Summary

Analysis of predictors for a higher-constrained total knee arthroplasty was performed in a retrospective single-center analysis of 1062 knees. Increasing coronal deformity, tibiofemoral subluxation and more severe bone defects are predictive for the use of a higher-constrained TKA in the primary setting.

Abstract

Background

In primary total knee arthroplasty (TKA), the preoperative assessment of knee stability and the need for a higher-constrained TKA remains challenging. The aim of the study was to (1) analyze risk factors for the use of a higher-constrained TKA and to (2) assess functional outcome.

Methods

Retrospective single-center analysis of 903 consecutive patients (n=1062 knees) that underwent a primary TKA using a patient-specific instrumentation system allowing intraoperative crossover to a higher-constrained TKA between 2015 and 2020 was conducted. Radiographic (hip-knee-ankle angle (HKA), joint line convergence angle (JLCA), coronal tibiofemoral (TF)-subluxation and bone defects) and demographic predictors (age, sex, and body-mass index (BMI)) for the use of a higher-constrained TKA were analyzed. Knee society score (KSS) and revision rates were assessed.

Results

In 77 out of 1062 knees (7.3%) an intraoperative crossover to a higher-constrained TKA was performed, resulting in 15 semi-constrained and 62 hinged TKAs. In varus knees, HKA (cut-off: <167.3°, OR: 10.0, 95% CI: 4.7-21.4; p<0.001), TF-subluxation (cut-off: >7.5 mm, OR: 5.4; 95% CI: 2.7-11.0; p<0.001) and bone defect (cut-off: ≥Grade 1, OR: 6.9 ;95% CI: 3.2-14.9; p<0.001) were significant preoperative risk factors for an intraoperative crossover. For valgus knees, HKA (cut-off: >193.8°, OR: 14.3; 95% CI: 7.0-29.4; p<0.001) and TF-subluxation (cut-off: >7.3 mm, OR: 3.5; 95% CI: 1.6-7.5; p<0.001) remained significant risk factors. The revision rate and KSS scores did not differ between primary and higher-constrained TKAs 1 year postoperatively.

Conclusion

Increasing coronal deformity, tibiofemoral subluxation and more severe bone defects are predictive for the use of a higher-constrained TKA in the primary setting. The identified risk factors allow for a more precise surgical planning and anticipation of the use for a higher-constrained TKA. Crossover to a higher-constrained TKA does not impair functional outcome or increase complications in the short term.