Testing of Osteosynthesis Implants

Osteosynthesis implants facilitate the stable fixation of bone fragments that belong to one another—the testing of bone plates and bone screws.
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Flexure Test on Metal Bone Plates and Fixation Devices to ASTM F382 and ISO 9585 (Osteosynthesis Plates)

In the medical industry, bone plates and fixation devices must meet many fundamental requirements defined by certain standards and norms, because they are used in the treatment of complicated fractures.
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Zwick's test kit for bone plates and fixation devices can assist in performing mechanical tests to ASTM F382 and ISO 9585 for quality control or for research and development purposes. The static and dynamic strength of bone plates are tested using a 3-point and 4-point flexure test, with the flexure test kit consisting of two fixed and parallel aligned supports. It is also possible to test bone pins to ASTM F1264 with a similar test arrangement.

Benefits of the Zwick test kit for bone plates

  • Easy to use and completely satisfies the requirements of ASTM F382 – Determining the flexural strength of metallic bone plates and fixation devices and ISO 9585
  • Universal flexure test kit featuring easy adjustment of upper or lower anvil diameter; specimen-specific anvils can also be used
  • Designed for quasi-static and pulsating compressive loads
  • Available with displacement transducer for direct measurement of deflection on the osteosynthesis specimen
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Testing of Bone Screws to ASTM F543 and ISO 6475

Testing of bone screws to ASTM F543 refers to four mechanical tests in simplified clinical use. The primary properties involved include torsional strength, insertion and removal behavior, pull-out strength and self-tapping performance of medical bone screws. The methods specify a multi-axial test in which a constant preload is applied to the bone screw and a superimposed torsional motion is introduced. The static Zwick testing machine allows easy, operator-friendly implementation of this sequence of motions despite complex control requirements. The optional testXpert® Master Test Program, "Evaluation of medical tests," provides automatic, standard-compliant evaluation of the test. These results are used in quality control or technical comparison of individual screw forms.

A1. TEST METHOD FOR DETERMINING THE TORSIONAL PROPERTIES OF METALLIC BONE SCREWS

Description

  • Bone screws are aligned via an auxiliary fixture and cast into embedding tubes so that 5 threads or 20% of the threaded length are exposed.
  • Embedding tubes are inserted directly into the testing machine.
  • Screw bits are mounted via a quick-acting chuck and the screw is driven at a test speed of 1 to 5 rpm in accordance with the standard. If required, a constant axial preload can be applied.

Result

  • Torque versus angle for entire duration of test
  • Axial force versus travel for entire duration of test
  • Torsional strength
  • Maximum torque
  • Angle at break

Benefits

  • No pre-existing damage to bone screws through clamping
  • Stress-free, centered fixing of bone screws
  • Embedding device for simultaneous casting in 6 bone screws
  • Multiple re-use of embedding tube possible

A2. TEST METHOD FOR DRIVING TORQUE OF MEDICAL BONE SCREWS

Description

  • Bone screws are inserted into and removed from a test block (may be predrilled); specifications as per ASTM F1839; clamping via specimen grips.
  • Screw bits are mounted via a quick-acting chuck and the screw is driven at a test speed of 1 to 5 rpm in accordance with the standard. If required, a constant axial preload can be applied.
  • A minimum of 4 screw revolutions are required.

Result

  • Insertion/removal torque versus angle for the entire duration of the test
  • Axial force versus travel for entire duration of test

Benefits

  • Easy test performance and evaluation via testXpert® II software

A3. TEST METHOD FOR DETERMINING THE AXIAL PULLOUT STRENGTH OF MEDICAL BONE SCREWS

Description

  • Bone screws are driven into a test block (design as per ASTM F1839) at an insertion speed of 3 rpm for 20 mm or 60% of the thread length.
  • The screw head is pulled out of the test block at a rate of 5 mm/min.

Result

  • Axial tensile force versus travel for entire duration of test
  • Maximum tensile force

Benefits

  • Free frontal access to specimen grips for easy insertion of bone screws
  • Self-centering tensile axis
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A4. TEST METHOD FOR DETERMINING THE SELF-TAPPING PERFORMANCE OF SELF-TAPPING MEDICAL BONE SCREWS

Description

  • The bone screw is driven into a test block at a continuous rotational speed of 30 rpm.
  • The axial force is increased by 2.0 N/s during the insertion process until the torque or the axial travel increases significantly.
  • The axial force attained at the "biting point" is then maintained and a minimum of 5 screw revolutions are completed.
  • If the bone-screw does not bite after at least 5 revolutions a further increase of the axial force at 2.0 N/s is permitted.
  • The procedure is then repeated from the new "biting point" until at least 5 valid screw revolutions have been completed.

Result

  • Insertion torque versus angle for entire duration of test
  • Axial force versus travel for entire duration of test
  • Axial force required to insert a self-tapping bone screw into a test block

Benefits

  • Axial force required to insert a self-tapping bone screw into a test block
  • Integrated evaluation via testXpert® II software
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