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Implants Used in Spine Surgery

In today’s competitive economy, medical device companies are constantly looking for ways to innovate and improve surgical implants in order to gain more value. The past few decades have seen major breakthroughs in the development of state-of-the-art spinal implants for use in spine surgeries. Spine surgeons choose very carefully and utilize only the best implants that’s most suitable for each individual. The result? Better treatment for patients, and better lives lived by numerous patients across the globe.

While many corrective procedures involving the spine do not require surgery, there are instances where spine surgery is a necessity. Most of these surgical procedures make use of specially-designed spinal instrumentations. An implant is one example – it’s a device that effectively replaces a biological structure that can’t function due to massive trauma or cartilage and bone disorders.

3 Basic Methods of Implant Creation

  • Implants may be forged. The shape is created in the final form via use of force such as hammering, bending, etc.
  • Implants may be cast. The implant is created when molten metal is poured into a set mold.
  • Implants may be drilled or milled into the desired shape.

Types of Implant Material

You’ll find spinal surgical procedures that utilize stainless steel, titanium alloy, titanium and non-metallic implant devices that support the spine and solve spinal instability.

Metals are a staple when it comes to orthopedic implant manufacturing processes. They are introduced in a number of different forms. Surgeons and the medical industry have been using varying types to find the most effective replacement material for broken or fractured bones.

Implants in the 20th century saw a surge in the use of metallic alloys, more specifically noble metals. Implants that are made from tantalum, titanium and cobalt are not uncommon. Research has shown that these metals are more effective and safer for long-term orthopedic implants. They can be left in vivo for a far longer time than other metal-based implants. Moreover, the physical, biological and mechanical composition of these types of metal have proven to be beneficial in terms of implant lifespan.

Implants may be used in a number of ways by a professional spine surgeon. They can strengthen and stabilize one’s spine, correct any physical deformity and facilitate fusion. Some of the more common spinal conditions that benefit from fusion spinal implants include traumatic fractures, chronic degenerative spine disease, spondylolisthesis or spinal column slippage, and spinal instabilities such as scoliosis.

Common Metals for Surgical Implants

Here’s a list of the most common metals that are used in surgical implants:

Titanium Alloy

The use of titanium alloy as a medical implant has only grown in popularity since recent times. Compared to stainless steel alloy implants that have made the medical rounds since the 90s, titanium alloy is a relative newcomer in terms of replacing biological tissue with artificial metals. Perhaps the most notable advantage of titanium alloy over other implant material is its strength- this material has the same strength as steel and is up to 50 percent lighter than its cousin. This combination makes it ideal for use in the implant industry.

Moreover, titanium alloy has proven itself to be quite compatible as a surgical implant due to its low corrosion levels and its high biocompatibility level. Its elasticity is similar to that of human bone, which makes it excellent to use in porous implant materials for long-term processes. The low corrosiveness of titanium alloy has paved the way for more precise fittings and for the construction of different modular implants.

Titanium alloy is currently being employed as a material for the production of intramedullary rods and fracture plates on both acetabular and femoral implants. Fracture fixation components that utilize titanium alloys can be used to circumvent implant issues such as when the implant area is infected, or when the patient wishes for a shadow-free imaging after operation.

Titanium is chosen for surgical implants, more particularly for reconstructive surgery mainly because of its remarkable strength and relatively lightweight characteristic. The only disadvantage to using titanium alloy is that it is easily contaminated when exposed to oxygen, nitrogen and hydrogen. These elements may introduce corrosion to the said metal and could potentially compromise its role in certain medical implant surgeries.

Surgical Stainless Steel

Stainless steel has been around the medical industry since the early 1900s and continues to be a popular material for surgical procedures. Since then, it has evolved into many forms used for many surgical purposes. For example, type 302 stainless steel is mostly utilized in orthopedic surgeries, while type 316L stainless steel is mostly utilized in medical procedures that aim to stabilize a biological structure (such as bone tissue, cartilage, etc.) to accelerate the healing process or to replace biological tissue.

Type 316L stainless steel is the preferred material for surgical procedures because it possesses the best resistance to corrosion in instances where it is placed alongside biological fluids. One of the rules to surgical implants is that it should be highly resistant or immune to corrosion when placed inside a patient’s body to prevent the chances of implant infection. In cases where implants do corrode and infect the human body, an emergency treatment is done to remove the implant in order to prevent further damage from occurring to the surrounding tissue. Type 316L is particularly effective when the surgical implant procedure is done in cold-worked conditions. One of the most notable advantages surgical stainless steel has in comparison with other implant material is that there’s a lack of inclusion. This means stainless steel doesn’t have sulfur, which is a main component in the corrosion process involving metals.

316L, or surgical stainless steel alloys can be mixed with varying amounts of nickel, chromium and iron to manufacture different kinds of prostheses. Stainless steel is mostly made using different metal alloys. Adding a bit of the chromium elements can make stainless steel highly resistant to corrosion. Adding nickel and carbon in the stainless steel mix stabilizes the austenite contained within. Most, if not all 316L type stainless steel surgical implants contain about 14 percent nickel and about 17 to 19 percent chromium. Molybdenum may be added to stainless steel alloys to create an effective barrier against acidic environments inside the human body. Adding the carbon element may safeguard against further instances of corrosion as long as the carbon introduced is in its solid solution state.

Stainless steel surgical implants should not have any ferrite element contained within. Adding ferrite lends the stainless steel a magnetic property, which can prove to be dangerous when exposed with MRI, or Magnetic Resonance Imaging equipment. Furthermore, magnetic implants are prone to heating processes, which could change positions or the shape of the medical implant.

Stainless steel can still be seen as a primary material to many surgical implants, but it has been mostly relegated to screws, plates and intramedullary devices that act as temporary weight-bearing devices for short-term periods. A high corrosion rate and being relatively prone to fatigue prevents stainless steel from being used on modern replacement implants, especially in joints.

Cobalt-Based Alloys

Implants made from molybdenum, chromium and cobalt are used for their porous properties, which come in handy when targeting for ingrowth via biological fixation. These cobalt-based alloys prove to be the least ductile in comparison with other materials such as titanium and/or iron, and this property does not make them the best materials for spinal instrumentation and for intramedullary rods.

What cobalt-based alloys do, however is excel in implant production where bone replacement and permanent load-bearing applications are needed. Some examples of successful cobalt-based alloys are the Thompson prosthesis and the Austin Moore prosthesis. The first-gen fixed surgical implants such as the AML (anatomic medullary locking) implants and the PCA (porous coated anatomic) used cobalt alloy materials. Modern-day surgical implants can still utilize cobalt alloys to create both porous and cemented forms for knee and hip replacement applications.

It should be noted that stainless steel alloys and molybdenum/chromium/cobalt based alloys have proven to be more resistant to wear than titanium implant alloys.

Stainless Steel VS. Titanium Implants

  • Titanium has a lighter weight load and is stronger than stainless steel material.
  • Titanium enjoys a higher resistance on bearing repeated loads, which make it the better choice as an implant.
  • Titanium has a better tensile strength that can prove to be beneficial under repeated load stress. This means titanium is better at managing strain during internal fixation processes.
  • Titanium has a much less rigidity due to the element having a lower modulus of elasticity. This means there’s a limit on how much stress it can bear when implanted on bone structures.
  • Titanium has the ability to generate a lesser immune reaction because the material has a stronger resistance against corrosion when compared to its stainless steel counterparts.

Tantalum and Composites

Tantalum is quite resistant to the effects of corrosion and has enjoyed being a part of most super alloys used on spacecraft and aircraft engines. About half of tantalum is converted into metal powder form, mainly used in the manufacturing of capacitors and transistors.

Tantalum can be shaped into a porous substance. This state presents a higher modulus of elasticity, somewhat akin to bone as compared to cobalt-based or stainless steel implants. Balls made from tantalum are widely used for bone markers, but was only recently that tantalum was widely regarded for implant manufacturing. Due to having a remarkable resistance against corrosion, tantalum is mainly used to support biologic ingrowth.

In more recent settings, tantalum has been shaped into a honeycomb form, which positively affects its ability for supporting bone ingrowth and its porousness. Tantalum-based implants have become widely available in different forms; most of them are made to bridge bone defects.

Composites

Metallic alloys combined with other surgical biomaterials can certainly produce implants that have better physical and mechanical properties. Current studies and research are constantly evolving in the quest for composites that perform better than the traditional implant materials. The future of surgical implants is promising. Further development in both the metallurgical and composite industries will give rise to new implant materials that do well on all the important points on a long-term basis.

PEEK

PEEK is a thermoplastic that exhibits excellent chemical-resistant and mechanical properties that can be retained even when subject to high temperatures. PEEK implants are made from medical grade polyetheretherketone substances with tantalum radiopaque markers and a nitinol-based wire locking mechanism for placement.

Recent advances regarding PEEK has given way to shape memory behavior activated by mechanical applications. PEEK materials have excellent abrasion resistance and is great against everyday wear and tear. The many outstanding properties have made PEEK the choice material even outside medical device industries.

PEEK was first introduced within the interverterbral fusion cage in 1999 but has long since expanded its use within the medical fields. Its application has now expanded significantly, becoming one of the few key alternatives for metal implants in the anterior and posterior instrumentation, and in intervertebral cages. Renowned New Jersey spine surgeon Dr. Joshua Rover tells us, “PEEK mimics some of the mechanical properties of bone and does not show up on X-rays so it is ideal for spinal fusion surgery.”

As of today, PEEK-based interbody fusion devices and vertebral body replacements are standard care for lumbar fusion processes.

Spinal Implants Categories

Spinal implants can be classified into the following categories:

Rods

Rods belong to the original group of spine implants. Rods are put in place with screws and hooks to immobilize the spinal levels and to force the spine into the correct alignment. The rods are manufactured to be strong yet flexible enough for the surgeon to shape it and match the different contours of their patient’s spine

Pedicle Screws

Pedicle screws are specially designed to be implanted into the pedicle area of the spinal vertebrae. Traditionally, these screws are placed into lumbar spines. Thanks to newer technologies and medical breakthroughs, pedicle screws are now being applied to thoracic spine surgery applications as well. These screws offer excellent anchorage points on the rods they are attached with. The rods can then be contoured to correct spinal deformities and the spine surgeon can start the fusion process.

Hooks

Often used with rods and other surgical implants to anchor the vertebrae area.

Plates

Plates are often utilized to correct the cervical spine. Plates are manufactured specifically to the exact contour of the patient’s spine, which are then installed in place via screws set into the vertebrae. A contouring tool may be used to customize the plate’s fit when the adjustment time comes in order to provide a seamless anatomical fit for the patient.

Cages

Cages are also called interbody cages because they are normally placed in between two vertebrae areas. Cages are hollow devices that feature perforated walls. BMP or bone graft are often placed inside interbody cages to facilitate bone growth between two adjacent vertebras. Furthermore, they can be used to relieve nerve root pressure or restore the lost height on discs that are collapsed

Spinal pain can rob you of time spent on things and people that matter most. Not only does it affect one’s ability to work, but can prevent you from living the life you deserve. Conservative treatments are often the best place to start, but if they fail to deliver a cure, a spine surgery can usually give hope.

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