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

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

World J Orthop. 2021 Nov 18;12(11):850-858. doi: 10.5312/wjo.v12.i11.850.

Authors

Sandi Caus¹, Hailee Reist², Christopher Bernard³, Michael Blankstein², Nathaniel J Nelms²

Affiliations

¹ The Robert Larner College of Medicine, University of Vermont, Burlington, VT 05405, United States. sandi.caus@med.uvm.edu.
² Department of Orthopaedics and Rehabilitation, Unviversity of Vermont, Burlington, VT 05405, United States.
³ The Robert Larner College of Medicine, University of Vermont, Burlington, VT 05405, United States.

Abstract

Background: 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.

Aim: 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.

Methods: 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.

Results: 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 r ² 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.

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

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