You are three months into a new post when the department takes delivery of a robotic system. There are two types of trainee in that room. One assumes it will make arthroplasty easier. The other wonders what it means for learning to operate. Both need the same thing: a clear account of what these systems actually do — and what the evidence says they achieve.
The systems in brief
The platforms most commonly encountered in UK orthopaedic practice are Mako (Stryker) and ROSA (Zimmer Biomet). Both are robotic-arm assisted systems — they do not operate independently, but constrain the surgeon’s movements to a preoperatively planned zone, based on CT imaging and patient-specific anatomy.
Mako is used for total hip arthroplasty, total knee arthroplasty, and unicompartmental knee arthroplasty. ROSA is used primarily for TKA and has expanding spine applications. The underlying logic is the same: the robot enforces the plan. The surgeon still makes every incision, handles every instrument, and makes every intraoperative decision outside the constrained resection zone.
This is not autonomous surgery. It is planned surgery with mechanical enforcement of that plan.
What the evidence shows for TKA
The most consistent finding across the literature is that robotic TKA improves component positioning accuracy. A systematic review and meta-analysis from Edinburgh’s Royal Infirmary examined 16 studies and found significantly lower deviation from planned component position in robotic-arm assisted TKA compared with manual TKA — for both femoral and tibial coronal angles (Zhang et al., 2021). Short to mid-term Knee Society Scores also favoured robotic TKA.
The clinical outcome picture is less clear. A 2023 systematic review and meta-analysis of 14 randomised controlled trials found that robotic-assisted mechanically aligned TKA did not produce superior clinical or radiological outcomes overall compared to conventional TKA, and added a mean of 15.3 minutes to operative time (Bensa et al., 2023). An updated meta-analysis of 12 studies including 2,863 patients reached a similar conclusion: more accurate prosthetic alignment, but no better clinical results — and at follow-up beyond six months, conventional TKA showed better Knee Society Score and WOMAC outcomes (Fu et al., 2024).
The pattern is consistent. The robot hits the plan more reliably. Whether hitting the plan more reliably produces a better functioning knee, at the level of what patients report, remains to be convincingly demonstrated.
What the evidence shows for THA
For total hip arthroplasty the primary argument for robotic assistance is cup positioning accuracy — particularly relevant in the context of spinopelvic parameters and dislocation risk. A comparative study of Mako robotic THA versus CT-based navigation using the direct anterior approach found that Mako achieved a mean absolute error in cup inclination of 1.4° versus 2.7° for navigation, with 97.3% of robotic cases within 5 degrees of plan compared to 82.2% for navigation (Okazaki et al., 2024). Clinical outcomes at one year were similar between groups.
The same caveat applies: greater accuracy of execution does not yet translate to demonstrated superiority in patient outcomes at current follow-up lengths.
What this means for trainees
Two things are worth knowing specifically.
First, the learning curve for robotic TKA is shorter than most trainees expect. Zhang et al. (2021) identified an inflection point for proficiency — measured by operating time — of 7 to 11 cases. Critically, there was no learning curve for component positioning accuracy: the robot enforces the plan from case one, regardless of surgical experience. That changes what training on a robotic list actually involves.
Second, the constraint is also the limitation. Because the robot enforces the preoperative plan, trainees get less intraoperative exposure to the decisions that inform that plan — gap balancing feel, intraoperative alignment assessment, responding to unexpected anatomy. These are skills built in conventional surgery that robotic systems, by design, reduce the need for in the moment. What that means for long-term surgical development is the subject of an ongoing debate, which Post 19 will address directly.
For now: the robotic revolution is real in operating theatres. The evidence supports its precision. The evidence for its clinical superiority is not yet there. Understanding that distinction — before you scrub in — is what makes you useful in the room.
For a fuller explanation of how to read AI and robotic surgery evidence claims, see What do we actually mean when we say AI in orthopaedics?
References
- Zhang J, Ndou WS, Ng N, et al. Robotic-arm assisted total knee arthroplasty is associated with improved accuracy and patient reported outcomes: a systematic review and meta-analysis. Knee Surg Sports Traumatol Arthrosc. 2021;30(8):2677–2695. https://doi.org/10.1007/s00167-021-06464-4
- Bensa A, Sangiorgio A, Deabate L, et al. Robotic-assisted mechanically aligned total knee arthroplasty does not lead to better clinical and radiological outcomes when compared to conventional TKA: a systematic review and meta-analysis of randomized controlled trials. Knee Surg Sports Traumatol Arthrosc. 2023;31(11):4680–4691. https://doi.org/10.1007/s00167-023-07458-0
- Fu X, She Y, Jin G, et al. Comparison of robotic-assisted total knee arthroplasty: an updated systematic review and meta-analysis. J Robot Surg. 2024;18(1):292. https://doi.org/10.1007/s11701-024-02045-y
- Okazaki T, Imagama T, Matsuki Y, et al. Accuracy of robotic arm-assisted versus computed tomography-based navigation in total hip arthroplasty using the direct anterior approach: a retrospective study. BMC Musculoskelet Disord. 2024;25(1):787. https://doi.org/10.1186/s12891-024-07891-3
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