Background:

The effect of spinopelvic fixation in addition to LSF on dislocation/instability and revision in patients undergoing primary total hip arthroplasty (THA) has not previously been reported.

Methods:

The PearlDiver Research Program was used to identify patients age 30 and over undergoing primary THA who received 1) THA only, 2) THA with prior single-level LSF, 3) THA with prior 2-5 level LSF, or 4) THA with prior LSF with spinopelvic fixation. The incidence of THA revision and dislocation/instability was compared through logistic regression and Chi-squared analysis. All regressions controlled for age, gender, Elixhauser Comorbidity Index (ECI).

Results:

Between 2010 and 2018, 465,558 patients without history of LSF undergoing THA were examined and compared to 180 THA patients with prior spinopelvic fixation, 5299 with prior single-level LSF, and 1465 with prior 2-5 level LSF. At 2 years, 7.8% of THA patients with prior spinopelvic fixation, 4.7% of THA patients with prior 2-5 level LSF, 4.2% of THA patients with prior single-level LSF, and 2.2% of THA patients undergoing only THA had a dislocation event or instability (p<0.0001). After controlling for length of fusion, pelvic fixation itself was associated with higher independent risk of revision (at 2 years: 2-5 level LSF+spinopelvic fixation: aHR=3.15,95%CI 1.77-5.61,p<0.0001 vs. 2-5 level LSF with no spinopelvic fixation: aOR=1.39,95%CI 1.10-1.76,p<0.0001).

Conclusion:

At 2 years, spinopelvic fixation in THA patients was associated with a greater than 3.5-fold increase in hip dislocation risk compared to those without LSF, and an over 2-fold increase in THA revision risk compared to those with LSF without spinopelvic fixation.