Fragility fractures of the pelvis (FFP) are low-energy pelvic fractures in the elderly, often caused by osteoporosis, radiation therapy or metastatic disease that reduce the stability of the pelvic bone structure. The incidence is around 90/100.000 and rising due to the growing ageing population [1]. These low-energy fractures were traditionally managed conservatively. However, prolonged immobility in elderly patients can result in severe systemic complications, increased dependency, and increased mortality. Rommens and Hoffmann developed the classification system for these fractures and also suggested an algorithm for the operative treatment [2,3]. The goal of the operative treatment of these mostly frail patients is a stable pelvis with a minimal operative impact. The percutaneous sacroiliac and/or transsacral stabilisation of the sacral fracture, and in rare cases concomitant stabilisation of the anterior pelvic ring, is the surgical method of choice [4]. It requires only stab incisions for implantation of the screws, the duration of surgery is short, there is only minimal bleeding, and correctly implanted screws allow for full weightbearing immediately after surgery.

There are three methods of percutaneous screw implantation. The standard method was previously the intraoperative fluoroscopy. However, this imaging is limited by poor visualisation and offers only two-dimensional imaging of the sacrum [5]. The complexity of the intrapelvic structures requires knowledge and interpretation of various fluoroscopic images to ensure a correct and safe screw placement. Excessive bowel gas and obesity can increase the difficulty of the procedure [6]. Consequently, fluoroscopy-guided percutaneous sacral screw placement has a malposition rate of 2.6% - 25% even in the hands of experienced surgeons [7,8]. Navigated implantation of sacroiliac screws is more accurate. The method requires the implantation of a reference screw in the iliac bone, designated instruments with markers, two cameras, and a software program projecting the instrument position to a virtual image of the pelvis. There is a potential error if the reference screw is unstable and the hardware and software are expensive [9]. An accurate, simple and safe method is the CT-guided screw implantation using the technique that is used by radiologists for CT-guided biopsies. During insertion of the K-wire into the sacral body, the trajectory is controlled and optimised during its advancement with the help of a low-dose CT-scan [10]. The implantation can therefore be controlled and precision optimised. A correct placement is essential. The lumbar nerves and the presacral venous plexus are at danger should the screws perforate neuroforamina or the anterior sacrum. Therefore, the precision of the screw placement is an important parameter to assess treatment quality [7,11].

A common problem in osteoporotic bone is loosening of the implanted screws leading to backing out. The screws move retrograde into the gluteal muscle often causing pain in the buttock and also leading to loss of stability of the osteosynthesis. Literature describes a loosening rate of 10-20% in FFP [10,[12], [13], [14], [15], [16]]. The cause of loosening of screws in the pelvis is not always known. However, a significant association between osteoporosis and screw loosening has been reported [17].

The outcomes following surgical treatment are mostly good with preservation of self dependency. A recent study showed that 68.8% of the patients had regained their original mobility at the time of discharge following percutaneous sacroiliac screw fixation. The home situation remained unchanged in 73.9% of the cases [18].

The aim of the paper is to describe the precision, safety, and independence-preserving properties of percutaneous CT-controlled stabilisation of FFP fractures in the elderly and discuss possible factors affecting these outcomes. We also give a detailed description of the operative procedure and analyse the predictors for screw loosening.