Cementing is a medical procedure in which a specialized adhesive material is used to anchor an implant to bone or tooth structure. It’s most common in joint replacement surgery, dental restorations, and spinal fracture repair. The cement acts as a grout that fills gaps between the implant and the surrounding tissue, transferring mechanical loads and holding everything firmly in place.
How Bone Cement Works in Joint Replacement
In hip and knee replacements, bone cement is a two-part system: a powder and a liquid that are mixed together in the operating room. When combined, the mixture forms a moldable paste that hardens on its own inside the body without needing heat from an external source. The paste reaches mechanical stability in roughly 7 to 10 minutes, giving surgeons a narrow window to position the implant before the material sets.
The cement’s primary job is transferring your body weight and movement forces from the artificial joint to the surrounding bone. During a hip replacement, for example, the cement is pressurized into the prepared bone canal, and then the metal stem of the prosthesis is pushed into the cement before it hardens. The result is an interface layer, called a cement mantle, that locks the implant in place immediately after surgery. This means you can begin putting weight on the joint sooner than you might with an uncemented implant, which needs time for bone to grow into its textured surface.
The chemical base of virtually all surgical bone cements is polymethyl methacrylate, or PMMA. The polymerization reaction that hardens PMMA is exothermic, meaning it releases heat as it cures. Surgeons and anesthesia teams monitor this carefully because the temperature spike can affect surrounding tissue.
Cemented vs. Uncemented Implants
Not every joint replacement uses cement. Uncemented (also called “press-fit”) implants have a rough or porous surface that bone gradually grows into over weeks to months. The choice between the two approaches often depends on age and bone quality. Large registry studies show that cemented fixation tends to survive longer in older patients, while cementless fixation performs better in younger patients. For many people over 70, a cemented hip replacement remains the gold standard because it provides immediate stability in bone that may be thinner or more fragile.
Cementing in Spinal Fracture Repair
Vertebral compression fractures, common in people with osteoporosis, are sometimes treated by injecting bone cement directly into the damaged vertebra. Two related procedures handle this: vertebroplasty and kyphoplasty. In kyphoplasty, a small balloon is inserted through a needle into the fractured bone under X-ray guidance, inflated to create a cavity, and then removed. PMMA cement is injected into that cavity to stabilize the fracture from the inside.
The volumes are small. A typical kyphoplasty uses between 3 and 6 milliliters of cement per vertebra. Studies comparing lower volumes (around 3.6 mL) to higher volumes (around 4.9 mL) have evaluated whether more cement improves outcomes. Both procedures are minimally invasive, often performed through a single puncture site, and many patients notice significant pain relief within days.
Cementing in Dentistry
Dental cementing follows the same basic principle as orthopedic cementing: a material bonds a restoration (crown, bridge, veneer, or post) to the underlying tooth. But the specific cements vary widely, and each type suits different situations.
Zinc phosphate cement is one of the oldest options, offering moderate retention through a chemical bond. It works well for metal and metal-ceramic crowns but lacks the grip needed for more demanding restorations. Glass ionomer cement provides 65% higher retention than zinc phosphate while also releasing fluoride, which can help protect the tooth underneath. It bonds chemically and handles a broader range of restorations, including implant-supported crowns.
Resin cement is the strongest of the three, with tensile strength values ranging from about 5 to 41 megapascals compared to under 5 MPa for the other two. It bonds mechanically rather than chemically, making it the go-to choice for porcelain veneers, ceramic inlays, and situations where the tooth preparation doesn’t offer much natural grip. Resin cements are especially useful when a dentist has followed minimally invasive preparation principles, preserving as much natural tooth as possible.
The Three Phases of Cement Setting
Whether in a hip socket or a vertebral body, PMMA bone cement goes through three distinct phases after mixing. The first is the mixing phase, when the liquid monomer combines with the powder to form a sticky, runny paste. Next comes the working phase, when the cement becomes dough-like and loses its stickiness. This is the window during which the surgeon shapes and applies it. Finally, the hardening phase begins as the cement firms up and locks everything into position.
At room temperature (about 23°C), the transition from mixing to a non-sticky dough takes roughly 1.7 minutes, and the cement is fully set by about 4.4 minutes. Operating room temperature and humidity can speed or slow these times, so surgical teams sometimes use cooling techniques to extend the working window when they need more time to position an implant.
Limitations of Standard Cement
PMMA cement does not bond chemically to bone. Its hold comes entirely from mechanical interlocking: the cement seeps into tiny pores and irregularities in the bone surface and hardens there, like a key fitting a lock. Over time, a thin layer of fibrous tissue tends to form between the cement and the bone. This “weak-link zone” is the primary reason cemented implants can eventually loosen, particularly in active patients or after many years.
Newer bioactive cements aim to solve this problem by encouraging actual bone growth into the cement surface. In animal studies, modified bioactive cements showed direct bone contact at 6 weeks, while standard PMMA still had a dense fibrous barrier. By 12 weeks, bone had grown into the pores of the bioactive cement, and push-out testing showed it was 4.7 times harder to dislodge than standard PMMA. These materials are not yet widely used clinically, but they represent a shift toward cements that integrate biologically rather than relying purely on mechanical grip.
Antibiotic-Loaded Cement
One of the most important advances in cementing is the ability to mix antibiotics directly into the cement before it sets. The drugs then slowly release from the hardened cement over days to weeks, delivering high concentrations of medication right at the implant site where infection risk is greatest. This approach is now standard practice in many joint replacement surgeries, particularly revision operations where infection rates are higher.
Over 30 different antibiotics and three antifungal agents have been successfully delivered through bone cement. The specific drug and its ratio to the cement carrier are chosen based on the bacteria most likely to cause trouble. In complex cases involving drug-resistant infections, surgical teams typically coordinate with infectious disease specialists to select the right combination.
Risks of Bone Cementing
Bone cement implantation syndrome, or BCIS, is a recognized complication that occurs when cement is pressurized into bone during surgery. It can cause a sudden drop in blood pressure and a decrease in blood oxygen levels, likely triggered by fat, marrow contents, or cement particles entering the bloodstream. In a large review of over 3,200 arthroplasty procedures, some degree of BCIS was identified in 26% of cases, though most episodes were mild.
BCIS is graded on a severity scale. Grade 1 involves a moderate drop in blood pressure or oxygen. Grade 2 means a severe drop in either measurement. Grade 3 is cardiovascular collapse requiring resuscitation, which is rare. Anesthesia teams monitor blood pressure and oxygen saturation closely during and immediately after cement application. The risk is highest in elderly patients with pre-existing heart or lung conditions and in procedures involving long bones like the femur, where the medullary canal acts as a conduit for displaced material.