What’s in a Name? Understanding Progressive Collapsing Foot Deformity

In this lecture at the NYSPMA Clinical Conference, Allen Jacobs, DPM, shared that in 2020, AOFAS published a consensus, introducing the term progressive collapsing foot deformity (PCFD) and an associated classification system.¹ He adds that this consensus evolved for many reasons, including insurance considerations, lack of agreement in current terminology, and variation in currently and historically used classifications. He went on to review some of these previous classifications, including Johnson-Strom and Myerson’s adaptation thereof.

Per the AOFAS consensus, PCFD is delineated via two parts; stage and type. There are two stages, where stage 1 is flexible, and stage 2 is rigid. The classification also has 5 types, classes A through E, which includes:

Class A – indicates hindfoot valgus alignment, with an increased hindfoot moment arm. So, a flexible deformity with hindfoot valgus would be 1A,  and rigid 2A.

Class B – denotes forefoot/midfoot abduction, including decreased talar head coverage (less than 40%), increased talonavicular angle, and sinus tarsi impingement. Thus, a flexible foot with hindfoot valgus and less than 40% coverage of the talonavicular joint would be considered 1AB.

Class C – discusses forefoot varus and medial column instability, manifesting as an increased talar-first metatarsal angle, plantar gapping first metatarsal-cuneiform or navicularcuneiform joints, and clinical forefoot varus. Accordingly, a flexible deformity with hindfoot valgus and medial column instability would be 1AC, and a rigid deformity with hindfoot valgus, midfoot abduction and medial column instability would be 2ABC.

Class D – involves significant STJ subluxation with lateral (subfibular) impingement.

Class E – notes ankle instability, ie valgus tilting of the ankle joint.

Dr. Jacobs notes that he finds many surgeons already evaluate patients in this manner, but that the classification could be useful for teaching students. He points out that this is an anatomic classification, and it does not reflect function (ie control of midtarsal joint function with subtalar joint control). He adds that the classification does not result in a paradigm for treatment and still has a component of intraobserver subjectiveness. Lastly, he points out that this new system does not address things like equinus or suprapedal deformities.

Reference

1. Sangeorzan B, Hintermann B, de Cesar Netto C, et al. Progressive collapsing foot deformity: consensus on goals for operative correction. Foot Ankle Int. 2020;41(10): 1299-1302.