REVIEW ARTICLE Development and Biomechanical Testing of the SIGN Hip Construct Justin Roth, BS,* David Shearer, MD, MPH,† Lewis G. Zirkle, Jr., MD,‡ Amy Johnson, MS,§ and Paul LaBarre, MME, RAC,¶ Summary: The SIGN hip construct (SHC) was developed to treat stable and unstable intertrochanteric fractures in low and middle income countries. The design was based on previous hip stabilization devices with specific adaptations to accommodate the unique chal- lenges encountered in resource-limited settings. Specifically, our goal was to enable operative stabilization of all intertrochanteric hip frac- tures without the aid of C-arm imaging. The SHC evolved through 3 years of bench testing prior to clinical use. As more clinical chal- lenges are identified, we anticipate the testing and incorporation of new ideas to improve functionality and overall structural perfor- mance of the device. This article presents the design strategy and development of the SHC as well as a fatigue gait simulator that was used to evaluate the performance of the construct. Key Words: biomechanical testing—sign hip construct—intertrochan- teric fractures—fatigue. (Tech Orthop 2009;24: 265–272) T here has been a progression of innovations in treating hip fractures from the Smith-Petersen and Jewett nails to the sliding hip screw (SHS) and more recently, to intramedullary devices. Despite these advances, internal fixation devices for hip fractures have yet to find the optimal approach for all fracture configurations. 1–4 Each of these implants is an attempt to balance collapse of the fracture with rigid stability. Fracture collapse has the benefit of interfragment apposition and com- pression whereas rigid stability is the traditional goal of internal fixation. We have learned that achieving this balance is critical to successful treatment of hip fractures. The SHS was an attempt to attain this balance by allowing collapse of the fracture to create compression between the proximal and distal fragments. 5 The design works well for stable fractures, but unstable fractures are prone to excessive collapse, resulting in leg length discrepancy and implant cut- out. 6–9 The intramedullary hip screw (IMHS) utilizes the nail itself to prevent excessive collapse, but cut-out from the fem- oral head remains problematic. Regardless of their efficacy, both the SHS and the IMHS rely on real-time image guidance to be placed safely, which makes them unfeasible for the resource limited hospitals of the developing world. 10 MOTIVATION FOR THE SIGN HIP CONSTRUCT The inspiration for the SIGN hip construct (SHC) occurred in a similar manner as the early inspiration for Surgical Implant Generation Network (SIGN). During many visits to SIGN programs to teach the technique for the standard nail, one of us (L.G.Z.) observed wards full of patients with hip fractures being treated in skeletal traction then placed in a body cast. Due to the absence of an affordable implant suitable for resource-constrained hospi- tals, these patients could never undergo surgery. In contrast to the hip fractures treated in high income countries, these patients are often young with high-energy unstable fractures sustained in road traffic accidents. This ultimately led to an ongoing process of adapting the original SIGN system for the treatment of extracapsular hip fractures. Significance: High-energy fractures in young people must have robust stabilization. THE DESIGN PHASE In North America, the choice of fixation is based primarily on a binary classification of the fracture as stable or unstable. Unstable fractures may be further defined by obliquity of the fracture line and presence of comminution of the lesser tro- chanter, lateral trochanteric wall, or both. 11,12 The goal with the SHC was to design and manufacture a hip fixation device that could be used for both stable and unstable fracture patterns and inserted without using fluoroscopic image guidance. Evidence suggests fixation devices that securely stabilizes the femoral head as well as the junction of the proximal screw in the nail result in very stable fixation. 8 However, there is a trade-off because fixed angle devices do not allow for varia- tions in size of the proximal femur. To achieve the goal of a universal device for use in low and middle income countries, SIGN sought to develop a design that can accommodate the many hip sizes around the world. Diverse anatomy of the proximal femur is noted in several studies made up of localized cohorts of different ethnicities, but to the authors’ knowledge, a worldwide biometric analysis of proximal femur anatomy has not yet been conducted. 13–15 These observations led to the following priorities to guide the design process. Definite criteria ● The implant can be used in both stable and unstable hip fractures. ● Insertion can be done without C-arm using a reliable, repeat- able technique. ● The technique is transferable to surgeons in low and middle income countries (ie, feasible to teach and learn in a rela- tively short time-frame given prior orthopedic training). ● The device must accommodate variation in the anatomy of the proximal femur. From the *Western University College of Osteopathic Medicine, Pomona, CA; †Department of Orthopaedics, University of California, San Francisco, CA; ‡SIGN, Richland, WA; §Pacific Research Labs, Vashon, WA; Program for Appropriate Technologies in Healthcare, Seattle, WA; ¶Univer- sity of Washington, Seattle, WA. Address correspondence to Lewis G. Zirkle, Jr., MD, SIGN, 451 Hills St., Suite B. Richland, WA 99354. Email: lgzjr@sign-post.org. Copyright © 2009 by Lippincott Williams & Wilkins ISSN: 0148-703/09/2404-0265 Techniques in Orthopaedics • Volume 24, Number 4, 2009 www.techortho.com | 265