- Design
- Retrospective multicentre cohort, exploratory analysis
- Population
- 297 patients having primary robotic-assisted knee replacement
- Primary outcome
- Oxford Knee Score change at 3, 6 and 12 months by CPAK change
- Effect
- Smaller 3- and 6-month gains after moving two phenotypes (n = 19) or LDFA change >4°
A retrospective multicentre cohort of 297 robotic-assisted knee replacements classified each knee by Coronal Plane Alignment of the Knee (CPAK) phenotype before and after surgery, and tracked Oxford Knee Scores.
About 31% stayed in the same phenotype, 62% moved one and 6% (19 patients) moved two. Those who moved two had smaller Oxford score gains at three and six months than those who stayed the same. Changing the lateral distal femoral angle by more than 4° from native was associated with the smallest early gains, more than equivalent tibial changes.
This supports alignment strategies that respect the patient's native phenotype, especially on the femoral side. The two-phenotype group was very small and one-year outcomes were not reported as different, so it is an early signal.
- Classify each knee's CPAK phenotype from long-leg radiographs before planning alignment.
- Avoid moving a knee across two CPAK phenotypes where the implant plan allows.
- Keep femoral coronal correction within about 4° of native where feasible.
- Track early Oxford Knee Scores to see whether alignment choices affect your own patients' recovery.
Why it matters
It adds early functional data to the debate over mechanical versus more personalised alignment.
Don't overread it
The two-phenotype group had only 19 patients; this is an exploratory, early-outcome finding.
The statistics, in plain English
The comparison rests on a small subgroup, so a chance finding is possible. Differences at three and six months that do not persist to one year may matter to patients' early recovery without changing the final result.
Read the rest in the app
You have read your two free briefings this month. The app carries all 27 specialties, every morning, free — and this finding is waiting in it.
Scan to keep reading on your phone. No account needed to start.
Tomorrow morning, before your first patient
One edition a day for orthopaedics, written by the desk, every claim tied to its paper. Six minutes.
Get the app — free