Before you commit to a knee replacement

A knee replacement reliably takes the arthritis pain away. Most of my patients stand and walk the same day, are through the difficult part by six weeks, and keep improving for a year. It is a harder recovery than a hip, and I say so at the first visit, because a patient expecting a hip recovery decides something has gone wrong when nothing has.

A small number have a complication, and I will not pretend otherwise. What decides the result is the alignment, the balance and how the kneecap tracks — judgement in the room, not the technology that markets well. This page covers the knee I am willing to replace, how I do the operation, its risks, and what recovery actually asks of you.

The knee I am willing to replace

The patient who gets the most from this in my hands is one whose knee has taken something out of their life, whose examination and film agree, whose medical conditions are controlled, and who understands what they are buying. Age sits far down that list.

I replace knees for wear arthritis, for inflammatory arthritis such as rheumatoid disease, and for arthritis that has followed an injury years earlier.

Both knees replaced, seen on a standing film. Look at the metal surface on the end of the thigh bone, the plastic bearing between the two metal parts, and the metal tray on top of the shin bone. Those three components are what a total knee replacement consists of.

The parts of a primary total knee replacement: the metal femoral component, here posterior-stabilised, the polyethylene insert with its central post, the metallic tibial base plate with its keel, and the cam the post engages. Look at the post and cam at the centre — that is what supplies stability when the knee’s own ligaments cannot.

Which grades I actually operate on

Your report will probably carry a Kellgren and Lawrence grade from zero to four. Grade three means multiple bone spurs, definite narrowing and hardening of the underlying bone. A grade of four means large spurs, marked narrowing, severe hardening and a change in the shape of the bone.

Nearly everyone whose knee I replace is grade three or four, and none of them is operated on because of the grade. A grade four knee belonging to somebody who is coping stays where it is. A grade three knee in a patient who cannot work or sleep, with the alternatives behind them, gets replaced.

The grade also frequently understates what I find once the joint is open, and when the report and the joint disagree I follow the joint.

The grades I operate on — and why the grade does not decide it

What I need in place before I schedule you

Blood sugar in range, with a haemoglobin A1c below seven in a diabetic patient. Cigarettes stopped. Any active dental infection dealt with beforehand. Medical clearance from an internist who stays on the case, because I do not manage your other medication and I do not think I should.

Anti-inflammatory medication stopped a week ahead because it adds to bleeding, and blood thinners handled by the physician who prescribed them.

If you take strong pain medication, seen by a pain management specialist beforehand with the dose brought down as far as safely possible.

And at least three months since a steroid injection into that knee, preferably four to five or as much as possible.

What I need in place before I schedule you

Getting a knee replacement approved by Insurance

I cannot publish a figure that would be true for you. What I can describe is the process: nearly every insurer requires prior authorization and documentation that conservative treatment was tried and failed, and in practice authorization commonly takes a few weeks once that documentation is complete.

For workers compensation and no-fault claims the process is slower and your timeline is influenced by people who are not in the room. The paperwork is the part I govern: the note is finished before you stand up and leaves the office that day, the board included.

New York permits an injured worker to choose any physician the board has authorized, whatever anyone may have implied. For a personal estimate my office staff will go through your coverage with you.

Returning to work after a knee replacement

Light duty and full duty are further apart than most people expect. Full duty means the worst thing the job could ask of you on its worst day, and the employer defines that, not the surgeon. An occupational medicine physician performs the assessment; I supply the operative record, the findings and a signed opinion on what is safe, and that goes out the day it is requested.

Tell me at the first visit if your job involves kneeling, if you live in a walk-up, or if your commute involves platform stairs.

The anaesthetic, and the back pain that gets blamed on it

My preference is a spinal rather than a general anaesthetic. It gives better pain control through the first hours, it is associated with a lower rate of clots, there is less nausea, and patients surface clearer and get to their feet sooner.

You are sedated before it is placed, so most people do not really register the injection at all.

There is a belief that a spinal leaves you with a sore back. Comparative studies do not show more lasting back pain after a spinal than after a general anaesthetic.

The explanation I give is my own reasoning rather than a published finding. A large number of people coming in for a knee replacement have a bad back as well as a bad knee, and the knee has been shouting loudly enough to mask it.

Take the knee pain away and what is left in the quiet is the back, which was there all along. The needle gets the blame.
Waking up, the leg is heavy and numb and that feels strange. You will be asked to wiggle your toes. Once the strength is back a therapist gets you upright with a walker.

The moment people remember is standing for the first time, because that is when they notice the arthritis pain has gone and what is left is a different pain altogether.

Walking through a knee replacement as I do it

Everything that can be prepared beforehand is prepared beforehand. The instruments are assembled from a preference card I wrote myself. As one example, I use a patellar reamer before the saw blade, and it is on the table ready to go before the incision is made rather than being assembled while I wait.

I use a tourniquet only during cementation rather than for the whole operation. The reasoning is that limited tourniquet use is associated with less thigh pain and better early recovery of the quadriceps, and total blood loss, once the hidden losses are counted, is not meaningfully different. Deflated for most of the case, I can also see the tissue bleeding, which tells me something about the tissue.

The incision is over the front of the knee and I enter the joint alongside the kneecap. As with the hip, my incision is as small as possible and as large as needed.

Before I cut any bone, I check the resection. I place an instrument called a “angel wing” into the cutting guide, which sits in the plane the saw will follow and shows me exactly how much bone is about to be removed. I then compare that against the preoperative x-ray and against what I am looking at.

That check takes seconds and it is the difference between removing what I planned and removing what a guide told me. It is the same discipline I apply on the hip: I look at what I am about to cut.

The bone resection is based on what I find. How much cartilage has gone, how much bone has eroded, and how that compares with the film. In a knee where the bone is deficient I use metal augments to make up what is missing.

Then the balance. With trial components in, I take the knee through a full physiological range of movement and I assess whether it is balanced through that arc. Soft tissue releases are performed as needed, and this is exactly why I want the implant size to remain my decision in the room: releasing changes the space I have to fill.

Then the kneecap, which is where a great deal of the eventual satisfaction lives. I look at whether the kneecap sits high or low, which is described as patella alta or patella baja, and I position the patellar component accordingly so that it sits properly against the underlying thigh bone through the range of movement.

I take care to place the component towards the inner side, because that is what allows the kneecap to track correctly rather than pulling off to the outer side.

Then I test it again. Anything that needs correcting gets corrected now. I have never left an operating room thinking something would probably be all right, because it never is.

Skin to skin, a knee takes me a little over an hour.

The components of a total knee replacement laid out before implantation: the metal femoral component, the tibial component, the plastic insert that sits between them, the post that provides stability, and the patellar button. Look at the smooth articulating surfaces, which are what the joint moves on.

The four places a knee replacement is decided

Alignment. A knee left in poor alignment loads one side of the plastic bearing and wears it faster. This is decided at the moment the bone is cut, which is exactly why I check the resection with the angel wing before the saw goes anywhere near the bone.

Balance. A knee that is technically well aligned but unbalanced through its range is a knee a patient will not like, and unbalanced knees are among the more common reasons for an unhappy replacement. Balance is assessed with trials in, through a full range, by hand.

The kneecap. Position it badly and the kneecap tracks off to the outer side, which produces pain at the front of the knee and dissatisfaction that is hard to fix afterwards. Getting it right means looking at whether the kneecap sits high or low and placing the component towards the inner side.

And cutting before checking. That is the error the angel wing exists to prevent.

When the tourniquet is inflated in my cases against the common alternative. Look at how much of the operation is spent with it down.

What I put in, and how I choose

I use the Zimmer Persona system for primary knees and for most revision knees. I am not a consultant for Zimmer or for any implant company, and I use what suits the patient.

The femoral component is metal, the tibial component is a metal tray with a plastic bearing on top, and in most patients I resurface the kneecap with a plastic button.

The choice between a bearing that retains the posterior cruciate ligament and one that substitutes for it depends on what I find. I use only the substituting implants.

A cruciate-retaining femoral component — the design I never use.

Where bone is missing I use metal augments, and where the deficiency is larger I use trabecular metal cones, which are porous metal structures the remaining bone grows into. In my hands augments handle deficiency up to roughly thirty millimetres.

Beyond that I move to a salvage system, which for me is generally the Orthopedic Salvage System, and in certain reconstructions I will use the Stryker system instead if it suits the anatomy better.

Making up bone that is missing

When I trained at the Hospital for Special Surgery I had exposure to essentially every implant available. What that gave me was not brand loyalty. It gave me the habit of knowing the advantages and disadvantages of each so the decision belongs to the patient in front of me.

Two plastic bearing inserts. Look at the raised post in the centre of each, which engages a mechanism on the metal femoral component to provide stability when the knee’s own ligaments cannot. The taller and wider the post, the more stability the implant itself supplies.

Why I do not use a robot on a knee

I do not perform robotic knee replacement, and my objection is not to the machine itself.

A robot executes a plan. That plan is built from a scan and from points a human registers on the bone during the operation. If those inputs are inaccurate the machine delivers an inaccurate plan very precisely, and it delivers it with a number on the screen that makes everybody in the room more confident. Poor input, poor output.

I have worked with computer-assisted navigation and I know what that class of technology does well and what it does not. It reliably reduces alignment outliers. What it has not consistently demonstrated is that the patient walks better, hurts less at a year, or keeps the implant longer.

There are also costs specific to the technology: extra pin sites for the trackers, which can become infected and through which fractures have occurred; extra operative time, particularly during a learning curve, and operative time carries infection risk; and a preoperative scan in the systems that require one.

And these technologies are alternatives rather than additions. You cannot meaningfully combine patient-specific cutting guides with navigation or with a robot, because each is a different way of solving the same alignment problem.

What I do instead is check what I am about to cut, balance the knee by hand through a full range, and keep the implant size flexible until the releases are done. I have written about this at greater length on my robotic knee arthroplasty page.

Pain control, and why it matters more in a knee

A spinal anaesthetic wherever possible, local anaesthetic placed around the joint before I close, and a combination of medications afterwards so we are not relying on a single drug.

Knee replacement hurts more than hip replacement in the first fortnight and I do not pretend otherwise. Staying ahead of it matters more here than anywhere else, because pain that is not controlled means therapy that is not done, and therapy that is not done in the first six weeks costs range of movement that is difficult to recover.

Make sure the prescription is filled and physically in your hand before you leave the hospital, because strong pain medication has to be checked against the state prescription monitoring programme and cannot simply be telephoned in. Take a dose before you get into the vehicle.

The risks, and one of my own complications

I would like to tell you there are no complications and I cannot. I name them to every patient: infection, blood clot, a clot travelling to the lung, stiffness requiring manipulation, ongoing pain at the front of the knee, injury to the blood vessels or nerves around the knee which is genuinely rare, and wear or loosening in the long term.

I will tell you about one of mine. A knee replacement patient of mine was doing extremely well and then suddenly developed pain and swelling and was brought to the emergency room. I operated quickly, washed the joint out and exchanged the plastic bearing.

We watched him very closely. The infection recurred, and the second time it was not possible to save that knee. He went through a period with an antibiotic spacer and then a further knee replacement.

I researched that case thoroughly afterwards to establish what could have been done differently. On that occasion the honest answer was that there was nothing I could have done to prevent it.

The realistic worst outcome is a deep infection requiring the implant to be removed, a period with a spacer, and a second reconstruction. It is uncommon, and it is the reason behind precautions on this page.

Preventing a clot after a knee replacement

I lectured on clot prevention after joint replacement in 2012 and my thinking has not moved, so let me give you the argument rather than the prescription.

What kills people after this operation is not a clot in the calf. It is a clot that reaches the lung. Those are different targets, and a great deal of published guidance is constructed around preventing the first, which I have never thought was the endpoint that matters. I said so then and I would say it again.

So I attack it from several directions at once instead of trusting one drug. A spinal rather than a general anaesthetic, which on its own is associated with a substantial reduction in clot events. Standing and walking you the same day. Ankle pumping, which measurably lifts the rate of blood flow through the femoral vein. Compression. And aspirin.

For most knee patients aspirin is the only blood thinner I use. Stronger anticoagulation is reserved for people whose risk is genuinely elevated and for those already taking something when they came to me.

You should know this is contested. The 2018 randomized trial (EPCAT II) and The 2022 Australian cluster-randomized trial (CRISTAL). A large randomized trial in 2018 found aspirin held up against rivaroxaban when it followed a short initial course of it.

An Australian cluster-randomized trial in 2022 found aspirin used alone from the day of surgery produced more symptomatic clots than enoxaparin, three point four five percent against one point eight two. Those are published figures across many surgeons.

The other side of the ledger is that potent anticoagulants bleed, and bleeding into a fresh knee means haematoma, drainage and a raised infection risk. That trade is precisely why I match the drug to the patient.

The clot-prevention evidence, stated fairly

Why your legs are not scanned afterwards

Patients without symptoms do not get an ultrasound of the legs in my practice, and this is a considered position rather than an omission. The American Academy of Orthopaedic Surgeons strongly recommends routine screening of that kind after elective replacement, and I agree with them.

The logic is that scanning everybody turns up clots in the calf that were never going to do harm, and once one is on a report somebody feels compelled to treat it with a drug that carries a genuine bleeding risk. The patient absorbs the harm of the treatment without ever having been at risk from the finding.

Symptoms change that entirely, and a symptomatic leg is scanned the same day.

The rare patient who gets a filter

A very small number of patients whose risk of a clot reaching the lung is extreme have a filter placed in the large abdominal vein before surgery, so that anything travelling up from the leg is caught before it arrives.

This is not routine and no guideline supports doing it routinely. Filters bring problems of their own, including clotting, migration and difficulty with later removal, and the great majority of high-risk patients are managed with anticoagulation instead.

The situation where I do consider one is narrow: a patient whose clotting risk is very high and who, for some separate reason, cannot safely be anticoagulated. Faced with that, I would rather accept a filter’s known problems than send somebody to theatre unprotected. If it is being discussed for you, I will explain the reasoning in your case and I would encourage you to get a second view on it.

If this knee ever fails

Worth knowing the earliest signs in your own words. Pain that returns after a genuinely comfortable period. A knee that begins to feel unstable or gives way. New swelling. A knee that becomes acutely hot, swollen and painful, particularly with a fever, which needs assessment the same day rather than waiting.

A revision knee replacement is a larger operation than the first. Removing well-fixed components without destroying the bone around them is the real skill, missing bone has to be made up with augments or cones, and a stem is often needed to gain fixation in healthy bone further up or down.

The components of a revision knee replacement, a larger construct than a first-time knee. Look at the femoral and tibial stems that gain fixation in healthy bone further up and down the leg, the attachment points for metal augments that make up missing bone, and the tibial post and femoral cam that supply the added stability a revision usually needs.

And the honest answer on results: a revision usually leaves a patient much better than they were, and generally not as good as a well-functioning first-time knee in the same person.

What a replaced knee will not give you back

It will not give you the knee you had a while ago. An artificial joint cannot repair itself.

Kneeling is the specific thing. A good number of patients find kneeling uncomfortable or simply do not do it afterwards, and I tell people directly that they may not be able to kneel in church.

Many patients have a numb patch on the outer side of the front of the knee, because a small skin nerve crosses the incision and is unavoidably divided. Most patients never notice it and most of those who do find it shrinks over a year. It does not affect how the knee works.

Impact activity is off the list permanently. Running and jumping shorten the life of the implant. Golf, swimming, cycling, doubles tennis, skiing for experienced skiers on groomed runs and riding for experienced riders are all reasonable. Singles tennis generally is not, and I say so.

Activities after a knee replacement

On how long it lasts: published registry figures across many surgeons suggest a little over eight in ten total knee replacements are still in place at twenty-five years. Those are literature figures rather than mine.

What makes one fail early in my experience is impact and abuse, wear, and infection. What makes one last is correct alignment, a balanced knee, a patient who stays active without pounding it, and dental hygiene taken seriously for life.

The dental antibiotic rule, in brief

I ask my patients to take an antibiotic before any dental procedure that works on the gums or breaks the lining of the mouth, and to continue for life.

This differs from the current guideline from the American Academy of Orthopaedic Surgeons, updated in 2024, which states that routine prophylaxis may not reduce the risk. My full reasoning, and the counter-argument stated fairly, are on my knee replacement recovery page.

The questions every nervous knee patient asks

How many have you done. I have been performing hip and knee replacement and revision since 1997 and I have done thousands.

Have you ever had a bad outcome. Yes, and I have described one above. A surgeon who claims otherwise is either not operating enough or is not being straight with you.

Why you rather operate only at your preferred hospitals, than the hospital down the road. No hospital employs me, which means I operate where the room, the staff and the implants will be what I specified.

Some hospitals will not permit certain implants. Others will not staff the room properly, and that I will not work around. One assistant less is one complication more.

Will the knee last for the rest of my life? . In an older patient, usually. In a younger one it is a real question and I put it to them plainly. The poorest outcomes are in active people who punish the joint.

Would you have it yourself. I would not do anything to a patient that I would not do to my own family, and I have operated on my own family.

Should I get a second opinion. Yes, always, and I encourage it before any surgery.

The knee I am aiming for

A patient who is completely free of pain. The x-ray is secondary, although the two usually travel together. I treat patients rather than x-rays.
For a knee specifically, the target is a joint that is straight, that bends far enough to get out of a chair and up a stair without thinking, and that you stop planning your day around.

Knees I have replaced, before and after

Films from my own patients, from case studies published individually on this website.

What I look at afterwards is the same each time: the line running through the leg, whether the components sit flush on the cut bone without overhanging, and whether the kneecap is centred.

Postoperative X-ray of the left showing the anteroposterior and lateral view with total knee prosthesis in position, my published case Left Total Knee Replacement in a 62-year-old Male. Look at the line running through the leg and at whether the components sit flush on the cut bone.

Preoperative X-ray of both the knees in anteroposterior view, my published case Right Total Knee Replacement in a 72-year-old female with Arthritis. Look at how much joint space has been lost before surgery.

Preoperative X-ray of the left knee showing severe osteoarthritis in anteroposterior and lateral views, my published case Left Total Knee Replacement in a 68-year-old male.

Postoperative X-ray showing a total knee replacement, my published case Outpatient Knee Replacement.

Postoperative images at 2 months follow up,Management of Patellar Tendon Rupture in a 70-year-old Male.

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Postoperative X-ray of the left showing the anteroposterior and lateral view with total knee prosthesis in position, my published case Left Total Knee Replacement in a 62-year-old Male.

Postoperative X-ray of the right knee with a prosthesis in anteroposterior and lateral views, my published case Right Total Knee Replacement in a 72-year-old female with Arthritis.

Postoperative X-ray of the right knee with a prosthesis in anteroposterior and lateral views, my published case Right Total Knee Replacement in a 72-year-old female with Arthritis.

Knee replacements I have written up individually

Instead of describing my knee results in the abstract, here are the operations themselves with their films.

Each illustrates a decision rather than advertises a result, and no patient in them can be identified.

• Left Total Knee Arthroplasty – 66 year old male — https://www.cortho.org/case-studies/knee/left-total-knee-arthroplasty-66-year-old-male/
• Left Total Knee Replacement in a 62-year-old Male — https://www.cortho.org/case-studies/knee/left-total-knee-replacement-62-year-old-male/
• Left Total Knee Replacement in a 68-year-old male — https://www.cortho.org/case-studies/knee/left-total-knee-replacement-68-year-old-male/
• Left Total Knee Replacement – 63 year old Female — https://www.cortho.org/case-studies/knee/left-total-knee-replacement-63yo-female/
• Right Total Knee Arthroplasty – 51 year old male — https://www.cortho.org/case-studies/knee/right-total-knee-arthroplasty-51-year-old-male/
• Right Total Knee Replacement in a 72-year-old female with Arthritis — https://www.cortho.org/case-studies/knee/right-total-knee-replacement-72-year-old-female-arthritis/

My relationship with the makers of what I implant

No implant company pays me anything. This page names a specific system, so I want that stated before you read a word of it. My federal Open Payments record is public.

The three things a knee replacement turns on

A knee replacement is decided by three things and none of them is the technology used to make the cuts: whether the leg lines up, whether the knee is balanced through its whole range, and whether the kneecap tracks.

I check every bone cut before I make it, with an instrument that sits in the plane the saw will follow, compared against the preoperative film. That takes seconds and it is the difference between removing what I planned and removing what a guide told me.

I inflate the tourniquet only while cementing rather than throughout, because full-time inflation costs thigh pain and early quadriceps recovery and buys nothing in total blood loss once the hidden loss is counted.

And I tell every patient at the first visit that a knee is a harder recovery than a hip, because a patient expecting a hip recovery concludes at week four that something has gone wrong when nothing has.

Case Studies:

• Case Study of Loose Knee Replacement
• Case Study of Knee Replacement with Articulating Antibiotic Spacer Staged Reconstruction

Knee Replacement FAQs

• What are the different types of knee replacement surgery?
• What conditions require knee replacement?
• How to prepare for knee replacement?

Find out the answeres to these and other questions here

Are you a good candidate for TKR surgery?

Total knee replacements can be a good option for many men and women, but they’re not for everyone. If you have been experiencing knee pain, have had a prior knee surgery, or have injured ligaments, you may need a complete knee replacement.

To schedule your evaluation, call (516) 735-4032 or use our online contact form to learn more.

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