How are Spinal Implants Tested? – Spinal implants are a relatively new development in the field of spine surgery. Each implant boasts its own advantages, as well as its own set of drawbacks that can be related to any number of factors. This article will outline how spinal implants are tested and what factors physicians consider before deciding whether to implant one.
The first step relating to testing involves the product’s design. The design must withstand the stresses of spinal movement while being as thin and as light as possible to prevent interference with movement. A company will test a design by creating a computer model based on it and using it to simulate the forces placed on the implant during normal activity. A device used in biomechanical studies called a biaxial loading system can then be used to measure how well certain designs hold up under pressure.
The following factors may be considered to determine the design’s viability:
- How well does the implant withstand normal loading, which includes stress placed on it by movement, flexion, extension, and traction?
- How stable is the implant when loaded? (Does it deform easily or return to its original shape?)
- Is there a risk of infection? (How easy is it to clean and disinfect?)
- How easily can a surgeon access the implant? (How well does the implant allow for the passage of surgical instruments and provide visibility for a surgeon during an operation?)
The main idea in testing designs is that spinal implants should be as small as possible while still supporting the spine. If they are too bulky, they will push against adjacent vertebrae and will not provide enough room for movement.
The next step in deciding whether or not to use an implant involves manufacturing testing. Manufacturers must adhere to strict standards set by the U.S. Food and Drug Administration and the International Standards Organization. Manufacturers may perform effects testing, mechanical testing, and microbiological testing.
Effects testing is conducted on the finished product and involves three main tests:
- Mechanical test – It is a standard measure of strength as well as durability under pressure. The FDA standard requires the implant to withstand a load of 2,000 pounds per square inch for a minimum of one minute.
- Acetabular test – The acetabular component is tested by applying pressure to the shell; it must withstand the pressure of 3,500 pounds per square inch for two minutes while not showing signs of stress.
- Bending test – A force of 20,000 pounds per square inch is applied to the shell, and one minute must pass without failure.
In addition to these tests, manufacturers must also test for biocompatibility. The most common testing method includes exposing the implant to bacteria to determine whether or not the implant is likely to be rejected by the body. Finally, manufacturers must conduct a wet-chemical analysis on all components of the finished product.
The FDA and International Standards Organization must approve materials used in implants. Substances that can appear in these materials include:
- Silicone – a non-toxic polymer that acts as a glue to hold the various components of the implant together.
- Hydroxyapatite – a type of calcium found in human teeth; it provides wear resistance and shape retention.
- Titanium – a material that doesn’t corrode under normal conditions and is very durable; it can replace stainless steel and steel in implants.
- A mixture of titanium and zirconium – also known as zirconia, it is a biocompatible material used for implants such as screws, pins, and plates.
- Nitinol – a nickel-based alloy that is more flexible than stainless steel but more durable than titanium, it can be used instead of stainless steel in implants.
- Gold – a precious metal that people add to many of these materials to prevent corrosion and provide additional strength.
Microbiological testing ensures that all materials used are free of toxic chemicals and bacterial colonies. The second step in the process involves analyzing the finished product and all of the components. Test results will show whether or not there is evidence of microbial growth and whether any chemical contaminants were present during production.
Safety testing is a final step that manufacturers must pass before a device can be cleared to be used in humans. Safety testing ensures that the device is potentially dangerous but is not harmful to any of the parts it contacts, including body tissues. For a product to receive clearance for safety testing, it must undergo three steps:
- Classification – This is a procedure that is conducted on the device to determine if any of its components are potentially harmful.
- Determination – The manufacturer must demonstrate that the product will not cause skin irritation or damage to the body.
- Testing – Products that have failed to pass classification can be retested until they pass and do not need to undergo re-classification for them to be approved for safety testing.
The final step is pre-market approval. All manufacturers must obtain pre-market approval through the FDA before they can market any of their products. Spinal implants that undergo FDA approval are required to be labeled with a specific warning, which must be posted on every package and advertisement. The warning must describe the risks involved with the use of the implant, and it must be changed to reflect any new information learned about the product.
Spinal implants are important tools for the field of neurosurgery, and for patients as well. This field has benefited from the development of various types of spinal implants, all of which have helped provide support to the spine and restore functionality to patients. The first spinal implant was created in 1954, and since then, new designs have been created that are more effective than the first model. While it is impossible to predict what advancements will be made in this field in the future, scientists promise that improvements will be made on any previous design that can benefit future patients.
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