Orthopaedic fixation devices are used during reconstructive surgery to treat fractures of bones and soft tissue injuries normally caused by trauma. Devices, such as bone plates, compression screws and femoral nails, are used to provide stability and maintain the alignment of bone fragments during the healing process. Quantification of important characteristics, such as bending strength or stiffness, can provide surgeons with insight into implant performance, while allowing researchers to compare device materials and designs. The fatigue life of the implant over a specific time period or range of maximum loading must also be determined.
Typically following ASTM guidelines, fixtures are often unique to the objective and application of the tests and results. Features of both the ElectroPuls™ test instruments and 8870 servohydraulic testing systems, such as integral t-slot base, ability to mount the Dynacell® load cell to the moving actuator, and saline chamber accessories for in vivo simulation, allow laboratories to investigate a comprehensive range of device characteristics and performance.
For this test a small implant, commonly used to treat fracture of the phalangeal, metacarpal or carpal bones, was subject to dynamic loading to verify the fatigue life. The fixation plate was set up on both the ElectroPuls E3000 and E1000 machines. After a simple stiffness tune, a compression bending test was run at 20 Hz between 0.3 and 3 N. The test was successfully run by utilizing a lower force Dynacell load cell, a small compression platen and a clamp to fix the implant, and mounting block in position on the lower t-slot table.