Dr. Sebastian Rodriguez answers the most common questions about knee replacement surgery—from understanding bone-on-bone arthritis to recovery expectations and robotic-assisted techniques.
Anterior Hip & Robotic Knee Surgery
View ProfilePeople who have arthritis in their knee usually have known they've had this for a while. Their knee's been "twingy" since they've been 40 or 50, and it's progressively gotten a little bit worse and a little bit stiff. Knee pain also typically presents with a limp—people can't fully straighten their knee or fully bend their knee, and it hurts to walk. Stairs are especially difficult.
Knee pain can look vague because people can point to anywhere around their knee. There's not one specific spot that's a hallmark of knee arthritis. But generally, stiffness or crepitus (a sort of crunchiness inside the knee) or deformity of the knee are signs. If you notice varus—where the inside part of your knees are starting to wear out and you're becoming more bow-legged—or valgus where you're becoming more knocked-knee on one side, that's often a sign of cartilage erosion.
"Bone on bone" is a term thrown around a lot, mainly by radiologists. Typically in your knee—no joint in your body is ever bone on bone. There's hyaline cartilage, a smooth articular cartilage on all the surfaces of our bones when they're in an articulation.
With time, age, trauma, or in the setting of osteoarthritis, that cartilage becomes eroded and gone. Think of the teflon on a pan being scratched away—underneath that teflon is the metal, which would be bone. So now you have bone on bone when those two surfaces contact.
I think it's more functional and how it's impacting your life. I've seen a lot of people with stage four severe arthritis of their knee who say, "it doesn't really bother me" or "I take a Tylenol once or twice a week and I can walk and do everything I want to do."
In that case, we would never prescribe surgery. These are quality of life surgeries. If it's affecting your quality of life and the diagnosis is you have arthritis in that joint, and you can't manage it simply with any other adjuncts, then you're looking at surgery.
Your femur is your thigh bone—the bottom of the femur (the femoral condyles) is resurfaced with a metal cap. That articulates with the tibia, which is your shin bone. The top of the tibia is also cut and a metal plate is put on top of that.
In between those two metal structures, we put a plastic insert which serves as the cartilage or the meniscus inside your knee. Those are the three pieces every knee replacement has:
In some cases we also replace the patella. Underneath the kneecap, the surgeon may elect to resurface or cut off the arthritic piece and put on a plastic button. It's a mix of whether people need this or whether it's done all the time.
Prehabilitation in knee replacement is even more important than in hip replacement. Going into the knee really affects the quadriceps, and if you anyone who's ever hurt their knee knows—if you don't move it for very long or don't put weight on your leg, your thigh muscle mass goes down really, really fast.
An exercise bike is one of the best ways to maintain that muscle. It's non-impact, you can measure it, add resistance, and do intervals—going really hard, then slow, then really hard again. This has been shown to be great for hypertrophy (muscle growth).
Resistance exercises are also important: bands, squats, deadlifts, glute work—all under the guided supervision of a therapist or trainer. That interval exercise is also time-efficient. If you're doing one-minute bouts over 10 minutes, you're in and out of the gym pretty quick.
Typically you can divide knees into cemented and uncemented. For the most part we've used cement to affix those metal pieces to the bone. The trend now is moving toward more uncemented metal pieces where the bone grows into the implant.
In younger people with good bone, they statistically do better with an uncemented component—which is why we offer that. Even heavy-set people do a little bit better with uncemented knee replacements.
We know the 20-year data on past knee replacements is pretty good—about 85-90% success rate. We anticipate with newer surgical techniques and improved inserts that people should be able to keep their knee replacement even longer. We often quote people 20 to 25 years.
Unlike the hip where partial replacements aren't really done anymore, partial knee replacements are very popular for a subset of people with arthritis on just one side of their knee.
A partial knee replacement resurfaces the inside part of the knee, the outside part, or just underneath the patella. The number of people with osteoarthritis who are great candidates for a partial knee replacement is probably 15 to 30% depending on the referral pattern.
Big knee, big incision—but at the end of the day, you're having an incision right down the middle of the knee. In extension (straight), it could be about 8 to 10 centimeters. As you bend your knee, it flexes more.
What's really important is what's done underneath. If you're using a robot (which we do), you have to have access to put pins in to have robot trackers. Personally, I do a subvastus approach—going underneath the muscle in the knee. This muscle-sparing technique allows people to have a little less pain and more strength in their leg during recovery.
A typical knee replacement takes 30 to 60 minutes—typically around 30-40 minutes before you're starting to close and finish up the skin incision.
How long people stay in hospital is dictated by the patient—anesthesia, good spinal anesthetic that wears off quick with good nerve blocks, education ahead of time, and support at home. About 85% of our knee replacements go home the same day.
You want to get people home quickly but safely. They have to have their pain well controlled and support at home—family, friends, and other adjuncts.
Infection is one of the big concerns—you could need antibiotics for skin infection or another operation if the infection is really deep. One of the biggest complaints with knee surgery is that some people still have some degree of discomfort after surgery.
Some older papers said up to 20% of patients were dissatisfied with their knee replacement. Newer literature shows about a 90% success/happy rate. We're making advances with robotics and alignment philosophies that will narrow that gap even further.
A knee replacement, unlike a hip replacement, may still feel foreign for some people. They may not have sharp pain like they used to, but it might not feel like their knee. You might have the odd click or feel like it's not necessarily part of your body.
Swelling is normal after any surgery. Your body is naturally going to swell due to the inflammatory cascade. We combat this with:
We've narrowed the gap significantly with muscle-sparing techniques and robotic alignment philosophies. About 40-50% of patients still require some narcotics after surgery. But unlike 10 years ago when people would need narcotics for 6 weeks or 3 months, now people often discontinue narcotics after a week or a few days.
It depends on patient comfort and fitness. Someone who's done a lot of work ahead of time and can support their weight might get rid of a walker or cane pretty quickly and resume more normal activities. For some people, they might need something for the first six weeks.
It's important to start range of motion, exercise, and proprioception early. But you don't want to make the knee angry or inflamed. People used to get "beat up" in physiotherapy—if you weren't taking narcotics before your physio, they weren't doing it right. I'd disagree with that these days.
You don't want to get someone so painful that the next two days they can't even move. That's counterintuitive—everything's swollen and painful and you're not getting things to settle down.
Can people work their way back and do some light jogs? Can people run 3-5k a few times a week? Potentially. But a lot depends on the patient and their physiology. Some people are built to run and some people aren't.
If someone truly was a runner with bad knee arthritis, they probably haven't been running in a long time by the time they get to someone like me. It's hard to say "I'm going to go back to running 10k three times a week" after surgery.
Book a consultation with Dr. Rodriguez or one of our specialized knee surgeons. Virtual appointments available across Canada.