Peroneal spastic flatfoot (PSFF) is a rigid, painful valgus deformity of the foot historically associated with protective spasm of the peroneal muscles, now recognized as a clinical syndrome rather than a single disease entity. While often linked to tarsal coalition, it can also occur in the absence of developmental anomalies, and in many cases the “spasm” is more accurately an adaptive shortening or reactive contraction secondary to an irritative lesion in the peritalar region. Because of its variable etiology and outdated terminology, modern podiatric and orthopedic literature frequently uses broader terms such as “rigid valgus foot” or specifies the underlying pathology (e.g., calcaneonavicular bar, talocalcaneal bridge, inflammatory arthritis)
Definition and Terminology
Peroneal spastic flatfoot describes a foot in which the arch is flattened, the heel is in valgus, and the foot is stiff or rigid, with apparent spasm of the peroneal muscles causing pain and limiting motion. Classic descriptions emphasize unilateral or bilateral rigid flatfoot with peroneal muscle tenderness and a foot that resists manual correction into inversion or neutral.
The term is now considered imprecise by many authors. In cases where tarsal coalition is present, the deformity is primarily a fixed structural problem due to abnormal bone union; the peroneal “spasm” is then an adaptive shortening rather than true primary spasm. In inflammatory cases (e.g., rheumatoid arthritis), peroneal spasm may be more genuine, but these are better classified separately as arthritic flatfoot with peroneal spasm. Consequently, contemporary texts often prefer “rigid flatfoot due to [specific coalition]” or reserve PSFF for idiopathic presentations where no coalition or other cause is identified.
Etiology
The most common cause of PSFF is tarsal coalition, particularly calcaneonavicular bars and talocalcaneal bridges. These congenital or developmental unions between tarsal bones restrict motion at the subtalar and peritalar joints, producing a rigid valgus deformity and peroneal irritation. Radiographs with special oblique views are often required to detect rudimentary forms of these coalitions.
However, PSFF can occur without detectable tarsal anomalies. Historical series have documented cases with normal tarsal skeletons in which peroneal spasm was clinically evident, suggesting that any irritative lesion in the peritalar region—such as trauma, sinus tarsi pathology, neoplasm, or inflammatory disease—can provoke protective peroneal contraction and a rigid flatfoot posture. Idiopathic peroneal spastic flatfoot (IPSF) is used when no cause is found after thorough clinical, laboratory, and imaging evaluation.
Less common etiologies include inflammatory arthropathies (notably rheumatoid arthritis), where true peroneal spasm may accompany joint destruction, and rare neoplasms manifesting as a rigid flatfoot deformity. Heavy mechanical stress on an architecturally abnormal or even normal foot is also hypothesized to contribute, with tarsal anomalies increasing susceptibility to breakdown under average stress.
Clinical Features
Patients typically present in childhood or adolescence with a painful, stiff foot that is flat and in valgus. The deformity is often unilateral but can be bilateral. The foot is rigid: inversion and abduction are limited, and the foot cannot be passively corrected into a neutral or varus position. Peroneal tenderness along the lateral foot and behind the lateral malleolus is characteristic, and patients may report pain in the sinus tarsi or lateral aspect of the foot
Gait may show an antalgic pattern, with avoidance of pronation and altered weight distribution. There may be a history of recurrent ankle sprains or minor trauma, but in some cases the onset appears spontaneous. In older children and adolescents, the deformity may be more established, with secondary changes in the soft tissues and alignment of the lower limb.
Diagnosis
Diagnosis relies on clinical examination, plain radiography, and advanced imaging. Clinical assessment confirms a rigid valgus flatfoot with peroneal tenderness and limited subtalar motion. Standard weight-bearing radiographs show a flattened longitudinal arch, valgus tilt of the calcaneus, and possible uncovering of the talonavicular joint
Specialized radiographic views (e.g., oblique calcaneonavicular views, lateral talar–calcaneal angle) are essential to detect calcaneonavicular bars and talocalcaneal bridges, which may be missed on routine films. CT is now the gold standard for defining the morphology and extent of tarsal coalitions, while MRI is valuable for evaluating soft tissue irritation, sinus tarsi pathology, and inflammatory or neoplastic processes. In cases where no coalition is identified, the diagnosis of IPSF is considered, and further investigation for inflammatory, neurologic, or neoplastic causes is warranted.
Management
Conservative management is the initial approach, particularly in children and those with mild symptoms. This includes activity modification, avoidance of high-impact loading, and use of immobilization or short-term casting in severe, refractory cases to reduce peroneal irritation and restore some flexibility. Orthotic devices designed to support the medial arch, control valgus, and offload the peroneal tendons are commonly used, along with physical therapy to improve peroneal and intrinsics strength and flexibility.
Surgical intervention is indicated when there is persistent pain, functional limitation, or progressive deformity despite conservative measures. For coalitions, the standard procedure is resection of the bar with interposition of fat, tendon, or other material to prevent recurrence and restore motion. In idiopathic cases or when resection is not feasible, procedures such as peroneal tendon lengthening, medial soft-tissue releases, or corrective osteotomies (e.g., calcaneal osteotomy, triple arthrodesis) may be required, depending on the degree of rigidity and deformity. The choice of procedure is guided by the underlying etiology, age, and functional demands of the patient.
Peroneal spastic flatfoot is best understood as a heterogeneous clinical syndrome characterized by rigid valgus flatfoot with peroneal irritation, rather than a single pathologic entity. While tarsal coalition is the predominant cause, idiopathic and inflammatory forms exist, and the term “spastic” is often misleading. Accurate diagnosis requires careful imaging to identify or exclude coalitions and other structural abnormalities, and management should be tailored to etiology, with conservative measures first and surgery reserved for refractory or advanced cases.