Leg length discrepancy assessment in total hip arthroplasty: is a pelvic radiograph sufficient?

Aims Leg length discrepancy (LLD) is a common pre-and postoperative issue in total hip arthro-plasty (THA) patients. The conventional technique for measuring LLD has historically been on a non-weightbearing anteroposterior pelvic radiograph; however, this does not capture many potential sources of LLD. The aim of this study was to determine if long- limb EOS radi-ology can provide a more reproducible and holistic measurement of LLD. Methods In all, 93 patients who underwent a THA received a standardized preoperative EOS scan, an-teroposterior (AP) radiograph, and clinical LLD assessment. Overall, 13 measurements were taken along both anatomical and functional axes and measured twice by an orthopaedic fellow and surgical planning engineer to calculate intraoperator reproducibility and correla-tions between measurements. Results Strong correlations were observed for all EOS measurements (rs > 0.9). The strongest cor-relation with AP radiograph (inter-teardrop line) was observed for functional-ASIS- to- floor (functional) (r(s) = 0.57), much weaker than the correlations between EOS measurements. ASIS- to- ankle measurements exhibited a high correlation to other linear measurements and the highest ICC (r(s) = 0.97). Using anterior superior iliac spine (ASIS) - to-ankle, 33% of pa-tients had an absolute LLD of greater than 10 mm, which was statistically different from the inter-teardrop LLD measurement (p < 0.005). Discussion We found that the conventional measurement of LLD on AP pelvic radiograph does not cor-relate well with long leg measurements and may not provide a true appreciation of LLD. ASIS- to- ankle demonstrated improved detection of potential LLD than other EOS and radio-graph measurements. Full length, functional imaging methods may become the new gold standard to measure LLD.