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Tomasz Poboży

Robotic unicompartmental knee arthroplasty: greater precision, but better outcomes?

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Tomasz Poboży

Polish version: Robot w endoprotezie częściowej kolana — większa precyzja, ale czy lepszy wynik?

A randomized trial published around August–September 2026 found that robotic unicompartmental knee arthroplasty more accurately reproduced planned component positioning and improved some early recovery measures. At 2 years, however, Oxford Knee Score, KOOS and WOMAC did not favour robotics. Technical precision does not automatically translate into better patient-reported outcomes.

Why this study matters

Positioning, soft-tissue balance and joint mechanics are particularly important in unicompartmental arthroplasty. The key clinical question is whether more accurate execution improves function, pain and durability. Kayani and colleagues’ prospective randomized trial in The Bone & Joint Journal compared conventional jig-based surgery with navigation control against robotic-arm assistance for medial compartment osteoarthritis.

Study design

The interim analysis included 107 patients: 52 assigned to conventional surgery with navigation control and 55 to robotic surgery. Both groups used CT-based planning, a medial parapatellar approach and standardised postoperative care. Follow-up extended to 2 years. The published protocol planned 140 patients, so this report concerns an interim cohort.

The authors described a double-blind trial. Patients and clinical assessors were intended to remain masked, but complete radiographic masking was impossible because different implants were used: Oxford UKA and Mako/RESTORIS.

Main results

  • Robotic surgery more accurately achieved planned femoral and tibial positioning (both P < 0.001).
  • Inpatient pain was lower (P < 0.001).
  • Inpatient opioid use was lower (P = 0.008).
  • Hospital stay was shorter (P = 0.004).
  • At 2 years, there were no significant differences in Oxford Knee Score (P = 0.299), KOOS (P = 0.261) or WOMAC (P = 0.281).
  • Forgotten Joint Score, reflecting awareness of the operated joint in daily life, favoured robotics at 6 months (P = 0.002) and 2 years (P = 0.021).

Clinical interpretation for an orthopaedic surgeon

The most secure conclusion is improved execution of the surgical plan. Early pain, opioid and length-of-stay findings are also of interest, but do not establish faster complete recovery. Care organisation, rehabilitation, team experience and implant design can affect those outcomes.

The FJS advantage may reflect a subtler difference in joint awareness that other questionnaires missed. It requires confirmation after full recruitment and in other centres, particularly given the absence of differences in three widely used scales at 2 years.

Limitations and funding

  • This was an interim analysis of 107 rather than the planned 140 patients.
  • Recruitment slowed as more patients preferred robotics and surgeons reported diminishing equipoise, potentially affecting completion as planned.
  • The study came from one highly specialised centre.
  • Different implant designs prevent complete separation of robotic and implant effects.
  • Two years is too short to establish long-term durability or late revision risk.
  • The trial protocol was funded by Stryker Limited, a relevant consideration when assessing independence.

Implications for practice

Robotics may improve reproducibility and some early outcomes, with a signal of better FJS. The trial does not establish clinical superiority for every patient, fewer revisions, longer implant survival or economic benefit. Appropriate indications, surgeon experience, implant selection and soft-tissue balance remain central.

References

  1. Kayani B, Fontalis A, Tahmassebi J, et al. A prospective double-blinded randomized controlled trial comparing conventional jig-based versus robotic arm-assisted medial unicompartmental knee arthroplasty. Bone Joint J. 2026;108-B(9):1113-1120. DOI: 10.1302/0301-620X.108B9.BJJ-2025-1481.R1. PMID: 42674575.
  2. Kayani B, Konan S, Tahmassebi J, Ayuob A, Moriarty PD, Haddad FS. Robotic-arm assisted medial unicondylar knee arthroplasty versus jig-based unicompartmental knee arthroplasty with navigation control: study protocol for a prospective randomised controlled trial. Trials. 2020;21:706. DOI: 10.1186/s13063-020-04631-5.

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Content prepared by: Tomasz Poboży - orthopaedic surgeon.

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