Shape Memory Alloy staples made of nitinol have been used in orthopedics for over two decades due to their biocompatibility, good corrosion resistance, super-elasticity, and shape-memory properties. With the recent development of below-body-temperature activated implants, ease of implantation has improved markedly. These nitinol implants are manufactured such that the legs are toed-in or "closed", and then loaded in the open/active position on an insertion device used for implantation. Upon release from their "active" position, the implants immediately impart compression across the fusion site as the implant attempts to return to its "closed" state. With advances in manufacturing techniques, the amount of compression is tunable, allowing for applications across various bones.Several studies have been published showing the compression produced by nitinol implants across the fusion site [1]. Another key advantage for nitinol staples is that they provide continuous compression; after repetitive loading, compression is maintained at the fusion site [2]. This continuous compression as well as dynamization, has been shown to improve bone healing [3]. Several plates and screws, commonly used in orthopedics for bone healing, have been designed to apply compression to the fusion site, however they are typically rigid constructs which do not allo-w for dynamization and are unable to recover compression after bone movement [4]. Recent studies at our laboratory have shown both the tunability of nitinol implant compression, as well as compression recovery after loading.
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