Peroneal Spastic Flatfoot

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Peroneal Spastic Flatfoot (PSF) is a condition characterized by a rigid flatfoot accompanied by spasms of the peroneal muscles, which run along the outside of the lower leg and ankle. Unlike flexible flatfoot, where the arch can still appear when non-weight-bearing, PSF involves a fixed or stiff flattening of the medial longitudinal arch. The spasm of the peroneal tendons contributes to the foot being held in an everted (outward-turned) position, limiting normal motion of the subtalar joint. This condition is often painful, especially during walking or weight-bearing activities, and may severely limit mobility if left untreated.

The underlying causes of PSF are often linked to tarsal coalition, which is an abnormal fusion between two or more of the bones in the hindfoot (commonly the talus and calcaneus). This abnormal bony connection restricts normal joint movement, leading to compensatory muscle spasms, particularly of the peroneal muscles, as the body tries to stabilize the foot. Trauma, inflammatory conditions, or idiopathic (unknown) factors may also trigger PSF. In some cases, patients may initially present with vague ankle pain or recurrent ankle sprains before the flatfoot deformity and peroneal spasm become evident.

Diagnosis of Peroneal Spastic Flatfoot typically involves a combination of physical examination, imaging studies, and clinical history. On examination, the foot appears flat and rigid, and attempts to invert the foot (turn it inward) may trigger pain or muscle spasms. Radiographs can reveal bony abnormalities like tarsal coalitions, while advanced imaging such as CT or MRI may be necessary for detailed evaluation. Sometimes, a diagnostic injection of local anesthetic into the subtalar joint can temporarily relieve the spasm, confirming the joint’s involvement and helping guide treatment decisions.

Treatment for PSF often starts conservatively with rest, physical therapy, anti-inflammatory medications, and orthotic devices to support the arch and reduce muscle spasm. If conservative measures fail, more invasive treatments such as immobilization in a cast or injection therapy may be considered. In cases where tarsal coalition or another structural abnormality is present, surgical intervention might be necessary to either resect the coalition or realign the foot. Postoperative rehabilitation plays a crucial role in restoring mobility and function. Early diagnosis and intervention are important to prevent long-term disability and chronic pain.