3D Printed Cups For Acetabular Reconstruction: A 3D-CT Implant Study

DI LAURA, ANNA; HENCKEL, JOHANN; BELZUNCE, MARTIN A.; HART, ALISTER

Lisboa

Conferencia; EFORT 2022; 2022

BackgroundCustom 3D printed titanium acetabular implants have only recently been introduced and enable surgeons to treat traditionally unreconstructable massive acetabular defects, allowing patients to walk again. Whilst there is an accepted threshold for implant migration (proximal translation of >1 mm within 2 years) that constitutes loosening in primary and revision uncemented hip implants, there is no reference threshold for custom acetabular implants used to treat massive defects, with no long-term outcome studiesObjectivesWe performed bone-to-bone registration of sequential Computed Tomography CT imaging with the aim to help define radiological loosening of custom-made three-dimensionally 3D printed trabecular titanium cups for the management of massive acetabular defects. Our primary and secondary objectives were to assess implant position and orientation 1-year post surgery in comparison with the immediate post-operative CT imaging. Study Design & MethodsThis was a single-centre prospective cohort study of 19 patients from a single surgeon. We prospectively recruited patients with massive acetabular defects Paprosky type 3B or above treated with 3D printed custom implants, which 1-year post-operatively had no evidence of radiological or clinical implant loosening. The mean follow-up time was 46 months (32 to 62). Using specialised software solutions, the CT images were rendered to produce 3D reconstructions of the patients’ bony pelvis for relative comparison of the two imaging timepoints (immediate post-operative, 1-year post-operative). Bone-to-bone registration allowed for the assessment of implant movement over time, this was studied in terms of difference in centre of rotation (CoR), cup inclination INC and version VER. Our primary outcome measure was the change in centre of rotation (CoR) between CT scans carried out immediately and 1 year post-operatively. Our secondary outcome measure was change in orientation (cup inclination and version). Meticulous patient follow-up by was undertaken. ResultsAll patients presented acetabular defects classified Paprosky type 3B and beyond. One year post-operatively the deviation of CoR was a mean (± SD) of -0.1 ± 0.9 mm (median = 0.1 mm; IQR -0.8, 0.6 mm, min = -1.9 mm, max = 1.3 mm) in the ML plane, 1.6 (± 1.6) (median = 1 mm; IQR 0.2, 3 mm, min = -0.8 mm, max = 5.4 mm) in the IS plane and 0.8 (± 2) (median = 0.2 mm; IQR -0.8, 2.4 mm, min = -2 mm, max = 4.4 mm) in the AP plane. The orientation of the acetabular implants changed on average by 1.4 and 2º (inclination and version respectively). The 3D analysis revealed local bony shifts around the implants suggestive of bone remodelling. There was no clinical indication of implant loosening, oxford hip score was a mean of 33/48, both plain radiographs and CT cross-sectional imaging did not show radiolucent lines at the bone/implant interface. ConclusionsMonitoring of 3D printed custom-made titanium cups is challenging. Advances in medical image analysis, allowing robust assessment of patients with newly introduced implants, provide novel insights in the evaluation of their in-vivo performance. This study has showed that the threshold value of 1mm used to diagnose early loosening in THA is not applicable to custom-made acetabular implants designed to reconstruct massive acetabular defects.