Association Between Middle Facet Subluxation and Foot and Ankle Offset in Progressive Collapsing Foot Deformity

Abstract

Background: Subtalar middle facet (MF) subluxation was recognized as a reliable marker for progressive collapsing foot deformity (PCFD) diagnosis. Foot and Ankle Offset (FAO) is an established measurement, predictive of malalignment severity. The objective of this study was to assess the potential association between MF subluxation and FAO in PCFD patients. Methods: 56 individuals with flexible PCFD (74 feet) were assessed. Two blinded foot and ankle surgeons calculated MF uncoverage, MF incongruence, and FAO. Agreement was quantified using intraclass correlation coefficient (ICC). A multivariate regression analysis and partition prediction models were applied to assess relationship between values. Results: All ICCs were >0.80. MF subluxation and FAO were found to be correlated ( rs = 0.56; P < .0001). Changes in the MF subluxation were noticeably explained by FAO and BMI ( R2 = 0.33). MF incongruence was not correlated with the assessed variables ( P = .10). In this cohort, an MF subluxation of 27.5% was a threshold for increased FAO (FAO of 3.4%±2.4% when below; FAO of 8.0% ±3.5% when above). Conclusion: We found a correlation between MF subluxation and FAO. An MF subluxation of 27.5% was found to be a threshold for higher FAO, which corresponded to a greater malalignment. These data may help surgeons optimize treatment decisions in PCFD patients. Level of Evidence: Level III, retrospective comparative study.

What’s New in Foot and Ankle Surgery

“…The middle facet of the subtalar joint can now be reliably evaluated using weight-bearing CT scans, and de Cesar Netto et al 45 established that the middle facet represents a particularly sensitive location to detect early peritalar subluxation in progressive collapsing flatfoot deformity. Barbachan Mansur et al 46 further showed that middle facet subluxation is correlated with foot and ankle offset, a well-established measure of global hindfoot alignment on weight-bearing CT scans. Middle facet subluxation of 27.5% represented a threshold that correlated with higher foot and ankle offset values, suggesting hindfoot collapse.…”

Coverage maps demonstrate 3D Chopart joint subluxation in weightbearing CT of progressive collapsing foot deformity

“…The recent use of WBCT to evaluate PTS has produced important data to help understand this pathological functioning 11 , 12 . Using two-dimensional tools in coronal plane imaging, the amount of subluxation at the posterior and middle facets was found to be correlated with PCFD diagnosis and severity 6 , 11 , 13 , 14 . Dibbern et al performed an objective three-dimensional (3D) WBCT analysis of the subtalar joint in PCFD using 3D distance maps (DMs) and introducing the concept of coverage mapping (CM) 15 .…”

Foot and ankle offset in the setting of severe rotational foot and ankle deformities

“…Foot and ankle offset (FAO) is a three-dimensional (3D) measurement for overall foot and ankle alignment assessment. It is characterized by the relation between the weight-bearing tripod of the foot and the center of the ankle joint (1)(2)(3) . The most plantar voxel of the heads of the fifth and first meta-tarsal and the calcaneal tuberosity make up the tripod of the foot, while the most proximal and central points of the talus represents the center of the ankle.…”

“…The FAO is clinically relevant due to its ability to produce an objective value portraying the foot alignment (3)(4)(5) . In addition, it represents a measurement of the offset between the body weight vector and the ground reaction force vector, thus making it a biomechanically relevant measurement.…”