Metastatic Bone Disease (MBD), the spread of cancer cells from a primary tumour to bone, typically results in pain, pathological fractures, hypercalcaemia, spinal cord compression and other complications with significant impact on patients’ quality of life [1,2,3,4]. Due to better cancer survival rates the number of patients presenting with MBD is increasing and projections estimate a total of 2.5 million cancer patients in 2040 in the UK [5]. The most common visceral carcinomas causing orthopaedically relevant bone metastases are breast (28%), lung (17%) and renal (15%) cancers [6]. In addition, a relevant number of patients with haematological tumours (multiple myeloma and lymphoma) require surgical treatment due to the resulting osteolysis. The proximal femur is most frequently operated on, but the pelvis is also affected by relevant MBD in 16% of cases.

Pathological fractures pose a particular problem, as patients are usually already weakened and vulnerable due to the underlying disease. Additionally, pathological fractures have a high rate of non-unions and related implant failures [7, 8]. For this reason, prophylactic treatment of impending pathological fractures is more cost-effective and has a better functional outcome by preserving the patient’s independence [9, 10]. While the Mirels’ scoring system (MSS) used for long tubular bones enables a relatively good prediction of pathological fracture risk, no such scoring system has been established for the pelvis to date, which makes the treatment of patients with bone lesions in this area even more difficult [11,12,13]. Typical surgical options for the treatment of MBD include osteosynthesis, endoprosthesis, cryotherapy, radiofrequency ablation and cementoplasty; typical non-surgical options are radiotherapy, embolization, chemotherapy and bisphosphonates/denosumab [4].

For the surgical treatment of traumatic fractures of the posterior pelvic ring, percutaneous iliosacral screws or, in the case of more complex involvement of the sacrum or spinopelvic dissociation, spinopelvic fixation are traditionally used [14, 15]. In this context, fragility fractures of the pelvis (FFP) pose a particular problem due to poorer bone quality and associated slower bone healing, which is closer to the reality of pathological fractures. Both transsacral stabilisation and spinopelvic fixation are used for FFP, with Mendel et al. 2021 demonstrating significant outcome improvement and fracture healing. However, the subjective outcome in this study was better with transsacral stabilisation [16]. Gras et al. showed in 2015 that 88% of the population had a sufficient S1 or S2 corridor for an intraosseous transsacral implant on CT [17]. Based on this work, an angle-stable transsacral nail (SACRONAIL®, SIGNUS, Alzenau, Germany) was developed that can be locked in both ilia and showed no implant failure or malpositioning in the first pilot study by Marintschev et al. in a 1-year follow-up with immediate postoperative full load-bearing capacity [18].

For pathological fractures of the pelvis, various procedures have been described, particularly minimally invasive ones, which involved filling the defect with bone cement (e.g. sacroplasty) with and without screw fixation or percutaneous screw stabilisation alone, all of which were able to increase the VAS and the patient’s mobility [19, 20]. The combination of bone cement and screw fixation showed the highest biomechanical stability in the model [21]. Lee et al. have supplemented this procedure with an additional ablation of the lesion as “Ablation, Osteoplasty, Reinforcement and Internal Fixation” (AORIF) and were able to show good results in their case series [22, 23].

In our view, the disadvantage of cemented screws is their spatial limitation and thus less broad anchoring in the existing pelvic bone than a wide-span intraosseous implant such as the SACRONAIL® could offer. Due to the very good results in the pilot study by Marintschev et al. in FFP, we have used the implant in pathological fractures of the posterior pelvic ring and present this case series below.

This study was approved by the local ethics committee. Patients provided written informed consent to participate in the study, which included preoperative and postoperative assessments of pain using the Numeric Rating Scale (NRS); evaluation of pain medication use; assessments of walking distance and walking time; and measurement of quality of life using the SF-12 questionnaire. Additionally, we monitored medical and implant-related complications. The structured follow-up consisted of consultations at 3 and 12 months, as well as telephone interviews at 6 and 9 months.

The inclusion criteria were skeletal involvement from an underlying oncological or haematological disease without curative resection intent, along with pathological sacral fracture and no symptom improvement following conservative therapy (outpatient for 4 weeks vs. inpatient 1 week). The exclusion criteria included ilium involvement, extensive osteolysis of the sacral body requiring spinopelvic fixation, or a poor prognosis for patients in palliative care, as determined by the multidisciplinary tumour board.