## 2 Materials and Methods
### Surgery and Postoperative Rehabilitation  
All TKA surgeries were performed by the same surgeon or first assistant (A.K.). A midline longitudinal skin incision was made, and the medial parapatellar approach was used. The distal femoral cut was set at a 6\({}^{\circ}\) valgus angle with an intramedullary alignment rod, and the tibia was cut 90\({}^{\circ}\) from the mechanical axis, using an intramedullary rod. The ACL was removed in all cases, and the PCL was removed in highly degenerative cases. The flexion and extension gaps were determined using the measured resection technique. In all cases, the knee could bend from 0\({}^{\circ}\) of extension to 110\({}^{\circ}\) of flexion during surgery. Depending on the degree of cartilage damage and deformation, the patella was either resected or replaced. In all cases, patellar tracking was good, and lateral release was not required. Rehabilitation was initiated immediately after surgery using the same protocol, including range-of-motion training and full-weight-bearing walking training, with pain control.  
The STS movement was analysed by synchronising a three-dimensional motion analysis device (Vicon MX; Vicon Motion System Inc., Oxford, UK), a floor force plate (AccuGait; AMTI Inc., Watertown, NY, USA), and wireless surface electromyography (Trigno Lab; Delsys, Inc., Boston, MA, USA). The STS movement was performed by adjusting the height of the chair such that the knee joint was flexed to 90\({}^{\circ}\) and aligning the rotation of the knee and ankle joints to ground, with both feet on the floor force plate. Both hands were fixed in a position adjacent to the iliac crest, and the patients performed three STS movements at their comfortable speed (Figure 2).  
Sixteen infrared cameras (MX-T20; Vicon Motion System Inc., Oxford, UK) were used, and the sampling frequency was set at 100 Hz. Fourteen-millimetre infrared reflection markers were affixed at 40 points, in accordance with the Plug-in Gait model [25]. The force plate measured the ground reaction force at a sampling frequency of 1000 Hz when in contact with the ground. Surface electromyography was used to measure the muscle activity at six locations on each lower limb (vastus medialis, rectus femoris, vastus lateralis, semitendinosus, biceps femoris, and gluteus medius) during the STS movement, at a sampling frequency of 2000 Hz. Electrode placement for the surface electromyography was performed as previously described [43]. Before measuring the motion, the maximum voluntary isometric contraction (MVC) during knee flexion, extension, and hip abduction was measured.  
\begin{table}
\begin{tabular}{l c c c} \hline \hline  & **Group I** & **Group II** & \\  & \(n\) = **10** & \(n\) = **10** & _p_-Value** \\ \hline Age (years) & 69.4 \(\pm\) 5.3 & 70.3 \(\pm\) 6.8 & 0.76 \\ Sex (male/female) & 2/8 & 3/7 & \\ Side (right/left) & 5/5 & 6/4 & \\ Height (m) & 1.54 \(\pm\) 0.06 & 1.56 \(\pm\) 0.08 & 0.56 \\ Body mass index (kg/m\({}^{2}\)) & 23.3 \(\pm\) 3.9 & 25.0 \(\pm\) 1.8 & 0.26 \\ Postoperative time (months) & 14.1 \(\pm\) 6.8 & 16.7 \(\pm\) 5.8 & 0.4 \\ ROM (\({}^{\circ}\)) & & & \\ Flexion & 124.3 \(\pm\) 9.7 & 126.5 \(\pm\) 6.0 & 0.57 \\ Extension & \(-\)0.5 \(\pm\) 1.0 & \(-\)0.9 \(\pm\) 1.1 & 0.44 \\ Preoperative tibofemoral X-ray & 183.2 \(\pm\) 4.6 & 179 \(\pm\) 11.6 & 0.33 \\ Tibofemoral X-ray axis (\({}^{\circ}\)) & 176.1 \(\pm\) 1.6 & 175.3 \(\pm\) 2.9 & 0.47 \\ KOOS & & & \\ Symptoms & 83.9 \(\pm\) 9.2 & 82.1 \(\pm\) 8.5 & 0.67 \\ Pain & 86.1 \(\pm\) 9.8 & 83.9 \(\pm\) 14.9 & 0.71 \\ ADL & 88.8 \(\pm\) 8.5 & 87.5 \(\pm\) 8.5 & 0.74 \\ Sport & 67 \(\pm\) 22.2 & 50.5 \(\pm\) 19.9 & 0.11 \\ QOL & 76.3 \(\pm\) 12.1 & 70.6 \(\pm\) 14.5 & 0.38 \\ \hline \hline \end{tabular} Data are expressed as average \(\pm\) standard deviation. ROM, range of motion; KOOS, Knee injury and Osteoarthritis Outcome Score; ADL, activities of daily living; QOL, quality of life.  
\end{table}
Table 1: Patients’ demographic data.