Robotic unicompartmental knees were more accurate and recovered faster, but scored the same at two years

Design

Double-blinded randomised controlled trial, interim analysis

Population

107 patients with medial compartment knee osteoarthritis

Primary outcome

Component position accuracy, early recovery and patient-reported outcomes

Effect

Better accuracy (P < .001) and shorter stay (P = .004); Oxford Knee Score at 2 years P = .299

An interim report of a double-blinded randomised trial in The Bone & Joint Journal (1 September 2026) compared conventional jig-based with robotic arm-assisted medial unicompartmental knee replacement in 107 patients with medial compartment osteoarthritis, all planned on CT.

The robotic arm placed femoral and tibial components closer to plan. It was associated with less inpatient pain, less opioid use and a shorter stay. At two years, Oxford Knee, KOOS and WOMAC scores did not differ. The Forgotten Joint Score, a measure of how often patients are aware of the knee, was better with the robot at six months and two years.

This is an interim analysis from a single high-volume group, and recruitment fell as patients and surgeons came to prefer the robot. The trial cannot yet say whether accuracy translates into longer implant survival, which is the reason most surgeons would pay for it.

• Expect easier early recovery with robotic unicompartmental knee replacement, not better two-year function scores.
• Do not promise longer implant survival with the robot; that is not yet shown.
• Weigh the cost of robotic surgery against an early-recovery benefit when counselling patients who pay.
• Audit component position and early outcomes whichever technique you use.

Why it matters

It separates what the robot reliably delivers, precision and a quicker start, from what it has not yet shown.

Don't overread it

These are interim results from one group; implant survival has not been compared.

The statistics, in plain English

Several outcomes reached significance, but the main patient-reported scores did not differ at two years. When many outcomes are tested, one or two will look different by chance, which is a reason to weight the Forgotten Joint Score result less than the null main scores.

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