## 2 Materials and Methods  
The study enrolled 20 patients (10 males and 10 females) with MRI-confirmed complete ACL rupture and 20 healthy subjects as control (Table 1). The mean age of the patients was 34.2 years, ranging from 16 to 56 years. The clinical manifestations included seven cases of instability alone, seven cases of instability and discomfort, and six cases of pain. Instability was present in a total of 14 cases. The mean time from knee joint injury to ACL surgical reconstruction was five months. Promptly after injury, the knee joint was immobilized for a period of 1-3 weeks (depending on the injury severity and concomitant disorders). After the surgical reconstruction, a hinged knee orthosis was applied. Rehabilitation included knee flexion to 90 degrees (later adding full flexion, for two weeks) and walking with additional support from the first days after surgery, followed by expansion of the motion regimen and removal of the orthosis. Exercise therapy sessions also started from the first day after surgery. The control group included 20 healthy adult subjects (14 males and 6 females). Their mean age was 29.7 years. The study was conducted according to the principles of the Declaration of Helsinki \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Parameter** & **Assessment** & \begin{tabular}{c} **Number of** \\ **Assessed Subjects** \\ \end{tabular} & \begin{tabular}{c} **Time Point of** \\ **Assessment** \\ \end{tabular} & \begin{tabular}{c} **Male/Female** \\ **Years** \\ \end{tabular} & \begin{tabular}{c} **Mean Age,** \\ **Years** \\ \end{tabular} \\ \hline \multirow{4}{*}{Patients} & 1 & 20 & Before surgery & 10/10 & 34.2 \\ \cline{2-6}  & 2 & 20 & \begin{tabular}{c} Three months \\ after surgery \\ \end{tabular} & 10/10 & 34.2 \\ \cline{2-6}  & 3 & 12 & \
\begin{tabular}{c} 12 months after \\ surgery \\ \end{tabular} & 7/5 & 35.2 \\ \hline
\begin{tabular}{c} Healthy \\ controls \\ \end{tabular} & 20 & - & 14/6 & 29.7 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Subject characteristics. and was approved by the local ethics committee. All subjects gave a written informed consent before the tests. Gait biomechanics was assessed at three time points: at the initial consultation (before surgery) and then three months and a year or more after the surgical reconstruction. The first two assessments were done for all 20 patients, and the last one for only 12 patients. In healthy subjects, gait biomechanics was assessed only once. The rehabilitation exercises were recommended on an individual basis for each patient. In the pre-operative period, they were strength exercises for both legs. In the post-operative period, rehabilitation included 2-3 weeks of individual sessions with a kinesotherapist and a home exercise program. The sessions included manual kinesotherapy, workout on special movement therapy devices, and muscle stimulation. The rehabilitation program was adjusted after the second assessment of walking biomechanics. Biomechanical gait analysis was done using a procedure we had described earlier in reference [10]. The procedure was the same for all the subjects (patients and healthy controls). The kinematic parameters of the lower limb joints during walking were measured using inertial sensors. The sensors help evaluate the spatial characteristics of each movement in three mutually perpendicular planes. The recorded parameters included gait cycle time, hip and knee joint movements in three mutually perpendicular planes, and impact loads during walking. In this study, we used a human movement analysis system with five inertial sensors (Figure 1). The sensors were fixed with special cuffs to the lower back, the lower third of the thigh and the lower third of the shank of the right and left legs. The movements and temporal characteristics were recorded while the subject was first walking 10 meters at an arbitrary pace. The walking trial was repeated 2-4 times, as appropriate.