Axial Rotation of the Talus in Progressive Collapsing Foot Deformity: A Weightbearing Computed Tomography Analysis

Abstract

Category: Hindfoot; Midfoot/Forefoot Introduction/ Purpose: Progressive collapsing foot deformity (PCFD) is recognized as a three-dimensional deformity centered around the talus. Although sagittal plane talar sagging or coronal plane valgus talar tilt have been well described, axial plane alignment referencing the talus, calcaneus and second metatarsal to the ankle has not been studied in PCFD patients. The purpose of this study was to examine the axial plane alignment of PCFD versus controls using weightbearing computed tomography (WBCT) and to determine if talar rotation in the axial plane is associated with increased abduction deformity. We hypothesized that the talus would exhibit greater internal rotation in PCFD patients than in control patients, and that this rotation would increase with worsening abduction deformity. Methods: Multiplanar reconstructed (MPR) WBCT scans of 79 patients with PCFD were analyzed. Patients were divided into two groups according to their preoperative talonavicular coverage angle (TNC): moderate abduction (TNC 20-40, n=57) and severe abduction (TNC >40, n=22). 39 WBCT scans from healthy patients without PCFD or hindfoot deformity were included as controls. Using the MPR WBCT images, the axis of talus (TM [transmalleolar]-Tal), calcaneus (TM-Calc), and 2nd metatarsal (TM-2MT) were measured in reference to the transmalleolar axis (Figure 1). Smaller angles represented internal rotation relative to the TM axis. The difference between TM-Tal and TM-Calc was calculated to assess talocalcaneal subluxation. The prevalence of medial tibiotalar joint space narrowing, which was assessed with medial to dorsal tibiotalar joint space ratio (M/D ratio < 0.5 was defined as ‘narrowing’), and medial ankle spurs were also evaluated. Results: TM-Tal was significantly smaller in PCFD patients compared to controls (Figure 2). This difference was accentuated in PCFD with severe abduction, who saw significantly smaller TM-Tal than the moderate abduction group. TM-Calc did not differ between groups, indicating similar axial calcaneal orientation. The TM-2MT revealed a significant difference between groups, reflecting foot abduction in PCFD. Diff Tal-Calc values were greater in PCFD patients, indicating that PCFD patients have more talocalcaneal subluxation in the axial plane. The severe abduction group had a higher Diff Tal-Calc value than the moderate abduction group. PCFD patients had a significantly higher prevalence of medial ankle joint space narrowing and medial spur formation than controls; however, there were no significant differences between the severe and moderate abduction groups. Conclusion: This study found that internal rotation of the talus is a key component of PCFD and is accentuated in more severe abduction deformities. These findings suggest that talar malrotation in the axial plane should be considered an underlying feature of abduction deformity and that this deformity should be corrected at the time of reconstructive surgery, especially in cases of severe abduction deformity. In addition, these findings support the observations of medial joint narrowing and medial spur formation in PCFD patients. Further research is warranted to identify optimal strategies for correction of talar rotation and how to reproducibly assess this intraoperatively.