Development of 3-dimensional Printed Distal Finger Prosthesis With Assembly-free Joint

Abstract

PURPOSE: Finger and fingertip amputation is common, with tens of thousands of cases occurring yearly in the United States.1 Distal fingertip amputation occurs more frequently than complete finger amputation and often in young and productive populations.2 Apart from loss of sensation, the loss of one or more fingertips often results in drastic functional deficits. Current options for functional finger prostheses are often cost-prohibitive and generally require additional refinement after fabrication. The purpose of this study was to design an option for prosthesis made exclusively via 3-dimensional (3D) printing. In doing so, we hoped to restore an adequate level of function to patients while keeping costs low and requiring minimal postproduction refinement and maintenance. METHODS: Our prototype was made for a patient with amputation at the distal interphalangeal joint (DIJ) of the left ring finger. The patient’s intact ring finger was measured in order to produce a digital model using computer-aided design (CAD) software. Measurements utilized included metacarpophalangeal (MCP) joint to distal tip, and the widths of proximal, middle, and distal phalanx segments. The length of the amputated digit was also measured from MCP joint to amputation stump. This CAD design was finally submitted to an online 3D printing service (Shapeways) to allow for replicas to be ordered by the patient directly while maintaining low production cost. RESULTS: Our final model utilized a single, flexible joint consisting of 2 pins molded directly into the medial and lateral aspects of the prosthesis immediately after 3D printing. High grade nylon material was used during the fabrication process to confer low cost while maintaining comfort and durability. Quality range of motion and improved anatomical grasping of objects was achieved, creating significant return of function. CONCLUSIONS: Our device accomplishes the goal of creating a functional prosthetic fingertip using exclusively 3D printing. In addition, while other 3D printing prosthetics have required significant postproduction customization and maintenance, this device’s intrinsic joint system makes it essentially maintenance free and can be used immediately following printing. The use of high-grade nylon confers stability and durability at a fraction of the cost of previously used materials. Utilizing a third-party 3D-printing company and freely available CAD plans, a patient will be able to upload their measurements and a device can be created and shipped to them for around $20 USD. We see particular utility of our device in pediatric populations as the customizable design and economical production allow for several devices to be used throughout a child’s development. REFERENCES: 1. Reavey PL, Stranix JT, Muresan H, et al. Disappearing digits: analysis of national trends in amputation and replantation in the United States. Plast Reconstr Surg. 2018;141:857e–867e. 2. Østlie K, Skjeldal OH, Garfelt B, et al. Adult acquired major upper limb amputation in Norway: prevalence, demographic features and amputation specific features. A population-based survey. Disabil Rehabil. 2011;33:1636–1649.