Modified less invasive anterior subcutaneous fixator for unstable Tile-C-pelvic ring fractures: a biomechanical study

BACKGROUND: Operative procedures for unstable pelvic ring fractures remain controversially discussed. Minimally invasive treatment options for pelvic ring fractures have several benefits for the patient. But they can also provide disadvantages. Anterior subcutaneous pelvic fixation (INFIX) has shown promising biomechanical results in pelvic ring fractures, but there is a high complication rate of nerve injuries. An additional screw to the INFIX seems to be more stable. The aim of this study is to compare biomechanical stability of a new modified unilateral INFIX fixing the unilateral injured pelvic ring with the standard INFIX. METHODS: 24 composite synthetic full pelvises were used in this study. 4 groups each with a number of six pelvic specimens were randomly assigned. A C1.3-type pelvic fracture was made with an osteotomy of the sacrum and an osteotomy of the anterior pelvic ring. Fracture fixation was performed within the four groups: (1) unilateral INFIX, (2) “extended” unilateral INFIX + additional pubic ramus pedicle screw, (3) bilateral INFIX, (4) “extended” bilateral INFIX + additional pubic ramus pedicle screw. All specimens were cyclic loaded with 200 N until maximum of 300 N. Distance/dislocation of the fracture fragments were detected with 3D-ultrasound measuring system. Stiffness was calculated. RESULTS: Extended unilateral INFIX showed the lowest mean dislocation. Lowest rotational stability was displayed by the standard bilateral INFIX. A significant difference (P = 0.04) was shown between the extended unilateral INFIX and the “standard” bilateral INFIX in terms of rotational stability. Extended unilateral INFIX showed significantly improved stability of anterior fracture dislocation (P = 0.01) and unilateral INFIX showed the highest rotational stiffness. Anterior fixation stiffness of the unilateral INFIX was significantly improved using an additional symphysis/pubic ramus screw (P = 0.002). CONCLUSION: Extended unilateral INFIX (+ additional pubic ramus pedicle screw) is a feasible minimally invasive treatment for anterior pelvic ring fractures. Higher stability and lower probability of bilateral nerve damage is provided by the extended unilateral INFIX compared to the standard bilateral INFIX.