Progressive Collapsing Foot Deformity (PCFD) is a complex, multiplanar condition characterized by hindfoot valgus, peritalar subluxation, midfoot abduction, and collapse of the medial arch, which may progress to rigid deformity with pain and functional impairment. In advanced stages, subtalar arthrodesis is a well-established surgical option to restore hindfoot alignment and stability.
Subtalar Arthrodesis with Mini/Medial Bone Block (SAMBB) is an evolution of the Grice-Green technique, using an autologous bone graft to achieve stable correction of talocalcaneal alignment and improve joint congruency, with favorable clinical and radiographic outcomes.
This study aims to evaluate the three-dimensional corrective effect of SAMBB using weight-bearing CT (WBCT), focusing on hindfoot alignment and talocalcaneal and talonavicular relationships.
Patients of both sexes, aged between 18 and 80 years
Patients affected by grade A2 Progressive Collapsing Foot Deformity (PCFD)
Patients who have provided informed consent to participate in the study
Patients who have previously undergone corrective surgery on the deformity under study.
Patients with prior lower limb fractures resulting in altered biomechanics.
Patients affected by PCFD of grade A1, B2, C2, E1, or E2 according to the PCFD classification [2].
Patients with active acute or chronic infections.
Single group
Weight-Bearing CT scan
Diagnostic testWeight-Bearing CT scan after surgery
Foot and Ankle Offset
A three-dimensional parameter derived from weight-bearing CT (WBCT) acquisitions that allows objective quantification of the global alignment of the foot-ankle unit. It measures the spatial relationship between the functional tripod of the foot (first metatarsal, fifth metatarsal, and calcaneus) and the geometric center of the tibiotalar joint, effectively representing a synthetic index of the morpho-functional balance of the hindfoot-midfoot complex.
Talo-navicular congruency angle
A three-dimensional parameter that assesses talonavicular joint alignment and quantifies the degree of midfoot abduction (PCFD class B). It reflects the extent to which the talar head is "uncovered" relative to the navicular, indicating external rotation and lateral translation of the midfoot typical of PCFD. An increased TNCA corresponds to greater talonavicular incongruity and represents a three-dimensional marker of the transverse component of the deformity.
Middle facet Incongruency angle
The degree of incongruity between the talus and calcaneus at the level of the middle facet of the subtalar joint. It is a direct indicator of peritalar subluxation, one of the key features of PCFD (class A/D). Increased values suggest instability of the subtalar complex, loss of joint congruency, and three-dimensional hindfoot malalignment, with impairment of the subtalar joint's rotational function and load distribution.
Forefoot arch angle
A three-dimensional parameter that evaluates the stability and morphology of the medial and transverse arches at the level of the midfoot (PCFD class C). It reflects the behavior of the medial cuneiform and the first ray under load, describing the ability of the medial column to maintain adequate structural support.
Hindfoot moment arm
A three-dimensional measure of calcaneal alignment relative to the tibial axis, representing a direct index of hindfoot valgus. It quantifies the lateral displacement of the calcaneus under the tibial load, objectively describing the hindfoot deviation that characterizes the coronal component of PCFD (class A).
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