Which Type of Implant is Right For You?

Just as in any other industry, the medical (and surgical) field is constantly evolving their procedures, techniques and technology. Specifically in orthopedics and knee replacement, leading manufacturers tinker with the shape, material and overall design of their knee implants…with the hopes of gaining an edge. As it stands, there’s really no undisputed implant leader, so the decision essentially comes down to a combination of your needs and your doctor’s experience and preference. So that you have a solid frame of reference, let’s go over a few of the finer details…

The Basic Anatomy of a Knee Implant

The image to your right breaks down the 3 basic parts (components) of a total knee replacement implant:

  1. Femoral Component – the metallic piece that attaches to the end of your femur (thigh bone).
  2. Plastic, Articulating layer – “articulate” means to bend and since it needs to give, all knee implants are made of a plastic composite intended to mimic cartilage and miniscus.
  3. Tibial Component – the plastic layer needs a solid support that that’s exactly what the tibial piece does. It permanently binds the top of your shin bone (tibia) to the articulating layer.

How do Implants Differ?

Materials – Metal
There are a variety of different metal alloys used but a few of the more popular include:

implant

Titanium and its alloys – because titanium is so inert (it doesn’t react with the human body) and robust, its been the preferred material of implants for years. The most popular titanium alloy in use is Ti6Al4V.
Cobalt-chromium – just as widely used as titanium, cobalt-chromium is extremely inert, bio-compatible, and durable…ideal properties for a surrogate knee joint. The only potential downside here is the purported release of tiny metal ions due to friction – when you move, walk, etc. While the fragments are generally harmless (and may never occur), folks with sensitivity to nickel or other metals have been known to develop a reaction.
Tantalum – the key component of a new bone/metal mix called Trabecular Metal, Tantalum has excellent biological-friendly properties. Trabecular Metal is manufactured with small mesh holes that foster bone regrowth, creating a better bridge between metal and bone.

Shapes – Rotating vs Regular
As you know, the knee primarily moves in a back and forth motion (much like a hinge on a door). There isn’t much side-by-side movement, but it does happen, especially when you pivot and change direction. For that reason, a few implant manufacturers have begun to
develop product lines that rotate inwards and out as well as hinge. There isn’t a big case available study to substantiate their claims of markedly better movement and range of motion, but the occasional feedback from early adopters seems to be positive. Of course, the real test would be someone with a traditional implant on one knee and a rotational model on the other. There just aren’t a lot of folks in that camp, so it really boils down to your doctor and his experience with rotating implants. If he’s had good luck with them in the past and you’re fairly active, rotating implants may become an option for you.

Gender-Specific
For years, implants came in the standardized sizes for both men and women (size Y for men = size X for women). There has been a recent trend to create specific models for each sex, however. Essentially, manufacturers slightly adjust the relative size and angle of each part to accommodate for the anatomical differences between sexes (different hip angles, size of the tibia, etc). Just as with the rotational implants, there really isn’t enough data to give the upper hand (or knee!) to gender-specific implants. It literally takes decades to begin to fully understand the short and long-term success rates of new implants.

Final Thoughts

With all the options out there (and, trust me, this is just the tip of the iceberg), it’s tough to objectively compare them all, even for doctors. There’s no doubt knee implant manufacturers will do anything and everything to stand apart from the crowd, so a good number of the newer, “gotta have” models are probably more marketing hype than anything, so tread carefully. If you’re unsure, carefully discuss all the options with your physician – in a lot of cases, it’s simply the best and safest route to go with a tried and true model that’s been around for decades.

{ 9 comments… read them below or add one }

lynn S. June 24, 2013 at 12:00 pm

Hello: Could you tell me if the Sigma Tc3 revision knee systems are made with titanium materials and if so can you get an MRI or No?

Thank you in advance for your anticiapted response.

Lynn S.

Reply

Douglas June 27, 2013 at 8:52 pm

Hi Lynn,

I’m familiar with Sigmas but only vaguely with the TC3. I believe the only titanium it has is on a reinforcing pin (if you’re concerned about a titanium reaction or other day-to-day issues, definitely ask your DR). In case you haven’t seen it, here’s the TC3 page on Depuy’s site (click “features and benefits” or try downloading the product details PDF). Good luck!

Reply

Qasem September 25, 2013 at 11:43 am

Dear Sir,
I am a master student in biomedical engineering department- near east university-north cyprus.
i have a thesis of CUSTOM DESIGN FEMORAL KNEE IMPALNT.
I want to make new approach of bone implant interface as smooth surface instead of five cut faces of internal side in femoral implant.

I wanted to ask you if you like this new design and if its possible and good for human patient to fit in femoral bone. I want replace the five cut faces , and change it as smooth surface .

Reply

Douglas September 29, 2013 at 11:58 pm

Hi Qasem,

It certainly sounds like an interesting engineering and design shift – hopefully it makes it to testing phase. Keep up the good work!

Reply

Patrice Cossey May 14, 2014 at 7:36 pm

I had a partial knee replacement at the end of January and everything was going great. After I had several weeks of physical therapy I started going to a gym to exercise. But now my knee is very painful again. How do I know how much is too much exercise?

Reply

Ken Siegel May 21, 2014 at 6:12 am

What is the recommended treatment for patients who have a severe allergy to nickel and a minor allergy to cobalt. Leg has been stiff and painful for many years, blood test showed these allergic reactions to metals.
Thank you.

Reply

Donna Rodriguez June 6, 2014 at 7:07 am

Two weeks after knee replacement 9/13/11 I developed psoriasis which started in the knee area and has spread to arms and legs and back. Is this a known reaction to knee replacement materials? The knee replacement is otherwise wonderful but the psoriasis is an awful trade-off.

Thank you

Reply

aerial June 27, 2014 at 11:01 pm

Yes I am just wondering….
I have had my acl,mcl, and PCL all replaced in my knee 3 times. I was just wondering should I replace them again in this up coming surgery or do a total knee replacement. Btw I am only 21.

Reply

Sharleen July 14, 2014 at 11:25 am

I had a full knee replacement using a titanium implant and after 4 months I still am dealing with stiffness and a lot of inflammation. I have had no official blood tests, but I do have a sensitivity to metal, as I have to be careful wearing jewellery. I definitely cannot wear anything with nickel, as my body reacts in a few hours of wearing it. Most other type of metals, such as gold and silver, I can wear for a few days only, as I develop blisters, especially under rings.
I have rescheduled an appointment with my surgeon on the suggestion of my family doctor, but now I am worried.
Can you please recommend a treatment for others with metal allergies.
Thank you.

Reply

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