Reliability and correlation of weight-bearing cone beam CT and Foot Posture Index (FPI) for measurements of foot posture: a test-retest study.

Abstract

To assess test-retest reliability and correlation of weight-bearing (WB) and non-weight-bearing (NWB) cone beam CT (CBCT) foot measurements and Foot Posture Index (FPI) MATERIALS AND METHODS: Twenty healthy participants (age 43.11±11.36, 15 males, 5 females) were CBCT-scanned in February 2019 on two separate days on one foot in both WB and NWB positions. Three radiology observers measured the navicular bone position. Plantar (ΔNAV_plantar) and medial navicular displacements (ΔNAV_medial) were calculated as a measure of foot posture changes under loading. FPI was assessed by two rheumatologists on the same two days. FPI is a clinical measurement of foot posture with 3 rearfoot and 3 midfoot/forefoot scores. Test-retest reproducibility was determined for all measurements. CBCT was correlated to FPI total and subscores. Intra- and interobserver reliabilities for navicular position and FPI were excellent (intraclass correlation coefficient (ICC) .875-.997). In particular, intraobserver (ICC .0.967-1.000) and interobserver reliabilities (ICC .946-.997) were found for CBCT navicular height and medial position. Interobserver reliability of ΔNAV_plantar was excellent (ICC .926 (.812; .971); MDC 2.22), whereas the ΔNAV_medial was fair-good (ICC .452 (.385; .783); MDC 2.42 mm). Using all observers' measurements, we could calculate mean ΔNAV_plantar (4.25±2.08 mm) and ΔNAV_medial (1.55±0.83 mm). We demonstrated a small day-day difference in ΔNAV_plantar (0.64 ±1.13mm; p<.05), but not for ΔNAV_medial (0.04 ±1.13mm; p=n.s.). Correlation of WBCT (WB navicular height - ΔNAV_medial) with total clinical FPI scores and FPI subscores, respectively, showed high correlation (ρ: -.706; ρ: -.721). CBCT and FPI are reliable measurements of foot posture, with a high correlation between the two measurements.