Pes Planus: Abnormally Lowered Medial Longitudinal Arch
Pes planus (flatfoot) refers to a condition in which the medial longitudinal arch is chronically lowered or abnormally diminished. This pathological state primarily arises from excessive stretching or functional weakening of the plantar fascia, the spring ligament, and the posterior tibial tendon, combined with abnormal laxity of the midfoot and medial forefoot joints. In particular, during the stance phase of gait, the rearfoot exhibits an excessive eversion posture (where the calcaneus is displaced laterally away from the midline), which leads to excessive dorsiflexion at the talonavicular joint. These structural changes result in the talus and navicular descending abnormally, and the sustained pressure on the overlying skin in that area frequently leads to callus formation.
Footprint Examination and Load Distribution
Figure B illustrates in detail the foot structure of an individual with typical flatfoot. A notable finding in the footprint analysis is the marked widening of the midfoot region, which clearly indicates the excessive laxity of several joints supporting the arch. In patients with moderate to severe pes planus, normal load distribution through the foot during weight-bearing is not achieved. In such circumstances, both the intrinsic and extrinsic foot muscles remain chronically overactivated in order to compensate for the tension that should normally be generated by the overly stretched or weakened connective tissues. This chronic overuse of muscles persists even during static standing, ultimately leading to various fatigue injuries and overuse syndromes, including shin splints, bone spur formation, as well as hypertrophy and chronic inflammation of the plantar fascia.
Rigid vs. Flexible Pes Planus
Clinically, flatfoot is broadly classified into two main types: rigid and flexible.
Rigid Pes Planus:
In rigid pes planus, the medial longitudinal arch remains persistently lowered even in the absence of weight-bearing. This structural deformity is usually congenital, with skeletal formation anomalies—such as tarsal fusion (for example, partial fusion of the calcaneus and talus in a laterally deviated state)—being a primary cause. In some cases, abnormal tension in certain muscle groups due to spastic paralysis may also contribute. Because rigid flatfoot is characterized by a fixed structure and a high risk of persistent pain, surgical correction is typically required during childhood.Flexible Pes Planus:
Flexible pes planus is the most commonly observed form of flatfoot in clinical practice. The characteristic feature of this type is that the medial longitudinal arch appears normal in the absence of weight-bearing but collapses excessively when weight is applied. Acquired flexible flatfoot is closely associated with chronic tendinopathy of the posterior tibial tendon, widespread functional impairment, a general increase in the laxity of peritalar connective tissues, or various structural abnormalities and compensatory mechanisms that lead to excessive dorsiflexion of the foot. In cases of flexible flatfoot, surgical treatment is considered only in limited situations; most cases are managed conservatively using custom orthotics, specially designed footwear, and systematic exercise therapy programs.