Background
The purpose of this retrospective cohort study was to investigate the influence of parameters of malalignment on knee function 5 years post TKA and, additionally, to explore alterations in patellar height after TKA.
The purpose of this retrospective cohort study was to investigate the influence of parameters of malalignment on knee function 5 years post TKA and, additionally, to explore alterations in patellar height after TKA.
All 661 patients undergoing TKA between 2010 and 2011 were considered for inclusion. Preoperative and 1-year postoperative short-leg radiographs were assessed for malalignment parameters: coronal tibial angle (cTA), sagittal tibial angle (sTA), femoral flexion angle (FFA) and mediolateral tibial mismatch. Patellar height was measured using the modified Insall-Salvati ratio. We determined improvements in knee function utilizing the Knee Society Score (Function score, KSS-F), Oxford Knee Score (OKS) and Algofunctional index (AI). Influences of malalignment parameters were analyzed univariate and selected (p < 0.10) for multivariate linear regression analysis. Inter-observer reproducibility was assessed by test–retest analysis of 30 randomly selected radiographs and calculation of an intra-class correlation coefficient (ICC) for all radiographic parameters.
Three-hundred and four patients were included. Multivariate regression showed degrees of cTA malalignment to be significantly associated with only the KSS-F (β = −3.52). Correction of coronal deformity was stronger associated with knee function (KSS-F β = 2.81; AI β = −0.36). Patellar height was significantly reduced after TKA (1.51 vs 1.44). Decrease of patellar height was weakly associated with the OKS (β = 10.69). ICC scores were: cTA 0.81, sTA 0.57, IS 0.72, FFA 0.75.
Postoperative coronal tibial plate alignment and correction of preoperative coronal deformity are associated with improved knee function 5 years post TKA. Decrease in patellar height was weakly associated with knee function. Short-leg radiography can be a sufficient screening tool for prosthesis alignment.