Hindfoot Alignment Measurements: Rotation-Stability of Measurement Techniques on Hindfoot Alignment View and Long Axial View Radiographs

OBJECTIVE. The purpose of this article is to identify the most rotation-stable hindfoot alignment measurement techniques on hindfoot alignment view and long axial view radiographs. MATERIALS AND METHODS. Hindfoot alignment was quantified on hindfoot alignment view and long axial view radiographs of a phantom in different rotation positions. Rotation stability of measurements using the calcaneal axis, the medial and lateral calcaneal contour, and the apparent moment arm were graphically compared. Interreader agreement was quantified using intraclass correlation coefficient. RESULTS. On hindfoot alignment view radiographs, measurements using the medial and lateral calcaneal contour were rotation stable (+/- 5 degrees). Measurements using the calcaneal axis were not reliable and showed considerable divergence with phantom rotation. Measurements using the apparent moment arm manifested an almost linear relationship to phantom rotation. On long axial view radiographs, all measurements manifested an almost linear relationship to phantom rotation, whereas those using the calcaneal axis were the most rotation stable. Interreader agreement of all measurement techniques was perfect on both hindfoot alignment and long axial view radiographs (intraclass correlation coefficient, 0.8-0.98; p < 0.001). Interreader agreement was slightly better on long axial view radiographs. CONCLUSION. Hindfoot alignment measurements should be performed on hindfoot alignment view radiographs using the medial or lateral calcaneal contour or on long axial view radiographs using the calcaneal axis. Interreader agreement of hindfoot alignment measurements is slightly better on long axial view radiographs than on hindfoot alignment view radiographs.