Midflexion Instability in Primary Total Knee Arthroplasty

Instability is one of the most common causes of failure in total knee arthroplasty. Traditionally, it has been classified into three types: extension instability, flexion instability, and hyperextension instability. More recently, a fourth type of instability has been proposed, namely “midflexion instability” (MFI). Whether MFI is distinct from the aforementioned types of instability is contentious, and at present, the condition is yet to be clearly defined. This article reviews the current literature and identifies the best available evidence relevant to the concept of MFI. Our aim is to present an overview of the proposed causes and mechanisms for MFI. By doing so, we also aim to provide a focus on how MFI presents, whether it is indeed a discrete form of instability, and if it influences clinical results.

Factors Contributing to Patient Satisfaction and Expectations following Computer-Assisted Total Knee Arthroplasty

The purpose of this study was to determine which factors contribute to patient satisfaction and expectations after total knee arthroplasty (TKA). A total of 109 patients (130 knees) with knee osteoarthritis who underwent primary TKA with navigation were studied. Intraoperative mediolateral laxity was measured. The factors including mediolateral laxity that affected patient satisfaction and expectations were evaluated using the 2011 Knee Society Score. Patient satisfaction after TKA correlated positively with symptoms and functional activities, and negatively with old age in univariate analysis. Multivariate analysis showed that symptoms and functional activities remained statistically significant; however, old age showed no difference. Patient expectations after TKA correlated positively with symptoms and functional activities, and negatively with mediolateral laxity at 60 degrees in univariate analysis. Multivariate analysis showed that symptoms, functional activities, and mediolateral laxity at 60 degrees remained statistically significant. In conclusion, midflexion instability was associated with worse expectations.