CT-Guided vs Imageless Orthopedic Robots: Pros & Cons
Robotic assistance has become a mainstream option for total knee arthroplasty (TKA), but not all systems work the same way. Two broad paradigms dominate: image-based and imageless. Image-based (CT- or MRI-based) robotic procedures rely on a preoperative computed tomography (CT) scan or magnetic resonance imaging (MRI) to build a 3D model, while imageless robots register anatomy intraoperatively without the use of preoperative imaging.
Each approach brings distinct trade-offs in planning, accuracy, workflow, radiation, and cost. Let’s explore these two approaches in greater depth, taking current evidence into account to better understand the pros and cons of each strategy.
What’s the Difference Between CT-Guided and Imageless Robotic Systems?
Preoperative data source and 3D model
CT-guided systems (e.g., robotic platforms that require hip-to-ankle CT) generate a patient-specific 3D bone model before surgery. This can enable more granular templating of component size, joint line, and alignment strategy before entering the OR.1 Intraoperative registration then aligns surface points to the CT model so the robot can execute the preplanned resections and implant positions.
Imageless systems build a model intraoperatively by mapping bony landmarks using tracked pointers or proprietary handpieces. The software fits these points to a generic model to create reference planes and joint kinematics; the surgeon then iterates the plan in real time.1
Registration and execution
CT-guided platforms like the TMINI® Miniature Robotic System use anatomy-to-CT surface matching with a relatively larger set of registration points. After which, the state-of-the-art miniature, handheld, wireless robotic system locates bone pins along precisely defined planes from the CT-based 3D surgical plan.
The TMINI Robot locks in and continuously orients within the operating envelope, automatically compensating for the surgeon’s hand movement. It will suspend activity if the handpiece exits the operating envelope. The cutting guides are then connected to the bone pins to ensure accurate bone resection.2
Imageless platforms just rely on landmark and surface mapping – with no image to verify their validity against – to personalize cuts. Execution is similarly done in a semi-active manner.3
Radiation exposure
CT-guided workflows necessitate a degree of preoperative radiation, but effective doses vary widely with protocol and scanner.4
Imageless systems do not require preoperative CT scans and thus avoid radiation, though some imageless robots can optionally incorporate low-dose radiographs or EOS imaging for planning.3
Which Approach Provides Better Surgical Accuracy and Outcomes?
Robotic assistance, whether CT-guided or imageless, tends to reduce alignment outliers and improve plan reproducibility compared to conventional instrumentation.5 When it comes to evidence comparing the two different systems, studies suggest that there are no significant differences between the two systems in terms of femoral and tibial coronal plane alignment.6 However, notable differences have been observed in the planned versus achieved bone cuts.7
Specifically, imageless systems tend to show a greater tendency toward unintentional varus alignment in femoral and tibial coronal cuts when compared to image-based systems.7 This variation can be largely attributed to the reliance of imageless systems on intra-articular anatomy for reference.7 Precise placement of intra-articular landmarks thus becomes essential to prevent the system from incorrectly registering a joint line that differs from the native anatomy.
When it comes to evaluating outcome data, the results of limited high-quality, head-to-head studies comparing imageless and CT-guided platforms are conflicting.
On one hand, CT-guided raTKA has been shown to yield similar range of motion measurements as well as Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) and Knee Society Scores (KSS) at one-year follow-up.6 On the other hand, CT-guided raTKA has been associated with shorter hospital stays, fewer manipulations under anesthesia, and improved mid-term patient-reported outcomes over imageless systems.8
Overall, when comparing accuracy and outcomes, the differences may be attributed to surgeon experience, surgical execution, and specific device features. The research does seem to indicate, however, some clear advantages to CT-guided platforms compared to imageless systems.7
How Do Workflow and OR Efficiency Compare Between the Two?
Robotic-assisted knee arthroplasty requires surgeons to coordinate preoperative planning, intraoperative workflow, and operating room (OR) efficiency to achieve optimal outcomes. The TMINI® Miniature Robotic System includes automatic bone segmentation from the pre-op CT-Scan. Additionally, THINK Surgical provides a dedicated staff of Case Planners that develop a plan that can be reviewed by the surgeon, edited, and approved. This allows surgeons more time to focus on clinical duties and patient management.
While obtaining CT-scans pre-operatively introduces additional upstream logistical steps and scheduling demands, it streamlines the intraoperative registration process since the 3D model is already prepared, allowing plan modifications to be performed quickly in the OR.9
By contrast, imageless systems shift the mapping process entirely into the OR, where the surgeon must acquire bony landmarks and surface points. This approach eliminates the need for preoperative imaging but can lengthen the setup phase, particularly during early adoption when surgical teams are still gaining experience.10 Additionally, unlike CT-based programs, surgeons using imageless systems are unable to verify the registration points, which could lead to inaccuracies and downstream problems during the surgery.
Operative times appear to follow the same learning curve with both CT-guided and imageless platforms.11 While the TMINI® Miniature Robotic System can increase operative times during the initial adoption of this technique, surgeons are able to achieve similar times to manual techniques after as few as five to seven cases.12
In contrast to large console-based platforms, the TMINI System is a miniature, handheld, wireless robot designed to provide accurate and precise implant placement without relying on bulky robotic arms. This minimizes the space burden in the OR and integrates more seamlessly into existing OR setups, adding only one tray of robotic instruments.
Overall, efficiency across robotic platforms is less about whether the system is CT-guided or imageless and more about team familiarity, institutional processes, and the specific device’s workflow.11 CT-guided systems add preoperative imaging steps but can streamline in-room execution, whereas imageless systems avoid preoperative CT but may demand more intraoperative mapping effort. While differences in operative times occur during early adoption of these technologies, operating times achieve time neutrality with manual cases after a short learning curve.
What Are the Practical Considerations for Each System? 
1. Radiation exposure
CT-guided workflows do involve pre-operative radiation exposure. Reported effective doses for preoperative knee or hip-to-ankle CT protocols range from 2.5 to 8.5 mSv, with optimization techniques—such as tube current modulation, automated kV selection, and iterative reconstruction—capable of lowering exposures closer to 2–3 mSv.13 This exposure is comparable to the average dosage of background radiation each human is exposed to yearly, which is 2.4 mSv.14
2. Implant choice
Both CT-guided and imageless platforms are traditionally closed, which restricts implant choice. This is where the TMINI Miniature Robotic System disrupts the status quo, introducing an open platform offering the most implant systems and design philosophies available of any orthopedic robotic system currently available in the US.15
3. Downstream outcomes
Beyond the immediate perioperative setting, value arguments for raTKA often extend to downstream outcomes. Complicating the cost-effectiveness argument are the potential downstream offsets of using raTKA, such as a decrease in early readmissions and fewer post-acute services.16
Hospitals must also recognize the marketing dimension as patient surveys consistently demonstrate strong interest in robotic branding and perceptions of enhanced precision, which can influence patient choice, case capture, and regional differentiation.17
Conclusion
Compared to manual techniques, both CT-guided and imageless robotic TKA systems deliver higher accuracy with lower alignment outliers.5 Image-based systems leverage preoperative 3D planning at the expense of added radiation, while imageless systems prioritize intraoperative adaptability without CT, potentially trading off additional mapping time early in the learning curve.
For hospitals and surgeons, the “best” choice is less about a categorical winner and more about compatible institutional infrastructures, surgeon alignment philosophies, and implant preferences. As comparative registries mature and long-term survivorship data accumulate, the field will better define whether subtle accuracy differences translate into durable outcome advantages for one platform or the other.
1 Hirschmann MT, Avram G, Graichen H, Tandogan RN, Mengis N, Zaffagnini S. Same same but different-Image-based versus imageless robotic-assisted total knee arthroplasty!. J Exp Orthop. 2024;11(4):e70062.
2 MKG-23-16Rev0 – TMINI Capital Deck.pptx.
3 Wu M, Charalambous L, Penrose C, Belay E, Seyler TM. Imageless Robotic Knee Arthroplasty. Operative Techniques in Orthopaedics. 2021;31(4):100906.
4 Ponzio D, Lonner JH. Preoperative Mapping in Unicompartmental Knee Arthroplasty Using Computed Tomography Scans Is Associated with Radiation Exposure and Carries High Cost. The Journal of Arthroplasty. 2015;30(6):964–967.
5 Alrayes MM, Sukeik M. Robotics in total knee replacement: Current use and future implications. World J Orthop. 2024;15(6):489-494.
6 Zhou G, Wang X, Geng X, Li Z, Tian H. Comparison of Alignment Accuracy and Clinical Outcomes between a CT-Based, Saw Cutting Robotic System and a CT-Free, Jig-guided Robotic System for Total Knee Arthroplasty. Orthop Surg. 2024;16(5):1168-1174.
7 Yee DK, Ng JP, Lau CT, et al. Surgical accuracy of image-free versus image-based robotic-assisted total knee arthroplasty. Int J Med Robot. Published online September 6, 2023.
8 Tay ML, Kawaguchi K, Bolam SM, Bayan A, Young SW. Robotic arm-assisted total knee arthroplasty is associated with improved surgical and postoperative outcomes compared with imageless computer navigation: a large single-centre study. Bone Joint J. 2025;107-B(8):804-812.
9 TMINI 1.1 FDA 510(k) Press Release.
10 Bolam, S.M., Tay, M.L., Zaidi, F. et al. Introduction of ROSA robotic-arm system for total knee arthroplasty is associated with a minimal learning curve for operative time. J Exp Orthop. 2022;9:86.
11 Paravath SA, Prasad AAB, Parambil NMT, Gafoor BA, Damsas L, Prince A, et al.(2024). Comparison of surgical times of various total knee replacement techniques and assessment of learning curve of robotic total knee replacement: a retrospective study. International Journal of Research in Orthopaedics. 2024;10(3):606–612.
12 Experience Adopting the TMINI Miniature Robotic System. Under Review for presentation at: Annual Meeting of the American Association of Hip and Knee Surgeons (AAHKS); November 7, 2024; Dallas, USA.
13 D’Amore T, Klein G, Lonner J. The Use of Computerized Tomography Scans in Elective Knee and Hip Arthroplasty-What Do They Tell Us and at What Risk?. Arthroplasty Today. 2022;15:132-138.
14 Health Effects of Ionising Radiation on People. National Environment Agency. Updated June 6, 2024. Accessed October 23, 2025. https://www.nea.gov.sg/our-services/radiation-safety/understanding-radiation/health-effects-of-ionising-radiation-on-people.
15 MKG-24-09 ID-HUB Interactive Brochure.
16 Inabathula A, Semerdzhiev DI, Srinivasan A, Amirouche F, Puri L, Piponov H. Robots on the Stage: A Snapshot of the American Robotic Total Knee Arthroplasty Market. JBJS Open Access. 2024:e24.00063.
17 Brinkman JC, Christopher ZK, Moore ML, Pollock JR, Haglin JM, Bingham JS. Patient Interest in Robotic Total Joint Arthroplasty Is Exponential: A 10-Year Google Trends Analysis. Arthroplasty Today. 2022;15:13-18.
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