Technological advances in medical equipment and implants have driven
worldwide spinal implant sales to $10 billion annually.
Like orthopedic implants used for joint reconstruction and the surgical
fixation of a bone fracture, spinal implants are subject to very specific and
strict surface finishing requirements.
Mass finishing and shot blasting play a key role in creating the right
finish for spinal implants, not only for intermediate surface treatment after
forging, casting, machining, additive manufacturing, etc., but also for placing
the final surface finish before implantation.
Rosler Metal Finishing has extensive experience in surface finishing spinal implants using mass finishing, shot blasting, and a combination of both methods.
In a series of posts, we’ll analyze the specific surface finishing
requirements for spinal implants based on their functional and performance
characteristics and describe the respective mass finishing and shot blasting
equipment and methods available to fulfill these requirements.
Types of Implants
When physical therapy and medication aren’t enough to treat spinal
problems, surgical procedures may be necessary. Depending on the issue at hand,
a variety of spinal implants may be utilized, including:
- Spinal rods.
- Pedicle screws.
- Spinal hooks.
- Cervical plates.
- Interbody fusion cages or spine cages.
- Artificial disks.
The Importance of Finish
To ensure a zero-defect policy, these implants must be created with the
right material, in a highly controlled manufacturing process, and finished to
exact standards. Finishing requirements can range from simple cleaning,
deburring, or edge radiusing to defined surface smoothing, surface texturing,
and high-gloss polishing. They can even include inducing a compressive residual
stress into the components for extending their life span.
The finish of a spinal implant often corresponds to a particular use and
- Biocompatibility – The implants must not be toxic, injurious, or physiologically reactive while avoiding immunological rejection. They must also resist corrosion in reaction to bodily fluids.
- High tensile strength and long-life span – Some implants such as spinal rods and cervical plates are exposed to considerable loads. They must withstand these loads for a lifetime without breaking.
- High ductility – Rods and cervical plates must allow adjustment to follow the spine contours.
- High osseointegration – Some implants must encourage the attachment of the surrounding bone tissue to the implant. Examples include interbody cages and artificial disks.
- Low osseointegration – For both the comfort of the patient and later removal, some implants must resist the attachment of bone tissue. For example, if after a fusion procedure the bone graft between spine segments has grown, the rods, screws or plates can theoretically be removed. This is normally not recommended but can become necessary if pedicle screws cause discomfort for the patient. Implant removal is especially important in children.
- Non-magnetic – Materials used for implants cannot be magnetic as magnetism can pose a risk for the patient.
To date the most common materials for spinal implants have been
titanium, various titanium alloys, and stainless steel. Occasionally, even
platinum is used.
All these materials are ductile and highly corrosion resistant while
offering relatively high tensile strength and excellent biocompatibility.
Recent material developments have focused on organic thermoplastic
polymers and special coatings for thermoplastic as well as metal implants.
- Polyether Ether Ketone (PEEK) – This material has excellent biomechanical properties and offers a very high degree of biocompatibility. It can be made in a porous form which promotes osseointegration and has been utilized for interbody fusion cages and spinal rods.
- Porous Titanium Coating – Plasmapore, a porous titanium coating, promotes increased bone formation and implant stability. The coating is equally applicable on implants made from PEEK or metal and has been applied to artificial disks and interbody fusion cages.
The Rosler Way
The complete Spinal Implants Series includes:
- Part 1 – Surgical Specifications.
- Part 2 – Processed to Perfection.
- Part 3 – Mass Finishing Versus Shot Blasting Methods.
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