Adult acquired flatfoot deformity, recently renamed Progressive Collapsing Foot Deformity (PCFD), is challenging to diagnose and treat due to the still poorly understood nature of its pathogenesis, which involves a complex interaction between soft tissues and bony structures. Long regarded as being primarily linked to posterior tibial tendon dysfunction, PCFD is now considered a multifactorial deformity (osseous dysplasia, joint malposition, tendon muscle imbalance, etc.), with many aspects yet to be explored. This study aims to provide an update on this pathology by addressing the following five key questions: (1) Is flatfoot truly a problem? A stable congenital flatfoot is generally asymptomatic. However, a sagging foot, regardless of its flatness, characterized by a progressive arch collapse (PCFD), is painful. (2) What role do soft tissues play in its pathogenesis? The previously central role attributed to the posterior tibial tendon and its rupture, which was thought to trigger a chronological cascade of deformations, is now being reconsidered. (3) How should we classify a flatfoot? The Progressive Collapsing Foot Deformity (PCFD) classification distinguishes five types of deformities: hindfoot valgus, midfoot abduction, forefoot varus, peritalar subluxation, and tibiotalar valgus. These deformities can occur in isolation or in combination, without a predetermined chronological order, and each of them can be either flexible or rigid. (4) What is the contribution of modern imaging? Weightbearing Cone Beam CT enables the early identification of subluxations and joint impingements, clarifying the distinction between a stable flatfoot and PCFD while revealing complex deformities that conventional methods may not detect. (5) What are the current perspectives and future directions? Research aims to differentiate stable congenital flatfeet from PCFD in order to better identify risk factors for symptomatic progression. Dynamic imaging techniques, such as biplanar fluoroscopy, offer real time analysis of bone motions, while computational simulations, integrating both soft tissues and bony structures, contribute to a deeper understanding of the onset and progression of deformities.

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