Secondary patella resurfacing worked, and worked better the longer you waited

Design

retrospective single-centre cohort from a local arthroplasty register, 2006-2022

Population

182 patients undergoing secondary patella resurfacing after primary TKA; 158 at one year, 143 at two

Primary outcome

Oxford Knee Score, EQ-5D and satisfaction at one and two years

Effect

OKS +6.8 (95% CI 4.7-8.9) at one year and +8.1 (5.9-10.2) at two; satisfaction 79.7% and 85.7%; prior satisfaction with index TKA OR 10.4 (3.10-34.85)

One hundred and eighty-two patients who had secondary patella resurfacing after a primary total knee arthroplasty were followed through a local arthroplasty register over 16 years, with Oxford Knee Score, EQ-5D and satisfaction collected before surgery and at one and two years.

Oxford Knee Score improved by a mean 6.8 points at one year (95% CI 4.7-8.9) and 8.1 at two (5.9-10.2), with EQ-5D gains of 0.174 and 0.187. Satisfaction was 79.7% at one year and 85.7% at two. Two things independently predicted satisfaction: having been satisfied with the original knee replacement (odds ratio 10.4, 95% CI 3.10-34.85 at one year) and a longer interval between the primary and the resurfacing (odds ratio 2.32 per additional year at two years, 1.23-4.38). A 2.5-year cutoff best separated satisfied from unsatisfied patients, though with modest accuracy - sensitivity around 66-71% and specificity around 68-69%. At a median ten years, no knee had been re-revised.

The pattern is clinically coherent and slightly uncomfortable. A patient who was never happy with their knee replacement, and whose anterior knee pain started early, is the patient least likely to be helped by resurfacing the patella - and is exactly the patient most likely to be asking for it. The odds ratio of 10.4 for prior satisfaction is the number to carry into that conversation.

• Ask whether the patient was ever satisfied with the index knee replacement before offering secondary resurfacing
• Note the interval since the primary - anterior knee pain appearing within the first couple of years predicts a worse result from resurfacing
• Exclude infection, malalignment, component malrotation and instability before attributing pain to the unresurfaced patella
• Set expectations against an Oxford Knee Score gain of about 7 to 8 points, not against a normal knee
• Use the reassurance the data do support: no re-revisions at a median of ten years

Why it matters

It identifies, before the operation, the patient for whom secondary resurfacing is least likely to work.

Don't overread it

A single-centre retrospective series with no comparison group - the improvements cannot be separated from the natural course or from the effect of any operation.

The statistics, in plain English

The Oxford Knee Score gains of 6.8 and 8.1 points clear the usual minimal clinically important difference for that score, so this is a real improvement rather than a statistically detectable one. The satisfaction odds ratios are less solid than they look: 10.4 with an interval of 3.10 to 34.85 confirms the direction but says almost nothing about the size, and the 2.5-year cutoff with sensitivity and specificity near 67-70% is barely better than a coin weighted slightly in your favour - it is a discussion aid, not a selection criterion.

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