A prospective double-blind randomised trial compared conventional jig-based with robotic arm-assisted medial unicompartmental knee arthroplasty.
Robotic assistance improved accuracy of planned femoral and tibial component positioning (both p<0.001), reduced inpatient pain scores (p<0.001) and opioid consumption (p=0.008), and shortened hospital stay (p=0.004). Forgotten Joint Score was better at six months (p=0.002) and two years (p=0.021).
But the three conventional outcome measures — Oxford Knee Score, KOOS and WOMAC — showed no difference at two years (p=0.299, 0.261, 0.281). So the picture is faster early recovery and a better sense of the knee being unnoticed, without a difference on the scales that guide most arthroplasty decisions.
The methodological note the authors include is unusual and worth reading. Recruitment declined during the trial as more eligible patients expressed a preference for the robotic arm, and operating surgeons experienced reduced clinical equipoise. That is a threat to the trial's completion and a data point about adoption: the technology became difficult to randomise against before the evidence settled whether it should have.
- Interim results — the trial did not complete recruitment as planned
- Oxford Knee Score, KOOS and WOMAC all null at two years
- Forgotten Joint Score, a more sensitive measure, favoured robotic
- Shorter stay and less opioid use are real system-level benefits
- Loss of equipoise is itself a finding about how the technology spread
The statistics, in plain English
When a trial reports significance on some outcome measures and not others in the same domain, the sensitivity of each scale matters. The Forgotten Joint Score is designed to detect differences among patients who are already doing well, where Oxford and WOMAC have ceiling effects. That pattern — sensitive measure positive, established measures null — is compatible with a small real difference and with a chance finding.
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