By Cory Calendine, MD · Updated September 6, 2026, Board-Certified Orthopedic Surgeon
Robotic partial knee replacement is how I do nearly every partial knee in my practice. A partial knee is a small operation with a very small margin for error. After twenty-plus years and more than 700 joint replacements a year, I can tell you the robot doesn’t make my decisions. It makes the plan I already made happen inside the knee, every time.
This article helps explain the differences between doing a partial knee by hand and doing the procedure with robotic guidance. If you’re still weighing partial versus total knee replacement, start with how partial knee replacement differs from a total knee, then come back here.
What is robotic partial knee replacement?
Robotic partial knee replacement is surgery that resurfaces one worn compartment of the knee using a CT-based 3D plan and a robotic arm that holds the cutting tool inside a pre-set boundary. The surgeon makes every decision and controls every cut. The robot’s job is to stop the instrument from leaving the plan.
Your knee has three compartments: inner, outer, and the front where the kneecap rides. When arthritis has worn through only one, a partial knee (a unicompartmental knee arthroplasty, or “uni”) replaces just that surface. The healthy cartilage and both cruciate ligaments stay put.
In my practice I use the Mako® SmartRobotics™ system from Stryker®. I’m a paid consultant to Stryker on the robotic platform, and I’d use it whether they paid me or not. It solved the problem I’ll describe next.
Why is a partial knee harder to do by hand than a total knee?
A partial knee is harder by hand because there’s less bone, less room to see, and no way to “balance around” a mistake. A few degrees of tilt on a small tibial implant changes how the whole joint loads. In a total knee you can adjust the other side to compensate. In a partial, there is no other side.
Here’s what I tell my patients. A total knee is like re-flooring a whole room. A partial is like replacing three boards in the middle of a finished hardwood floor and making them sit flush. Smaller job, and the one where a careless cut shows.
That’s the main reason partial knees are underused. Research suggests a quarter to a half of knee replacement candidates could qualify for a partial, yet more than 90 percent get a total. That’s a technique problem, not a partial knee problem.
How is robotic partial knee replacement different from manual surgery?
Robotic partial knee replacement differs from manual surgery in three places: the plan is built from your CT scan before the incision, ligament balance is measured in millimeters before any bone is cut, and the robotic arm physically stops the saw from drifting outside the plan. Manual surgery relies on metal jigs sized to an average knee and on the surgeon’s eye for the rest.
Does the robot do the surgery?
No. I hold the instrument the entire time. The Mako arm works like a set of guardrails: inside the planned zone it moves freely with me, and at the edge it stops. If I push against the boundary, the burr simply won’t cut. That one feature is why a robotic partial knee is so hard to over-cut.
What does the CT plan change?
Before surgery, a CT scan of your knee becomes a 3D model. On that model I size the implant, set its angle, and decide exactly how much bone comes off, to a fraction of a millimeter. Manual guides assume your knee looks like the average knee. It doesn’t.
In the operating room, small tracking arrays pinned to the thigh and shin bones tell the system where your knee is in real time. I move the leg through a full arc and the screen shows the gap at every angle. If I don’t like the numbers, I change the plan before I cut.
How does robotic partial knee replacement handle ligament balance?
In a partial knee, ligament balance is the whole game. The ACL and collateral ligament are kept, so the implant has to sit at a depth and angle that holds them at natural tension through the full arc. Too tight and the knee feels stiff; too loose and it feels wobbly and wears the plastic early.
Robotic guidance lets me measure that tension at 0, 30, 60, 90, and 120 degrees before I commit to a cut. By hand, you learn how it balances after the bone is gone. That difference in timing is the biggest reason to want a robotic partial knee.
What are the proven benefits of robotic partial knee replacement?
The proven benefits of robotic partial knee replacement are fewer early complications, more accurate implant position, and strong long-term satisfaction. A 2025 national database study matched robotic and manual partial knee patients and found an overall complication rate of 3.7 percent with the robot versus 13.2 percent without. The biggest drops were in implant malposition and in fractures around the implant.
Long-term data is catching up. A series of 236 robotic partial knees followed for at least ten years found 210 of the 212 patients still available were satisfied or very satisfied, with low reoperation rates. An Australian registry study also found better three-year survivorship for robotic partial knees than for non-robotic ones.
Honesty about what the evidence doesn’t show matters too. That 2025 study found no difference in hospital stay, cost, or readmissions, and a randomized trial of robotic partial knees against manual total knees is still enrolling. What we have today is consistent evidence that the robot makes the operation more accurate and safer early on.
Who qualifies for a robotic partial knee?
You qualify if your arthritis is confined to one compartment, your ACL is intact, your knee still bends and straightens reasonably well, and your leg isn’t badly bowed. The robot doesn’t loosen those rules. It makes the operation reliable for the people who meet them.
Patients with inflammatory arthritis usually aren’t candidates, because that disease attacks the whole joint. Neither are patients with cartilage loss in two or three compartments. Age by itself is not a cutoff.
Deciding takes standing X-rays, a hands-on exam, and sometimes an MRI. If your knee doesn’t qualify, a robotic total knee replacement through the subvastus approach is an excellent operation, and I’ll tell you that directly.
What is recovery like after robotic partial knee replacement?
Recovery after robotic partial knee replacement is fast. Most of my patients walk the day of surgery, go home the same day, and are back to daily activities in three to four weeks. Golf, cycling, and doubles tennis usually return between six and ten weeks.
The reason recovery is quick isn’t the robot; it’s the operation. A partial knee keeps your ACL and healthy cartilage and disturbs far less muscle and bone than a total knee. Robotic guidance protects that advantage by keeping bone removal exactly as small as the plan calls for.
What are the honest risks and limits of a robotic partial knee?
The main risk of any partial knee, robotic or not, is that the rest of the knee can wear out later. A partial replaces one compartment; it doesn’t stop arthritis in the other two. That is the main reason registry data shows a higher lifetime revision rate for partials than for totals.
The robot helps with the part of that risk that comes from surgical error. It can’t help with biology. Converting a well-placed partial to a total knee is generally a straightforward operation with good results.
Does surgeon experience with the robot matter?
Yes, more than the robot itself. A robotic arm run by a surgeon who does a handful of partial knees a year is still a low-volume partial knee. Learning-curve research shows operative time settles after roughly six robotic partial knee cases, but judgment about candidacy and balance keeps improving for years.
Ask any surgeon two questions: how many partial knees do you do each year, and how many are robotic. At the Bone and Joint Institute of Tennessee in Franklin, I do more than 700 joint replacements a year. That’s the number I’d want to know if I were the one on the table.
Next steps for patients in Franklin, Nashville, and Middle Tennessee
If you’ve been told you need a knee replacement and nobody mentioned a partial, ask. I see patients from Franklin, Brentwood, Nashville, Columbia, Spring Hill, and Murfreesboro at 3000 Edward Curd Lane in Franklin, just off Interstate 65 at Exit 65.
You can schedule a consultation online or call (615) 791-2630. More on my partial knee replacement and robotic joint replacement pages, and on how long joint replacements last.
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Watch: how robotics makes partial knee replacement better
In under a minute, I explain what the robotic arm actually changes during a robotic partial knee replacement and why it matters for a small implant with no room for error.
This article is for educational purposes only and is not a substitute for a medical evaluation, diagnosis, or treatment. Individual results vary. Talk with a board-certified orthopaedic surgeon about whether robotic partial knee replacement is right for you. Dr. Calendine is a paid consultant to Stryker Corporation. Mako, SmartRobotics, and Stryker are trademarks of Stryker Corporation; mention of these products does not imply sponsorship or endorsement.
References
- Shih CM, et al. Short-term outcomes of robotic versus conventional unicompartmental knee arthroplasty: evidence from a national database. J Orthop Traumatol. 2025;26(1):74. doi:10.1186/s10195-025-00896-1
- Perazzini P, Sembenini P, Alberton F, Cochetti A, Innocenti B, Bori E. Robotic-assisted partial knee surgery performances: a 10-year follow-up retrospective study. Knee Surg Sports Traumatol Arthrosc. 2025;33(6):2197-2203. doi:10.1002/ksa.12599
- Madden K, Flood B, Malek M, et al. Robot-assisted partial knee replacement versus standard total knee replacement (RoboKnees): a protocol for a pilot randomized controlled trial. Pilot Feasibility Stud. 2024;10:39. doi:10.1186/s40814-024-01463-x
- St Mart JP, de Steiger RN, Cuthbert A, Donnelly W. The three-year survivorship of robotically assisted versus non-robotically assisted unicompartmental knee arthroplasty. Bone Joint J. 2020;102-B(3):319-328. doi:10.1302/0301-620X.102B3.BJJ-2019-0713.R1
- Kayani B, Konan S, Pietrzak JRT, Huq SS, Tahmassebi J, Haddad FS. The learning curve associated with robotic-arm assisted unicompartmental knee arthroplasty. Bone Joint J. 2018;100-B(8):1033-1042. doi:10.1302/0301-620X.100B8.BJJ-2018-0040.R1
- Zambianchi F, Seracchioli S, Franceschi G, et al. Image-based robotic-arm assisted unicompartmental knee arthroplasty provides high survival and good-to-excellent clinical outcomes at minimum 10 years follow-up. Knee Surg Sports Traumatol Arthrosc. 2023;31(12):5477-5484. doi:10.1007/s00167-023-07599-2
