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BACKGROUND: Mechanical testing of newly designed implants provides valuable insight into their mechanical properties. This provides surgeons with information about implant choice for the treatment of fractures and the effect of the implant's mechanical properties on fracture healing METHODS: A novel interlocking forearm nail was subjected to standardised mechanical testing according to the Standard Specification and Test Methods for Intramedullary Fixation Devices (ATSM 126416), using static and dynamic four-point bending and static torsion (ASTM STP 588). Three nails were used for the static bending and torsion and nine for the dynamic bending tests. All nails were catalogued, numbered and photographed before testing RESULTS: The mechanical testing results showed a mean force yield (Fy) of 566 ± 20 N, a moment of yield (My) 10.75 ± 0.37 Nm, a stiffness of 67.10 ± 2 N/mm and structural stiffness of 1.53 ± 0.50 m2. The torsional stiffness of the nail was 0.088 ± 0.002 Nm/°. The four-point dynamic bending test showed a fatigue strength of 5.23 Nm. This value was determined using the semi-log moment/ number of cycles (M-N) diagram and showed a 50% failure at a million cycles. If the moment were reduced to 4.4 Nm, mathematically, the survival rate would improve to 90% CONCLUSION: The results from this mechanical testing show that this novel intramedullary forearm nail can resist mechanical forces experienced during fracture healing and could potentially be used in future clinical studies Level of evidence: Level 4

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.

Introduction: High energy fractures like gunshot-related injuries or high velocity road traffic accidents are often complex to treat and have been associated with a higher non-union rate, especially when there is extensive bone loss. Fractures with severe comminution may not heal due to bone loss and an inability to achieve adequate fracture stability. Treatment of fractures that are not amenable to plating or nailing may lead to non-unions, septic or aseptic, that need repeat surgeries. Stabilisation with external fixation is a reliable option to maintain stability and provide a suitable environment for union. Materials and methods: This retrospective study used medical records of all patients with complex mid-shaft humerus fractures, as well as their complications, that were treated with hexapod circular external fixation between January 2009 and September 2015. All the patients in this case series presented with severe humerus fractures or complications thereof which were not amenable to conventional therapy. Results: Union was achieved in ten out of the 12 cases (83.3%). Union was achieved without bone graft or any other interventions at the fracture site except implant removal where indicated. The median time in external fixation was 196 days (interquartile range: 112-228). The most common complication encountered in this series was pin-site infection. Fixation points were noted to be infected in 33% of cases at some time during the treatment period. Conclusion: This study suggests that humeral non-unions and complex humerus fractures that are not amenable to conventional fixation methods, such as intramedullary nails and plates, can successfully achieve union when treated with a hexapod circular external fixator.

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