The influence of the number of postoperative radiological outliers on the survival and clinical outcome of total knee arthroplasty.

Introduction: After total knee arthroplasty (TKA), dissatisfaction rates are described up to 30 %. Optimal alignment of the prosthesis in TKA is believed to improve clinical outcome and survival rates. Radiological outliers after TKA are used to define this alignment. Limited evidence is available on the cumulative effect of these outliers on survival or clinical outcome. The purpose of this study is to assess whether the amount of postoperative femoral and/or tibial radiological outliers, measured in different planes, influences the survival and clinical outcome after TKA.

Methods: Prospective data were used from a previously published randomized trial, with a mean follow-up of 5-years after surgery. Data of 168 patients who received TKA were assessed. Patients were divided into four groups: 0, 1, 2 or ≥3 postoperative radiological outliers of the femoral and/or tibial component in different planes (e.g. frontal, sagittal). Revision rates were analysed and clinical outcome was assessed using PROMs. The study used a general linear model for repeated measures to compare the difference of each questionnaire over time between the groups.

Results: No statistically significant differences were found between patients with 0, 1, 2 or ≥3 outliers regarding improvement of postoperative PROMs. Data was underpowered to detect a possible relationship between the number of outliers and the survival of the prosthesis.

Conclusion: The number of postoperative radiological outliers did not influence clinical outcome after TKA. High-powered studies are needed to examine the influence of these outliers on survival rates.