Association between Hindfoot Moment Arm on Weightbearing CT Scans, Radiographs, and Patient-Reported Outcomes in Flexible Progressive Collapsing Foot Deformity

Research Type: Level 4 – Case series Introduction/Purpose: Progressive collapsing flatfoot deformity (PCFD) comprises several deformities including: hindfoot valgus, forefoot abduction, medial arch collapse with medial column instability, forefoot varus, and ankle valgus. Hindfoot valgus can be evaluated with the hindfoot alignment view (HAV) or weight bearing computed tomography (WBCT). Quantification of hindfoot valgus with the hindfoot moment arm (HMA) can be achieved with either imaging modality. Correction of hindfoot valgus surgically is achieved with a medializing calcaneal osteotomy (MCO). This study aimed to assess how the amount of hindfoot valgus correction from an MCO correlated with measured HMA on WBCT versus HAV. Additionally, the impact of the correction on patient-reported outcomes measurement information system (PROMIS) scores – Pain Interference (PI), Pain Intensity and Physical Function (PF) was investigated. Methods: A retrospective review of 35 patients who underwent flexible PCFD reconstruction, including an MCO, was conducted. All patients had pre- and post-operative HAV and WBCT scans. HMA was measured on both modalities by the distance from the most inferior aspect of the tibial anatomic axis to the central aspect of the calcaneal tuberosity. Demographic, PROMIS, and radiographic data were collected. Correlation between HMA on WBCT versus HAV was measured using Pearson’s correlation and Bland-Altman plots to assess agreement between the measurements. Linear regressions were used to assess the association between absolute postoperative HMA and PROMIS outcomes for WBCT and HAV measurements, respectively. Linear regressions were performed to evaluate the relationship between pre-to-postoperative change in HMA and PROMIS outcomes for both WBCT and HAV measurements. Pearson’s correlation was applied to evaluate the association of HMA (on WBCT and HAV) with talonavicular coverage angle (TCA), Meary’s angle (MA) and calcaneal pitch (CP). Results: Mild correlation was shown between WBCT and HAV measurements of HMA for preoperative (r=0.41, CI 0.079-0.666, p=0.017) and postoperative measurements (r=0.41, p=0.017, CI= 0.061-0.672). However, when pre- and post-operatively measured HMA were combined, the correlation was moderate (p=0.71, p< 0.001, CI 0.54-0.8). A linear regression showed that patients with a greater HMA change from pre-operatively to 2-years post-operatively measured on HAV were associated with a worse PROMIS Pain Intensity postoperatively (r=0.37, p=0.039, CI 0.02-0.73). There were no other associations of HMA with outcomes. There was mild to moderate correlation between WBCT measured HMA and TCA, MA and CP (r [-0.53 to 0.45], p< 0.01). There was a moderate negative correlation with HMA measured on HAV for calcaneal pitch (r=-0.51, p< 0.01). Conclusion: Prior studies demonstrated an excellent correlation between HMA measured on HAV and WBCT scans, however, a lower correlation between the hindfoot moment arm and the hindfoot alignment on WBCT and radiographs (HAV) was shown. This may be due to poor radiograph calibration and variable patient positioning. Although there was some evidence that changes in HMA on HAV may predict PROMIS Pain Intensity, no such relationship was found for HMA measured on WBCT. Further work with an increased study population is needed to assess the relationship between measurements on either modality and their effects on patient-reported outcomes. Figure 1 Combined pre-operative and post-operative HMA correlation between WBCT (y-axis) and HAV (x-axis)