Testing standard
Standard Specification and Test Methods for Intramedullary Fixation Devices
Written and technically reviewed by Dak System Inc. engineeringLast reviewed
ASTM F1264 combines a specification with four test methods for intramedullary fixation devices: static four-point bend, static torsion, bending fatigue, and bending fatigue of locking screws. It states explicitly that it does not define levels of performance or predict clinical outcome.
Four methods sit in annexes to the specification. Annex A1 is a static four-point bend, giving bending strength and stiffness from the load-displacement curve using the fixture's outer and inner spans. Annex A2 is a static torsion test, recording torque against angle of twist over a stated gauge length. Annex A3 cycles the device in bending at a chosen load to a defined run-out. Annex A4 repeats that fatigue arrangement on the locking screws. Each annex is reported separately, with its own geometry and parameters.
How an intramedullary nail behaves in the two modes that matter clinically, statically and then over time. Bending is the obvious one. Torsion is the one more easily overlooked, and it is a primary function: a nail that resists bending well but twists easily lets the fracture fragments rotate against one another, which is a failure of fixation with nothing broken. The locking screws earn their own annex because they are the smallest section in the construct and frequently the first thing to break, so a nail can pass its own fatigue test while its screws fail in service.
Bending and torsion, each statically and then in fatigue, plus the locking screws that are usually the weakest part.
An unusually honest scope. The standard states that it identifies needs for further development of test methods and performance criteria — that is, it says openly where the science is not yet settled.
From the load-displacement curve in four-point bending, using the fixture spans
Both spans are needed to interpret the result, so both belong in the report.
Torque per unit angle of twist over the gauge length
The gauge length must be stated — a longer nail twists further for the same torque and the same material.
Survival at a stated load to a stated run-out, or the cycle at failure
Load and run-out together, as for every fatigue figure.
A four-point bend fixture gives a constant bending moment between the inner rollers, which is what lets a nail be assessed without the result depending on exactly where along it the load happened to land.
SpecificationsA load cell matched to the device rather than the frame — a small-diameter nail and a femoral nail differ by an order of magnitude.
SpecificationsA wide range of force, since a small-diameter nail and a femoral nail differ by an order of magnitude, which argues for a load cell chosen per device rather than per frame. A four-point bend fixture with settable spans, a torsion capability for Annex A2, and cyclic loading for the two fatigue annexes with the applied force verified dynamically at the test frequency — a statically calibrated frame that under-delivers in motion passes that error into every cycle of a long run.
Reporting a stiffness without the fixture spans, or a torsional stiffness without the gauge length, either of which makes the figure unreproducible. Testing the nail and not the locking screws. Quoting a fatigue result without both the load and the run-out. Verifying force statically for a dynamic test. And presenting results as evidence of clinical performance, which the standard explicitly declines to support on the grounds that the necessary knowledge does not yet exist — a rare piece of candour, and one worth quoting back when a submission overreaches.
| ASTM F1264 | ISO 7206-4 | |
|---|---|---|
| Device | Intramedullary nails and rods | Stemmed femoral components |
| Loading | Bend and torsion, static and fatigue | Cyclic, at specified angles |
| Performance criteria | Explicitly not defined | Specified in the standard |
| Both require | Dynamic force verification | Dynamic force verification |
A useful contrast in philosophy. The ISO hip standard fixes the forces and cycles a device must survive; this ASTM standard supplies methods and says openly that the criteria are not yet settled.
It is the ASTM document for intramedullary fixation devices — the nails and rods placed inside the medullary canal to fix long bone fractures. It combines a specification covering design characterisation, materials and labelling with four test methods in annexes: static four-point bend, static torsion, bending fatigue, and bending fatigue of locking screws. The current designation is ASTM F1264-24.
Because four-point loading produces a constant bending moment between the two inner rollers, whereas three-point produces a peak directly under a single load point. On a long nail that distinction matters: with four-point the result does not depend on exactly where along the device the load happened to land, and any weak section within the constant-moment region will find itself equally loaded.
Because rotational control is one of the primary clinical functions of an intramedullary nail. A nail that resists bending well but twists easily allows the fracture fragments to rotate relative to one another, which is a failure of fixation even with nothing broken. Torsional stiffness and strength are therefore measured in their own right rather than inferred from the bending behaviour.
Because they are frequently the first thing to fail. The screws are the smallest section in the whole construct and they carry load between the nail and the bone, so a device can pass its own bending fatigue test comfortably while its locking screws break in service. Testing them separately is what stops that being discovered clinically.
No, and it says so explicitly. Its stated intent is to characterise design and mechanical function and to provide test methods, not to define levels of performance or predict case-specific clinical performance — because, in its own words, clinical outcome prediction requires knowledge that is not yet available. It also states that it identifies needs for further development of test methods and performance criteria, which is an unusually candid thing for a standard to say.
Because the geometry determines the result. Bending stiffness computed from a load-displacement curve depends on both the outer and the inner roller separations, so a stiffness quoted without them cannot be reproduced or compared. The same logic applies to the torsion gauge length: a longer nail twists further for the same torque and the same material.
They differ in philosophy, which is instructive. ISO 7206-4 specifies the endurance forces and the cycle counts a hip stem must survive, so it returns a pass or fail against a requirement in the standard. F1264 supplies methods and leaves the criteria open, on the stated grounds that the knowledge to set them does not yet exist. Both approaches are defensible; knowing which one you are working under changes how a result should be presented.
A fatigue frame is judged on whether it holds amplitude at frequency, not on peak load, so the figures that matter here are the cycling ones.
| The method asks for | Dak supplies | |
|---|---|---|
| Load & frequency | Wide — a small-diameter nail and a femoral nail differ by an order of magnitude | Load upto 500 kN at upto 100 Hz, 60 mm actuator stroke with travel resolution upto 0.1 µm |
| Load accuracy | ASTM E4, with dynamic verification for the fatigue annexes | ±0.5% of reading |
| Gripping | A four-point bend fixture for the static bend, a torsion arrangement for the torsion method, and cyclic fixtures for the fatigue annexes | Grips built to the specimen, with alignment held through the cycle |
| Environment | 23 ± 2 °C standard laboratory atmosphere | 3009 series chambers, −150 °C to +400 °C — temperature only |
This page describes the method as practised. The governing text is the current edition from the issuing body. Tell us what you are testing and we will answer with the machine, the fixture and a quotation.
