Best Quality Orthopedic Knee Implants

How Are Knee Implant Materials Chosen?

If implant materials are not chosen carefully, they can result in allergic or toxic reactions in the patient’s body, so all implant materials are chosen after careful consideration. While choosing the materials, implant manufacturers follow the given considerations:

• The material must be biocompatible, i.e., it should not react with any tissues in the body.
• It must be able to duplicate all possible knee joint movements. 
• They must come together to form an implant that is strong and flexible enough to bear the weight-bearing loads without breaking.
• All components must move smoothly against each other without any friction.
• The materials must retain their strength and shape without distortion or wearing for a long time.
• The implant must not weigh more than 400-600 grams (15-20 ounces) to avoid undue stress on tissues supporting the knee joint.
• The materials should be as resistant to wear as possible so that they won’t leach into the body and cause complications.
• The most commonly used material for manufacturing knee implants are titanium, nickel, zirconium, or cobalt-chromium based alloys used for metal components. These metals have high durability and are very stable, so they generally do not react with the body tissues.
• For plastic components, medical-grade ultra-high molecular weight polyethylene is used as it can easily glide on metal components and mimic hinge movements of the knee joint.
• If a ceramic material is to be used, it can be alloyed with a metal, like oxidized zirconium, for added strength.

What Are the Most Common Designs for Knee Implants?

Though the knee joint is a hinge joint, its design is very complex to allow for different types of bending and gliding motions. The design of the knee implant mimics the knee joint as much as possible to retain proper knee function after joint replacement.

There are more than 150 designs available in the market currently for knee implants. Though these designs vary a lot, no research study has proven any one design better than the other. Rather the choice of the best implant design depends on the patient’s individual knee condition.

The most commonly used designs for knee implants are:

• Posterior-stabilized Implant Design (Semi-constrained Implants)

This design is preferred when both the cruciate ligaments, i.e., the ACL and PCL, are to be removed, so a part of the implant is used to mimic its function. In these implants, since the PCL is removed, the tibial component is fixed to the femoral component with an internal post and cam to prevent the thigh bone from sliding too forward while bending.

• Cruciate-retaining Implant Design (Non-constrained Implants)

This implant design is used in patients with a healthy PCL. Since the PCL is retained (though ACL is still removed), the implant does not have a center post and cam design.

• Bicruciate-retaining Implant Design (Hinged Implants)

Most knee replacement surgeries allow for the removal of ACl to provide better implant fixation. However, bi-cruciate implants are used when both ACL and PCL are retained. 

• Unicompartmental Implants

These implants are used when only a part of the knee joint is to be removed, i.e., partial knee replacement surgery. These implants are smaller and specially designed to replace only one side of the knee joint.

Based on the range of motion these implant designs provide, they can also be classified as:

• Fixed-bearing Implants

For a fixed-bearing design, the plastic part of the tibial component is fixed to the metal surface under it. The femoral component rolls on this plastic cushion to provide knee motion.

• Mobile-bearing Implants 

This design is also known as a rotating platform. For this design, the plastic component can rotate a little inside the metal tibial tray. This joint allows for greater rotation in the medial and lateral sides of the joint compared to fixed-bearing designs.

• Medial Pivot Implants

Medial pivot implants are a recent innovation. They borrow from the mobile-bearing design to replicate knee movements more effectively than both other designs. These implants rotate, twist, bend, and flex like a natural knee joint. 

These implants follow a ball and socket design rather than a hinge design like a natural knee. However, one drawback of this design is that it relies more heavily on the surrounding soft tissues for support and thus can cause strain on them.

What Are the Different Types of Knee Implants Based on the Components and Design?

Based on the materials used and the configuration of these materials, knee implants can be classified as follows:

• Metal on plastic

It is the most affordable type of implant, so it is used very commonly. This implant is made using a metal femoral component that is attached to the plastic spacer of the tibial component. 

One of the disadvantages of this type of implant is that the plastic or metal parts of the implant can eventually wear away, leaking small particles into the bloodstream. This can lead to an autoimmune reaction or can loosen the implant leading to implant dislocation.

• Ceramic on plastic

In this type of implant, the femoral component is made of ceramic material (or metal covered with ceramic) instead of metal alloy. It is normally preferred for patients who are allergic to nickel or prone to autoimmune disorders.

• Ceramic on ceramic

For these implants, both femoral and tibial components are made from ceramic material or ceramic-coated metal. These implants completely eliminate the chances of metal particles leaking into the bloodstream.

However, due to the brittleness of ceramic material, these implants can completely shatter if too much force is applied to them.

• Metal on metal

For metal-on-metal implants, both the tibial and femoral components are completely made of metal. It is not used very commonly nowadays due to increased risks of metal leakage.

Originally, these implants were suggested to young people due to their long retention time without breaking. But nowadays, they are generally avoided except for some select cases.

How Are Knee Implants Fixed?

During knee replacement surgery, the implant is fixed to the surrounding bone and tissues so that it can mimic knee movements. Your surgeon will carefully evaluate your case and determine the best method for you. There are 3 ways of fixing knee implants:

• Cemented Fixation: For cemented fixation, the implant is fixed to its articulating bones using a fast-curing bone cement like PMMA – polymethylmethacrylate.
• Cementless Fixation: This method of fixation involves press-fitting, i.e., instead of relying on cement, the implant is made of a material that attracts bone-forming cells to form new bone around it. To improve bone growth, the implant surface can be textured or coated with osteopoietic material. 
• Hybrid Fixation: For hybrid fixation, a mixture of cemented and cementless fixation is used.

How Is the Best Knee Implant Chosen for the Patient?

Faced with so many choices, it is easy to become confused while choosing the right knee implant for you. When choosing a knee implant that suits your needs the best, you should keep the following criterion in mind:

• your activity level
• knee joint stability
• implant customizations that you might need according to your size, gender, etc.
• your current and required range of knee motion (flexion and extension angles)

Prioritize your needs and connect with your surgeon accordingly. Your surgeon will be responsible for customizing the implant and surgery for you based on the extent of your condition, knee anatomy, needs, etc., so it is very important that they know your expectations in detail.

What Are the Risks & Complications Associated With Knee Implants and Replacement Surgery?

Knee replacement surgery can be performed as a traditional open surgery or with minimally invasive (arthroscopic) or robotic techniques. But, like any other surgery, knee replacement surgery may also involve a few potential risks. 

In some severe cases of postsurgical complications, the patient may need revision knee surgery for relief. However, prompt management of such complications can help avoid re-surgery. That’s why you should consult your surgeon immediately if you notice signs of complications like fever, uncontrolled bleeding, discharge from the wound, etc. 

Some of the risks of knee replacement surgery are- 

• Infections
• Ligament damage during or after knee replacement surgery
• Allergic reaction to bone cement
• Nerve and artery damage around the affected knee joint
• Poor reaction to administered anesthesia during knee replacement surgery
• Excess scar tissue buildup
• Pain and stiffness in the knee joint post-surgery

What Happens if a Knee Implant Is Dislocated?

Knee joint/implant dislocation is very rare, especially after total knee replacement. It is extremely dangerous and can result in permanent disability or neurovascular damage. However, if the implant does dislocate, it happens in the posterior direction due to a lack of PCL cartilage.

If an implant dislocates within the first few weeks of knee replacement surgery, then the orthopedist might perform a closed reduction of the implant. However, even after that, careful observation is necessary to ensure there is no extensive soft tissue damage.

If the implant becomes loose over time due to wear and tear damage, then your surgeon might suggest revision knee replacement surgery. Most knee implants last for at least 15-20 years without the need for replacement, however, if the patient is overweight or performs high-impact activities, i.e., places a lot of stress on the implant, then that can accelerate wearing of the implant.

If you are looking for the best and most advanced orthopedic care from highly skilled and expert orthopedic surgeons, schedule an appointment with us. We will select the best possible knee implants for you based on your individual condition to ensure the best results. Consult the best orthopedic experts in your city at Pristyn Care.