A Novel Minimally Invasive Surgical Technique for Fragility Fractures of the Pelvis with Iliac Screws via Two Small Incisions

The number of fragility fractures of the pelvis (FFP) is increasing quickly due to the ageing of society, and the treatment remain controversial. Long-term immobilization during conservative treatment can lead to secondary systemic complications, conventional open reduction and internal xation is highly invasive. We have developed a novel minimally invasive surgical technique for FFP. We made a 3-cm incision along medial borders of the posterior superior iliac spine, inserted one iliac screw on each side, and created a tunnel below the fascia connecting the two incisions. The interconnecting rod was slid across the tunnel on the dorsal surface of the sacrum and then xed with iliac screws. We evaluated the outcomes of this new stabilization technique in 9 patients, the average age and follow-up period were 80.8 years and 10.0 months. According to the Rommens classication, there was 1 patient with IIIc fracture, 1 with IVa, 6 with IVb and 1 with IVc. The average surgical time was 60.7 minutes with an intraoperative blood loss of 2.0 ml, and bony union of the posterior part of the pelvic ring was achieved in all patients. This method is a useful and safe minimally invasive option for high-risk elderly patients.


Introduction
The number of fragility fractures of the pelvis (FFP) is increasing along with the rapid ageing of the population and the increase in osteoporotic patients [1][2][3] . FFP occur in elderly, severe osteoporotic and frail patients who have several comorbidities, such as anaemia, malnutrition, cardiopulmonary insu ciency and renal dysfunction, and these fractures are treated conservatively in many cases. However, conservative treatment requiring long-term immobilization has a major impact on not only activities of daily living but also the incidence of systemic complications such as aspiration pneumonia, urinary tract infection, decubitus and disuse syndrome 4 . Moreover, nonunion development and/or fracture progression of the pelvic ring are often detected in patients with FFP during conservative treatment, which leads to physical dysfunction 5 . Because conventional open reduction and internal xation (ORIF) such as spino-pelvic xation is highly invasive, there are limitations to applying ORIF in elderly patients with poor general conditions. Our novel minimally invasive surgical (MIS) technique has an advantage for FFP in elderly patients with poor conditions.

Surgical Technique
In a prone position under general anaesthesia, we made two 3-cm incisions along the right and left medial borders of the posterior superior iliac spine (PSIS). Minimal bone resection of the posterior top of the PSIS was performed to prevent protrusion of the heads of the screws and postoperative irritation (Fig. 1a). We inserted one iliac screw (6.5-8.5 mm in diameter) on each side using uoroscopy (Fig. 1b) and created a tunnel below the fascia connecting the two incisions for the passage of the rod. After rod contouring to avoid the median sacral crest, the interconnecting rod was slid across the tunnel on the dorsal surface of the sacrum and then xed with iliac screws (Fig. 1c, 1d).
Patients were allowed non-weight bearing for a period of 2-4 weeks after surgery, and then full weight bearing was allowed depending on their tolerance. Table 1 shows the demographic details of the 9 patients. The average time of the surgical procedure was 60.7 minutes (range, 41-90 minutes), with an intraoperative blood loss of 2.0 ml (range, 1-10 ml). Postoperative complications developed in 4 patients: 2 with wound dehiscence requiring re-suture, 1 with deep vein thrombosis and 1 with lower gastrointestinal bleeding. There were no systemic complications, such as aspiration pneumonia or urinary tract infection. Bony union of sacral fractures, which occur in the posterior part of the pelvic ring, was achieved in all patients (100%). Five patients recovered their walking abilities to preinjury levels. The mean BMD T-score was − 3.4, and we prescribed daily teriparatide in 3 patients, romosozumab in 2 patients and denosumab in 2 patients for osteoporosis treatment.

Representative cases
An 85-year-old female with hypertension and diabetes mellitus fell from a standing height and was diagnosed with non-speci c low back pain and treated conservatively with analgesics. Two months after the trauma, she could not walk because of severe buttock and leg pain.
CT showed left rami fracture, bilateral sacral ala fractures and S3 vertebral fracture (Rommens classi cation type IVb FFP) (Fig. 2). We treated her using this MIS technique on the 9th day after admission. The surgical time was 58 minutes, and the intraoperative blood loss was 1.0 ml. She was allowed to walk with full weight bearing 2 weeks after the surgery; at 6 months postoperatively, complete bone union was achieved, and she was ambulatory without symptoms (Fig. 3).

Discussion
The number of FFP is increasing quickly due to the ageing of society. Previously, conservative treatment had been considered a standard treatment for FFP, providing good clinical results. However, the outcomes in elderly and severe osteoporotic patients who experience nonunion and fracture progression of the pelvic ring of prolonged pain and pain-induced immobility during conservative treatment are not rare, and long-term immobilization can lead to secondary systemic complications such as aspiration pneumonia and urinary tract infection. Rommens developed a comprehensive classi cation for FFP with suggestions for the management of each injury type 6 . Type I FFP can be treated conservatively. For type II FFP, conservative treatment is recommended initially, and percutaneous xation is required when conservative treatment is not successful. Type III and IV injuries require surgical treatment. However, conventional ORIF is highly invasive and not necessarily safe for elderly patients with poor general conditions. It has been a desire to make the surgery less invasive. minutes and 299 ml using the crab-shaped xation technique) 8 . These surgical techniques are less invasive than conventional ORIF but are still highly invasive for frail patients. In this study, the use of our novel MIS technique further decreased the surgical time and intraoperative blood loss (mean surgical time and intraoperative blood loss were 60.7 minutes and 2.0 ml, respectively), which has an advantage for FFP in elderly patients with poor conditions. Full weight bearing is allowed 2-4 weeks postoperatively, which means that sacral bone healing progresses because the stiffness of our stabilization is less than that of transiliac screw and rod xation and crab-shaped xation.
relief and early mobilization, such as posture changes, maintaining a sitting position and wheelchair transfer. Our MIS technique is bene cial, especially in elderly and frail patients, to avoid long-term immobilization and subsequent systemic complications.

Conclusion
We reported a new MIS technique for the treatment of FFP. This method is a successful and su cient minimally invasive option for highrisk elderly patients.

Methods
Ethical consideration.   a. Anteroposterior radiograph just after the surgery. b,c,d. Axial, coronal and sagittal plane of the spiral CT 6 months after the surgery.