Impact Performance of Cervical Disc Implants
As a part of the aging process many people begin to suffer from herniated discs and degenerative disc disease in their neck. As the discs that connect the vertebrae loose their flexibility and shock absorbing capabilities, the disease can cause nerve root and spinal cord compression, resulting in chronic arm and neck pain. For the past 40 years cervical spine fusion procedures have been performed to address the problem. This procedure usually results in the immobilization of the neck bone causing the other discs in the neck to work harder.
Currently under going clinical trials is a new artificial cervical disc assembly. With a ball and socket configuration made from titanium and a ceramic composite the artificial disc can be inserted in place of the damaged one enabling the recipient to maintain the range of motion found with a normal disc. In addition to clinical trials producers of these assemblies are interested in establishing how they will hold up to impact events. Areas of interest include splintering or chipping in the ceramic ball possibly caused by the edge of the titanium cup and any loosening or failure in attachment of the ceramic to its base.
When approached about providing a testing solution for this application we recommended the use of our Model 9250HV Drop Weight System with Impulse Data Acquisition and Machine Control. A Model 8496-02 ; 45 kN (10,000 lb) force capacity instrumented tup provided a sufficient level of load capacity for the test. Pneumatic rebound brakes were included to prevent any secondary impact to the specimen. Due to the different assembly sizes, shapes and styles, a custom flat faced tup insert and support fixture, designed for the customers’ specific configuration were required.
Utilizing the 9250HV’s machine control feature and choosing impact energy as the drop point control the customer was able to systematically increase the amount of energy used to test each specimen. By doing this they are able to gather data as to how their discs will perform when subjected to a variety of impacts. They are able to then develop an impact performance record of their product. The Impulse Data Acquisition System allowed the customer to gather information on not only how well the existing design performs, but data and insight into how existing designs can be improved.
Impact resistance is one of the most important properties for component designers to consider, as well as the most difficult to quantify. Impact resistance is a critical measure of service life and more importantly these days, it involves the perplexing problem of product safety and liability. With the combined experience of Dynatup® and CEAST, Instron® has more than 80 years experience in designing impact testing systems to simulate real-life impact conditions.
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