Impact of abscess type on outcomes following posterior fixation for thoracolumbar pyogenic spondylitis: a multicenter retrospective cohort study

STUDY DESIGN: Multicenter retrospective cohort study. PURPOSE: To evaluate the impact of abscess presence and type on treatment duration and clinical outcomes in patients undergoing minimally invasive posterior fixation for thoracolumbar pyogenic spondylitis. OVERVIEW OF LITERATURE: Surgical management is increasingly favored for pyogenic spondylitis. Abscesses, particularly epidural and iliopsoas, have been linked to poorer prognoses, and empyema, though uncommon, tends to be particularly severe. However, the effect of specific abscess types on surgical outcomes remains unclear. METHODS: This study included 92 patients who underwent minimally invasive posterior fixation across 10 centers between 2014 and 2024. Patients were classified into an abscess group (epidural, iliopsoas, empyema, or other) and a non-abscess group. Clinical outcomes, including total duration of intravenous antibiotics and unplanned additional surgeries, were compared. Subgroup and regression analyses were conducted to assess the impact of specific abscess type. RESULTS: Abscesses were present in 65 patients (71%): epidural (n=51), iliopsoas (n=38), and empyema (n=3), with some overlap. Compared with the non-abscess group (n=27; 29%), there were no significant differences in antibiotic duration or rates of unplanned additional surgery. However, iliopsoas abscess was associated with longer antibiotic duration (8.1 weeks vs. 6.6 weeks, p =0.044), while all empyema cases required additional surgery for poor infection control (p =0.000). Regression analysis identified iliopsoas abscess and age ≥65 years as independent predictors of prolonged antibiotic use, whereas epidural abscess was associated with shorter antibiotic duration. CONCLUSIONS: Iliopsoas abscesses were associated with longer antibiotic courses, while empyema was linked to poor infection control and a higher likelihood of additional surgery.