Trans-obturator cable fixation of open book pelvic injuries

Abstract

Operative treatment of ruptured pubic symphysis by plating is often accompanied by complications. Trans-obturator cable fixation might be a more reliable technique; however, have not yet been tested for stabilization of ruptured pubic symphysis. This study compares symphyseal trans-obturator cable fixation versus plating through biomechanical testing and evaluates safety in a cadaver experiment. APC type II injuries were generated in synthetic pelvic models and subsequently separated into three different groups. The anterior pelvic ring was fixed using a four-hole steel plate in Group A, a stainless steel cable in Group B, and a titan band in Group C. Biomechanical testing was conducted by a single-leg-stance model using a material testing machine under physiological load levels. A cadaver study was carried out to analyze the trans-obturator surgical approach. Peak-to-peak displacement, total displacement, plastic deformation and stiffness revealed a tendency for higher stability for trans-obturator cable/band fixation but no statistical difference to plating was detected. The cadaver study revealed a safe zone for cable passage with sufficient distance to the obturator canal. Trans-obturator cable fixation has the potential to become an alternative for symphyseal fixation with less complications.

Figure 1

Different groups tested. (A) Stabilization with a four-hole 3.5-mm stainless steel plate. (B) Trans-obturator wire using a 1.7-mm cable system. (C) Trans-obturator fixation using a broad titan band. Ten specimens were tested in each group.

Figure 2

Stepwise application of a trans-obturator fixation in Group C. (A) Instruments and titan band (B) Tensioner (C) Fixation of the clamp using a screw driver (B) Final position.

Figure 3

Biomechanical testing. (A,B) Fixation of the pelvis to the material testing machine. (C) Single-leg-stance model in which load can be applied to one side.

Figure 4

Peak-to-peak displacement of the different groups tested under 200-, 400- and 600-N Load. Displacement was measured for the whole pelvis. Displacement rises under increasing load. No implant failure was observed. Statistically significant differences were not detected between the groups (asterisk = outlier).

Figure 5

Total displacement represents the final change of the probe after all load levels were applied. Plastic deformation represents the permanent and irreversible strain of the hole construct. The plate and cable systems showed only minimal amounts of deformation. Even though group B had the highest stiffness, no statistical difference was found.

Figure 6

Anatomical landmarks. (A) Pubic symphysis anteriorly fixed with a trans-obturator cable. (B) Dotted line encircles the obturator foramen. The membrane does not seal the whole foramen. The asterisk marks the vessels and the nerve leaving for the obturator canal. (C) Obturator foramen from a more lateral perspective. Note the distance to the cable system. (D) View from the cranial pubic rim of the pubic branch. The bladder is retracted.

Figure 7

Schematic illustration of the obturator foramen. The obturator artery divides into medial and lateral branches as it emerges from the obturator canal. An acetabular branch rises from the lateral part and runs towards the hip joint. The obturator nerve divides into anterior (Pectineus m., Adductor longus m., Adductor brevis m. Gracilis m.) and posterior divisions (Obturator externus m., Adductor magnus m.). At the medial border, a safe zone can be identified in which the cable wire can be passed with limited risk.

Figure 8

Complication that may occur using trans-obturator cable fixation. (A) Horizontal dislocation of the pubic rim is possible because of shear stress. (B) In case of a very unstable posterior pelvic ring that has not been stabilized, dislocation of the pubic rim in the axial plane may be a problem.