Purpose. The aim of the study was threefold: to determine the active rotation range of a healthy and post-traumatic knee joint; to evaluate the torque of muscles responsible for internal and external rotation of a healthy and post-traumatic knee joint; and to determine differences between a healthy knee joint and knee joint with the ruptured anterior cruciate ligament (ACL). Differences between active axial rotation and muscular strength of rotators in the healthy and post-traumatic knee joints of 40 hospitalized patients were examined. Basic procedures. The static torque evaluation of the shank rotating muscles included 40 patients of the Endoscopic Surgery Clinic in Żory, with the ruptured ACL of the right knee, qualified for surgery (ACL reconstruction). On the basis of a medical interview, the ACL ruptures were found to have occurred during football games. Main findings. ACL damage leads to an increased rotation range, with a subsequent decrease of the rotators' strength and increased joint instability. The patients examined showed a substantial level of thigh quadriceps atrophy - a typical symptom associated with an ACL rupture. Our findings indicate that the internal and external rotators in intact knees were stronger than the rotators in post-traumatic knees (p < 0.05). Conclusions. The analysis of the torque of the shank rotating muscles at two knee joint flexion angles was an attempt to proceed with a laboratory diagnosis of the condition of the motor system in 40 patients following severe trauma (such as the ACL rupture of the right knee) prior to surgical intervention, and, in a longer perspective, after treatment completion. The results obtained will supposedly be useful as indicators for future rehabilitation pathways, and of the condition of the motor system following treatment completion.