Summary

Postoperative infection following intraarticular hip injection =3 months prior to hip arthroscopy is rare (<0.5%) and no more common than in patients who did not undergo preoperative injection.

Abstract

Introduction

The purposes of this study were to assess the risk of infection associated with image-guided intraarticular injections prior to hip arthroscopy and compare that risk between US and FL- guidance.

Methods

This was a retrospective cohort study of patients undergoing hip arthroscopy in a large commercial claims database (MarketScan) from 2007-2017. Patients were required to have 1-year of continuous enrollment prior to and 6-months after hip arthroscopy. For both the US and FL cohort, patients who underwent injection =3 months preoperatively and >3-12 months preoperatively were compared to those who did not undergo preoperative injection. The primary outcome of this study was surgical site infection within 6 months of surgery. Chi-squared or Fisher’s exact tests and multivariable logistic regressions were used to assess the association between preoperative hip injection and infection. Finally, we performed sensitivity analyses that did not exclude patients with an infection at time of hip arthroscopy.

Results

We identified 17,093 hip arthroscopy patients (mean [SD] age 37.2 [14.0] years; 14,685 [85.9%] no injection control patients and 2,408 [14.1%] patients who underwent hip arthroscopy within 12-months of image-guided hip injection). In the FL cohort (n=1,219 [50.7%]), 673 (55.2%) patients underwent hip arthroscopy =3 months after hip injection, while 546 (44.8%) patients underwent hip arthroscopy >3-12 months following hip injection. Similarly, for the US cohort, 673 (56.6%) patients underwent hip arthroscopy =3 months after their hip injection, while 516 (43.4%) patients underwent hip arthroscopy >3-12 months following hip injection. Patients undergoing FL-guided (0.55%) and US-guided (0.58%) hip injection >3-12 months prior to hip arthroscopy had similar infection rates as those who did not undergo intraarticular injection in the 12 months prior to hip arthroscopy (0.50%, p=0.76 and p=0.75, respectively). Similarly, the infection rates for patients undergoing US-guided (0.45%) and FL-guided (0.45%) injections in the 3-months prior to arthroscopy were not significantly different from control patients who did not undergo preoperative hip injection (0.50%, p=1 for both). Results held in adjusted analysis controlling for age, sex, geography, year, smoking, and comorbidities. In reference to the no injection cohort, the adjusted odds ratio (95% CI) of postoperative infection for patients undergoing FL-guided injection =3 months and >3-12 months prior to hip arthroscopy were 0.90 (0.28-2.94, p=0.87) and 1.17 (0.36-3.84, p=0.80), respectively. For US-guided injection, the adjusted odds ratios at =3 months and >3-12 months were 0.89 (0.28-2.87, p=0.84) and 1.11 (0.34-3.60, p=0.86), respectively. Notably, infection rates in the arthroscopy =3 months cohort were substantially higher when including patients with an infection at the time of hip arthroscopy (FL 1.18%, US 0.74%).

Discussion And Conclusion

Postoperative infection following intraarticular hip injection =3 months prior to hip arthroscopy is rare (<0.5%) and no more common than in patients who did not undergo preoperative injection. Moreover, there do not appear to be substantial differences in infection risk between imaging-modalities. Notably, postoperative infection rates were substantially higher in sensitivity analyses where we did not exclude patients who had an infection at the time of the hip injection/aspiration.