Biomechanics and clinical outcomes of “barrel handle” connecting rods used in INFIX internal fixation for unstable pelvic fractures: a cadaveric biomechanical study and retrospective cohort study

Abstract

Background This study aimed to compare the biomechanical stability and clinical outcomes of a bent “barrel handle” connecting rod with a conventional “arc” rod when using the anterior subcutaneous internal fixator (INFIX) for unstable pelvic fractures. Method Type C1 pelvic ring injury model specimens were created by performing sacral foramen and pubic ramus osteotomies in 16 cadaveric pelvises. The models were randomly divided into group A (INFIX S1 screw fixation using a “barrel handle” connecting rod) and group B (INFIX S1 screw fixation using an “arc” connecting rod). Each model underwent vertical loading of 200–800 N, and the horizontal and vertical displacement distances of the fractured ends of the pubic ramus were recorded at 200, 400, 600, and 800 N. The treatment outcomes of 37 patients with unstable pelvic fractures were retrospectively evaluated. Among these, 15 patients were treated with the INFIX using the “barrel handle” connecting rods, while 22 were treated with the INFIX using the “arc” connecting rod. Outcome measures were postoperative complications (ectopic ossification, anterior exothelial nerve injury, infection), fracture reduction quality (Matta score), and postoperative function (Majeed score). Results The experiments showed no significant differences between groups A and B in the horizontal and vertical displacements after vertical compression. Among the 39 clinical cases, two patients were lost to follow-up. The demographic characteristics (sex and age), fracture classification, Injury Severity Score, and body mass index of the two groups were not comparable (P > 0.05). There were no significant differences between the two groups in fracture reduction quality, postoperative function, and postoperative complications, except for ectopic ossification. The incidences of anterior exothelial nerve injury and wound infection were significantly lower in the group treated with the INFIX using the “barrel handle” connecting rod than in the group treated with the INFIX using the “arc” connecting rod. Conclusion The INFIX using a “barrel handle” connecting rod achieves similar biomechanical stability and favorable clinical outcomes compared with the INFIX using an “arc” connecting rod. Furthermore, use of the INFIX with “barrel handle” connecting rods significantly reduces the incidences of postoperative wound infection and anterior exocortical nerve injury.