Testing External Skeletal Fixation Devices
External skeletal fixation devices (ESFDs) are used in the treatment of complex fractures. These devices allow for continuous injury treatment and bone fragment repositions during convalescence and clinical procedures or operations. ESFD designs must have fixators that can adjust to the screws’ position to make configurations and adjustments—for example, when the mechanism is utilized for the stimulation of bone tissue during the healing process.
Materials typically used for external skeletal fixation devices typically include metals and metal alloys, such as titanium, aluminum, and stainless steel. Polymeric materials such as polyetheretherketone (PEEK) or carbon-fiber enforced PEEK are also frequently utilized in ESFD designs.
The ASTM F1541 standard is the standard mechanical testing methodology for external skeletal fixation devices (ESFD). The test is used to measure the mechanical characteristics of external skeletal fixation devices (ESFD) and how they attach and fixate to the bone. The series of tests involved with ASTM F1541 further identify performance criteria and the development of test methods.
ASTM F1541 Testing Methods
ASTM F1541 covers the methods used for testing external skeletal fixation devices. The tests that are selected depend on those applicable to the specific design of the device. Individual elements are tested, such as anchorage elements and bridge elements, connectors, joints, ring elements or other subassemblies, or the entire mechanical fixator.
External Fixator Connections
External fixator connections are tested using axial or torsional load applications via input platen bonded to the connector.
For the determination of ESFD’s in-plane compressive properties of ring segment bridge elements or circular rings, compressive quasistatic loading is applied at 180 degrees until failure. Plot load versus displacement, compressive yield, compressive stiffness, in-plane compressive strength is designated at an offset yield.
External skeletal fixator joints and pins testing
For external skeletal fixator joints, testing is a bit more complicated, involving the testing of part dynamics, stiffness, and the connector’s durability. Elastic flexure in the loading input element of the device should be minimized.
Fixator pins are tested by running static four-point bend assessments on pin samples to obtain a flexural deformation curve and a bending moment. Measurements calculated include the designated percentage of flexural strain, bending stiffness, and strength. These results determine bending rigidity. A static torsion test is performed involving both ends of a fixator pin. One end remains stationary while the other is gripped as the torsional load is applied. This allows for torque vs. angle plotting and calculations of rigidity, strength, and stiffness.
External Skeletal Fixator Subassemblies
Individual bridge and connector elements differ in size, pattern, and material. These tests include axial, anterior-posterior shear, lateral shear force loadings, torsion, anterior-posterior bending, and medial-lateral moment loadings. When assessed, the top grip is at the loading end, while the subassemblies’ bottom grip holds it in a rigid position. Chord stiffness, ultimate strength, and yield strength of the subassembly are calculated.
External Skeletal Fixator-Bone Constructs
To establish the design’s performance characteristics, angular and linear load conditions are conducted with static tests to determine strength and stiffness. Multi-cycle dynamic fatigue tests are performed to test it for repeated loading conditions.
Working with Empirical Technologies Corp.
If your external skeletal fixation device needs to undergo ASTM F1541 testing before FDA submission, Empirical Technologies Corp. can help. Our team of experts has the resources and knowledge necessary to meticulously test your product design. We have a track record of successfully helping businesses and individuals prepare their medical devices for FDA submission. Contact us today to request an estimate.