Prepared by Dr. Kayahan KARAYTUG
Knee osteoarthritis is an increasingly prevalent condition, particularly among individuals over the age of 45. It significantly impairs quality of life and often necessitates medical or surgical treatment.
While most patients with knee osteoarthritis present with degeneration involving all three compartments of the joint, approximately 20% exhibit isolated disease limited to either the medial or lateral tibiofemoral compartment. Among these, medial compartment osteoarthritis is roughly four times more common than lateral involvement.
In patients with advanced, isolated unicompartmental (Kellgren–Lawrence grade IV) osteoarthritis, unicompartmental knee arthroplasty (UKA) is considered an appropriate and effective surgical option. Compared with total knee arthroplasty (TKA), UKA offers several advantages:
smaller incision and less intraoperative blood loss,
shorter recovery and rehabilitation period,
preservation of more natural knee kinematics,
faster postoperative range-of-motion recovery,
lower risk of infection, and
higher patient satisfaction rates.
However, one of the main limitations of conventional UKA lies in its technical sensitivity. Even minor component malalignment can compromise implant longevity and clinical outcomes. As a result, registry data and meta-analyses have reported shorter survivorship rates for conventional UKA compared to TKA. Furthermore, the learning curve for UKA is longer, and better outcomes have been associated with surgeons whose annual arthroplasty volume includes at least 40% unicompartmental cases.
The Role of Robotic Assistance in Unicompartmental Knee Arthroplasty
To reduce human error and shorten the learning curve, navigation-assisted and robotic-assisted systems have been developed.
Robotic unicompartmental knee arthroplasty (R-UKA) was first introduced in the early 2000s. Over the following decade, refinements in computer-assisted surgical platforms, software precision, and intraoperative feedback systems transformed it into a highly accurate and reliable technique.
In surgical terminology, a system is considered truly robotic if it actively participates in the procedure, rather than serving as a passive navigation tool. Consequently, classifications have been made between non-robotic (navigational), semi-active, and fully active robotic systems.
Commonly used robotic platforms in UKA include:
ACROBOT (The Acrobot Co. Ltd., London, UK)
MAKO System (Stryker, Mahwah, NJ, USA)
NAVIO and CORI® Systems (BlueBelt / Smith & Nephew, Plymouth, MN, USA)
Among these, the MAKO system is the most widely studied and reported in the literature.
Accuracy and Alignment in Robotic-Assisted UKA
Most clinical studies on robotic-assisted surgery (RAS) in UKA evaluate surgical accuracy, component alignment, mechanical axis restoration, and implant positioning across coronal, sagittal, and axial planes. These technical outcomes are also correlated with patient satisfaction and implant survivorship.
Accuracy and Alignment in Robotic-Assisted UKA
Multiple studies have demonstrated that robotic-assisted unicompartmental knee arthroplasty (R-UKA) provides superior accuracy and precision compared with conventional techniques.
Robotic systems achieve more consistent coronal and sagittal alignment, with significantly reduced tibial slope variation and component positioning errors. The rate of coronal alignment deviations greater than 2° is notably lower with robotic assistance.
Furthermore, robotic-assisted procedures demonstrate minimal tibial component overhang, more accurate femoral and tibial placement, and improved restoration of the joint line. While most research supports enhanced mechanical alignment with robotic systems, a few studies have shown similar or slightly variable results, suggesting that accuracy may depend on the specific robotic platform and surgical protocol employed.
Overall, the evidence indicates that robotic assistance increases the precision of implant positioning and alignment, which may contribute to improved early functional outcomes and potentially longer implant survival.
Functional and Clinical Outcomes
Comparative studies between robotic-assisted unicompartmental knee arthroplasty (R-UKA) and conventional techniques have assessed short- and mid-term functional outcomes, pain levels, rehabilitation progress, and overall quality of life. Commonly used evaluation tools include the WOMAC, American Knee Society Score (AKSS), Oxford Knee Score (OKS), SF-12/SF-36, UCLA Activity Score, and International Knee Society (IKS) Score.
Overall, results suggest that robotic-assisted procedures provide equal or superior functional outcomes compared to conventional UKA. Early postoperative assessments often demonstrate higher functional scores, lower pain levels, and quicker recovery in patients undergoing robotic-assisted surgery.
In particular, R-UKA has been associated with:
Improved early postoperative range of motion,
Earlier initiation of physiotherapy, and
Shorter hospital stays compared to conventional surgery.
Patients treated with robotic-assisted techniques also tend to experience less postoperative pain, reduced opioid use, and earlier mobilization, while maintaining comparable safety and alignment outcomes.
Gait analysis studies have indicated that, at one year after surgery, robotic-assisted UKA allows for a more natural knee motion pattern during the early stance phase, whereas conventional procedures may show transient flexion deficits. However, no significant long-term differences have been consistently observed in walking speed or overall gait efficiency.
In summary, the available evidence indicates that robotic-assisted UKA offers enhanced short-term recovery and potentially improved functional performance, with mid-term outcomes comparable to those achieved through conventional techniques.
Implant Survivorship
Long-term outcomes of robotic-assisted unicompartmental knee arthroplasty (R-UKA) are generally promising.
Large multicenter analyses have reported implant survival rates approaching 99% within the first two to three years after surgery, with very low annual revision incidences.
Comparative studies between robotic and conventional UKA have shown similar overall revision rates, but with notable differences in the causes of failure. In conventional procedures, most revisions are attributed to aseptic loosening and component malalignment, whereas such alignment-related failures are rarely observed following robotic-assisted surgery.
Nevertheless, a few investigations have reported higher revision rates in robotic cases, emphasizing that implant survivorship may vary according to patient selection criteria, surgical technique, and the specific robotic system employed.
In summary, the current evidence suggests that robotic assistance provides reliable short- to mid-term implant durability, with potential advantages in minimizing alignment-related complications. However, long-term follow-up data are still required to confirm whether these early benefits translate into superior implant longevity.
Summary of robotic- assisted UKA
Robotic-assisted unicompartmental knee arthroplasty represents a significant technological advancement in orthopedic surgery. It allows surgeons to execute preoperative plans with greater accuracy, optimize implant positioning, and potentially improve early functional outcomes.
Our own clinical experience, in alignment with published evidence, indicates that robotic assistance provides superior radiographic and early functional results compared to conventional methods.
Nevertheless, several studies demonstrate comparable long-term outcomes between the two approaches. Thus, longer-term follow-up data and larger patient cohorts are essential to establish definitive benefits regarding implant survivorship and patient satisfaction.
Finally, it is important to recognize that despite consistent surgical precision, anatomical variations across populations and standardized implant designs may influence long-term functional and radiological outcomes. Continuous innovation and adaptation to patient-specific anatomy will further refine the role of robotics in knee arthroplasty.
