Rotational or vertical instability? An analysis of 144 pelvic ring injury patients with unilateral sacrum and pubic rami fractures.

Abstract

Background: Pelvic ring injuries (PRIs) involving the unilateral sacrum and pubic rami fractures often appear radiographically similar but differ biomechanically in their stability profiles. Consequently, accurate early differentiation between Arbeitsgemeinschaft für Osteosynthesefragen (AO) type B2.1 (rotationally unstable) and C1.3 (vertically unstable) is critical for determining appropriate surgical intervention.

Hypothesis: We hypothesized that specific preoperative clinical and radiological factors could help differentiate between AO B2.1 and C1.3 fracture patterns, enabling more accurate diagnosis and optimized treatment planning.

Patients and methods: This retrospective study included 144 adult patients with unilateral sacrum and pubic rami fractures treated surgically between 2014 and 2021. Clinical data, including mechanism of injury, injury and new injury severity scores (ISS/NISS), and associated injuries, were collected. Radiological assessments focused on L5 transverse process (TP) fractures, sacral fracture completeness, and vertical displacement. Logistic regression and receiver operating characteristic analysis were used to identify predictors of C1.3 injuries.

Results: Of the 144 patients, 60 (41.7%) had AO B2.1 fractures, while 84 (58.3%) had AO C1.3 fractures. C1.3 injuries were significantly associated with male sex, high-energy mechanisms (e.g., fall from height), higher ISS/NISS, concomitant abdominal and urogenital injuries, and longer hospital/ICU stays (P < 0.05). Additionally, L5 TP fractures and vertical sacral displacement were radiologically more common in C1.3 cases than in B2.1 cases. Logistic regression identified NISS > 19 (OR: 1.17) and L5 TP fracture (OR: 9.02) as independent predictors of vertical instability.

Discussion: In the emergency setting, the presence of L5 TP fractures and a NISS > 19 can help clinicians anticipate vertical instability in patients with sacrum and pubic rami fractures. Furthermore, identifying these indicators preoperatively may facilitate more accurate classification and selection of appropriate fixation strategies, thereby improving outcomes in patients with pelvic ring injuries.

Level of evidence: III.