H. John Cooper, MD

Knee replacement · New York City

Robotic knee replacement

A knee replacement planned on a computer model of your knee and performed with a robotic arm that keeps each bone cut inside the plan.

Dr. H. John Cooper has used robotic assistance for effectively every total knee replacement since 2020.

Call (212) 305-6959

Midtown · Uptown · Westchester

How it works

A knee replacement removes worn cartilage and a thin layer of bone from the thigh bone, shin bone and kneecap, and fits metal and plastic parts in their place. How well the parts are positioned and balanced affects how the knee feels and how long it lasts.

In robotic-assisted surgery, the surgeon builds a plan for your knee on a computer, then uses a robotic arm to keep the saw within that plan while cutting the bone. The surgeon controls the operation throughout. The robot does not operate on its own.

  • The plan is made around your knee, using your imaging and your measurements in the operating room.
  • The robotic arm limits each bone cut to the planned position and depth.
  • The surgeon checks the balance of the knee as it moves and adjusts the plan if needed.

Dr. Cooper's approach

Dr. Cooper plans each knee to put back what wear has taken away, aiming to restore the knee's own alignment and joint line where it is safe to do so, instead of making every knee the same. Alignment is planned within safe limits, and the ligaments are balanced so the knee feels stable and natural.

Details such as how the implant is positioned, how much support the ligaments need, and whether the parts are fixed with cement are chosen for each patient, based on the shape of the knee, the quality of the bone, and the patient's age and activity.

Who it suits

Robotic assistance can be used for total knee replacement and for partial (unicompartmental) knee replacement. Most people who need a knee replacement for arthritis are candidates for a robotic-assisted operation.

Studies show robotic assistance improves how closely the bone cuts and implant position match the plan. Whether this leads to better long-term results for patients is still being studied, and results are good with conventional instruments too. Dr. Cooper leads a randomized trial comparing the two and has published widely on the topic; see the research.

Before surgery

The office gives you written instructions and takes care of most of the preparation. The main steps are:

Testing
Blood tests and an EKG within 90 days of surgery, and occasionally other tests. It is easiest to have them done through the Columbia system. If you have them done elsewhere, the results need to reach the office at least a week before surgery, or surgery may be postponed.
Medical clearance
When it is needed, clearance comes from your primary care doctor, ideally two to four weeks before surgery. The Columbia anesthesia pre-operative clinic reviews your tests and clearance remotely.
Education
Read the "What to Expect" book you are given, and schedule a phone session with the joint replacement educator. It helps to include the person who will help you at home.
Medications
If you take a prescription blood thinner, a GLP-1 medication for diabetes or weight loss, or an SGLT-2 inhibitor, call the office for instructions. These medicines usually need to be stopped ahead of surgery, so please do not stop or continue them on your own.
Eating and drinking
Stop eating at least 8 hours before surgery. You are encouraged to keep drinking clear fluids, such as water, black coffee or tea, and sports drinks, until 2 hours before your scheduled time. This lowers the chance of dizziness or low blood pressure afterward.

Recovery

Recovery depends on your age, strength and health before surgery. Most patients start walking and bending the knee soon after surgery and work with a physical therapist to regain strength and motion.

Going home
Patients go home either the same day as surgery or the next morning, depending on the patient and the plan made beforehand.
Knee motion
Regaining bend and straightening is a main goal. How well the knee bends after surgery is closely related to how well it bent before, and many people with arthritis end up with better motion than before without reaching the motion they had before arthritis. Most patients can expect to bend and straighten the knee, climb stairs, and get in and out of a car. Kneeling is usually uncomfortable but is not harmful.
Therapy

For the first 10 to 14 days at home, take it easy: ice and elevate the leg often and keep walking to a minimum (under about 1,000 steps a day). During this time, keep working on motion on your own, but only for a few minutes at a time: get the knee fully straight, then bend it as far as you comfortably can. About 5 minutes in the morning, afternoon and evening is enough.

Starting around 2 weeks after surgery, most patients begin outpatient physical therapy 2 to 3 times a week.

Swelling and bruising
Expect significant swelling around the knee, which can spread up toward the hip and down to the ankle and foot, along with bruising down the leg. Swelling usually builds for about a week before it improves. Ice the knee for 20 minutes at a time, several times a day, and elevate the leg for 20 to 30 minutes at least three to four times a day, with your toes above your nose.
What is normal
Numbness in the skin around the incision is common. You may feel or hear soft clicking of the metal and plastic when the knee bends or when you walk, which is normal and often fades with time.
Pain control
A combination of medicines is used: acetaminophen, an anti-inflammatory medicine when it is safe for you, and a stronger medicine only for severe pain. Stop the stronger medicine as soon as the pain is tolerable. A bowel regimen is important while taking it.
Blood clot prevention
Most patients take aspirin for three weeks. Patients at higher risk are prescribed a blood thinner instead.
Incision care
The dressing is waterproof, so you can shower right away. Keep the incision out of a bath or pool for three to four weeks. The outer bandage usually stays on until your first visit. Some patients are sent home with a suction dressing that stays on for about a week. Eating more protein and fewer sugary foods helps healing.
Dental work
Avoid elective dental visits for about three months after surgery. After that, most patients do not need antibiotics for dental work.
Driving
You may drive once you are off narcotic pain medicine and your leg strength and coordination are good enough. Most patients return to driving between 2 and 6 weeks after surgery, depending on comfort and which knee was operated on.
Return to work
It is safe to return to work as soon as you wish, but return to work varies from patient to patient. The large majority return 2 to 3 months after surgery, and some return sooner if their function and job demands allow.
Walking
Increase your walking gradually and return to your normal routine step by step. Slow and steady works best.

Recovery supplies

Some patients like to have recovery supplies at home that insurance does not usually cover. Recovery Shop is an independent third-party vendor that makes it simpler to order these items. Using it is optional, and many patients find the supplies helpful for their recovery.

Visit Dr. Cooper's Recovery Shop page

Risks

Knee replacement carries risks with any technique, including infection, blood clots, stiffness, ongoing pain, injury to nerves or blood vessels, and wear or loosening of the implant over time. Points specific to robotic assistance:

  • Some systems use small pins in the bone to track the knee's position. These leave tiny pin sites and carry a small risk of infection or fracture at those sites.
  • Setting up the robot can add a few minutes to the operation.
  • If the robot cannot be used for any reason, the operation is completed with conventional instruments.

Experience

Total knees
232 total knee replacements in 2026, effectively all robotic-assisted since 2020
Revision knees
29 revision knee replacements in 2026
Research
39 peer-reviewed papers on knee replacement, including robotic-assisted surgery, and principal investigator of a randomized trial comparing robotic-assisted and conventional total knee replacement
Recognition
Best Poster, American Orthopaedic Association, adult reconstruction knee; Young Investigator Award, The Knee Society
Published outcomes
ComplicationPooledRate
Infection (revision or surgical drainage)6 / 6580.9%
Periprosthetic fracture requiring revision2 / 6580.3%
Instability requiring revision3 / 6580.5%
Aseptic loosening requiring revision4 / 6580.6%
Reoperation for any reason13 / 6582.0%
Total knees658

Sources:
Herndon et al., J Orthop Exp Innov 2022 (n = 405 knees)
Woelfle et al., The Knee 2024 (n = 173 knees)
Woelfle et al., Arthroplasty Today 2026 (n = 80 knees)

The research

Questions

Does the robot do the surgery?

No. The surgeon plans and performs the operation. The robotic arm keeps the saw within the planned limits, and the surgeon is in control throughout.

Is robotic knee replacement better than the conventional kind?

Robotic assistance improves the accuracy of bone cuts and implant position. Evidence that it leads to better long-term results is still developing, and conventional knee replacement also works well. Dr. Cooper finds that robotics allows him to personalize the operation to each patient and deliver a more individualized result, which is why he prefers to use it in the vast majority of cases.

Do I need a CT scan before surgery?

It depends on the robotic system and your knee. Dr. Cooper and his team will let you know if you need one.

How long will I stay in the hospital?

Dr. Cooper's patients go home either the same day as surgery or the next morning, depending on the patient and the plan made beforehand.

A stay in a rehabilitation facility or nursing home after hospital discharge is strongly discouraged, to avoid a higher risk of postoperative complications. It is rarely recommended, and only for elderly, frail patients who do not have a support system at home.

How long does a knee replacement last?

Most knee replacements last many years, and many last 20 years or more. How long yours lasts depends on your activity, weight, bone quality and the implant.

Can a partial knee replacement be done robotically?

Yes, for patients whose arthritis is limited to one part of the knee. A full examination and X-rays show whether a partial or total replacement is the better choice.

What should I bring to my first visit?

Bring any X-rays, MRI or CT images or reports, a list of your medications, and records of previous surgery on the knee or leg.

Schedule a surgical consultation

Offices are in Midtown, Uptown and Westchester. See locations.

Call (212) 305-6959