Retrospective Study
Copyright ©The Author(s) 2021. Published by Baishideng Publishing Group Inc. All rights reserved.
World J Orthop. Nov 18, 2021; 12(11): 850-858
Published online Nov 18, 2021. doi: 10.5312/wjo.v12.i11.850
Reliability of a simple fluoroscopic image to assess leg length discrepancy during direct anterior approach total hip arthroplasty
Sandi Caus, Hailee Reist, Christopher Bernard, Michael Blankstein, Nathaniel J Nelms
Sandi Caus, Christopher Bernard, The Robert Larner College of Medicine, University of Vermont, Burlington, VT 05405, United States
Hailee Reist, Michael Blankstein, Nathaniel J Nelms, Department of Orthopaedics and Rehabilitation, Unviversity of Vermont, Burlington, VT 05405, United States
Author contributions: Caus S contributed to project design, data collection, analysis and production of the written manuscript; Reist H contributed to production of the manuscript and specifically contributed to content review; Bernard C contributed to initial data collection and review of manuscript content; Blankstein M contributed to project design and to the review of manuscript content; Nelms NJ contributed to project design, data collection, data analysis and production of the manuscript.
Institutional review board statement: The study was reviewed and approved by the University of Vermont Institutional Review Board (Approval No. STUDY00000725).
Informed consent statement: Waiver of consent was granted by the institutional review board at the University of Vermont.
Conflict-of-interest statement: We have no financial relationships to disclose.
Data sharing statement: No additional data are available.
Open-Access: This article is an open-access article that was selected by an in-house editor and fully peer-reviewed by external reviewers. It is distributed in accordance with the Creative Commons Attribution NonCommercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See:
Corresponding author: Sandi Caus, BSc, Academic Research, The Robert Larner College of Medicine, University of Vermont, 89 Beaumont Ave., Burlington, VT 05405, United States.
Received: May 24, 2021
Peer-review started: May 24, 2021
First decision: July 16, 2021
Revised: July 28, 2021
Accepted: September 15, 2021
Article in press: September 15, 2021
Published online: November 18, 2021

Direct anterior approach (DAA) total hip arthroplasty (THA) in a supine position provides a unique opportunity to assess leg length discrepancy (LLD) intra-operatively with fluoroscopy. Reported fluoroscopic techniques are useful but are generally complicated or costly. Despite the use of multiple techniques for leg length assessment, LLD continues to be a major post-operative source of patient dissatisfaction further emphasizing the importance of near-anatomic restoration. The utility of an alternative direct measurement of LLD on an intra-operative fluoroscopic pelvic image during DAA THA has not been reported.


To determine the reliability of a novel simple intra-operative measurement of LLD using a parallel line technique on a single fluoroscopic digital image of the pelvis.


One hundred and seventy-one patients who underwent DAA THA were included for analysis. Intra-operative fluoroscopic and post-operative anterior-posterior radiographs were imported to TraumaCad and calibrated for LLD measurement. LLD was measured on each image using the right-left hip differences in lesser trochanter to pelvic reference line distances. Pelvic reference points included the teardrops and ischia. Fluoroscopic LLD was compared to the gold-standard measurement of LLD measured on a post-operative radiograph.


Mean absolute difference in teardrop referenced LLD between fluoroscopic and post-operative radiographs was 2.17 mm and based on the ischia mean absolute difference was 2.63 mm. Linear regression of fluoroscopic and post-operative radiograph LLD based on teardrop and ischia LLD found r2 values of 0.57 and 0.84, respectively. Mean absolute difference between fluoroscopic and post-operative x-ray LLD was within 5 mm in 95% of cases regardless of pelvic reference.


This study demonstrates that a single fluoroscopic view obtained during DAA THA for leg length assessment is clinically useful.

Keywords: Leg-length discrepancy, Total hip arthroplasty, Intra-operative fluoroscopy, Direct anterior approach, Limb asymmetry

Core Tip: The direct anterior approach (DAA) for total hip arthroplasty (THA) has grown in popularity among Orthopaedic Surgeons in recent years. Despite the growth in this approach for THA, leg length discrepancy continues to be a major source of post-arthroplasty dissatisfaction in patients. Here we demonstrate that a single intra-operative fluoroscopic image for leg length assessment has clinical significance among patients undergoing DAA THA.