**1. Introduction**

In light of epidemiological studies, 30% of joint injury cases concern knee joints. Of all knee ligament reconstructions, anterior cruciate ligament (ACL) reconstructions account for 80%, with 65% cases occurring during physical activity, both during recreational activity and practicing sports [1]. The most frequent injury mechanism is twisting movement at stabilized foot and flexed knee. Knee dislocation is usually connected with the impact of substantial external forces and is characterized by permanent or temporary losing the contact by the opposite articular surfaces [2]. In order for the injury to be categorized as dislocation, at least two of four ligaments that stabilize knee joint should be torn [3]. This injury is connected with the damage of various articular structures, sometimes also neurological and vascular.

Crucial ligaments protect the knee joint from excessive anterior-posterior translation. The posterior cruciate ligament (PCL) ensures the major force that resists the posterior drawer effect (95% of the force), whereas the anterior cruciate ligament (ACL) prevents the anterior drawer displacements and overextension of the leg in the knee joint [4]. The ligaments interweave with each other, thus limiting internal rotation of the knee. Another function of cruciate ligaments is also initiation of the correct sliding of the joint surfaces in the direction opposite to the rolling motion. Two collateral ligaments control joint displacements in the frontal plane: tibial collateral ligament, which prevents from the valgus movement, and fibular collateral ligament, preventing from the varus movement, with the most effective stabilization observed at the extended knee.

Structural deformation and the related functional failure of the ligament typically lead to the development of joint instability, termed disturbed joint movement control. In the case of tearing an individual ligament, the instability pattern is simple (e.g. tibial collateral ligament rupture: medial instability) or rotational (ACL rupture: anterior-medial-anterior-lateral instability). Knee dislocation with damage to all the stabilizing elements represents a complex instability: in addition to all the above types of instability, additional anterior-lateral-posterior-lateral instability and anterior-medial-posterior-medial instability are also observed [5].

Conservative therapies and surgical interventions have been used in the treatment of cruciate ligament injuries. The conservative treatment is used in the case of partial ligament damage, without substantial symptoms of joint instability in people with low physical activity aged over 40 years of age, leading little active lifestyles [6]. In the case of acute injuries, conservative treatment is aimed to eliminate edema, joint hydrarthrosis, and pain syndromes, ensuring proper and painless joint mobility and adequate muscular tension and neuromuscular control (proprioception).

The surgical interventions are used in patients with positive results of functional tests for evaluation of anterior cruciate ligament, such as the Lachman test, the anterior drawer test, and the pivot-shift test with coexistence of subjective symptoms of instability reported by patients during the interview, such as knee giving way. In young patients, especially those who are involved in sports, the sufficient indication for the surgery is ligament rupture diagnosed during a diagnostic examination using magnetic resonance (MR) or ultrasonography examinations.

An integral part of the patient treatment process is preoperative and postoperative rehabilitation. The procedures before the surgery are mainly aimed to obtain the range of joint motion needed for the reconstruction, prevent muscle atrophy, increase muscle strength, and improve proprioception. Early postoperative rehabilitation accelerates recovery and is usually started a day after the surgery. This procedure impacts significantly on reducing the time of patient's regaining full health [7, 8].
