Background: Access to custom 3D printed pelvic implants (3DPI) is improving for application in both arthroplasty revision and tumour reconstruction. There is limited evidence regarding the safety and outcomes of such implants for large bony defects of the pelvis. Purpose: To report the incidence of complications, patient mortality and implant survival following pelvic reconstruction using custom 3Dprinted prostheses in the setting of extensive pelvic bone defects following pelvic tumour resection or failure of total hip arthroplasty (THA) Methods: Patients who underwent reconstruction with a custom 3D printed pelvic prosthesis (3DPI) were identified from our clinical outcomes registry (Complex Reconstruction and Sarcoma Surgical Outcomes Registry; ANZCTRN 12621001421820). Indications for surgery, adverse events, reoperations and rates and modes of failure were recorded. Kaplan-Meier and multistate survival curves were generated for cumulative survival based on indication. Results: One hundred and six procedures were completed(RevisionTHA = 33; TumourPelvis = 73) with a median follow up of 4.1 years, ranging from 0.6 to 10 years. Acetabular loosening was the most frequent indication for the RevisionTHA cohort, while indications for tumour varied across primary presentations, metastases and failures of previous resection/reconstruction. Intraoperative complications were observed in 4.1% (95%CI 1.1 - 12.3) of TumourPelvis cases. Overall implant retention was 96% (90 - 99). No mortality events were observed in the RevisionTHA cohort, with 5-year patient survival 79% (70-90) in the TumourPelvis cohort. Procedure-survival free from periprosthetic infection was 86% (74-100) in the RevisionTHA cohort and 85% (76 - 95) in the TumourPelvisCohort. Modelling adverse events using multistate survival models in both cohorts revealed complex time-varying presentation of adverse events, with a significant burden of reoperations and local tumour recurrence in the TumourPelvis cohort. Conclusion: 3DPIs are a safe and viable option for complex reconstruction of the pelvis across a range of oncological and non-oncological indications. The initial results of the present study provide important information to aid in counselling patients about such procedures and allocating healthcare resources for ongoing care. Further work is required to document functional and biomechanical outcomes in these patient populations.

Funding for the establishment of the COMPRESSOR registry was received by Ossis Ltd. CS and ME declare institutional funding from Johnson and Johnson MedTech ANZ and MatOrtho Australia. RB declares institutional funding from Stryker South Pacific and Corin Australia. RB and PS declare prior ownership of stocks in Ossis Ltd. MG and DF declare no conflict of interests.

This study was funded by RB

I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.

Yes

The details of the IRB/oversight body that provided approval or exemption for the research described are given below:

Ethical approval for the COMPRESSOR Registry was obtained from the Local Health District (RPA Zone) Human Research Ethics Committee.

I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals.

Yes

I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance).

Yes

I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable.

Yes

All data produced in the present study are available upon reasonable request to the authors