Introduction

Insufficiency fractures in elderly people sometimes require percutaneous posterior ring fixation [1–3]. In this patient population, the treating surgeons face special problems in terms of screw migration. There are multiple reasons for this. First, steel screws do not really incorporate in bone and are prone to dislocation. Second, osteoporotic bone offers only little resistance to screw pullout forces. Third, the patients are often not able to partially bear weight, which further enables screw dislocation before healing of the fracture can occur.

In some countries, fenestrated screws are available; in others, custom-made implants are manufactured off-label (by drilling additional holes at the screw tip). Other methods like trans-iliac–sacral–iliac bars [3] might not be possible in patients with a dysplastic sacrum with special anatomic conditions. Fenestrated screws are expensive and hence might not be affordable for every trauma center in times of financial resources shortage. This report outlines an easy technique for cement augmentation using regular screws and bone cement without the need of special implants like bars or fenestrated screws.

Surgical technique

The patient was positioned supine on a radiolucent table under general anesthesia. After aseptic preparation and drape, a standard two-dimensional C-arm was used to determine the ideal insertion point, as well as the pelvic inlet and outlet view [1, 4].

In alternating inlet and outlet view, a threaded 2.7 mm K-wire was slowly advanced after a small skin incision into the first sacral vertebral body. In cases where an additional screw was deemed necessary, the optimal entry point and trajectory for K-wire insertion in S2 was done as described by Osterhoff et al. [1, 2] (Fig. 1).

Fig. 1
figure 1

Inlet view (left) and outlet view (right). Placement of K-wires into the vertebral body of S1 and S2 using conventional C-arm fluoroscopy

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The appropriate screw length was determined by measuring the K-wire. A cannulated fully threaded screw (7.3 mm) was inserted over the K-wire to its final position in the vertebral body under constant fluoroscopic control (Fig. 2). If needed, an additional screw was inserted in S1 or in S2, which led to a higher rigidity of the posterior pelvic ring. A washer was used in every patient to avoid accidental intrusion into the iliac cortical bone.

Fig. 2
figure 2

Outlet view placement of a cannulated fully threaded 7.3 mm screw into S1

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After radiological positioning control, the screw was turned back by approximately 1 inch. This created a threaded template for the following cement distribution into the drill hole (Fig. 3). The K-wire was then used for the screwdriver (Longitude® Medtronic) to be mounted on the screw. After that, the wire was removed.

Fig. 3
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Screw draw-back and K-wire removal

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The PMMA cement was mixed. The bone filler device was introduced through the screwdriver and approximately 2–3 mL of cement were applied carefully to the preformed drill hole in the first sacral vertebral body in front of the screw tip (Fig. 4). Constant fluoroscopic control was maintained for cement leakage detection. Augmentation was performed only in the first sacral vertebral body, since the safety margins of the screw trajectories for the vertebral body of S2 are narrower than for S1. The safe zone for cement deposition in the second vertebral body, even when implying accurate screw placement, is distinctly smaller. In addition, because of the narrow margins, the S2 screw had more bony purchase than the one in S1 even in osteoporotic bone.

Fig. 4
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In-screw cement augmentation

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The screw was carefully reinserted and tightened to its final position imbedded in cement in the S1 vertebral body (Fig. 5). The screwdriver was left holding the recess of the screw head until the setting of the cement, keeping it from getting clogged and therefore becoming an additional challenge for emergency or routine screw removal.

Fig. 5
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Careful reinsertion of the screw after cement augmentation

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For final screw positioning control and adequate cement distribution, an intraoperative CT scan with 3D reconstruction was performed (Fig. 6). The skin closure was done after imaging analysis.

Fig. 6
figure 6

Intraoperative 3D scan for screw positioning and cement distribution control

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Patients and methods

Twenty consecutive patients were enrolled in this study between December 2013 and December 2014. The data were collected prospectively and analyzed retrospectively, and are summarized in Table 1. There were 11 female and 9 male patients included, with a mean age of 74.4 years (range 48–98). 13 patients were admitted to the hospital due to pelvic ring traumas. The injury pattern was classified according to Young et al. [5]. In four cases, an S1 osteolytic metastasis with impending fractures and three patients with sacral insufficiency fractures due to osteoporosis were included. In nine patients, osteoporosis was diagnosed prior to admission. Two had acquired osteoporosis due to prednisone therapy after solid organ transplantation. All patients received a preoperative CT scan of the pelvis to evaluate the bone stock of the posterior pelvic ring. In cases of metastatic diseases and unknown osteoporosis, the senior author and the radiologist assessed the bone stock quality. The senior author then made the decision for in-screw cement augmentation.

Table 1 Summary of data
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Pain was evaluated according to the VAS score preoperatively, postoperatively and after 6 weeks. In addition, intraoperative complications were noted. The mobility of the patients and the duration of the in-hospital stay, as well as newly appeared neurological dysfunctions, were additional outcome parameters. If available, late complications were noted in the outpatient clinic.

Results

Twenty six screws were implanted according to the above-mentioned surgical protocol. The mean surgery time was 45.25 min (range 30–100 min).

Four patients received intended conservative treatment without medical improvement for a mean duration of 4 ± 2 days before undergoing surgery. In one case, the screw together with the washer intruded the cortical iliac bone due to severe osteoporosis. The screw positioning remained satisfactory and surgery could be continued as planned. No cement leakage or screw malpositioning occurred.

All patients were fit for immediate postoperative mobilization with considerably reduced pain and total weight bearing under the supervision of a physiotherapist. Five patients received crutches for a better balance of gait.

The mean duration of the hospital stay was 13 ± 5 days. Postoperatively, no patient presented with newly occurring neurological deficits.

In two patients, screw removal was necessary due to iliosacral arthropathy after 6 and 8 months. One screw migration was noted after 1 year due to severe osteoporosis (Fig. 7).

Fig. 7
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Patient 10 with late screw migration after 1 year

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Discussion

The aim of the present study was to describe in detail a promising technique for the treatment of pelvic ring fractures in patients with documented weak bone stock. The advantages of the combination of cement augmentation and minimal invasive screw placement are presented. Other studies have dealt solely with the treatment of sacral insufficiency fractures.

In 2002, Garant [6] first described sacroplasty, the minimal invasive application of PMMA cement to the fractured sacrum, in sacral insufficiency fractures as an alternative to conservative treatment. Since then, numerous authors have reported on sacroplasty as an effective method for prompt pain reduction [7–10]. Stabilization of the fracture fragments due to the cement could be the explanation for immediate pain relief [11].

Recently, methods of percutaneous internal fixation have been described as further alternatives. Iliosacral screw fixation, as described only in a few case reports for insufficiency fractures [12, 13], seems to hold no significant difference to sacroplasty in reducing fracture site motion in a biomechanical comparison in osteoporotic bone [14]. However, fracture site reduction is not the main reason to do surgery; the real aim is to stabilize and reduce pain [11, 14]. In sacroplasty, considering the cement deposition in between fracture fragments, bone healing is impossible. For the iliosacral screw, creating interfragmentary compression, required for adequate fracture healing, represents a challenge due to insufficient screw anchorage [11]. Furthermore, in case of transforaminal fractures, it prevents further sacral dislocations, which potentially could cause additional problems such as incontinence or sexual incompetence due to S2–4 foraminal stenosis.

Therefore, using a transiliosacral bar or longer screws engaging the sacrum was proposed to improve fixation strength in the presence of osteoporosis [3, 11, 15, 16].

Furthermore, combining the advantages of osteosynthesis and cement augmentation has proven in biomechanical studies to provide better screw fixation in osteoporotic bone [17]; this was illustrated for pedicle screws [18, 19] and for iliac screws using PMMA cement [20].

Cement-augmented percutaneous iliosacral screws appear to be a promising treatment option for sacral insufficiency fractures demonstrated in a few recent publications [21–25]. Wähnert et al. [25] describe a technique of cement application by means of perforations around the circumference of the screw tip, allowing cement discharge after final screw placement. In this study, 12 women with sacral insufficiency fractures were treated using intraoperative 3D navigation. No perioperative complications occurred. Screw placement and cement deposition were accurate. Postoperatively, all patients were immediately painless and mobilized. Another option would be to apply the cement before final screw positioning [21–23], either via separate Jamshidi needles or the cannulated screw itself, thereby abstaining from initial screw placement control. Intraoperative navigation or 3D position monitoring is used. No perioperative complications occurred and immediate mobilization with reduced pain was possible.

These results are in accordance with the findings of this study. No perioperative complications occurred apart from the singular intrusion of a screw including its washer, during insertion through the cortical bone. Nevertheless, this depicts an essential risk of this technique considering the need for screw reinsertion in weak bone mass. Reducing this hazard could be achieved by creating the possibility of cement application after the final screw placement. Likewise, this would decrease the weakening of the purchase of the screw.

This study used solely conventional C-arm fluoroscopy for screw positioning and cement deposition. The results suggest that the presented technique is reliable with regard to screw placement and accurate cement deposition. Comparing intraoperative navigation, 3D position monitoring or CT guidance to conventional visualization for iliosacral screw techniques in trauma patients, the study results are controversial. Some publications suggest intraoperative 2D or 3D navigation to improve precision [26–28], whereas others find no significant difference [29]. Yet, Osterhoff et al. [1] argue that if conducted by an experienced surgeon, C-arm fluoroscopy represents a safe technique for iliosacral screw placement. Last but not least, it needs to be considered that modern intraoperative navigation or 3D visualization is not at every surgeon’s disposal.

ISFICA is a fast, reliable alternative in patients with poor bone stock of the pelvic ring. Despite one intraoperative complication with a cortical breach and one screw migration after 1 year, this technique combines the advantages of two minimally invasive methods treating posterior pelvic ring pathologies. By only using 2D imaging, the surgery time is minimal, which reduces the risk of severe ventilation complications. In addition, all patients could be immediately mobilized with considerable pain reduction. However, to prove the superiority of this method in long-term follow-ups, more research is paramount, especially regarding screw pullout and long-lasting pain reduction.