Can robotics expand the use of unicompartmental knee arthroplasty?

At a Glance 

• Robotics may improve implant positioning and limb alignment in UKA. 
• Robotic systems may help reduce technical barriers and shorten the UKA learning curve. 
• Improved accuracy and survivorship could expand access to UKA for appropriate patients. 

Estimated read time: 6 minutes 

When compared with total knee arthroplasty (TKA), unicompartmental knee arthroplasty (UKA) is less invasive and offers quicker recovery, more natural kinematics, and excellent functional outcomes. UKA is often considered more cost-effective than TKA, although relative cost-effectiveness depends on how cumulative costs are measured. 

While restrictive indications for UKA were proposed by Kozinn and Scott, subsequent studies demonstrated that patients who were excluded by these criteria (on the basis of age, weight, or activity level) would receive greater or at least equal benefit from the procedure. Isolated medial compartment arthritis represents a significant proportion of knee osteoarthritis cases: a recent meta-analysis identified isolated medial compartment disease in 27% of osteoarthritic knees, suggesting UKA could potentially be offered to a considerable share of knee arthroplasty patients.  

Even so, many surgeons follow restrictive indications, while others preferentially offer TKA to all knee arthroplasty patients. The 2025 American Joint Replacement Registry report shows that use of UKA is declining as a share of knee arthroplasties, accounting for less than 5% since 2015. Furthermore, the majority of UKAs (93%) are performed by surgeons who complete 15 or fewer procedures annually. This may be problematic, given evidence linking outcomes to surgical volume in UKA. 

Many authors believe UKA remains substantially underutilized. The increased availability of robotic surgical tools, however, may directly or indirectly address several primary barriers to more frequent UKA use.  

Issue #1: Technical demands of UKA
UKA is technically demanding and leaves less margin for error than TKA: manual instrumentation achieves target component position in fewer than a third of knees, and malalignment has been linked to accelerated wear and early loosening. Robotic surgery directly addresses these challenges by enhancing the accuracy and precision of bone preparation. Multiple studies across multiple robotic platforms, including several randomized controlled trials, clearly show that robotic-assisted UKA (RA-UKA) improves several concrete measures of surgical success, including more accurate implant placement and more faithful restoration of lower-limb alignment relative to the preoperative plan. Not all data are concordant: one randomized trial found no two-year outcome difference between robotic and manual UKA, though it was small. Larger pooled analyses still favor RA-UKA for revision rates. 

Issue #2: Surgeon experience and the learning curve 
The steep learning curve of UKA is reflected in higher rates of error and early revision among low-volume UKA surgeons. This likely creates a self-reinforcing cycle: relatively few surgeons perform enough UKAs to reliably achieve the best results, while less optimal UKA outcomes discourage broader adoption.  

The accuracy and precision of robotic surgery may address this issue directly, improving the outcomes of lower-volume UKA surgeons sufficiently to encourage more patients to seek the procedure and more surgeons to offer it. Recent studies have shown robotics to alleviate the sharp learning curve associated with manual UKA while significantly improving implant placement and limb alignment in the hands of lower-volume UKA surgeons. RA-UKA carries its own learning curve of roughly 11 cases with initially longer operative times, but this is shorter than that of manual UKA, and efficiency improves with experience. 

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Related Content 

• Personalized alignment in UKA: Moving beyond mechanical neutral (AAOS Now) 
• Alignment and Balance Methods in Total Knee Arthroplasty (JAAOS®) 
• Cases Solved! Medial Unicompartmental Knee Arthroplasty (AAOS resource) 

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Issue #3: Survivorship and revision risk 
Concerns around early revision rates and implant survival represent a third barrier to UKA adoption. Because malalignment is a primary driver of UKA failure, enhanced positioning with RA-UKA is expected to improve implant longevity. Studies have demonstrated lower complication and revision rates overall with the use of robotics in UKA, even with surgeons who are less experienced. One prospective cohort showed no reduction in complications at 90 days, though pain and early recovery still favored RA-UKA; even so, longer follow-up analyses show revision risk to be lower with robotics. In these ways, robotics has shown promise in helping surgeons navigate a primary barrier to performing UKA.  

Issue #4: Ease of conversion  
A frequently cited advantage of UKA is preservation of bone stock and the cruciate ligaments. Conversely, asymmetric bone loss and compromise of ligaments can complicate subsequent conversion to TKA when UKA fails, resulting in conversion procedures that more often resemble revision TKA than primary TKA. If the index UKA is performed with minimal bone cuts in target alignment, the extent of bone loss and ligament damage at the time of any conversion surgeries should be minimized, making the occasional conversion to TKA more closely resemble primary TKA.  

Robotics may also help with the conversion procedure. In a matched case-control study, imageless robotic-assisted conversion of UKA to TKA achieved alignment accuracy, implant sizing, bone preservation, and operative times comparable to primary robotic TKA, without the need for augments or increased implant constraint. Thus, the availability of robotic assistance for both UKA and TKA may allow the occasional UKA that ultimately fails to be revised with relative simplicity and reliability, similar to a primary procedure.  

Evolving cost considerations 
The economics are nuanced: RA-UKA carries higher upfront costs compared with manual UKA, but cost modeling suggests these are ultimately offset by better revision rates, with progressively greater savings at higher-volume facilities. While robotics was initially associated with added cost and longer operative times, accumulating data suggest these tradeoffs diminish as systems mature and case volumes grow. In contemporary platform-based adoption, support for UKA is available on existing robotic arthroplasty systems in use for TKA, rather than requiring the purchase of separate robotic platforms for the sole purpose of performing UKA. 

Robotics seems poised to make a positive impact on UKA  
Despite clear advantages for eligible patients, UKA remains underutilized. Concerns around the reliability of outcomes, together with barriers to technical accessibility and surgeon confidence, have prevented surgeons from embracing expanded indications for UKA and offering it to the many patients who could be eligible. The role of robotics in UKA is still evolving, and the literature reflects a mixed perspective on the net benefits.  

Nevertheless, data have clearly shown RA-UKA to improve technical aspects of the operation, including the accuracy and precision of implant positioning, with the potential to help expand the pool of surgeons who can reliably perform and confidently offer access to UKA. In this way, RA-UKA may offer meaningful potential for expanding both access to and the success of UKA for patients with isolated unicompartmental arthritis.  

Hadi Aziz, MD, is a PGY-3 orthopaedic surgery resident at NYU Langone Orthopedics. With research interests in improving outcomes in patients undergoing hip and knee replacements, he aims to pursue a fellowship in adult reconstruction. 

Siddhant Saxena, BS, is a second-year medical student at NYU Grossman School of Medicine with research interests in orthopaedic surgery and leadership in student-run community health organizations. 

Morteza Meftah, MD, is an associate professor of orthopaedic surgery and a member of the Division of Adult Reconstructive Surgery at NYU Langone Orthopedic Hospital, where his clinical and research focus is total and unicompartmental knee arthroplasty, robotic-assisted surgery, personalized alignment, and patient-reported outcomes. 

Matthew Hepinstall MD, FAAOS, is a board-certified orthopaedic hip and knee surgeon with expertise in robot-assisted and less invasive surgical techniques including partial knee replacement and anterior hip replacement. He is an associate professor of orthopaedic surgery at NYU Langone Health in New York. 

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