When knee pain reaches a point where it limits daily life and conservative treatments no longer provide relief, total knee replacement (TKR) is often the answer. For most patients, it’s a life-changing surgery — restoring mobility, reducing pain, and improving quality of life. Behind the scenes, orthopedic surgeons and implant engineers have spent decades refining not just the shape and material of knee implants, but how they are anchored to bone. The way an implant is secured to the bone is one of the decisions made by your surgeon in knee replacement surgery.
Today, two primary fixation approaches exist: cemented and cementless. Understanding the difference can help you and your surgeon discuss which is best for you.
A Brief History: From Early Implants to Modern Fixation
Total knee replacement surgery was first performed in the early 1970s. These first-generation implants were rudimentary with little concern for longevity or bone preservation.
Bone cement (polymethylmethacrylate, or PMMA) became the dominant fixation method by the late 1970s and through the 1980s. PMMA acts as a grouting agent, filling the microscopic gaps between implant and bone to create an immediate, reliable bond and it became the gold standard.
But as surgeons began following patients over time, a limitation emerged: aseptic loosening which is the gradual breakdown of the cement-bone interface over time. For younger, more active patients who might outlive their first implant, this was a concern.
This drove renewed interest in biological fixation, allowing bones to grow directly into the implant surface, eliminating cement entirely. Early cementless designs in the 1980s and 1990s showed promise but were inconsistent, largely because the porous surfaces of the time couldn’t reliably promote adequate bone ingrowth.
The revolution came with advanced manufacturing. The widespread adoption of 3D-printing and metal surface technologies in the 2000s and 2010s transformed cementless knee implants. Today’s cementless implants feature highly engineered porous surfaces that mimic the architecture of bone itself, enabling durable biological fixation that is reproducible.
How Cementless Fixation Works
To understand the advantage of cementless technology, it helps to understand the biology of bone ingrowth.
The Porous Surface
Modern cementless knee components are coated with an porous metal structure. The porous matrix sits in direct contact with living bone. Over the following weeks and months, bone tissue grows into the pores and is called osseointegration. The result is a biological bond. Over time, the implant becomes, in effect, part of the skeleton.
The Role of Additive Manufacturing
Traditional manufacturing couldn’t produce the intricate, consistent pore geometries required for reliable ingrowth. 3D printing changed that. Designs are so advanced today that they can eliminate some of the historical issues with uniform ingrowth surfaces.
Press-Fit and Initial Stability
The critical window for cementless fixation is the first 6–12 weeks after surgery, before ingrowth is fully established. During this time, stability depends on press-fit which is the precision with which the implant is sized and seated against the cut bone surface. Robotic assistance in particular has been a game-changer for cementless TKR, enabling cutting precision for near perfect bone fit and no additional bone cut to accommodate for cement.
Key Benefits of Cementless Technology
1. Durability and Longevity
Perhaps the most compelling advantage of cementless fixation is long-term durability. Because the fixation is biological rather than mechanical, there is no cement mantle to fracture, no cement debris to trigger inflammation, and no progressive loosening at the cement-bone interface.
Registry data and long-term clinical studies increasingly support superior survivorship of cementless implants, particularly in patients under 65 who are more active and more likely to outlive a traditional cemented implant.
2. No Cement-Related Complications
Bone cement, while generally safe, carries its own risks:
- Cement debris into the joint can cause mechanical symptoms
- Thermal necrosis: Cement gets very hot and the reaction of PMMA can generate heat damage
- Fat and marrow embolism: Pressurizing cement into the medullary canal can occasionally drive fat globules into the circulation, a rare but serious complication
3. Robotic-Assisted Surgery
Cementless knee replacement is uniquely well-suited to robotic-assisted surgical platforms. The precision required for optimal press-fit is achievable with robotic assistance in a way it simply wasn’t in prior eras.
Who May NOT Be a Good Candidate for Cementless Fixation?
While cementless technology has advanced dramatically, there remain patient populations for whom cemented fixation may be the safer, more reliable choice:
Patients with Osteoporosis or Low Bone Density
Osteoporosis is perhaps the most important contraindication to cementless fixation. When bone mineral density is significantly reduced, the bone may not have the structural integrity to support ingrowth. In these patients, cement fills the gaps and compensates for irregular bone surfaces in ways that press-fit cannot. Most women over 75 may benefit from cemented fixation.
Elderly Patients
While age alone is not an absolute contraindication, patients over 75 often have reduced bone quality, lower activity levels, and shorter time horizons that reduce the relative benefit of cementless fixation. For these patients, the proven track record and immediate stability of cemented fixation may make more sense.
Patients with Metabolic or Systemic Conditions Affecting Bone Healing
Patients who have Diabetes, are current smokers, or have chronic kidney disease may benefit from cement because they may have impaired blood supply and impaired ability to adequately grow bone into the implant within the desired 6–12-week time frame.
Patients who take steroids for underlying conditions may have weakened bone density and impaired bone healing limiting their ability to integrate bone into press fit implants. They may also benefit from cemented fixation.
Cemented Fixation: Still the Gold Standard for Many
It’s worth emphasizing that cemented total knee replacement remains an excellent operation with a long, proven track record. Decades of data demonstrate reliable outcomes, and for older patients or those with compromised bone, it is often the most appropriate choice.
The Bottom Line
The story of knee replacement fixation is one of continuous refinement. For the right patient (younger, active, with good bone quality) cementless total knee replacement represents a meaningful advance: a more durable, bone-preserving, biologically integrated solution that may outlast anything that came before it.
If you are considering knee replacement surgery, the best approach is a detailed conversation with your orthopedic surgeon about your age, bone density, activity goals, and overall health. Fixation method is one of many decisions that should be individualized. The answer is different for every patient.
This blog is intended for general educational purposes and does not constitute medical advice.
Catherine Cahill MD MBA is a board-certified orthopedic surgeon specializing in hip and knee replacement in Houston, TX. Appointments: 832-516-6997 or catherinecahillmd.com