Patient Education · Knee

Total Knee Replacement

What the operation actually does, how it goes, what the weeks afterward look like, and the numbers I give my own patients.

Dr. Darin W. Allred Darin W. Allred, MD Board-certified orthopedic surgery & sports medicine
1–2 hrsTypical time for the operation itself
85–90%Of patients rate their result good or excellent
3 monthsWhen about 80% of your improvement is on board
25 years82% of knees implanted in the early '90s were still working

Why the knee hurts

The end of your thigh bone (femur), the top of your shin bone (tibia), and the back of your kneecap (patella) are covered with smooth cartilage. Cartilage lets the joint glide and cushions every step. Arthritis is the wearing away of that cartilage. When it wears down to bare bone, bone rubs on bone — and that is the pain, swelling, and stiffness you feel.

Illustration of a total knee replacement in place, seen from the front through a transparent knee
A knee replacement in place, seen from the front. The metal cap on the thigh bone, the metal tray with its plastic insert on the shin bone, and the button behind the kneecap.

Two things worth knowing before we go further. First, the X-ray describes the structure, not the suffering — plenty of people with "bone-on-bone" X-rays live full lives without surgery, and I wrote a whole article about that. Second, most arthritic knees do not need a replacement. Surgery is the right answer when the pain runs your day, keeps you up at night, and has not responded to a real effort at the non-surgical tools.

What a knee replacement actually is

The name is misleading. We do not remove your knee. A total knee replacement is really a resurfacing: we remove the worn, damaged surfaces — the last of the cartilage and a thin layer of bone — and cap the ends of the bones with new, smooth surfaces.

Illustration of an arthritic knee seen from the front
An arthritic knee from the front. The cartilage that should cushion the joint has worn away and the gap between the bones has closed.
  • Femur: a shaped metal cap that follows the curve of the end of the thigh bone.
  • Tibia: a flat metal tray with a smooth, durable medical-grade plastic insert that the metal cap glides on.
  • Patella: usually a plastic button on the back of the kneecap so it tracks smoothly over the new surfaces.

Your ligaments, your muscles, and your own bone do the rest. The result is a smooth, cushioned joint that moves without bone-on-bone pain.

Illustration of the knee from the front showing its ligaments
The knee from the front with its ligaments. A replacement resurfaces the ends of the bones; your own ligaments and muscles do the rest of the work.

Who it is for — and who should wait

Surgery should come after non-surgical care has had a fair chance: activity changes, strengthening, weight loss, anti-inflammatory medicine, and injections. When those no longer control your pain and the knee is limiting your daily life, replacement is the reliable next step. The signs I take most seriously:

  • Constant pain that decides what you do each day — not just soreness after a hard day.
  • Night pain. Pain that wakes you is a different animal than pain with activity.
  • A real, months-long effort at the non-surgical tools without enough relief.
  • Advanced arthritis on X-ray to match those symptoms.

Your general health matters more than your age. Healthy patients in their 80s do well. Patients with uncontrolled diabetes, smoking, or significant obesity need those addressed first, at any age — not to be difficult, but because they drive the infection risk. If you're not sure where you stand, the two-minute knee self-check gives a straight answer, and this article walks through the decision the way I would in clinic.

How the operation goes

  1. Anesthesia. Most patients have a spinal (numb from the waist down, with sedation so you're asleep) plus a nerve block above the knee and numbing medicine placed in the joint during surgery. That combination is why most of my patients walk the same day and need very little narcotic.
  2. The incision runs down the front of the knee. We move the kneecap aside to see the joint.
  3. The worn surfaces come off. Precise cutting guides remove the damaged cartilage and a thin layer of bone from the femur and tibia, shaped to fit the implants exactly.
  4. The new surfaces go on. The metal cap on the femur, the metal tray and plastic insert on the tibia, and the button on the kneecap.
  5. Balance and motion check. Before closing, I take the knee through its full range and make sure the ligaments are balanced so it bends straight and true.
  6. Closing. The knee is closed in layers and covered with a waterproof antimicrobial dressing that stays on for a week — you can shower the next day.

The operation itself takes one to two hours. Most patients go home the same day or after one night, and you will be up walking with a walker before you leave.

Recovery: the Quiet Knee plan

Recovery from a knee replacement has a reputation for being brutal — forced bending, painful therapy, "no pain, no gain." I don't run it that way. The Quiet Knee plan calms the knee down first, then builds it back up. A calm knee lets the thigh muscle fire again, so motion comes back with less pain and less pain medicine.

  • Day of surgeryUp and walking with a walker. Home the same day or the next morning.
  • Weeks 0–2Calm the knee. Ice often, keep it elevated ("toes above the knee, knee above the hip"), light compression. Keep the knee straight when resting — never a pillow under it. Gentle quad sets and heel slides. Short, frequent walks. Aspirin twice a day for two weeks to prevent blood clots.
  • Weeks 2–4Restore motion, calmly. Bending comes back as the swelling goes down — nobody forces it. Stitches out around two weeks. Most people trade the walker for a cane in this window.
  • Weeks 4–8Add strength. Once the knee is quiet, therapy shifts to mini-squats, step-ups, stationary bike, and hip and core work.
  • 6 weeksThe motion check. By now the knee should straighten to within 20 degrees of fully straight and bend past 90. If it isn't there despite therapy, we often schedule a short manipulation under anesthesia to free up scar tissue — done early, it works well. Driving is usually possible around now if it was your right knee and you are off narcotics.
  • 3 monthsAbout 80% of your improvement is on board. Most people are back to walking, work, and daily life.
  • 1 yearFull recovery. Warmth and mild swelling can linger for six months to a year while the knee fully settles.

The risks, honestly

Serious complications are uncommon — overall in the range of a few percent — but no surgery is risk-free, and I won't pretend otherwise. These are the ones we watch for, and what we do about each:

  • Infection (about 1%) The complication we work hardest to prevent — it's why we ask for the skin washes, the nose treatment, blood-sugar control, and postponement when your risks aren't optimized. A deep infection can mean more surgery.
  • Blood clots A clot in the leg can travel to the lungs, which can be life-threatening. Prevention is early walking plus a blood thinner — aspirin for most patients, a stronger one if you're at higher risk. New calf pain or ankle swelling in the weeks after surgery is a call-the-office-today symptom.
  • Stiffness A small number of knees scar in and won't bend well. The Quiet Knee plan keeps swelling down so this is rare, and the 6-week motion check catches it early when a manipulation still works.
  • Numbness beside the scar A patch of numb skin on the outside of the incision is common and normal — a small skin nerve crosses the incision line. It usually shrinks over a year or two. Significant nerve or blood-vessel injury is a different, rare event.
  • Implant wear or loosening over the years Modern implants last decades, but they are mechanical parts. A second ("revision") surgery is possible if one ever wears out. Tell us if you have a known metal allergy.

What your new knee will feel like

  • Clicking with bending is normal — it is metal and plastic.
  • Kneeling is usually possible but often stays uncomfortable. It does not damage the knee.
  • A replaced knee is a very good knee. It is not a 25-year-old knee. About 1 in 10 to 1 in 5 patients say theirs is improved but not everything they hoped for. I'd rather tell you that plainly now than have you find it out later.
  • How long will it last? Far longer than the old "ten years" folklore. In the largest studies, 82% of knees implanted in the early 1990s were still going at 25 years — and today's implants are better. The full numbers are here.
This page is general education. It describes how I do this operation and what most patients experience. It does not replace the conversation we'll have about your own knee, your health, and your goals — and if anything here doesn't match what you were told in clinic, ask. Your instructions and your surgeon's word always come first.