Peroneal spastic flatfeet without coalition or other known etiologies in adolescence remain a challenge to manage.

We present eight such cases with radiological and surgical evidence of bony abnormalities in the subtalar region just anterior to the posterior facet. All patients had presented as tertiary referrals with recalcitrant pain and had undergone a trial of orthotics and physiotherapy. Diagnostic workup included a clinical and radiographic evaluation. Clinical examination consisted of gait examination, foot alignment, range of motion, torsional profile of the lower limbs and marking of symptomatic foci. All patients had standing weightbearing AP and lateral projections of the foot and ankle. CT and/or MRI scans of the foot were performed in axial coronal and saggital planes. Coalitions and other intraarticular known pathologies were ruled out. All patients had bilateral flatfeet but unilateral peroneal spasm.

All patients had an accessory talar facet in front of the posterior subtalar facet. This caused lateral impingement between the facet and the calcaneum, confirmed by bone edema around the sinus tarsi. All patients had stiff subtalar joints with very limited movement under anaesthesia, indicating peroneal muscle contracture.

Patients were treated with a combination of facet excision, peroneal lengthening and calcaneal lengthening to correct the flatfoot and prevent lateral impingement.

We propose a mechanism of subtalar impingement between the anterior extra-articular part of the talar lateral process and the Gissane angle and believe that resection of the accessory facet without addressing the the primary driving force for impingement, which is the structural malalignment in flatfeet, would only give partial relief of symptoms. This impingement appears to occur with growth spurts in adolescents, in patients with known flatfeet.