Long-term follow-up of patients with large segmental bone defects treated with 3D-printed polycaprolactone/tricalcium phosphate scaffolds.

INTRODUCTION: The Induced Membrane Technique (IMT) combined with autologous bone grafting has proven effective in achieving union in many cases of non-healing bone defects. However, this treatment strategy remainschallenging in very large defects (≥ 10 cm). Although the addition of a 3D-printed scaffold could enhance osteoconductivity and retention of cancellous bone, cells, and bioactive materials in the defect, the long-term outcomes of this innovative approach are not yet known. We therefore reviewed all patients with a very large posttraumatic segmental defect of a long bone treated with the IMT using a 3D-printed scaffold, cancellous bone, cells, and bioactive materials. METHODS: From 2018 to 2024, all consecutive patients with a large segmental defect who received a 3D printed scaffold were identified. All patients were treated with the two-stage IMT procedure. The defects were filled in the second stage procedure with a 3D printed scaffold made from poly-ε-caprolactone and Tricalcium Phosphate (PCL/TCP), autologous bone graft (bone marrow aspirate concentrate and RIA-autograft), and biomaterials(P-15 +/- bioactive glass). In the event of complications, samples from the defect site with the PCL/TCP scaffold were collected for analysis using scanning electron microscopy and histology. RESULTS: A total of ten patients were treated for a segmental bone defect median of 10.5 cm (IQR 3.25) of the femur (n = 3) or tibia (n = 7). Follow-up of the patients ranges between one and four years. The median age of the patients is 46 (range 23-62). Complications occurred in seven patients (one femur, six tibia). All patients with complications required additional surgeries. One patient had a local osteomyelitis infection at the defect site with complete integration of the scaffold into the proximal and distal tibia; one required negative pressure wound therapy for a soft tissue infection; and five required a revision of the first stage procedure due to surgical site infection (n = 3) or failure of the fracture fixation material (n = 2). Remarkably, scanning electron microscopy and histology showed limited formation and incorporation of newly formed bone into the scaffold. After revision surgery, all patients are currently improving, and no amputations have been performed so far. CONCLUSION: Reconstructive treatment of large bone defects remains challenging. The short-term follow-up of this treatment strategy showed promising results with progress in clinical and radiological follow-up. However, in this small cohort a lack of bone growth at the defect site was found in some of the cases that were clinically performing well. The use of PCL/TCP scaffolds remains a valuable treatment strategy in very large bone defects for retention and extension of the autologous bone and cells, though improvements in fixation, composition or structural properties could enhance their feasibility.