Reliability of a simple fluoroscopic image to assess leg length discrepancy during direct anterior approach total hip arthroplasty

ARTICLE HIGHLIGHTS

Research background

The direct anterior approach (DAA) in total hip arthroplasty (THA) with a patient in the supine position has gained popularity in recent years and provides an opportunity for intra-operative fluoroscopy for assessment of leg length discrepancy (LLD), as well as other intra-operative parameters of interest to Orthopaedic surgeons. LLD remains a significant source of patient dissatisfaction post-arthroplasty and we recognize an opportunity to evaluate the reliability of a novel simple parallel line technique on a single intra-operative fluoroscopic image.

Research motivation

The increase in popularity of the DAA THA combined with the opportunity to utilize intra-operative fluoroscopy has made surgeons wonder about the reliability of fluoroscopy in the clinical setting. We aimed to provide an assessment of this based on a simple parallel line technique on a single intra-operative fluoroscopic image of the pelvis once final arthroplasty components had been positioned.

Research objectives

The primary objective of this study was to understand the accuracy and reliability of a novel simple intra-operative fluoroscopy LLD assessment technique as compared to the standard post-operative x-ray.

Research methods

171 intra-operative fluoroscopic and anterior-posterior (AP) radiographs with final components in position were imported to TraumaCad for observer LLD analysis. LLD measurements were taken on each image utilizing right-left hip differences in lesser trochanters to two separate pelvic reference points. These were either the radiographic teardrops or ischia. Fluoroscopic LLD measurements were compared to the standard measurement of LLD on a post-operative AP radiograph.

Research results

Mean absolute difference between fluoroscopic and post-operative x-ray LLD was within 5 mm in 95% of cases regardless of pelvic reference point. Utilizing the simple parallel line technique on a single fluoroscopic image of the pelvis we achieved an LLD of < 5 mm in 88.9% of subjects and of < 10 mm in 98.8% of subjects as measured on the gold-standard post-operative x-ray.

Research conclusions

We demonstrate moderate accuracy in estimation of LLD intra-operatively by assessment of a simple AP fluoroscopic image, specifically with a novel simple parallel line technique. This technique is performed by visually comparing how parallel a digital line drawn trough the radiographic teardrops is to a line drawn between corresponding points on the lesser trochanters. We acknowledge the importance of continuing to have more than one technique intra-operatively to most accurately estimate LLD.

Research perspectives

Our study adds to a body of research investigating the clinical usefulness of intra-operative fluoroscopy in the DAA THA, specifically we demonstrate that this technique has clinical benefit in our cohort of patients. Not only do we hope this adds to the body of research and clinical understanding of fluoroscopy, but also hope it can be utilized as an additional reliable technique for assessment of intra-operative LLD.