What Happens During a Knee Replacement? A Step-by-Step Walkthrough

Most of the anxiety patients bring to knee replacement comes from not knowing what actually happens during the operation. The unknown is always scarier than the reality. So here is the honest walkthrough — from the time you arrive, through the surgery itself, the kneecap decision, the implants used, and the recovery room — for patients who want the real picture without the jargon.

Before you arrive

The work of a smooth surgery starts well before the day itself. At your preoperative visit, we go through your medical history, review your imaging, confirm the surgical plan, and walk you through what to expect — including the days leading up to surgery and the days immediately after. You will also be given specific instructions for medications, what to stop taking and when, and how to prepare your skin and gut for surgery.

For the full preparation picture, see our guide on preparing for joint replacement surgery.

The morning of surgery

You arrive at the surgical facility a couple of hours before your scheduled surgery time. Most patients are checked in by a nurse, who reviews your vital signs and asks about your pain level, allergies, and any last-minute changes since the preoperative visit.

You are then taken to a preoperative holding area where you change into a surgical gown and meet the people who will be caring for you:

Several medications are given in this holding area — typically a combination that helps prevent infection, controls nausea, provides preemptive pain control, and starts the multimodal pain regimen well before any incision is made. This is one of the reasons modern joint replacement is so much more comfortable than it used to be: pain management starts before pain.

Anesthesia — what to expect

For most patients, knee replacement is performed under spinal anesthesia rather than general anesthesia. Spinal anesthesia involves a small injection in the lower back that numbs the body from the waist down — you remain breathing on your own, and we add sedation so that you are comfortably unaware of the surgery and won't remember it.

The reasons we prefer this approach for joint replacement:

• Less pain after surgery
• Quicker recovery and earlier ability to walk
• Less blood loss
• Fewer of the post-anesthesia side effects (grogginess, nausea) that come with general anesthesia

In addition to the spinal, you typically receive regional nerve blocks — additional targeted anesthesia around the surgical area that extends pain control well beyond the operating room. The spinal can be placed either in the holding area or in the operating room itself.

Preoperative planning and precision

One of the most important pieces of modern knee replacement happens before the day of surgery. I use detailed preoperative templating with computer software to plan each procedure around your specific anatomy. The plan includes:

• The size of the implants that best fit your anatomy
• The intended alignment of the new joint
• The planned bone resections (how much bone is removed from each surface)

That plan is then carried into the operating room to guide the procedure. The aim is to support accurate implant positioning, appropriate alignment, and consistent execution of a strategy tailored to your knee.

The operation, step by step

Once anesthesia is in place and you are positioned on the operating table, the surgery itself follows a predictable sequence. The whole operative portion typically takes about 60–90 minutes for a primary knee replacement.

The kneecap decision

Whether to resurface the kneecap is one of the few real intraoperative decisions in knee replacement, and it is made based on what we find when we open the joint. My approach:

• If the kneecap shows minimal arthritis and tracks properly — I leave it alone. This preserves more of your native bone, tends to be associated with less pain, and avoids the small risk of kneecap fracture that comes with resurfacing.
• If the kneecap shows significant damage — it is resurfaced with a polyethylene button to address the arthritis on that surface.

This is one of the places where an experienced eye matters more than a protocol: not every kneecap needs to be replaced, and leaving a healthy kneecap alone is often the better long-term choice.

The implants used

The components of a modern knee replacement:

• Femoral component — a precisely shaped metal piece on the end of the thigh bone (the femur) that replaces the worn cartilage surface.
• Tibial component — a metal tray on the top of the shin bone (the tibia) that supports the bearing surface.
• Polyethylene bearing — a durable specialized plastic insert between the femoral and tibial components. Modern designs include medial-pivot patterns engineered for stable, natural-feeling knee mechanics — the implant is selected to fit the patient rather than the other way around.
• Patellar button (optional) — a small polyethylene piece for the back of the kneecap, used only when the kneecap shows significant arthritis.

Together, these components are highly durable — around 75% of modern knee replacements remain intact at 30 years in current data. For most patients today, a knee replacement is a once-in-a-lifetime procedure.

For some patients, only part of the knee is arthritic, and a partial knee replacement is a possible alternative that preserves more of the native knee.

Closing and the numbing injection

Before the incision is closed, I inject a long-acting local anesthetic into the soft tissues around the knee. This is one of the most important comfort steps in the operation: it provides substantial pain control for the first 12–24 hours after surgery — often well beyond when you have already gone home.

The incision is then closed in layers — deep tissue first, then the skin — and a sterile dressing is applied. By this point the operative portion is complete, and the team begins the transition to waking you up.

Waking up and the recovery room

Most patients wake up in the recovery room with very little sense that surgery just happened. The combination of spinal anesthesia, regional blocks, and the long-acting numbing injection means the first hour or two are often surprisingly comfortable — patients commonly say things like “wait, is it over?”

In the recovery room:

Walking and going home

For most patients, the surprise of the day is standing and walking the same day as surgery — often within a few hours of waking up in the recovery room. Physical therapy meets you in the recovery area, walks you through the first steps with a walker, and confirms that you can navigate stairs (or whatever you will face at home).

Most patients then go home the same day. Some patients spend one night — typically to make sure pain is well controlled, you can use the bathroom comfortably, and you have no nausea or vomiting. The decision is individual and made with safety as the priority. For more on this, see our article on outpatient (same-day) joint replacement.

From Dr. Harb

The biggest change in knee replacement over the last decade isn't any single piece of technology — it's how everything fits together. Spinal anesthesia, regional blocks, the soft-tissue–respecting approach, careful preoperative templating, modern medial-pivot implant designs, the long-acting numbing injection, scheduled non-opioid pain control, same-day mobilization. None of these is dramatic on its own. Together they make the experience of knee replacement fundamentally different from what your parents or grandparents remember.

For the broader picture of what happens after, see the knee replacement recovery timeline and our guides on how painful knee replacement actually is, sleeping, driving, and the medications around joint replacement. The whole library is here for you.