Background: Prostheses with varus-valgus constraint (VVC) are increasingly utilized in primary total knee arthroplasty (TKA) to address coronal malalignment and instability though little is known regarding the association between added constraint and aseptic loosening. We sought to systematically review the literature for reports of VVC in primary TKA and meta-analyze clinical results and implant survival.
Methods: PubMed was searched using broad terms to identify articles reporting VVC in primary TKA. Any article reporting clinical or survival outcomes was included. Clinical scores, close to 2 years postoperatively were converted to standardized mean differences, and the latest survival estimates were weighted using the inverse of their variance and meta-analyzed.
Results: Three hundred ninety-two search results were reviewed identifying 30 relevant articles reporting on 3620 knees in total. The estimate for the improvement in clinical scores postoperatively was 3.1 standard deviations (95% confidence interval 2.6-3.6). The estimate for implant revision slowly increased from 1% at 2 years to 2% at 6 years and then began to increase more rapidly beyond this point. The estimated revision rate was 9% by 12 years and 28% by 20 years. This revision rate estimate was stable with and without the inclusion of outlying studies.
Conclusion: VVC in primary TKA is associated with significant clinical improvement without significant risk of early failure. Meta-regression estimates raise concerns for significant revision risk with extended follow-up, especially beyond 5 years. In the absence of new data, VVC should continue to be used cautiously in the primary TKA.
Keywords: arthroplasty, replacement, knee; constrained total knee arthroplasty; joint deformities, acquired; joint instability; meta-analysis; prosthesis failure.
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