## 4 Discussion
\begin{table}
\begin{tabular}{l c c c c} \hline \hline
**Parameter** & **NTKR (_n= 17_)** & **TKR (_n = 14_)** & \(p\) & **t** \\ \hline \multicolumn{5}{c}{Injured limb tripped} \\ \hline CL knee range of flexion–extension * & 101.6 (11.7–408.2) & 80.2 (5.0–443.2) & 0.958 & \(-\)0.053 \\ OA knee range of flexion–extension & \(-\)7.8 (41.3) & \(-\)5.9 (39.9) & 0.011 & \(-\)0.988 \\ Maximal OA ankle plantar flexion & \(-\)34.0 (36.5) & \(-\)35.9 (17.2) & 0.049 & \(-\)0.157 \\ Maximal CL ankle plantar flexion * & 4.1 (\(-\)19.7–61.3) & 6.7 (\(-\)9.0–89.9) & 0.770 & \(-\)0.293 \\ \hline \hline \end{tabular} Abbreviations: OA = osteoarthritis; CL = contralateral; TKR = total knee replacement; and NTKR = no TKR * As the data were not normally distributed, values are shown as the median and interquartile percentage, and the Mann–Whitney test was used (Z value is presented instead of _t_).  
\end{table} 
Table 3: \(Cont.\)group, but not in the NTKR group, may be the key to clinical improvement of gait velocity and functionality in the TKR group. Two significant differences were found following the perturbation of the OA limb: more NTKR subjects decreased their OA knee flexion-extension range but more TKR subjects decreased their maximal ankle plantar flexion. These findings suggest that the kinematics of the NTKR group move away from the perturbation recovery strategy of healthy adults [23]. Conversely, the recovery strategy of the TKR group trends towards the recovery strategy of healthy adults [23]. The differences in change in recovery strategies of both groups in regards to that of healthy adults [23] might be explained by muscle weakness or joint stiffness around the knee due to the OA or secondary to surgery. Furthermore, the decrease in maximal ankle plantar flexion might result from co-contraction of the Gastrocnemius and Tibialis anterior before the initial contact of the perturbed limb which limits balance recovery, thereby increasing the risk of falling. Individuals after TKA rely on the non-operated limb, thereby exhibiting asymmetrical gait [46]. This was evident as TKR subjects decreased their OA hip extension when the CL limb was perturbed. This might result from latent activation of the muscles surrounding the knee or adjacent joints. Another explanation for the non-normal recovery strategy is the loss of proprioception due to OA [34] or the artificial prosthesis. Although the surgery aims to correct joint alignment [48], it is unable to compensate for proprioception insufficiencies and might lead to difficulties in responding to perturbation. These explanations were previously mentioned in literature concerning the dynamic balance during gait in individuals post-TKR [29; 49]. The study limitations include, firstly, the small single-center sample size that might not generalize for the entire OA population. Secondly, a learning effect might have been introduced following the first perturbation. Finally, we did not monitor ground reaction forces that might have added to our understanding of the response to perturbation. To conclude, although the surgery was successful in reducing pain and increasing functionality, individuals following TKR exhibited asymmetrical gait and unique compensatory strategies in response to perturbation. These findings might suggest that balance deficits remain in individuals following TKR and therefore are associated with the risk of falls. It might therefore be hypothesized that an optimal rehabilitation program following TKR that includes gait balance exercises will improve gait symmetry, balance recovery after perturbation, and reduce falls. Conceptualization, V.E., L.K. and S.P. ; methodology, V.E., L.K., D.R., I.S. and S.P. ; software, V.E. and S.P. ; validation, V.E. and S.P. ; formal analysis, V.E. and S.P. ; investigation, V.E. and S.P. ; resources, I.S., L.K., A.G. and R.G. ; data curation, V.E. ; writing--original draft preparation, V.E. and S.P. ; writing--review and editing, V.E., L.K., D.R., I.S. and S.P. ; visualization, V.E. and S.P. ; supervision, S.P. and D.R.