- Design
- 10-year follow-up of a randomised controlled trial using model-based radiostereometric analysis
- Population
- 50 patients (25 per group) undergoing bicruciate-retaining or cruciate-retaining total knee arthroplasty
- Primary outcome
- maximum total point motion of the tibial component at 10 years
- Effect
- 0.88 mm (95% CI 0.64-1.12) vs 0.64 mm (0.40-0.88); difference -0.23 mm (-0.57 to 0.10); 2 revisions vs 0
Fifty patients randomised to bicruciate-retaining or cruciate-retaining total knee arthroplasty were followed to ten years with model-based radiostereometric analysis, the most sensitive available measure of implant migration. Maximum total point motion of the tibial component was measured at 3 months and at 1, 2, 5 and 10 years.
At ten years the estimated mean migration was 0.88 mm (95% CI 0.64-1.12) in the bicruciate-retaining group and 0.64 mm (0.40-0.88) in the comparator, a between-group difference of -0.23 mm (-0.57 to 0.10). Oxford Knee Score and Forgotten Joint Score trajectories showed no evidence of differing between groups. Two revisions occurred in the bicruciate-retaining arm and none in the cruciate-retaining arm.
With 25 knees per group this trial was never going to settle the question, and the migration difference is both small and imprecise. The revision count is the part that carries weight clinically, not statistically: two against none in fifty patients is consistent with chance, but it points the same way as the wider experience with these implants, which is that the theoretical kinematic advantage of keeping both cruciates has been repeatedly hard to convert into a measurable patient benefit.
The honest summary is that after a decade the promised gain has not appeared and the complication count went the wrong way. For a surgeon considering a bicruciate-retaining implant, this supports treating it as a technically demanding option for carefully selected patients rather than a default, and it gives nothing to justify a switch.
- Do not expect better fixation or better patient-reported outcomes from a bicruciate-retaining implant on this evidence
- Where a bicruciate-retaining implant is used, select carefully and audit your own revision rate
- Counsel patients that the kinematic rationale has not translated into a measurable score advantage at ten years
- Radiostereometric migration at two years remains the best early surrogate for later loosening — read new implant data for it
- Treat two revisions in 25 knees as a signal to watch rather than a rate to quote
Why it matters
A decade is long enough that the absence of the promised benefit is itself the finding.
Don't overread it
Fifty patients cannot exclude a modest difference, and two revisions against none is not a comparison of revision rates.
The statistics, in plain English
The migration difference of -0.23 mm with an interval from -0.57 to +0.10 crosses zero, so no difference was shown; with 25 patients per group the trial could only have detected a large one. The two revisions against none cannot be tested meaningfully at this size — two events is not a rate. Radiostereometric analysis is used in small trials precisely because it measures sub-millimetre migration, which predicts later loosening; a null result on that measure is therefore more informative than a null result on a clinical score would be at this sample size.
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