Background
The success of modern total hip arthroplasty (THA) depends on accurate placement of implants in order to obtain a durable result. As direct anterior (DA) approach THA has become increasingly popular, more surgeons are now using intra-operative fluoroscopy to navigate cup position and to assess leg length. One limitation of traditional fluoroscopy is that it has historically been a qualitative, but not quantitative technology. Recently, fluoroscopy-assisted computer navigation software with the capability to assess intra-operative parameters quantitatively has emerged. Few studies have investigated the accuracy of this software in comparison to post-operative radiographs. Such a study would be an important contributor to the literature, as it would allow the arthroplasty surgeon to predict with confidence whether these measurements would be similar to those obtained by post-operative radiographs.
Methods
This is a prospective cohort study of consecutive patients undergoing unilateral anterior THA. 199 hips were analyzed fluoroscopically with intra-operative computer software (OrthoGrid Systems, Inc), determining LLD. At the two-week post-operative visit, these measurements were repeated on standing AP radiographs. Continuous variables were analyzed using Student’s t-test.
Results
The mean intra-operative LLD was 0.3 mm and the mean LLD on two-week follow-up was 0.6 mm (p=0.13). Intraoperatively, all 199 patients (100%) were navigated to LLDs within 5 mm; similarly on final standing AP films the number of patients with LLD within 5 mm was 196/199 (98%) (p = 0.25). The mean difference between the intra-operative LLD and post-operative LLD (ΔLLD) was 0 mm.
Conclusion
Total hip arthroplasty continues to be a tremendously successful procedure for eliminating pain and improving function of the arthritic hip, and a successful outcome in part depends on accurate placement of implants. We demonstrate in the present prospective study that fluoroscopy-assisted computer navigation software accurately predicts post-operative leg length discrepancy. For differences in measurements of leg-length discrepancy (ΔLLD), 69% of navigated measurements were within 2mm of those on post-op films, and 99% of measurements were within 5mm.

Does Fluoroscopy-Assisted Computer Navigation Accurately Predict Cup Position and Leg Length for Anterior Hip Arthroplasty?

 Orthopaedic Surgery

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Does Fluoroscopy-Assisted Computer Navigation Accurately Predict Cup Position and Leg Length for Anterior Hip Arthroplasty?

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