the spring ligament complex. The remaining two required a calcaneal osteotomy and flexor digitorum longus transfer as for a PTT reconstruction.ConclusionWe propose that early diagnosis (with ultrasound confirmation) and management of this condition would offer a better prognosis and allow less interventional surgery.