Which osteoarthritic gait features recover following total knee replacement surgery?

Abstract

Background: Gait analysis can be used to measure variations in joint function in patients with knee osteoarthritis (OA), and is useful when observing longitudinal biomechanical changes following Total Knee Replacement (TKR) surgery. The Cardiff Classifier is an objective classification tool applied previously to examine the extent of biomechanical recovery following TKR. In this study, it is further developed to reveal the salient features that contribute to recovery towards healthy function.

Methods: Gait analysis was performed on 30 patients before and after TKR surgery, and 30 healthy controls. Median TKR follow-up time was 13 months. The combined application of principal component analysis (PCA) and the Cardiff Classifier defined 18 biomechanical features that discriminated OA from healthy gait. Statistical analysis tested whether these features were affected by TKR surgery and, if so, whether they recovered to values found for the controls.

Results: The Cardiff Classifier successfully discriminated between OA and healthy gait in all 60 cases. Of the 18 discriminatory features, only six (33%) were significantly affected by surgery, including features in all three planes of the ground reaction force (p<0.001), ankle dorsiflexion moment (p<0.001), hip adduction moment (p = 0.003), and transverse hip angle (p = 0.007). All but two (89%) of these features remained significantly different to those of the control group after surgery.

Conclusions: This approach was able to discriminate gait biomechanics associated with knee OA. The ground reaction force provided the strongest discriminatory features. Despite increased gait velocity and improvements in self-reported pain and function, which would normally be clinical indicators of recovery, the majority of features were not affected by TKR surgery. This TKR cohort retained pre-operative gait patterns; reduced sagittal hip and knee moments, decreased knee flexion, increased hip flexion, and reduced hip adduction. The changes that were associated with surgery were predominantly found at the ankle and hip, rather than at the knee.

Fig 1. Simplex plot of the classification of the 30 NP (blue circle) and 30 pre-TKR (red cross) subjects which were used to train the Cardiff Classifier on the biomechanical features of severe osteoarthritic gait.

The three vertices represent the points where belief of non-pathological function B(NP), belief of osteoarthritic function B(OA) and uncertainty, U is equal to 1 (or 100%). The decision boundary where B(OA) = B(NP) is shown as a dashed line. The boundaries where B(OA) = 0.5 and B(NP) = 0.5 are shown as interior solid lines.

Fig 2. Exemplar PC reconstruction using the first three principal components (PCs) of the knee flexion waveforms during the gait cycle.

The mean and ±1 STD waveforms of 30 non-pathological (NP) and 30 osteoarthritic (OA) subjects are plotted for individual reconstructions of the first three principal components (PC1-3). The exemplar waveforms and intended to demonstrate how different PCs represent different modes of variation across the waveforms. For example, PC1 reconstructs variation in magnitude of knee flexion during stance phase which isn’t discriminatory of OA gait. The reconstruction using PC2 highlights that this component represents changes in range of motion throughout the stance phase of gait, which is related to a reduced and delayed peak knee flexion during swing phase. The third PC reconstructs only 13% of variance of all the waveforms–primarily representing differences during terminal swing phase of gait.

Fig 3. Simplex plot of the change in classification of the 30 TKR subjects between pre- and post-operative visits.

The three vertices represent the points where belief of non-pathological function B(NP), belief of osteoarthritic function B(OA) and uncertainty, U is equal to 1 (or 100%). The decision boundary where B(OA) = B(NP) is shown as a dashed line. The boundaries where B(OA) = 0.5 and B(NP) = 0.5 are shown as interior solid lines. The purple arrows represent the change in the body of evidence for each subject from the pre-operative visit (arrow tail), to the post-operative visit (arrow head).