Robotic Partial & Total Knee Replacement

Why Robotic Partial Knee Replacement?

The answer to the questions are related.

1) "Why would you resurface only part of the knee, when you could replace the entire thing?" 
2) "Why do you use a robot in the OR?"

The answer to the questions are related.

Robotic Partial Knee Replacement (also known as MAKOplasty) is a procedure for knee arthritis where only the arthritic portion of the knee is resurfaced while the remainder of the knee is left intact. It applies robotic technology to partial (or unicondylar) knee replacement. So to answer the questions, you need to understand why partial knee replacement may be preferable to total knee replacement AND why robotic techniques improve partial knee replacement.

The above video was filmed in 2012.

“Why would you resurface part of the knee, when you could replace the entire thing?”

Deciding between Partial
Knee Replacement and Total Knee Replacement

Total Knee Replacement

Total Knee Replacement

Interactive Educational Video: Total Knee Replacement

 Total knee replacement (TKR) is an excellent operation and one of the most successful procedures developed in the 20th century. However, total knee replacement often does not meet the expectations of those who currently undergo the procedure. Designed to allow patients to walk but not to run or play sports, the modern day total knee replacement removes the major ligaments in the knee (the ACL and PCL for example). Recent studies have demonstrated no functional limitations during swimming and biking; however, significant limitations were noted during more strenuous activities such as kneeling, squatting, moving laterally, turning and cutting, carrying loads, stretching, leg strengthening, tennis, dancing, gardening, and even sexual activity(1). Increasingly, this operation is performed on younger patients with over 40% of total knee replacements performed in patients under the age of 65 years old (there has been a 3 fold increase in TKR for this group over the last decade)(2)! The demands of this group often include a rapid return to work, participation in sports, and normal or near normal knee function.

Unfortunately expectations are not always met with TKR. Indeed 15-25% of patients who undergo TKR would not do the operation again(3)!! This is particularly sobering considering that we will spend up to 1% of the GDP on this operation in 2030. An emerging alternative to TKR is partial knee replacement. With this strategy, only the damaged portion of the knee is resurfaced; this is akin to filling a cavity rather than capping the entire tooth (as is the case with TKR).

Partial Knee Replacement

Partial Knee Replacement

Interactive Educational Video: Total Knee Replacement

With Partial Knee Replacement (PKR), only the arthritic region of the knee is resurfaced, conserving the central ligaments of the knee (the ACL and PCL) as well as near normal knee motion. Partial Knee Replacement was nearly abandoned over 40 years ago due to concerns about durability. In these early days, the materials and fixation were not developed enough for a partial solution to provide long lasting pain relief. However, over the past quarter century, the material and fixation improvements pioneered for total knee replacement have resulted in durable solutions for partial replacements as well.

Partial knee replacement is not possible for all patients with arthritis; indeed, it is indicated when the arthritic condition is fairly localized. However, when it is appropriate, it is important to educate patients of the pros and cons of partial vs total knee replacement.

Pros and Cons of Total Knee Replacement vs Partial Knee Replacement

Here is a list of the issues that are important to my patients and a review of the pros and cons of the two operations. The choice is personal as different patients have different goals and realities. Often, either operation would appropriately service the needs of an individual.

Pain Relief

Both TKR and PKR are expected to provide excellent and durable pain relief. However, patient satisfaction with total knee replacement is approximately 85%. Conversely, patient satisfaction with partial knee replacement is 90-95%.


Most studies suggest that TKR is more durable than partial knee replacements. 95% of TKR are expected to last 10 years and 85-90% are expected to last 20 years. Using modern implants, 90% of partial knee replacements are expected to last 10 years and 80% are expected to last 20 years. Our recent studies using robotic techniques for partial knee replacement demonstrate a 60-70% reduction in early failure compared to traditional partial knee replacements. This suggests that the dirability of robotic partial knee replacement is likely very similar that of total knee replacement.

These numbers are evolving as it takes 20 years to accumulate data; for example, I have been using robotic technology to insert partial knee resurfacing implants over the past decade and I expect these implants to last longer than the prior generation of implants.

If a total knee replacement fails, a revision total knee replacement is necessary. This requires specialized implants to make up for the loss of bone. Conversely, if a partial knee replacement fails, it can usually be converted to a normal total knee replacement.

Risks of the Procedure

The risk of complications after a surgery is an important factor when deciding between Partial and Total Knee Replacement. Recent studies have demonstrated that Partial Knee Replacement is the safer procedure.

In a large study published in 2012 of nearly 3000 patients, it was shown that the overall risk of complications for patients undergoing TKR was 11% compared to 4% with PKR(4). The finding that the risks associated with total knee replacement are approximately 3 times higher than partial knee replacement was also demonstrated in a study performed in 2011(5). These risks are both systemic risks such as heart attack or death as well as local risks such as infection, persistent pain, loss of motion requiring a manipulation, nerve injury and instability. Infection is particularly concerning after knee replacement; it is estimated that total knee replacement has twice the risk of infection as partial knee replacement.

Return to Sport

Return to sport and leisure activities is an important goal of many patients after partial knee replacement and the ability to return to sport is highly variable. In general, return to sport is easier and more predictable after partial knee replacement than total knee replacement. In a recent comparison study, 96% of patients returned to preoperative level of sports after partial knee replacement whereas only 64% of patients returned to their preop level after TKR(6). Another recent study demonstrated that the level of leisure activity participation after TKR failed to meet patient expectations; in this study, at 1 year post op, no TKR patients were playing tennis, skiing, jumping rope, skating, playing basketball or jogging. Less than 4% were playing golf, hunting or fishing(7). In another study, 28% of patients walked the golf course preoperatively whereas only 14% of patients walked the golf course after a TKR(8). In active golfers, the length of their drives decreased by an average of 12 yards and their handicap rose by an average of 4.6 strokes after TKR(9). Alternatively, 90% of patients maintained or improved their sporting activities after partial knee replacement(10).

Return to Work

Return to work after knee repair is highly variable; indeed, many patients are retired at the time of their surgery. However, I recommend 6 -12 weeks off prior to return to work after total knee replacement. Alternatively, I consider partial knee replacement a back to work operation. I encourage patients to go back to work after 1-2 weeks after a partial knee replacement.

Recovery Time

The recovery time for any operation varies. Here is a comparison of typical recovery times for partial vs total knee replacement.

  1. Hospital Stay

  • 2-4 days: Total

  • none-1 night: Partial

  1. In Patient Rehab Stay

  • 1-2 weeks: Total

  • none: Partial

  1. Outpatient Rehab

  • 12 weeks: Total

  • 6 weeks: Partial

  1. Time using walker or crutches

  • 6 weeks: Total

  • 2 weeks: Partial

  1. Need for pain meds

  • 6 weeks: Total

  • 2 weeks: Partial

  1. Loss of work

  • 6-12 weeks: Total

  • 2-3 weeks: Partial

Cost to Patient

Insurance covers both partial and total knee replacement. However, there are hidden costs to the procedures. A study from Canada demonstrated that patient costs are 30% of the mean total costs of total knee replacement; most of these costs occur after the acute inpatient stay. The mean cost of a total knee replacement to the patient in this study was approximately $7500; the majority of this is due to loss of work(11). Obviously, since partial knee replacement results in much quicker return to work, less need for rehabilitation, and less pain medication requirement, the cost to the patient is significantly lower.

Direct Comparison

There is only one randomized prospective clinical study comparing long term outcomes of total knee replacement versus partial knee replacement. In this study, partial knee replacement had better early and long term outcomes in terms of pain relief and function. Surprisingly, partial knee replacement demonstrated superior survivorship at 15 years than total knee replacement(13).

Summary - Deciding Between Partial and Total Knee Replacement

Both partial and total knee replacement can provide durable pain relief and improve function in patients with knee arthritis. Partial knee replacement is not appropriate for all patients with knee arthritis and may only be possible in 10-30% of patients.

Total knee replacement is a very durable operation that can last for 30 years. It predictably allows patients to walk, hike, ride a bike, and swim. It is less predictable in return to sporting activity. The recovery is long and arduous.

Partial knee replacement has a quicker recovery, permits rapid return to work, and often allows patients to expand their sports participation. In addition, the surgery has fewer risks than total knee replacement and is less costly to the patient. Though many studies have demonstrated excellent and long lasting durability, I still caution patients that partial knee replacement has a higher revision rate than total knee replacement.

“Why do you use a robot in the OR?”

Domo Arigato Mr Roboto (Thank you very much, Mr. Robot) -
The emergence of Robotic Knee Resurfacing

A Technical Problem

A downside of Partial Knee Replacement is that is may not be as long-lasting as Total Knee Replacement. One of the primary reasons for this is that Partial Knee Replacements can fail quickly if they are poorly positioned at the time of surgery. Indeed, PKR is a technically demanding procedure, and prone to surgeon error. Rather than making perpendicular cuts to remove the entire ends of the knee (as we do in total knee replacement), the surgeon has to preserve the inner ligaments (ACL and PCL) as well as the dimensions of the native knee in partial knee replacement. Technical error is a major source of failure in partial knee replacement. There are two main solutions to this problem: robotics and surgeon experience.

The Robotic Solution

I have pioneered the use of robotics for partial knee replacement (I call the procedure robotic partial knee replacement- it is also known as MAKOplasty) because robotics affords a level of precision and reproducibility that cannot be achieved with manual techniques. I have shown that implant position is 3x more accurate and less variable with robotic techniques

compared to manual tools and that alignment can be controlled with robotic resurfacing(14,15). My colleague in England, Justin Cobb, demonstrated in a prospective randomized trial that robotic partial knee resurfacing achieved accurate placement of the implant 100% of the time compared to only 40% with manual techniques(16). With robotics, I can reliably get it right the first time.

I have been using robotic assistance for more than a decade. On a preoperative CT scan, I make a virtual model of a patient's knee. On this model, I can virtually place the implants and position them perfectly, customizing them precisely for the individual anatomy. This allows me to test many different positions until I find the "sweet spot" for the implant - indeed, I will often perform the surgery on the computer 20 or 30 times until the implants fit just right. This ability to perform the surgery "virtually" on the computer screen before ever touching the patient's skin eliminates the guess-work of manual techniques. The plan is then programmed into the robotic arm which helps sculpt the bone so that the implants fit perfectly. The result is a robotic partial knee replacement of the damaged joint. So Domo Arigato, Mr Roboto - no more trial and error, no more removal of too much bone, no more blunt saw cuts and no more guess-work.

For the patient, the robotic assistance results in more refined bone resection (to preserve as much native bone as possible), smaller incisions, and a less painful recovery. The optimized positioning promises to ensure more durable results and better function.

Robotics and Experience - a winning combination

Another major factor in determining surgical outcome is after partial knee replacement is surgeon experience. Medical evidence has long shown that the more you do something, the better you get. This is particularly the case for partial knee replacement. In a recent study looking at partial knee replacement it was found that high volume surgeons had a revision rate of less than 1% over 5 years. Surgeons who performed 8-12 partial knee replacements per year had a revision rate of 5% while surgeons who performed less than 8 partial knees/year had a revision rate of 6-8% over 5 years(17). Low volume surgeons had a revision rate 6-8x that of high volume surgeons!! I currently perform over 200 partial knee replacements per year, which is the most of any surgeon in the greater New York area.

Another study demonstrated that there was a direct association between the number of partial knee replacements performed in the hospital and the revision rate. In this study, the greater the surgical volume of partial knee replacements performed, the lower the rate of revision(18). Surgical volume is one reason to choose Hospital for Special Surgery. No hospital in the world performs more joint replacement surgeries than HSS. We are truly experts at what we do. Because Hospital for Special Surgery is devoted exclusively to orthopedics, every one of our scientists, nurses, and therapists is a specialist in this field and aligned to provide the best possible care.

Coupling robotics with extensive surgeon experience in the world-class environment of the Hospital for Special Surgery is a winning combination.

Summary - Why Robotic Partial Knee Replacement

Robotic Partial Knee Replacement is not for everyone and Total Knee Replacement is an excellent solution for many patients. However, in patients with localized arthritic disease, Robotic Partial Knee Replacement offers the following advantages:

  1. Safer procedure than TKR

  2. More rapid return to work and play than TKR

  3. Lower cost to the patient than TKR

  4. Quicker recovery than TKR

  5. Smaller incision and less pain than TKR

  6. More reliable result compared with manual partial knee replacement techniques