Limb-Salvage Reconstruction of the Proximal Humerus Using Patient-Specific 3D-Printed PEEK Implants: A Midterm Clinical Study

<b>Background:</b> Reconstruction of the proximal humerus after wide tumor resection is technically demanding, and traditional methods such as allograft-prosthetic composites, reverse shoulder arthroplasty, and metal implants are limited by graft unavailability, pediatric size mismatch, their high cost, and metal-related stress shielding. Polyether ether ketone (PEEK), with its modulus closer to cortical bone and radiolucency, offers a promising alternative. Building upon the success in craniomaxillofacial surgery and its favorable physical characteristics, we applied personalized 3D-printed PEEK implants for proximal humerus reconstruction. This study reports the first evidence of applying patient-specific 3D-printed PEEK implants in the proximal humerus. <b>Methods:</b> A retrospective cohort study was conducted on seven patients who underwent wide resection of primary malignant bone tumors of the proximal humerus, followed by reconstruction using patient-specific 3D-printed PEEK implants. Implant design was based on preoperative computed tomography (CT) imaging, incorporating contralateral humeral mirroring and computer-aided design. The implants were fabricated using fused deposition modeling (FDM) with medical-grade PEEK under stringent thermal control (nozzle temperature > 400 °C and heated build chamber), followed by a controlled annealing process to minimize internal stress, optimize polymer crystallinity, and enhance mechanical durability. Outcomes assessed included implant survival, oncologic control, shoulder range of motion, and functional outcomes measured using the Musculoskeletal Tumor Society (MSTS) score. The mean follow-up duration was 56.3 months. <b>Results:</b> All patient-specific PEEK implants were successfully manufactured and implanted with satisfactory geometric accuracy. Mechanical implant survival was 85.7% at final follow-up, with one implant fracture occurring at 28 months. No cases of deep infection, dislocation, loosening, or permanent neurovascular injury were observed. Local soft-tissue recurrence occurred in two patients (28.6%), without distant metastasis or tumor-related mortality. The limb-salvage rate was 100%. At final follow-up, the mean MSTS score was 23.0 ± 1.6. Shoulder motion was limited but comparable to outcomes reported for conventional anatomic megaprosthetic reconstructions. <b>Conclusions:</b> Patient-specific 3D-printed PEEK implants provide a feasible and oncologically safe option for proximal humerus reconstruction after tumor resection, with acceptable midterm implant survival and functional outcomes. The favorable elastic modulus and radiolucency of PEEK offer distinct biomechanical and imaging advantages over metallic implants. Further design optimization and larger prospective studies are warranted to enhance mechanical durability and functional restoration.