A clinical and biomechanical comparison of INFIX plus single versus double sacroiliac screw fixation for unstable pelvic ring injury

Abstract

Background: The aim of this study is to compare the clinical and biomechanical outcome of INFIX plus single with two sacroiliac screw fixation for unstable pelvic fractures of Type C.

Methods: Sixteen cadavers were randomly subjected to INFIX plus single or double sacroiliac screw fixations and then mounted onto the ElectroForce loading machine under different vertical loads. To investigate the clinical outcomes of the two techniques, nineteen patients were retrospectively analyzed. The main outcome measures were postoperative radiographic reduction grading (using the Tornetta and Matta grading system), functional outcome (using the Majeed scoring system), and incidence of complications.

Results: In the biomechanical study, INFIX plus double sacroiliac screw fixation showed better biomechanical stability than fixation with a single sacroiliac screw (p < 0.05). In our clinical case series, all 19 patients had bony union 6 months after the operation. INFIX plus double sacroiliac screw fixation also demonstrated a better functional outcome and a higher radiographic satisfactory rate than INFIX plus single sacroiliac screw fixation (79.25 ± 5.47; 91.33 ± 4.97; p < 0.05), (77.78% vs. 60%; p = 0.05). One patient in INFIX plus single-screw fixation group had screw loosening at 6-month follow-up postoperatively. One case in each group suffered heterotopic ossification and the lateral femoral cutaneous nerve paralysis, and one patient suffered from infection.

Conclusion: INFIX plus double sacroiliac screw fixation demonstrated more stability in cadaveric biomechanical analysis and better clinical outcomes than INFIX plus single sacroiliac screw fixation.

Keywords: Biomechanics; INFIX; Internal fixation; Pelvic fracture; Sacroiliac screw fixation.

Fig. 1

Models of AO/OTA type C1 unstable pelvic fractures were created. Pelvic fracture C1 on diagrammatic pelvic model (a) and fresh human adult cadaver pelvis (b). A sacroiliac screw was fixed at S1 (c), and two multiaxial pedicle screws (6.5 mm × 70 mm) were inserted through the point of each anterior inferior iliac spine (d). Loading of the fracture models on a biomechanical testing machine using the two-limb-stance model (e)

Fig. 2

A series of images depicting the clinical course of a patient (male, 57 years, AO/OTA type C1) who developed loosening of screws at 6 months post-surgery. Preoperative images of the pelvis, including anteroposterior (a) and coronal (b) radiographs, and three-dimensional CT scan images (c), all depicting left sacroiliac joint fracture dislocation with complete instability, and anterior pelvis fracture with concomitant bilateral superior and inferior pubic rami fractures. Plain radiographs taken 1 day after INFIX surgery, showing anteroposterior (d), inlet (e), and outlet (f) views of the pelvis. Images taken 6 months after INFIX surgery, showing screw loosening on anteroposterior radiographs (g) and compression of the skin (h)