3-D Printing of a New Set of Knees

My fiancee needs new knees. Wow. I can’t begin to imagine the pain. That said, it seems there is an alternative that involves printing, particularly when you expand your definition to include 3D printing (also known as additive manufacturing).

When we got the bad news, my fiancee and I started doing research and came upon a procedure called the ConforMIS iTotal joint replacement system. (Sounds a bit like the iPad or iPhone.) While my fiancee and I are still not looking forward to the procedure, the pain, or the recovery, it is intriguing to see such a practical use for this additive manufacturing technology, and actually one that will minimize my fiancee’s pain, more accurately match her new knees to the old ones, quicken her healing time, and allow her more future mobility.

Here’s How It Works

First, here’s a brief description of subtractive and additive manufacturing:

1. Subtractive manufacturing involves the machining, or tooling, of a component part (say a metal gear). In this case, everything that is not wanted is ground away from the original block of metal. (Making keys at the hardware store would be another example. So would chipping away at a block of marble to create a single sculpture.)

2. Additive manufacturing is the alternative. It involves adding material to create a component part rather than subtracting waste from a block of wood, metal, or any other material. Your inkjet printer on your desk is an example. It creates a precise pattern of ink on a paper substrate. Three dimensional printing would be another example, using a resin instead of ink, and layering this substance to produce an object with depth (in addition to the dimensions of length and width that a desktop inkjet printer produces on paper). This process has the added benefit of being driven by digital information.

3. Within the additive manufacturing realm is also the domain of injection molding. This approach involves creating a mold of a component part, filling this mold with molten plastic, metal, or another substance, and then removing the mold to release the object you have just created.

What makes option #2 above ideal for knee replacement is that you don’t need a mold to create a single (or, in my fiancee’s case, two) final product(s). Mass customization, the same process that allows for the printing of an individual marketing piece (with your name in the text) also allows for the creation of two new knees for my fiancee (both exactly matching the original knees she had from birth).

How Do You Make One-of-a-Kind Knees?

First of all, prior to additive manufactured knees, knee replacement involved adjusting either the bone in the leg or the “off-the-shelf” standard issue knees to create a fit between existing bone and the new knees. Understandably, in spite of the skill of the surgeons, the one-size-fits-all artificial knees often either overhung or underhung the remaining bone in the femur and tibia (two of the three main leg bones). This increased pain and reduced mobility—permanently.

In contrast, the new ConforMIS 3D printed knees begin with a CT scan to capture all relevant anatomical data (to ensure that the fabricated knees will fit the patient’s body exactly).

(In some small way this reminds me of wire-frame creation in 3D modeling software, not for physical knees but for either offset printed images or videos. It seems that with advances in 3D additive manufacturing, we have graduated from virtual worlds—photos and videos—to fully functional body parts that can withstand the wearing effects of constant use over time.)

What Are the Knees Made Of?

While I could envision the product, I couldn’t quite visualize the material, so I did some further research and found that the ConforMIS process creates metal knee joints out of cobalt-chromium. And at the same time it produces the metal knee replacements (but using different materials), the 3D printer creates all of the tools used in the surgery, while tailoring these to the patient’s individual needs. (These would include the “jigs” and other inserts that accompany the metal joints, as well as other surgical instruments.)

Even with this information in hand, I still couldn’t imagine a 3D printer “jetting” metal. Would it be molten? How would the 3D printer deal with the intense heat? I had a lot of questions that none of the articles on 3D joint printing answered.

Then I found an article describing the same procedure performed on a cat. Granted, I’m not yet sure that the technology is the same, but I would assume it is similar. The method is called “laser sintering.”

The website www.materialise.com describes this process in an article entitled, “3D Printing Creates the World’s First Replacement Knee Joint in a Cat.” The article notes that “Laser Sintering is an Additive Manufacturing/3D Printing process that uses a high-powered laser to fuse small particles of powder together, layer by layer (with particle sizes in the order of magnitude of 50 µm).”

So my assumption is that this fusing process of metal particles is at least one option for creating cobalt-chromium 3D printed knee replacements for my fiancee as well.

Interestingly enough, the www.materialise.com article also notes that “Building the implant by Direct Metal Laser Sintering meant that mesh and porous areas that would promote integration of the implant into the bone could also be built into the piece as it was being created. These features, only achievable using Additive Manufacturing, provide enhanced long-term stability over traditional implants, giving surgeons a new option for non-standard cases...that can be tailored exactly to their needs.”

Benefits of 3D Printed Knee Replacement Surgery

My research on ConforMIS knee replacement technology provided some interesting facts and statistics:

1. An article entitled “Customized 3D Printed Implants from ConforMIS Make Knee Replacements Easy” (Clare Scott, 1/26/16, www.3dprint.com) notes that two months before the surgery, digital information from the CT scan is transmitted to ConforMIS for 3D printing. This allows the company to incorporate any relevant, updated information provided as close to the surgery as possible.

2. The surgery is completed in less than an hour. (My fiancee’s doctor said it would take 1.5 hours. Either way, that’s a quick turn on new knees compared to the prior technology.)

3. Apparently the majority of patients are up and walking (in the hospital) the same day and leave the hospital within 24 or 48 hours.

4. A number of athletes referenced in Clare Scott’s article who have had the procedure have gone back to their extreme sports within three months’ time.

5. All knees are the right size, in contrast to the two-thirds of traditional, off-the-shelf knee replacements that are too big or too small, causing reduced mobility and chronic pain.

6. A traditional knee implant often requires the removal of additional bone to achieve a good fit. In contrast, the ConforMIS procedure allows surgeons “to preserve 25 to 30 percent more bone than in standard knee replacements, and also greatly reduce blood loss.” (“Customized 3D Printed Implants from ConforMIS Make Knee Replacements Easy,” Clare Scott, 1/26/16, www.3dprint.com).

How Is This Relevant to “Printing”?

In today’s printing market, commercial printers are expanding their “paradigms.” Instead of just putting ink on paper, they are looking at the power of printed matter (offset, digital, large-format) to educate and persuade. Printing has become a vehicle for communication and brand recognition, and therefore revenue generation.

In much the same way, printing has matured. Instead of just producing virtual items and virtual experiences on a two-dimensional surface (and eliciting the accompanying thoughts and emotions), they have begun to produce three-dimensional items that can be used not virtually but in real life, to improve the quality of people’s day-to-day existence over extended periods of time.

[Steven Waxman is a printing consultant. He teaches corporations how to save money buying printing, brokers printing services, and teaches prepress techniques. Steven has been in the printing industry for thirty-three years working as a writer, editor, print buyer, photographer, graphic designer, art director, and production manager.]