Preface

This standard is drafted in accordance with the rules given in GB/T 1.1-2009.

This standard was prepared using the redrafting method with reference to Appendix A4 of ASTM F 543-2013, "Test Method for Self tapping Performance of Medical Bone Screws".

Please note that some content in this document may be affected. The publishing agency of this document does not assume responsibility for identifying these.

This standard was proposed by the State Food and Drug Administration.

This standard is under the jurisdiction of the Orthopedic Implants Subcommittee of the National Technical Committee for Standardization of Surgical Implants and Orthopedic Instruments (SAC/TC110/SC 1).

This standard was drafted by Tianjin Medical Device Quality Supervision and Inspection Center.

The main drafter of this standard is Gao Jintao Li Nan Duan Qingjiao.

Surgical implants - Test method for self tapping performance of metal bone screws

1 Scope

This standard is used to measure the axial pressure required for metal bone screws (hereinafter referred to as "screws") with self tapping properties to be screwed into standard materials. The results obtained using this standard test method are not directly related to the axial pressure required for screws to be screwed into the human bone. This standard is only used to confirm the consistency of the tested product or to compare the relevant performance of different products with similar sizes.

This standard does not apply to metal bone screws in the form of "self drilling" or "self drilling/self tapping" that automatically squeeze and form mating threads with human bones during penetration and do not require pre drilled guide holes.

2 Equipment: Bone screw performance tester

2.1 Experimental apparatus

The experimental device used to determine axial self attack force is shown in Figure 1. The experimental device should include a variable speed electric motor that can continuously drive the spindle. The main shaft can perform axial motion and provide variable axial force while continuously rotating. The testing device and main shaft should have sufficient stiffness to ensure that neither deflection nor deformation occurs under the loading conditions of the test. In addition, the test device should include a test block fixture to fix the test block and be able to continuously monitor and record the forces generated during the screw test process. Calibrate the range of force, torque, and axial displacement during the calculation process.

2.2 Axial pressure sensor

A converter capable of converting applied axial pressure into electrical signals suitable for continuous recording, calibrated within the range used in the experiment. The pressure sensor should have an accuracy of 0.5% for full-scale output and a resolution better than 1.0N.

Calibration. The pressure sensor should have an accuracy of 0.5% for full-scale output and a resolution better than 1.0N.

2.3 Torque Sensor

A converter capable of converting applied torque into electrical signals suitable for continuous recording, calibrated within the range used in the experiment, including clockwise and counterclockwise directions. The torque sensor should have a full-scale output accuracy of 0.5% and a resolution better than 0.10N. m.

Note: Composite sensors with both pressure and torque measurement functions can also be used in this experiment if their indicators meet the requirements of 2.2 and 2.3.

2.4 Linear displacement sensor

A converter capable of converting axial displacement into electrical signals suitable for continuous recording, calibrated within the range used in the experiment. The displacement sensor should have an accuracy of 1% of full-scale output and a resolution better than 0.5mm.

2.5 Test block fixture

Clamps or fixing devices that can be used in conjunction with experimental equipment. The fixture should ensure that the pre drilled guide holes in the test block are aligned with the test sample. The fixture should have sufficient rigidity so that it will neither deflect nor deform under test loading conditions. At the same time, the test block should not be deformed during clamping or testing.

2.6 Test Block

The test block should be made of uniform materials that comply with ASTM F 1839. The upper and lower surfaces of the test block should be flat, smooth, and parallel to each other (with a deviation of ± 0.4mm) to ensure that its upper surface is perpendicular to the centerline of the test sample in the fixture. The test block should be square or other shape that ensures no relative motion or deformation during clamping and testing. The thickness of the test block should not be less than 25mm

2.7 Guide holes in the test block

Guide holes should be pre drilled in the test block before the screw in and screw out tests. The size of the guide hole should be specified by the manufacturer of the screw to be tested. The guide hole should be drilled perpendicular to the surface of the test block, and it should be ensured that the hole is straight, without any conical, bell mouth, bucket shaped or other situations. The guide holes on the test block should be drilled as through holes, and the debris should be cleaned before rotating the test sample. If there are multiple guide holes in the test block, each hole should be far enough from the edge of the test block to ensure that the test does not cause deformation of the edge of the test block. The spacing should be at least 5 times the diameter of the screw. After the test block is installed on the test device (see Figure 1), the guide hole, screw, and screw drive fixture should be on the same axis.

2.8 Test Samples

The test sample should be the final product and have sufficient length to complete the test.

2.9 Data recording equipment

The data recording device can continuously record axial pressure, torque, and axial displacement at a frequency of 10Hz. The data recording device should be able to simultaneously record the changes in two Y-axis data (Y-axis 1 for force and torque, Y-axis 2 for displacement) over time (X-axis), with pressure, torque, and axial displacement measured in Newtons (N), Newton meters (N ● m), and millimeters (mm), respectively. The accuracy of axial pressure and torque should reach 0.5% of the full-scale output, and be accurate to at least 1.0 N and 0.10 N. m. Axial displacement should be accurate to at least 0.5 mm

2.10 Test speed

The torsional force should be applied at a constant rate of 30 r/min. The axial compressive load should increase at a constant rate of approximately 2 N/s. The selection of torsion test speed should be representative of the situation of manually driving screws under clinical conditions. The axial loading rate that can easily identify or reflect the special self attack situation on the data recording device should be selected. If other test speeds and loading rates are chosen, their rationality should be confirmed and recorded. All controlled trials should be conducted at the same testing speed.

3 test samples

Representative samples should be randomly selected from each batch or process quantity according to ASTME122.

4 Experimental steps

4.1 Self attack power. Firstly, fix the test block with pre drilled holes rigidly onto the test block fixture, as shown in Figure 1. Select the appropriate screw drive fixture (fixture) and connect it to the spindle, and check the alignment of the guide hole and fixture. Then, assemble (load) the test sample onto the fixture. Finally, lower the spindle until the assembled test sample reaches the guide hole, and adjust the axial displacement of the spindle to achieve a maximum preload of 1.0N to ensure a tight fit between the screw and the fixture.

4.2 The testing machine drives the test sample at a constant rate of 30r/min. Real time monitoring of changes in axial force, torque, and displacement through data recording devices, while axial force increases at a constant rate of approximately 2.0N/s ± 1.0N/s. Continuously increasing the axial force until the self tapping characteristics of the screw result in a significant increase in torque and axial displacement of the test block, as shown in Figure 2.

4.3. The above features indicate that bone screws with self tapping characteristics enter the test block and begin self tapping. At this point, the increase in axial force should be interrupted and the initially observed load force (loading and holding) at the beginning of the self attack should be maintained. At the same time, the screw should be monitored in real time to ensure its continuous self insertion into the test block, and the continuously increasing torque and axial displacement can be recorded. (Note that in some cases, the axial force may decrease at the beginning of self tapping, as shown in Figure 2, which means that continuous force is no longer required when the test sample continues to enter the test block. Therefore, at this stage of the test, the axial force plays a role in maintaining the fit between the fixture and the screw.).

4.4 Data obtained from the experiment. An effective experiment should start with a complete rotation of 5 circles after the self attack. Take the maximum axial force obtained at the beginning of the self attack as the self attack force and record it in the report, with the value in Newtons (N). Sometimes, during the initial 5 rotations, the test sample will stop entering the test block after self tapping (stopping or internal thread failure of the test block), resulting in a rapid decrease in torque resistance and a constant axial displacement (flat line). When the test sample stops, the axial force increases again at a rate of 2.0N/s ± 1.0N/s to reach self attack again: (1) the maximum axial force that occurs for the second time will be recorded as self attack force in the report; (2) After the second self attack, the test sample needs to complete 5 rotations; (3) The remarks in the test report should indicate information about the stopping of the test sample or the failure of the internal thread of the test block. Samples that stop more than once will be considered invalid.

5 reports

The report should include the following information for each test sample (all values in the report are in international units SD:

a) Screw information refers to the national standards that the screw complies with Industry standard or ISO standard number. If it does not meet the standards, it should include the form of the screw head, thread form, maximum diameter/base diameter, pitch, total length of the screw, length of the head and shaft (excluding the part of the head without threads), and screw type;

b) Chemical composition of screws;

Ultimate tensile strength;

d) Surface treatment form;

e) Self attack capability;

f) Record of special test conditions and sample conditions:

g) Screw in speed (if not in accordance with the provisions of 3.10);

h) The description of the test block material is based on the grade specified in standard ASTMF 1839. For materials that do not comply with ASTMF 1839, the following should be provided:

Note: ASTMF139 is suitable for simulating cancellous bone, however, self tapping screws are also applicable to cortical bone. Therefore, other materials' test blocks can also be used for testing

1) Product name;

2) Ingredients

3) Density;

Tensile strength;

5) Compressive strength;

6) Shear strength