What Is Mako Robotic Knee Replacement and How Does It Work?

Mako is a robotic arm-assisted surgical system, made by Stryker, that helps orthopedic surgeons perform knee replacement with a level of precision that manual cutting and positioning struggle to match. The system builds a three-dimensional model of your knee from a preoperative CT scan, lets the surgeon plan every bone cut and implant position on a virtual model before touching a saw, and then guides a robotic arm during surgery that physically resists straying outside the planned boundaries. It can be used for both total and partial (unicompartmental) knee replacement, and the research so far points to tighter implant alignment, less soft tissue damage, and a faster early recovery compared to conventional surgery.

How Preoperative Planning Works

Before your surgery date, you get a CT scan of the affected knee. That scan feeds into the Mako system’s software, which constructs a detailed 3D model of your individual bone anatomy. Your surgeon then reviews this virtual knee and plans exactly where each implant component will sit, what angle it will be placed at, and how much bone needs to be removed. The surgeon records the expected component sizes before ever stepping into the operating room.¹

This is a meaningful departure from conventional knee replacement, where surgeons rely on standard X-rays and handheld cutting guides positioned by eye during the operation. The CT-derived model gives the Mako system a patient-specific blueprint rather than a one-size-fits-most template. Because the plan accounts for your actual bone geometry, the surgeon can anticipate problems like unusual bone shapes or asymmetric wear before they become surprises on the table.

What the Robot Actually Does During Surgery

A common misconception is that the robot performs the surgery autonomously. It does not. The Mako system is “semi-active,” meaning the surgeon controls the robotic arm throughout the procedure, but the arm provides haptic feedback. Think of it like power steering with guardrails: the surgeon moves the saw and makes every decision, but the robotic arm physically resists if the saw starts to drift outside the preplanned cutting zone. This haptic boundary keeps bone cuts within the intended area and helps protect surrounding soft tissues.²

Before any bone is actually cut, the system also allows the surgeon to simulate implant positioning and predict how the soft tissues around the knee will behave once the implants are in place. The Mako software can assess the gaps between compartments of the knee from its CT-derived models, giving the surgeon a virtual preview of the final balance.³ A feature called dynamic joint balancing lets the surgeon adjust the plan in real time, tweaking implant position to optimize how tight or loose the knee will feel in flexion and extension, all before a single cut is made.⁴

Getting soft tissue balance right is one of the trickiest parts of knee replacement. If the ligaments around the knee end up too tight on one side or too loose on the other, the result can be a knee that feels unstable, stiff, or painful. Conventional surgery relies heavily on the surgeon’s experience and intraoperative feel. The Mako’s ability to model these outcomes digitally before committing to irreversible bone cuts gives the surgeon an additional layer of information that manual techniques simply cannot provide.

Precision in Implant Alignment

The strongest evidence for the Mako system centers on how accurately it places implant components. In a study comparing robotic-assisted and conventional total knee replacement, the Mako group achieved a mean postoperative mechanical axis deviation of about 1.9 degrees, compared to about 2.8 degrees in the conventional group.⁵ That may sound like a small difference, but in joint replacement surgery, even a degree or two of malalignment can affect how evenly forces distribute across the implant, which may influence how long the replacement lasts.

A systematic review and meta-analysis looking at robotic-assisted versus conventional total knee replacement found that the robotic approach cut the rate of alignment outliers by roughly two-thirds and reduced deviation from the target mechanical axis by close to one degree on average.⁶ The pattern holds for partial knee replacement too. A meta-analysis specific to Mako-assisted unicompartmental knee replacement found fewer alignment outliers in both the femoral and tibial components compared to manual surgery.⁷

An important caveat here: better alignment on an X-ray does not automatically guarantee a better-feeling knee. The same meta-analysis on partial knee replacement noted that the improved precision had not yet translated into measurably superior short-term functional outcomes.⁷ There is a reasonable hypothesis that tighter alignment will pay off over a decade or more through reduced wear and fewer revisions, but the long-term data to prove that are still accumulating.

Less Damage to Surrounding Soft Tissues

Because the robotic arm constrains the saw to a predefined zone, it tends to cause less collateral damage to the ligaments and other structures around the knee. A blinded cadaver study compared robotic-assisted and manual total knee replacement and found that the posterior cruciate ligament sustained significantly less damage in the robotic group. Other structures like the deep medial collateral ligament, iliotibial band, and patellar ligament also showed less damage, though those differences did not reach statistical significance.⁸

Preserving the soft tissue envelope matters for recovery. When ligaments and tendons around the knee are nicked or bruised during surgery, it adds to swelling, pain, and rehabilitation time. The haptic boundary feature, combined with the precision of the preplanned cuts, appears to give the Mako system a meaningful edge here.²

Early Recovery and Pain

Several studies suggest that patients who have Mako-assisted surgery experience a smoother early recovery. A systematic review reported that robotic total knee replacement was associated with lower postoperative pain scores (roughly 2.6 on a standard pain scale versus 4.5 for conventional surgery) and a shorter time to hospital discharge, averaging about 77 hours compared to 105 hours.⁹ A separate study found that Mako-assisted patients experienced roughly a quarter less blood loss than conventional patients and had a much lower chance of needing a blood transfusion.¹⁰ Less blood loss and shorter hospital stays were also confirmed in a study examining whether a surgeon’s dominant hand affects outcomes with the Mako system.¹¹

The reduced tissue trauma from the haptic boundary system likely explains most of these benefits. Less collateral soft tissue damage means less inflammation, less pain medication, and an earlier return to weight-bearing and walking. A meta-analysis looking specifically at functional outcomes after Mako-assisted total knee replacement concluded that the system may result in improved functional scores, though the authors noted that high-level studies remain limited.¹²

Partial Knee Replacement with Mako

The Mako system was originally designed for unicompartmental (partial) knee replacement before expanding to total knee replacement. If only one compartment of your knee is damaged by arthritis, a partial replacement preserves the healthy portions and replaces only the worn-out section. This is a less invasive procedure with a faster recovery, but it demands very precise implant positioning because the remaining natural bone and cartilage must work in harmony with the new metal and plastic component.

A systematic review and meta-analysis of the Mako system specifically for partial knee replacement found that robotic assistance produced more precise implant positioning and fewer alignment outliers compared to the manual approach across multiple studies.¹³ The same analysis found lower overall complication rates in the robotic group, though it did not find a significant difference in revision rates, infection rates, or standard knee function scores in the short term. The precision advantage of the Mako system may be even more important in partial replacement than in total replacement, because the margin for error is smaller when you are working around preserved natural knee structures.

The Surgeon’s Learning Curve

Any new surgical technology requires time to master, and robotic knee replacement is no exception. A systematic review of learning curves across different robotic platforms found that surgeons using the Mako system typically reach proficiency after about 15 to 25 cases.¹⁴ That is somewhat shorter than some competing platforms. A single-surgeon study tracking the learning curve in more detail found that initial learning occurred over roughly the first 11 cases, followed by a competence phase, with fully optimized performance setting in after about 50 cases. Surgical time stabilized around 65 minutes after that point.¹⁵

If you are considering Mako-assisted surgery, asking your surgeon how many robotic cases they have completed is a reasonable question. A surgeon who has passed the 25-case mark has likely overcome the steepest part of the learning curve. Operative time tends to run a bit longer with robotic assistance than with conventional surgery, but that gap narrows substantially as the surgeon gains experience. One study on partial replacement confirmed that Mako surgery takes longer than manual surgery on average, which is a trade-off for the added precision.⁷

CT Scans and Radiation Exposure

Because the Mako system builds its 3D model from a preoperative CT scan, you will receive a dose of radiation that conventional knee replacement does not require. One study measuring the radiation from the Mako CT protocol found a mean dose of about 1,135 mGy·cm² per knee.¹⁶ An older study looking at CT scans used for robotic-assisted partial knee replacement found a mean effective dose of about 4.8 mSv, which the authors flagged as a disadvantage of the CT-based approach due to both the radiation exposure and added cost.¹⁷

For context, a single abdominal CT scan typically delivers around 8 to 10 mSv, so the knee-focused protocol used by Mako falls below that. Most experts consider the risk from this level of radiation exposure to be very low for the typical knee replacement patient, who tends to be older. Still, it is worth knowing about, and it is one of the reasons competing robotic systems have pursued “imageless” designs that skip the CT scan entirely.

Image-Based Versus Imageless Robotic Systems

The Mako system is image-based, meaning it relies on that preoperative CT scan to build its model. Other robotic platforms on the market, such as ROSA and NAVIO, can operate in an “imageless” mode, where the surgeon maps anatomical landmarks directly during surgery using special probes, and the system builds a model on the fly without any prior imaging.¹⁸

Each approach has trade-offs. Imageless systems eliminate the CT scan cost and radiation exposure, and they simplify the preoperative workflow because there is no scan to schedule weeks in advance. However, the anatomical model they create intraoperatively may be less precise because it depends on the surgeon manually identifying bony landmarks, which introduces some variability. A study comparing image-based and image-free approaches for partial knee replacement found that the image-based system produced better implant sizing.¹⁹ Whether this difference matters clinically in the long run is still being studied, but for now the CT-based approach gives the Mako system what appears to be an edge in the accuracy of its preoperative planning.

Costs and Access

Robotic-assisted surgery adds cost. The Mako system itself is expensive to purchase or lease, and each case requires dedicated single-use instruments on top of the CT scan. From the hospital’s perspective, these costs can potentially be offset if patients go home sooner and need fewer revision surgeries down the road. A protocol for a randomized controlled trial examining Mako cost-effectiveness noted that mitigating the added expense would require a reduction in hospital length of stay, fewer future revisions, or large differences in health outcomes favoring the robotic approach. One short-term analysis suggested a potential reduction in costs from the robotic group, though it leaned heavily on the assumption that hospital stays would be shorter. Another found that robotic surgery could be cost-effective when performed at high volume.²⁰

For you as a patient, the out-of-pocket difference depends on your insurance, your hospital, and your country. In many settings, the hospital absorbs the extra equipment cost and does not charge you more. In others, particularly outside publicly funded healthcare systems, you may see a line item for the robotic component. It is worth asking your surgical team directly whether there is any additional cost to you, rather than assuming it is bundled in.

Tracking Pins and Their Risks

One thing patients rarely hear about beforehand is the tracking pins. The Mako system needs to know exactly where your femur and tibia are in space at all times during surgery, so it attaches small arrays to pins drilled into the bone outside the surgical field. These pins are removed at the end of the procedure, and the holes typically heal without incident. However, pin site complications do occur in a small number of cases. The reported rate of pin site fractures ranges from about 0.06% to 4.8%, with most occurring within the first three months after surgery. Other potential pin-related issues include infection, delayed wound healing, and persistent drainage from the pin sites.²¹

Pin site fractures are rare enough that they should not deter you from choosing robotic surgery if you and your surgeon agree it is the right option. But you should know about them, particularly during the first few months of recovery when the pin holes are still consolidating. Avoiding heavy impact activities and following your rehabilitation timeline helps minimize this risk. Your surgeon will typically place the pins in locations that bear less mechanical stress and remove them carefully to avoid weakening the bone.

Surgeon Handedness and Robotic Standardization

Here is a detail that rarely comes up in patient consultations but turns out to matter: whether your surgeon is right-handed or left-handed can influence the precision and outcomes of conventional knee replacement. Approaching certain parts of the knee from the non-dominant side is simply harder with manual instruments. A study examining this question found that Mako-assisted surgery essentially leveled the playing field. Both right-handed and left-handed surgeons using the Mako system achieved comparable blood loss and hospital stay outcomes, and the robotic guidance compensated for the ergonomic disadvantages that handedness introduces in manual surgery.¹¹

This points to something broader about robotic assistance: it standardizes the procedure. The best conventional surgeons performing their thousandth knee replacement achieve excellent results, but there is inherent variability from case to case and surgeon to surgeon. The robotic system narrows that variability by enforcing the preoperative plan through physical constraints. It does not replace surgical skill, but it does act as a consistent safety net that reduces the gap between an average case and an ideal one.