Unicompartmental knee arthroplasty after failed high tibial osteotomy in appropriately selected patients: a systematic review and meta-analysis
Arthroplasty (London, England) · 2026
UKA after a failed HTO isn't ruled out, but the evidence against or for it versus TKA is too thin and indirect to guide the decision yet.
The paper
Systematic review and meta-analysis (Level III evidence), 41 studies (6 UKA-only, 33 TKA-only, 2 comparative) covering 226 UKA knees and over 6200 TKA knees in patients converting from a failed high tibial osteotomy.
What they found
Pooled revision was higher after UKA than TKA (10.2%, 95% CI 4.5-21.6% vs 5.0%, 95% CI 3.5-7.2%), as were reoperation (14.4% vs 11.1%) and PJI (0-3.3% vs 2.9%); KSS improvement ranged 34.1-38.8 points for UKA versus 25.0-57.0 for TKA. The only two direct comparative studies found no significant difference in survivorship or function.
Study design
Systematic review and meta-analysis of 41 studies (6 UKA-only, 33 TKA-only, 2 comparative, Level III) in patients having UKA or TKA after a previously failed HTO. Because almost all studies examined only one implant, the UKA vs TKA comparison is indirect, built from separate single-arm pools rather than within-study contrasts.
Methodology
Four databases were searched to August 2025, but the pooled evidence is almost entirely retrospective cohorts and case series rather than RCTs, so selection bias (surgeons publishing favourable series) and publication bias are real concerns. Heterogeneity was substantial to severe for the key estimates (I2 61.6% for UKA revision, 79.5-92.8% for TKA revision/reoperation), meaning the pooled percentages mask very different surgical eras, patient selection, and follow-up lengths. With only 2 of 41 studies directly comparing the two procedures, any apparent gap in revision rate could reflect case-mix (UKA reserved for simpler knees) rather than a true difference in implant performance.
The appraisal
The numerically higher UKA revision and reoperation rates are statistically imprecise (wide, overlapping CIs) and derive from an indirect, between-study comparison, so this is not evidence that UKA performs worse than TKA after failed HTO, as the authors themselves caution. Heterogeneity is substantial on both sides, not just the small UKA group: I2 61.6% for UKA revision, and even higher for TKA (I2 79.5% for revision, 92.8% for reoperation). That means the TKA 'default' comparator numbers are themselves unstable pooled estimates across very mixed study populations, so this isn't simply a small-sample problem for UKA versus a solid number for TKA, both are soft. The post-2020 subgroup (6.3% vs 3.9% revision) hints the gap may be narrowing with modern technique, which is the more clinically interesting signal, but it is exploratory, unadjusted, and based on very few events.
The gap
There is no adequately powered, prospective, directly comparative study; the entire UKA-after-HTO literature amounts to 226 knees across six small, heterogeneous case series, so the 10.2% pooled revision estimate is fragile.
Landmark context
This builds on the established convention that TKA is the default salvage after failed HTO, and extends a growing but still small body of cohort data questioning whether modern UKA implants change that calculus. There is no single landmark RCT underpinning this question; the evidence base remains registry and case-series data.
What to do Monday
Not practice changing yet. TKA stays the default conversion procedure after failed HTO; UKA can be considered in carefully selected patients (isolated medial disease, intact MCL, acceptable residual alignment) where the surgeon has specific expertise, but patients should be told the comparative evidence is weak and mostly indirect. Since lateral compartment OA progression is the leading cause of UKA revision in this group, confirming a healthy lateral compartment preoperatively, and keeping a lower threshold for investigating new lateral-sided knee pain postoperatively, matters more here than in primary (non-HTO) UKA.
In practice
This is an orthopedic-surgeon decision paper more than a clinic-floor one, but it changes what physios and S&C coaches should expect and watch for in the subset of patients who've had an HTO and are now being converted. In the clinic: if your post-HTO patient ends up with a UKA rather than TKA, don't assume it behaves like a routine primary UKA, build in longer-term surveillance for lateral joint line pain and swelling (the leading UKA failure mode here) rather than assuming the faster early recovery UKA usually offers means lower long-term risk. On the S&C side, for the physically active post-HTO patients this population skews younger and more active than typical arthroplasty candidates, so return-to-loading and return-to-running progressions after UKA conversion should stay conservative and criterion-based rather than time-based, given the meaningfully higher revision signal even if the confidence intervals are wide. The caveat in applying this: don't let a surgeon's choice of UKA versus TKA change your rehab expectations wholesale, the two direct comparative studies found no real difference in function, so day-to-day rehab progression and goals should look similar regardless of which implant was used.
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