The Mako knee replacement uses a combination of cobalt-chromium alloy, titanium, and ultra-high-molecular-weight polyethylene (a medical-grade plastic). These three materials serve different roles in the implant, chosen for their durability, compatibility with human tissue, and ability to replicate the smooth motion of a natural knee joint.
How Mako Knee Replacement Works
It helps to understand that “Mako” refers to the robotic arm system that assists the surgeon during the procedure. The implant itself is Stryker’s Triathlon Total Knee System, which is the company’s flagship knee replacement design. The robot helps position and fit the implant with high precision, but the materials inside your knee afterward are the same proven components used across modern total knee replacements.
The Femoral Component
The largest piece of the implant caps the bottom end of your thighbone. It’s made from a cobalt-chromium alloy, a metal that’s extremely hard, resistant to wear, and smooth enough to glide against the plastic bearing surface below it. Cobalt-chromium has been the standard material for the weight-bearing surfaces of knee implants for decades because it holds up well under the repetitive stress of walking, climbing stairs, and bending thousands of times a day.
This component is shaped to closely mimic the natural curves of your femur, which is part of what allows the knee to bend and straighten with a more natural feel after surgery.
The Tibial Component
A flat metal tray sits on top of your shinbone. This baseplate is typically made from a titanium alloy or cobalt-chromium, depending on the specific version used. Titanium is lighter than cobalt-chromium and bonds well with living bone over time, which makes it a strong choice for the surface that interfaces directly with the cut bone of your shin.
Sitting on top of that metal tray is a plastic insert, sometimes called the bearing or spacer. This piece is made from ultra-high-molecular-weight polyethylene, an extremely tough, low-friction plastic engineered to absorb shock and allow smooth movement between the metal femoral component above and the metal tray below. Think of it as the replacement for your cartilage. Modern versions of this plastic are cross-linked or specially treated to resist wear, which helps the implant last longer.
The Patellar Component
If your kneecap surface is also damaged, the surgeon may resurface it with a small button-shaped piece. This patellar component is fabricated entirely from ultra-high-molecular-weight polyethylene. It comes in symmetric and asymmetric shapes depending on your anatomy. Not every patient needs this piece, but when it’s used, the all-plastic design reduces the risk of metal-on-metal friction behind the kneecap.
Cemented vs. Cementless Fixation
How the implant attaches to your bone also affects what materials you end up with. In a cemented knee replacement, the surgeon uses bone cement (polymethyl methacrylate) to bond the metal components to the prepared bone surfaces. This creates an immediate, stable bond and has been the gold standard for decades.
Stryker also offers a cementless option that uses their proprietary Tritanium technology. This is a 3D-printed, highly porous titanium surface built into the back of the implant components. The porous structure features interconnected, irregularly shaped pores designed to mimic the spongy interior of natural bone. Over the weeks following surgery, your bone grows directly into these tiny openings, creating a biological bond without cement. This approach is sometimes chosen for younger, more active patients whose bone quality supports strong ingrowth.
The choice between cemented and cementless fixation is something your surgeon determines based on your bone density, activity level, and age. Both approaches use the same core materials for the bearing surfaces.
Why These Specific Materials
Each material in the implant solves a specific engineering problem. Cobalt-chromium is one of the hardest biocompatible metals available, so it resists scratching and maintains a polished surface even after years of use. Titanium integrates with bone better than almost any other metal, making it ideal for the surfaces that sit directly against your skeleton. And medical-grade polyethylene provides a low-friction cushion that lets the metal components glide against each other without grinding.
Together, these materials are designed to last 15 to 20 years or longer in most patients. The primary reason knee replacements eventually wear out is gradual breakdown of the plastic bearing surface, which is why improvements in polyethylene processing have been one of the biggest advances in implant longevity over the past two decades.
Metal Allergy Considerations
A small percentage of people have sensitivities to nickel, cobalt, or chromium. Since cobalt-chromium alloys contain trace amounts of nickel, this can occasionally cause reactions ranging from skin irritation to persistent pain or swelling around the implant. If you have a known metal allergy, mention it before surgery. Hypoallergenic options exist, including implants with special coatings or those made from oxidized zirconium (a ceramic-like metal surface) that reduce contact between the allergenic metals and your tissue.