3D Printed Patient-Specific Implants

Abstract

Standard orthopaedic implants are manufactured in discrete sizes that approximate average patient anatomy, yet anatomical variability means that 15-30% of patients receive suboptimally fitting prostheses, leading to increased micromotion, stress shielding, aseptic loosening, and revision surgery rates of 8-12% within 10 years. Three-dimensional (3D) printing -- also termed additive manufacturing (AM) -- enables fabrication of patient-specific implants (PSIs) matched to individual anatomy from computed tomography (CT) or magnetic resonance imaging (MRI), promising superior fit, reduced surgical time, and improved biomechanical load transfer. This study designed, fabricated, and evaluated five 3D-printed PSI configurations -- solid titanium (Ti-6Al-4V) by selective laser melting (SLM), porous titanium lattice (gyroid TPMS, 65% porosity), cobalt-chromium (CoCr) by electron beam melting (EBM), polyether ether ketone (PEEK) by fused filament fabrication (FFF), and a proposed functionally graded titanium implant (FGT) with dense cortical shell and porous trabecular core -- for patient-specific acetabular cup reconstruction in 24 patients with complex acetabular defects (Paprosky type IIB-IIIB). FGT achieved the highest primary stability (micromotion 18.4 +- 6.2 um vs 42.8 +- 12.4 um for standard off-the-shelf cups; p < 0.001), the best bone-implant contact (BIC 68.4 +- 8.2% at 12 months vs 48.6 +- 10.8% for porous titanium; p = 0.004), and stress shielding reduction of 42.6% compared to solid titanium (finite element analysis, validated by strain gauge measurements). At 24-month follow-up, no FGT implants required revision (0/8) compared to 1/8 (12.5%) for standard cups. These results establish functionally graded 3D-printed implants as the next generation of patient-specific orthopaedic reconstruction.