Modified pedicle screw–rod fixation as a minimally invasive treatment for anterior pelvic ring injuries: an initial case series

If posterior instability existed, it is addressed first fixing with the pedicle screws and rod for reduction and fixation. The prone position was employed. We marked the posterior superior iliac spine (PSIS) and dorsal iliac crest preoperatively. Bilateral 3 cm incisions were made along the PSIS. A pedicle finder was used at the medial side of the dorsal iliac crest and 1 cm cranial to the PSIS to make a bony corridor toward the anterior inferior iliac spine (AIIS). After ensuring the corridor did not penetrate the bony cortex, we inserted two 7-mm-diameter pedicle screws with a length of 50 to 60 mm. Partial resection of the PSIS at the entry point for settling the screw heads was performed to minimize implant prominence and soft tissue irritation. A 6-mm-diameter titanium rod was slid through the subfascial plane to connect two screws. To complete reduction of the posterior pelvic ring, compression, distraction, or even injured leg traction was applied according to the fracture pattern. The screw caps were locked at last to maintain the reduction.

After stabilizing the posterior elements, anterior pelvic ring was addressed. The patient was positioned supine on a radiolucent table. As with routine INFIX, the AIIS was located as the osseous entry with the C-arm fluoroscopy. A “teardrop shape” of the AIIS, the safe zone for pedicle screw placement, was obtained on the obturator outlet view. A 3-cm longitudinal incision was then made centered over the AIIS in line with the groin crease, care being taken to protect the lateral femoral cutaneous nerve (LFCN) which often runs across the surgical field. Access to the AIIS was obtained via a blunt dissection through the interval between the sartorius and tensor fascia lata. A pedicle awl was advanced to open the cortex at the starting pointing, the middle of the AIIS or the center of the “teardrop.” A pedicle finder was then positioned to create a bony corridor for the screw toward the PSIS, using the obturator inlet view to ensure that the corridor did not penetrate the ilium and the iliac oblique view to ensure that the pedicle finder was well clear of the hip joint and greater sciatic notch. Into the corridor, a polyaxial pedicle screw was inserted to an adequate depth positioned roughly 2 cm proud of the bone. Considering the habitus of the patients, screws used for this series were 60 to 80 mm in length and 6.5 to 7 mm in diameter. The procedure was repeated for the contralateral hemipelvis. We modified the INFIX by adding a 3-cm Pfannenstiel incision 2 cm over the pubic symphysis, and the blunt dissection was continued to the level of pubic tubercle. A polyaxial pedicle screw was driven through either ipsilateral or contralateral pubic tubercle down into the inferior ramus, using the pelvic inlet view to confirm the safe placement of this additional screw. Based on our experience, the screw was advanced at a tilt angle from 45° to 60°, also positioned 2 cm proud of the pubic tubercle. The screws used were 35 to 50 mm in length and 6.5 to 7 mm in diameter. When the three screws were positioned in the appropriate depth, a 6-mm-diameter long titanium rod was placed over them to adjust its length and curve. The rod was precontoured with an anterior and inferior bow to avoid compressive neurovascular complications. To develop a corridor just superficial to the fascia, long hemostats were inserted into the subcutaneous tissue from the incisions at bilateral AIIS to the Pfannenstiel incision. The rod was gently slid in the corridor from the incision at ipsilateral AIIS to contralateral AIIS via pubic tubercles and was connected to three screw heads, whose caps were loosely secured to maintain the rod in place. At this point, the reduction tools were attached to the pedicle screws at the bilateral AIIS to manipulate both hemipelvis into place. Reduction of the anterior pelvic ring was achieved by compression or distraction of the rod, depending on the fracture pattern. Finally, the screw caps were locked with a torque screwdriver to maintain the reduction, with the screws at bilateral AIIS being tightened prior to the one at the pubic tubercle (Fig. 1).

Non-weight-bearing functional exercise on function of lower limbs and joints was initiated for all patients from postoperative day 1. It was important for prophylaxis against deep venous thrombosis. The patients with only anterior ring fixation were allowed partial weight-bearing while sitting on the bedside at postoperatively 4 weeks, and it was allowed at postoperatively 6 weeks for the patients with both anterior and posterior ring fixation. Gradually, they were allowed to walk with full weight-bearing when the union occurred as indicated by callus formation shown on postoperative radiograph. The implant was removed at an average of 7 months postoperatively (range, 4–10 months). Routine follow-up were arranged at postoperatively 4, 6, 3, 6, and 9 months and 1 year for clinical and radiological examinations. Follow-up was continued after this period if necessary. At the last follow-up, the outcome was assessed clinically (Majeed scores) [8] with five functional indicators: pain, sitting, standing, sexual intercourse, and work. Postoperative reduction was evaluated according to the criteria of Matta [9], graded by displacement as excellent (0–4 mm), good (5–10 mm), fair (11–20 mm), and poor (>20 mm) (Table 1).