Orthopedic implant design from concept to final tested product: A design surgeon's experience

Abstract

Background: Orthopedic surgeons are invariably faced with situations where contemporary surgical techniques and implants are not satisfactory for a specific clinical scenario. One such scenario frequently arises around the lack of implant choice for intramedullary fixation of radius and ulna fractures. We will describe our experience designing and testing a new radius and ulna nail, inclusive of protecting the underlying intellectual property. Design Process: Phase 1: Identifying a need: Current intramedullary forearm devices have abandoned the ability to place interlocking screws at the nondriving end and are therefore not length stable. As current nails only come in 20 mm length increments, this may pose challenges in attaining accurate anatomical length restoration. Phase 2: Concept: (1) Anatomically designed in terms of length, diameter, and radius of curvature. (2) Nail inventory that has the optimal choice of implants to manage the majority of forearm injuries. (3) Locking system at the nondriving end that is easily targeted and has an acceptable radiation exposure for freehand locking. Phase 3: Anatomical study: Multiplanar reconstruction of upper limb computer tomography angiography scans were used to analyze the forearm osteology of 98 individuals. Primary measurements included the lengths of both radius and ulna shafts, the minimum canal diameter size, the proximal shaft angle of the ulna, and the radius of curvature of the radius. The size of the proximal ulna and distal radius were also measured for design parameters of the nondriving end of the nail. Phase 4A: Prototype design: To improve the usability of these nails, the design priorities were set as: (1) Locking hole design. (2) Jig and instrument design for insertion and removal. (3) Pressure release during insertion. Phase 4B: Prototype testing: Prototype testing consisted of nail insertion into human cadaver forearm bones using the initial prototype and instruments. The design aspects of the implant such as the locking holes with X-ray-assisted screw insertion or the radius of curvature were also evaluated. Mechanical testing will also be done.