Analysis of principles inspiring design of three-dimensional-printed custom-made prostheses in two referral centres

Background Three-dimensional (3D) printing is an emerging technology used in numerous medical fields. Reconstruction of large bone defects after tumor resections or complex revision surgeries is challenging especially in specific sites where modular prostheses are not available. The possibility to realize custom-made 3D-printed prostheses improves their application in surgical field despite the complication rate, gaining a lot of attention for potential benefits. Objectives We asked: (1) What are the emerging indications and designs of 3D-printed prostheses for complex bone reconstructions? (2) What complications occur with the use of custom implants considering site? Study design and methods We performed a retrospective analysis of every patient in whom a custom-made 3D-printed prosthesis was used to reconstruct a bone defect after resection for a bone tumour or challenging revision surgery from 2009 to 2018 in two referral centres. Forty-one patients (11 males [27%], 30 females [73%]) with a mean age of 41 years (range, 10-78 years) were included. Our general indications for using these implants were complex reconstructions of massive bone defects, in the absence of available modular prostheses. Seven were non-oncologic patients, whereas 24 patients were mainly treated for their malignant bone tumours. Custom-made 3D-printed prostheses were used in pelvis (29), forearm (6), scapula (2), distal tibia (2), calcaneus (1), and femoral diaphysis (1). The reconstruction included complete articular replacement in 24 cases (58%) whereas a combined spinopelvic implant has been used in two cases. Flaps were used in 25 cases (61%). Statistical analyses include Kaplan-Meier curves of survival. Results The mean follow-up was 20 months. In the oncologic group, overall survival was 89% at five year follow-up and only three patients died of disease. Only one patient required implant removal due to deep infection. Overall major and minor complication rate was 22% (14 complications in 9/41 patients), mainly wound-related problems. One patient reported a periprosthetic fracture, one had hip dislocation, and four (12% [4/34 cases]) had local recurrence. Mean MSTS functional outcome score at follow-up was 73% (range, 23-100%), with a full weight bearing at an average time of 73 days from surgery of lower limbs. Conclusions Custom-made 3D-printed prostheses represent at today a promising reconstructive technique, maintaining however the correct indications for their use in musculoskeletal oncology and challenging revision surgery. Complication rate is acceptable, with infection and wound healing problems relatively common after complex pelvic reconstructions. We will continue to follow our patients over the longer term to ascertain the role of these implants; however, larger studies will need to confirm indications and control for prognostic factors.