New Designs of Spinal Screws and Middle Ear Implants Need Axial-Torsion Testing

Doctors around the world encounter patients who are in need of bone implants or other surgeries involving medical devices. Innovative body fusion devices and metallic bone or dental screws are continually being improved to benefit mankind as a whole.

In Georgetown, Texas, one osteological technology company – Eminent Spine – recently performed its first minimally invasive percutaneous pedicle screw surgery, according to a company press release.

“[This was the] most user friendly ‘true’ Percutaneous System I have used,” Dr. Ross Sherban, who performed the surgery, said in the release. “The patient had minimal blood loss, with less than 15mm incisions. Eminent Spine has done an excellent job engineering and manufacturing a fabulous Percutaneous Posterior Pedicle Screw System.”

This type of screw employed triple lead thread technology and uniquely tailored extended towers. The company also conducted biomechanical tests on the percutaneous pedicle screw as well as all new designs for bone screws or spinal devices.

Another company in Sioux Falls, South Dakota also took part in developing an enhanced screw for treating sacroiliac joint dysfunction. Recently, the U.S. Food and Drug Administration approved the SAMBA Screw System, which was designed by Medical Designs LLC.

The SAMBA Screw System is a hollow titanium bone screw that features radial slots for promoting fusion of osteogenic and osteoconductive materials. Additionally, an innovative precision engineered applicator tool allows for easier insertion of the bone screw into the sacroiliac joint.

“We have completed thirty SAMBA Screw procedures here in Sioux Falls and the results have been outstanding,” Dr. Wilson Asfora, the inventor of the bone screw, said in a company press release. “Our design team has optimized the surgical protocol to have fewer steps compared to other techniques. The result is less time in the OR and faster patient recovery.”

In addition to these unique bone screws, the Chalmers University of Technology has created a new implant that repairs functionality of the middle ear, according to a January 2013 article from the Science Daily. The first operation using this device was performed in December 2012.

The new implant, which is approximately six centimeters long, is meant to provide deaf patients with normal hearing functionality. The device is currently undergoing a clinical trial. The implant is inserted beneath the skin and attached directly to the skull bone. The biggest benefit of this new implant is that it does not need to be attached to bone using a titanium screw, which prevents the risk of skin infections around the site of attachment.

These developments provide great promise for the physical health of countless patients as well as the betterment of surgical processes. However, before bringing these solutions to the healthcare sector, the materials must be tested to ensure their strength, durability and safety.

Manufacturers of bone screws must test them according to ASTM F543 Standard Specification and Test Methods for Metallic Bone Screws.  ASTM F543 includes 5 annexes, four of which require an axial-torsion testing machine.  An axial-torsion mechanical testing machine is capable of applying tension or compression and torsional forces simultaneously.  In annex A1 of F543, the screw is clamped along the threads and torque is applied to the head until failure.  During Annex A2, the maximum insertion and removal torques are determined as the screw is rotated clockwise at least four turns and then counterclockwise until it is removed from the test block.  Annex A3 is used to measure the maximum force required to pull a screw out of a test block.  Annex A4, the most difficult method to perform is used to determine the self-tapping properties of a bone screw.

ADMET offers the eXpert 8600 series Axial-Torsion Testing Machines for performing all parts of ASTM F543. Biomedical companies that have developed new implants or bone screws have benefitted greatly by performing axial-torsion tests on eXpert 8600 series test systems. For more information on the eXpert 8600 Series or other ADMET products and services, please contact Vinny Milano, our Account Director for the Biomedical Sector, at 781-769-0850 x21.

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