No differences in objective dynamic instability during acceleration of the knee with or without subjective instability post-total knee arthroplasty

Abstract

Introduction: Instability after total knee arthroplasty is a critical problem. The purpose of this study was to clarify the stability of implanted knees during walking by comparing differences in dynamic instability during knee acceleration between individuals with or without previously experienced subjective instability, as measured by self-reported questionnaire.

Materials and methods: We examined 92 knees with medial pivot implants. Mean patient age and follow-up duration were 78.4 years and 32.8 months, respectively. An accelerometer was used to investigate the accelerations along three axes; that is, vertical (VT), mediolateral (ML), and anteroposterior (AP) directions in 3-dimensional (3D) space. The analysis in the stance phase and gait cycle was performed by: (1) root mean square (RMS) values of acceleration and (2) frequency domain analysis using fast Fourier transformation (FFT). A self-reported knee instability score was used for the subjective feeling of instability.

Results: A total of 76 knees did not feel unstable (group 0), but 16 knees felt unstable (group 1) in patients during activities of daily living. Regarding the RMS, there were no differences in each direction between the groups. For FFT, the cumulative amplitude in the frequency < 30 Hz also showed no significant differences in all directions between the groups during the stance phase (VT, p = 0.335; ML, p = 0.219; AP, p = 0.523) or gait cycle (VT, p = 0.077; ML, p = 0.082; AP, p = 0.499).

Discussion: Gait analysis based on the acceleration data showed that there were no between-group differences in objective dynamic instability during acceleration of the knee, with or without reports of previously experienced subjective instability, as assessed by the self-reported questionnaire.

Fig 1. The summary of self-reported knee instability score.

Fig 2. The average wave patterns of accelerations along three axes, including vertical (VT, positive superiorly), mediolateral (ML, positive medially), and anteroposterior (AP, positive anteriorly) directions between the groups with or without subjective instability, are shown.

The colored range means standard deviation (SD) in all groups.

Fig 3. The average wave patterns of accelerations along three axes, including vertical (VT, positive superiorly), mediolateral (ML, positive medially), and anteroposterior (AP, positive anteriorly) directions among four groups with or without subjective instability in the contralateral or bilateral implanted knees, are shown.

The colored range means standard deviation (SD) in all groups.

Fig 4. The cumulative amplitude in the frequency < 30 Hz in the fast Fourier transform (FFT) between the groups with or without subjective instability is shown.

The colored range means standard deviation (SD) in all groups.

Fig 5. The cumulative amplitude in the frequency < 30 Hz in the fast Fourier transform (FFT) among four groups with or without subjective instability in the contralateral or bilateral implanted knees is shown.

The colored range means standard deviation (SD) in all groups.