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Thumb amputations leads to 50 % loss in hand functionality. To date, silicone vacuum prosthesis and autologous transplantation are the most adopted treatment solutions: nevertheless, vacuum prostheses lack in stability and cause skin issue and surgical treatment is not always accepted by patients. Osseointegrated implants were demonstrated to enhance stability, restore osseoperception and increase the time of prosthesis use. Thumb amputations present varying stump sizes: a standard size implant cannot address specificity of each patient, while a patient matched solution can meet surgeon requirements, by geometrical features of implant. The fixture presented in the current paper is the first additively manufactured patient matched osseointegrated implant for the treatment of thumb amputees. The current work aims to verify and validate a predictive finite element model (FEM) for mechanical strength of the presented fixture. FEM was demonstrated to correctly evaluate the mechanical strength of patient matched device. Minimum strength requirements were calculated in different core diameters: FEM were experimentally validated. Safety factor of 1.5 was guaranteed. Finally, considerations on performance of the prototype were carried out by means of insertion tests in Sawbones and axial pull-out force assessment. Cadaver tests to evaluate the entire procedure and production process are ongoing., Competing Interests: Declaration of competing Interest The authors declare no conflict of interest., (Copyright © 2023 IPEM. Published by Elsevier Ltd. All rights reserved.)

Multi-fragmented fractures of the proximal humerus are difficult to treat, especially in the case of osteoporotic bone. Intra-operative risks include cartilage damage when inserting multiple screws. A common post-operative complication is distal-varus collapse of the head. The aim of this study was to investigate if an Innovative technique (reduced number of screws and injection of a beta-TCP additivated partially resorbable cement) provides the same or better stability of the reconstructed head compared to the Standard technique (using more screws). A four-fragment fracture was simulated in six pairs of humeri, with partial removal of the cancellous bone to simulate osteoporotic "eggshell" defect. One humerus of each pair was repaired with a Standard (locking plate, 2 cortical and 6 locking screws), and the other with the Innovative technique (same plate, 2 cortical and only 3 locking screws, plus cement injection). The reconstructed specimens were subjected to a biomechanical test where a cyclic force of increasing amplitude was applied axially until failure. The Innovative reconstructions withstood a force 3.49 times larger than the contralateral Standard reconstructions before failure started. The maximum force before final collapse for the Innovative reconstructions was 4.24 times larger than the contralateral Standard reconstructions. These differences were statistically significant. The Innovative reconstructions, based on fewer screws and beta-TCP additivated acrylic cement, showed positive results, demonstrating better biomechanical properties compared to the Standard reconstructions. These laboratory findings, along with the advantages of a reduced number of screws, may help perform a surgically safer, and more effective procedure in osteoporotic patients., Competing Interests: Declaration of Competing Interest None, (Copyright © 2020. Published by Elsevier Ltd.)