Robotic knee surgery has introduced a new level of precision to joint replacement procedures across Australia. But while many people understand the benefits of “robotic-assisted surgery,” far fewer know how these robotic systems actually work.
This page provides a detailed, technical explanation of the major robotic knee systems used in Australia, specifically MAKO, ROSA, and CORI. If you’re wondering what the robotic arm does, how surgeons interact with the system, and what makes one platform different from another, you’re in the right place.
Understanding Robotic Knee Surgery Systems
Robotic knee systems are not autonomous machines. They are advanced tools that assist a trained orthopaedic surgeon during joint replacement procedures. Different types of robotic knee surgery systems vary in how they collect anatomical data, guide bone preparation, and support surgical accuracy during joint replacement.
Some systems rely heavily on pre-operative imaging, while others collect information in real time during the operation. Their design influences how data is captured, interpreted, and applied to surgical decision-making. Understanding this technical workflow helps clarify how robotic knee systems work with the surgeon rather than independently of them.
Let’s explore how the MAKO, ROSA and CORI systems, three of the most widely used in Australia, work in practice and what makes each one unique.
MAKO: CT-Guided Precision With Haptic Boundaries
The MAKO robotic-arm assisted surgery system by Stryker is one of the most established platforms used in Australia for partial and total knee replacements. It is best known for using a pre-operative CT scan to create a detailed 3D model of the patient’s knee before surgery. This personalised model forms the basis for a surgical plan that is mapped to the patient’s unique anatomy.
How it works:
- Pre-op imaging: The process begins with a CT scan of the patient’s knee joint. This image is converted into a 3D virtual model, which the surgeon uses to plan implant positioning and alignment.
- Haptic feedback: During surgery, the robotic arm provides tactile resistance. This means it will only allow the burr (a tool used to shape bone) to move within pre-defined boundaries. The surgeon is always in control, but the system prevents them from going outside the planned area.
- Intraoperative adjustments: The surgeon can fine-tune alignment and soft tissue balance during the procedure using real-time data from the system.
MAKO also allows the surgeon to simulate multiple implant configurations before cutting bone, helping anticipate how each change could affect joint movement and stability. Its use of haptic feedback sets physical limits, similar to a virtual fence. These constraints help prevent excessive resection of bone.
The robotic arm actively resists movement if the tool approaches outside the planned area, which supports precise execution of the surgical plan. MAKO’s reliance on pre-operative imaging makes planning highly structured, but it also requires accurate CT data and proper patient positioning during scanning for best results.
In most Australian hospitals using MAKO, the planning is completed before the day of surgery, then reviewed and refined once the procedure begins.
ROSA: Motion-Sensing With Real-Time Surgical Insight
The ROSA (Robotic Surgical Assistant) knee system by Zimmer Biomet is a sensor-based robotic system that uses real-time data instead of CT scans. It relies on optical tracking and smart instruments to gather information about the knee’s motion and alignment throughout the procedure.
Key features:
- No pre-op CT: Instead of pre-surgical imaging, ROSA uses X-rays combined with intraoperative data collection.
- Dynamic tracking: During the procedure, ROSA uses infrared sensors to monitor the position of the femur and tibia. This allows it to adjust the surgical plan in real-time based on how the knee behaves when moved.
- Integrated workflow: Surgeons can use ROSA to track limb movement, joint spacing, and flexion-extension balance as they operate.
What makes ROSA technically unique is its ability to map live joint kinematics, which means it captures how the joint moves through space under stress and flexion. The system registers fine-grained anatomical landmarks using bone-mounted tracking pins and a camera tower, which communicate with the ROSA interface in real time.
Surgeons can assess ligament tension and rotational alignment dynamically, rather than relying on static measurements alone. This supports adaptive surgical planning even mid-procedure, especially in cases where soft tissue balancing requires close attention.
While ROSA doesn’t include a robotic cutting arm, its passive navigation and data overlay allow for high surgeon autonomy with enhanced visual feedback.
CORI: Imaging-Free Flexibility With Intraoperative Mapping
The CORI robotic-assisted knee surgery system from Smith+Nephew is known for its imageless navigation technology, which does not require a pre-operative CT or MRI. Instead, the system builds a virtual model of the knee during the operation by mapping the joint surface and registering key landmarks.
What sets CORI apart:
- No radiation required: Unlike CT-based systems, CORI does not require any radiation-based imaging, which may be preferred in some clinical scenarios.
- On-the-spot modelling: Surgeons use a handheld scanner to gather data intraoperatively. This creates a 3D map of the joint that guides bone resections in real time.
- Custom planning on the table: Because the data is collected during surgery, the surgical plan can be adjusted immediately, without needing to pre-load a fixed image model.
CORI uses a handheld sculpting tool that enables robotic navigation in knee surgery, allowing precise bone adjustments directly within the intraoperative mapped anatomy. This approach reduces setup time and may be beneficial for clinics where access to pre-op imaging is limited.
Intraoperative data is gathered through tactile surface registration, where the surgeon moves a mapping probe across specific anatomical points to build the virtual model. The software then provides guidance on implant position, joint line restoration, and ligament balance based on those live inputs. This model can be iterated and updated during the procedure, making it one of the most adaptable systems currently available in Australia.
What the Robotic Arm Really Does
Despite the name, robotic arms do not perform the surgery autonomously. Instead, they act as precision guidance tools for the surgeon.
Here’s what a robotic arm is designed to do:
- Navigation: Robotic arms follow a planned surgical path based on the system’s input data, either from imaging (like CT) or live mapping.
- Constraint control: Through haptic feedback or real-time tracking, they restrict tool movement to safe zones, helping avoid unintended damage to bone or soft tissues.
- Stability: The robotic arm holds the cutting instrument steady, reducing small variances that may occur with manual instruments.
Most robotic arms in current orthopaedic systems serve one or more of the following functions: they anchor cutting tools, provide force feedback to prevent deviation, and offer visual overlays that track instrument location in 3D space. Depending on the system, the arm may be rigid (as with MAKO), assistive (as with CORI), or passive (like ROSA, which has no robotic arm but uses navigation).
By integrating bone landmarks, implant orientation, and soft tissue considerations into a virtual coordinate system, robotic arms help standardise accuracy and maintain reproducibility across varied patient anatomies. It’s a technical safeguard, not a substitute for human control.
How Surgeons Use Robotic Software During Surgery
Robotic systems are only as effective as the software that supports them. Each system includes a surgical planning interface that the surgeon uses to:
- Design a personalised implant plan (e.g. positioning, sizing, rotation)
- Simulate joint movement and assess ligament balance before making cuts
- Adapt the plan in real time based on soft tissue behaviour or alignment data
- Visualise bone resections and compare actual vs. intended results
These software platforms also allow “what-if” testing, where different implant options or alignments can be virtually trialled and assessed before bone resection begins. Most systems display force vectors, range of motion estimates, and real-time feedback that alerts the surgeon to potential imbalance or overcorrection.
In MAKO, for example, the surgeon can see how adjusting tibial rotation may influence patellar tracking. In CORI or ROSA, software overlays guide depth of resection and final implant placement based on real-world ligament responses. While each platform has a distinct interface, they all aim to help the surgeon convert anatomical complexity into safe, measurable action.
Robotic Knee System Comparison Table
| Feature | MAKO | ROSA | CORI |
|---|---|---|---|
| Pre-operative imaging | CT scan required | X-ray-based | No imaging required |
| Intraoperative data | CT + real-time sensors | Motion sensors + optical tracking | Handheld mapping during surgery |
| Robotic guidance type | Robotic arm with haptic boundaries | Passive robotic guidance | Handheld robotic sculpting tool |
| Soft tissue balancing | Intraoperative adjustment possible | Real-time kinematic feedback | Dynamic planning based on mapping |
| Flexibility | Requires pre-op CT planning | Real-time flexibility during op | Highly adaptable on-the-spot |
| Radiation exposure | CT-based (higher exposure) | X-ray based (moderate exposure) | No pre-op imaging (minimal exposure) |
| Use in Australia | Common in public and private sectors | Growing use in private hospitals | Expanding across both sectors |
Note: The availability of specific systems may vary depending on your hospital or treating surgeon. Some centres may use multiple systems depending on the procedure type or surgeon preference.
Choosing the Right System: What Matters for Patients?
While each robotic system has technical differences, the clinical decision about which system to use depends on multiple factors, including:
- The surgeon’s training and familiarity with a given platform
- The hospital or clinic’s access to robotic systems
- The complexity of the patient’s anatomy or surgical history
- Patient-specific factors like bone quality, alignment, or soft tissue condition
It’s worth noting that some Australian surgeons are trained on multiple platforms and may select the system that aligns best with the specific surgical goals for your case. In complex scenarios, such as significant deformities or prior knee surgeries, systems with flexible intraoperative adaptation (like CORI or ROSA) may be prioritised. However, system selection is always part of a broader clinical strategy, not a standalone choice.
No system is objectively “better” in every scenario. What matters most is that the technology is used by a skilled surgeon in a well-planned procedure tailored to your needs.
For patients planning surgery, understanding robotic knee surgery costs and access in Australia can also help clarify how technology type, hospital setting, and coverage may influence planning discussions with your healthcare team.
Robotic Technology as a Surgical Tool
Robotic knee systems are evolving quickly and play an increasingly important role in Australian orthopaedic surgery. However, they are not a replacement for surgical experience or professional judgement. Instead, they provide a framework of precision and real-time feedback to support safer, more consistent outcomes when used appropriately.
Robotic technology is best understood as an extension of the surgeon’s skill, not a replacement for it. Each platform translates the surgeon’s plan into actionable, quantifiable movement within a 3D framework.
If you’re looking to understand the broader process—including what happens during the operation and how the system supports surgical accuracy—it may help to explore the fundamentals of how robotic knee surgery works.
At the same time, not every patient is automatically suited to this approach. Your individual health profile, joint condition, and surgical goals all factor into whether you may be a candidate for robotic knee surgery. Discussing these elements with a qualified orthopaedic surgeon can help determine if robotic assistance aligns with your treatment plan.
As robotic systems continue to advance, so too will the integration of AI-driven planning tools, machine learning from surgical datasets, and even greater customisation. But for now, your choice of surgeon, along with their ability to interpret and apply these tools, is what ultimately shapes your surgical experience.
If you’re considering knee surgery and want to understand your options, it’s important to speak with a registered orthopaedic surgeon who can explain which approach may suit your situation best.
Disclaimer: This content is intended for informational purposes and does not replace professional medical advice, diagnosis, or treatment. Always consult a registered health practitioner before beginning any treatment or making decisions about your healthcare. You can verify registration at AHPRA’s public register. Individual outcomes may vary depending on personal health circumstances and the nature of the injury.
Frequently Asked Questions (FAQs)
1. Is the robotic arm doing the surgery, or is it just guiding the surgeon?
The robotic arm does not perform the operation autonomously. It acts as a precision-guidance tool that follows a pre-planned path based on either CT imaging (like MAKO) or live intraoperative mapping (like CORI). The surgeon remains in full control of all decisions and movements. The robotic arm may restrict movement beyond planned boundaries (as in MAKO) or provide real-time visual cues (as in ROSA), but it never replaces the surgeon’s hands-on role.
2. Why do some systems use a CT scan while others don’t?
CT-based systems like MAKO rely on detailed pre-operative imaging to create a 3D model of the knee before surgery, enabling highly structured planning. In contrast, systems like CORI build the model during surgery using real-time mapping tools, avoiding radiation exposure and allowing greater intraoperative flexibility. ROSA takes a hybrid approach using X-rays plus intraoperative sensors. The choice depends on the surgeon’s preference, case complexity, and available technology.
3. Can the surgical plan be changed mid-procedure with robotic systems?
Yes, most robotic platforms allow surgeons to adapt the surgical plan during the operation. For example, MAKO enables real-time adjustments to implant alignment and soft tissue balance. CORI builds the model on the table, so the plan can be updated instantly as mapping continues. ROSA provides dynamic feedback that may prompt surgical refinements during key stages of the procedure. This flexibility is crucial when responding to the patient’s real-time anatomical feedback.
4. What’s the difference between haptic feedback and passive navigation in these systems?
Haptic feedback, used in systems like MAKO, physically limits tool movement through resistance or force control. The robotic arm will only allow the instrument to operate within the pre-set boundaries. In contrast, passive navigation systems like ROSA do not apply force but instead provide visual and data guidance, requiring the surgeon to stay within the planned parameters based on continuous feedback. CORI combines navigation with a sculpting tool but does not use haptics in the same way as MAKO.
5. How do surgeons decide which robotic system to use for each patient?
Surgeons consider several factors when selecting a robotic platform. These include the type of procedure (e.g. total vs. partial knee replacement), patient anatomy, bone quality, prior surgeries, and whether advanced pre-op imaging is available or appropriate. A surgeon trained on multiple systems may choose the one that offers the most useful intraoperative feedback for a particular case. Hospital access to specific platforms can also influence this decision.
