What is the relative importance of anterior ring intramedullary implant diameter and cortical purchase on outcomes following percutaneous fixation of lateral compression pelvic ring injuries?

Abstract

Fixation of the anterior pelvic ring improves outcomes in operatively treated lateral compression (LC) fractures (AO/OTA 61-B1/B2). Despite a high variability in the choice of intramedullary implants used for anterior ring fixation, the relative importance of implant diameter and cortical purchase (length) remains unclear. This study compared reoperation rates and radiographic outcomes between implants of various diameters and lengths in LC pelvic ring injuries. This retrospective multicenter study included patients from three international centers with acute (<3 weeks) LC injuries treated with percutaneous anterior and posterior ring fixation (January 2019-December 2025). Anterior ring implants (screws, Fasteners, or CurvaFix) were classified by outer diameter (small: 3.5-4.0 mm; medium: 4.5-5.0 mm; large: ≥ 6.5 mm) and purchase (unicortical vs. bicortical purchase), creating six possible groups for comparison. Variables collected included LC subtype, modified Nakatani zone, comminution, displacement, angle, bilaterality, and Mizzou Pelvic Displacement Predictor (MiPDiP) score. The primary outcome was unplanned reoperation (for loss of fixation, deformity correction, nonunion, or symptomatic implant). The secondary outcome was radiographic loss of reduction (>1 cm medial displacement on final healed radiographs vs. immediate postoperative). A sub-analysis was performed for LC1 injuries and associations with reoperation and deformity development were assessed in a multivariate analysis. One hundred eighty-one LC injuries were included (mean age 59.2 ± 21.9 years; 52% female [n = 95]; 70% LC1 [n = 127], 16% LC2 [n = 29], 14% LC3 [n = 25]; 48% (n = 87) large diameter bicortical implants, 36% (n = 66) medium diameter bicortical implants, 13% (n = 23) large diameter unicortical implants, 3% (n = 5) medium diameter unicortical implants). One small diameter (3.5 mm) implant was performed and excluded from statistical analysis. Overall reoperation occurred in five patients (2.8%), most frequently in the large diameter unicortical implant cohort (8.7%, n = 2/23, p = 0.245). Among all patients, deformity occurred in 9.4% (n = 17) and most frequently in the large diameter unicortical implant cohort (35%, n = 8/23; p < 0.001). Multivariate analysis demonstrated significantly increased odds of deformity with unicortical relative to bicortical fixation (OR = 11.24, 95%CI = 3.15 - 45.57, p < 0.001) and increasing MiPDiP score (OR = 1.73, 95%CI = 1.27 - 2.46, p = 0.002) but not implant diameter. There was no significant correlation between reoperation and purchase, MiPDiP score, or implant diameter. There were 127 LC1 injuries (mean age 64.0 ± 19.7 years; 59% female [n = 75]; 48% (n = 61) large diameter bicortical implants, 35% (n = 44) medium diameter bicortical implants, 15% (n = 19) large diameter unicortical implants, 2% (n = 3) medium diameter unicortical implants). Overall reoperation occurred in four patients (3.1%), most frequently in the large diameter unicortical implant cohort (11%, n = 2/19; p = 0.241). Among LC1 fractures only, deformity occurred in 13% (n = 17) and was significantly more frequent in the large diameter unicortical implant cohort (42%, n = 8/19; p = 0.005). Multivariate analysis demonstrated significantly increased odds of deformity with unicortical relative to bicortical fixation (OR = 11.10, 95%CI = 2.96 - 48.06, p = 0.002) and increasing MiPDiP score (OR = 1.64, 95%CI = 1.22 - 2.31, p = 0.004) but not implant diameter. There was no significant correlation between reoperation and purchase, MiPDiP score, or implant diameter. Bicortical purchase of superior ramus implants was associated with statistically lower rates of radiographic deformity compared with unicortical fixation. Larger-diameter implants offered no additional benefit over medium-diameter implants when bicortical purchase was achieved.