Dislocation rate after hip arthroplasty due to metastatic bone disease: a retrospective cohort study evaluating the postoperative dislocation risk across different articulating solutions.

BACKGROUND AND PURPOSE: Joint stability after hip replacement (HR) in patients with metastatic bone disease (MBD) is of special importance. Dislocation is the second leading cause of implant revision in HR, while survival after MBD surgery is poor with an expected 1-year survival of around 40%. As few studies have investigated the dislocation risk across different articulation solutions in MBD, we conducted a retrospective study on primary HR for patients with MBD treated in our department. PATIENTS AND METHODS: The primary outcome is the 1-year cumulative incidence of dislocation. We included patients with MBD who received HR at our department in 2003-2019. We excluded patients with partial pelvic reconstruction, total femoral replacement, and revision surgery. We assessed the incidence of dislocation with competing risk analysis with death and implant removal as competing risks. RESULTS: We included 471 patients. Median follow-up was 6.5 months. The patients received 248 regular total hip arthroplasties (THAs), 117 hemiarthroplasties, 70 constrained liners, and 36 dual mobility liners. Major bone resection (MBR), defined as resection below the lesser trochanter, was performed in 63%. The overall 1-year cumulative incidence of dislocation was 6.2% (95% CI 4.0-8.3). Dislocation stratified by articulating surface was 6.9% (CI 3.7-10) for regular THA, 6.8% (CI 2.3-11) for hemiarthroplasty, 2.9% (CI 0.0-6.8) for constrained liner, and 5.6% (CI 0.0-13) for dual mobility liners. There was no significant difference between patients with and without MBR (p = 0.5). CONCLUSION: The 1-year cumulative incidence of dislocation is 6.2% in patients with MBD. Further studies are needed to determine any real benefits of specific articulations on the risk of postoperative dislocation in patients with MBD.

Surgical Treatment of Metastatic Bone Disease in the Appendicular Skeleton: A Population-Based Study.

Background: Population-based studies of patients with bone metastases in the appendicular skeleton (aBM) requiring surgery for complete or impending fracture are rare. In this epidemiologically-based observational study we created a large population-based cohort of patients treated for aBM, aiming to: (1) monitor possible time-related changes of the incidence of surgical treatment of aBM-lesions, (2) examine differences in the population and care of patients treated at different treatment centers and (3) examine if findings from a previous pilot study regarding absence of a suitable biopsy of the lesions representing debut of cancer or a relapse has improved the awareness of aBM and hereby increased the focus on regular tumor biopsies and follow-up imaging of cancer patients. Methods: We examined a population-based cohort consisting of all patients treated for aBM 2014−2019. Procedures were performed at five secondary surgical centers (SSC) or one tertiary referral Musculoskeletal Tumor Center (MTC). Patients were followed until end of study (30 September 2021) or death. No patients were lost to follow-up. Results: Four-hundred-fifty-seven patients (493 primary aBM-lesions, 482 procedures) were included. Annual incidence of aBM-surgery was 46 aBM-lesions/million. MTC-patients had a significant better preoperative status than SSC-patients considering factors known for survival. Patients with complete fracture experienced longer surgical delay when treated at MTC compared to SSC: 4 (1−9) and 1 (1−3) days (p < 0.001), respectively. Overall survival for the entire cohort was 37% and 11% at 1 and 5 years (MTC and SSC 1 and 5 year respectively: 44% and 15% vs. 29% and 5%, p < 0.001). In patients with debut or relapse of cancer, 8% and 9% had insufficient biopsies, and 21% and 12% had no biopsy, respectively. Comparison showed no change over time. Conclusions: The current study highlights the low awareness on treating aBM at SSC and emphasizes the importance of caution in interpretation of studies not representing an entire population, thus introducing selection bias.