Fatigue Testing of a New Locking Plate for Hip Fractures

Femoral neck shortening and varus deformity can have a significant effect on functional outcomes in patients with femoral neck fractures, particularly in young trauma patients. This study proposes a locking plate construct to address femoral neck fractures. The biomechanical properties of the locking plate are investigated with a specific focus on fatigue performance. The challenges associated with the development of a standardized pre-clinical testing model are also discussed. The development of a testing strategy and three mechanical tests are described. Each of the testing phases compare the proposed plate construct against the currently accepted gold standard of three cancellous screws. The first phase of biomechanical testing involves cadaveric specimens, which are statically loaded until ultimate failure of the construct. The second phase cyclically loads instrumented synthetic bone substitute samples with hardware installed without compression at the fracture site. The third phase cyclically loads samples with hardware installed with compression at the fracture site. Static testing results indicate that the proposed locking plate construct can withstand significantly higher static loads before failure than can the three cancellous screw technique. Fatigue testing results show that without compression across the fracture site, the samples instrumented with the locking plate construct had a shorter fatigue life than samples instrumented with 3 cancellous screws. With compression across the fracture site, the fatigue performance of the proposed locking plate is equivalent to that of 3 cancellous screws. The results indicate that the proposed locking plate construct for hip fractures has superior static strength and equivalent fatigue life compared to those of 3 cancellous screws. Biomechanical testing results show that compression across the fracture site is critical to the fatigue performance of both constructs. The development of a preclinical testing strategy for trauma products requires an understanding of the intended application of the product, expected modes of failure, and a thorough understanding of the product's service requirements.