Knee Replacement Complications: What Can Go Wrong?

One of the most common questions patients ask me before surgery is: “What can go wrong?” What they're really asking is: what are the complications, how common are they, and what are you doing to prevent them? That's exactly the right question.

Every operation carries risk. Knee replacement is one of the most successful procedures in modern medicine, but no surgery is completely risk-free. My philosophy is simple: be honest about the risks, aggressively work to minimize them, and help you make an informed decision. The good news is that serious complications are uncommon.

Infection: the complication we worry about most

When orthopedic surgeons talk about major complications, infection is usually at the top of the list. Nationally, infection rates after knee replacement are often reported between roughly 0.5% and 2%. My personal infection rate is approximately 0.1% — and that doesn't happen by accident. Prevention starts before surgery and continues long afterward.

One of the most important factors is operative efficiency. I never rush — but because I perform a high volume of joint replacements, the operation is streamlined and reproducible, and a routine primary knee replacement typically takes me about 45 minutes. Multiple studies link longer operative times to higher infection rates, so knowing exactly what you're doing and executing efficiently genuinely lowers risk.

Blood clots

Blood clots are one of the complications patients hear about most — and, fortunately, they're uncommon. The single most effective way to reduce clot risk is early mobilization, which is why my patients are typically up and walking within hours of surgery rather than lying in bed. On top of that, I use a blood thinner for about four weeks afterward — more on that in aspirin and blood thinners after joint replacement.

Stiffness (arthrofibrosis)

Most patients gradually regain motion as swelling improves and strength returns. A small percentage form excessive scar tissue — a condition called arthrofibrosis. Risk tends to be higher in patients with a history of thick (hypertrophic) or keloid scars, or limited motion before surgery.

Because we monitor your motion closely during recovery, we usually catch stiffness early. In rare cases, a manipulation under anesthesia may be recommended to restore motion.

What's normal — and not a complication

Two things patients often worry about are actually expected parts of healing:

The rare risks: fracture, nerve, vessel & anesthesia

Because a knee replacement is performed close to major nerves, blood vessels, and bone, injury to those structures is theoreticallypossible — but these are among the rarest complications we discuss. Careful technique, preoperative planning, and experience keep the risk very low.

On anesthesia: most of my patients receive spinal anesthesia rather than general, which is associated with excellent pain control and a lower rate of many traditional anesthesia issues. Serious anesthesia complications are uncommon, particularly in otherwise healthy patients having elective surgery.

Implant loosening, instability, and wear

Modern knee replacements are built to last for decades. When the implant is well positioned and fixed, loosening is uncommon — though poor bone quality, severe osteoporosis, trauma, or rare biologic responses can raise the risk. Instability can occur if the soft tissues aren't properly balanced, which is exactly why one of the most important parts of the operation is confirming the knee is stable through its full range of motion before I finish.

As for wear: today's highly engineered polyethylene bearings have excellent wear characteristics, and significant wear is far less common than it was decades ago. For most patients, a modern knee replacement is a once-in-a-lifetime operation — see how long a knee replacement lasts. In the uncommon event a problem does develop, revision surgery can address it.

The bigger picture

When patients ask me what can go wrong, I tell them two things. First, every operation has risk. Second, severe arthritis has risks too — loss of mobility and independence, declining fitness, weight gain, worsening balance, chronic pain, and slowly giving up the activities you enjoy all carry real consequences.

So the decision isn't whether risk exists. The decision is whether your arthritis is taking more from your life than the operation is likely to risk.