Long-Term Clinical and Radiographic Osseointegration Outcomes of a Highly Porous 3D-Printed Titanium Collar Compared with a Hydroxyapatite-Coated Collar in Megaprostheses

This is a retrospective, single-center cohort study comparing the long-term radiographic osseointegration and aseptic loosening between a 3D-printed EPORE® collar and a prior generation HA-coated collar in endoprosthetic reconstructions. Achieving stable bone integration in endoprosthetic reconstructions remains challenging, with hydroxyapatite (HA)-coated collars being the only option available in the past. Earlier studies from our center have shown reliable and accelerated osseointegration at the bone–collar interface using a novel highly porous 3D-printed EPORE® collar system compared to a previously used HA-coated collar. Methods: Twenty-eight patients who underwent an implantation of endoprostheses utilizing the novel 3D-printed EPORE® collar system were case-matched to 24 patients who had previously undergone surgeries using a HA-coated collar. The mean age at surgery was 65.2 years (range: 17–95 years). Patients in the HA-coated collar group had a mean age of 63.8 years (range: 17–86 years), while those in the 3D-printed collar group had a mean age of 66.7 years (range: 32–95 years), with no statistically significant difference between groups (p = 0.876). A minimum radiological and clinical follow-up of 2 years was available in all included cases. Osseointegration was evaluated using postoperative plain radiographs in two planes based on a previously validated semi-quantitative score. Results: When aseptic loosening was used as the primary endpoint, no failures occurred in the 3D-printed EPORE® group during the study period. The overall rate of stem loosening (including both aseptic and septic causes) was 7% (2/28) in the 3D-printed group and 16% (4/24) in the HA-coated group. All cases of loosening in the 3D-printed cohort were related to septic failure. This translates into a 2-year aseptic-loosening-free survival of 100% in the 3D-printed group. When the radiographic osseointegration was analyzed as the endpoint, the rate of successful osseointegration was significantly higher in the 3D-printed group (92.9%, 26/28; 95% CI 76.5–99.1%) compared with the HA-coated group (70.8%, 17/24; 95% CI 48.9–87.4%; p = 0.04). The distribution of ongrowth scores also differed significantly between groups. The highest ongrowth score (grade 4) was achieved in 82.14% of 3D-printed implants (23/28; 95% CI 63.1–93.9%), compared with 37.5% of HA-coated implants (9/24; p = 0.0002). The time to achieve grade 4 ongrowth was significantly shorter in the 3D-printed cohort, with a median of 470 days (IQR 360–610), compared with 1482 days (IQR 1020–1860) in the HA-coated group (p < 0.0001). In addition, patients in the 3D-printed implant group had a significantly higher mean body mass index compared with the HA-coated group (32.51 vs. 28.36, p = 0.01). Conclusions: These results show that the novel highly porous 3D-printed EPORE® collars reduce aseptic loosening and accelerate extracortical bridging in endoprosthetic replacements. This benefit persisted even in higher BMI or revision contexts when compared to the previously used HA-coated collars.