Evaluation of the knee kinetics and kinematics in functional tests with muscle strength, balance, proprioception, and subjective measurements in male athletes after anterior cruciate ligament repair

Anterior cruciate ligament (ACL) injuries are common among athletes and their incidence is progressively increasing. Professional athletes are predominantly treated with surgical reconstruction following ACL injury. Although rehabilitation programs and assessment methods for return to play have advanced after ACL reconstruction (ACL-R), the rates of return-to-sport at pre-injury levels are still well below expected levels. This is believed to be due to the persistence of biomechanical deficits. This study aimed to identify an objective, specific, and consistent metric for use in post-ACL-R rehabilitation and return-to-sport assessment. For this purpose, 35 athletes who underwent ACL-R were subjected to objective and subjective tests, as well as two different jump tests, at least one year post-surgery. The rotational axis variation at the landing interval of jump tests was calculated using the helical axis method. Subsequently, it was normalized by the landing interval, rendering a deviation metric quantified per unit time. (NormSumVar). Results from the triple and crossover hop tests revealed that participants obtained significantly higher scores in NormSumVar for the operated limbs (0.045 and 0.043) compared to the non-operated limbs (0.035 and 0.0356), with statistically significant differences (p=0.0012, p=0.024). Additionally, individuals achieved similar results in the rotational axis variation per unit time of non-operated knees when they regained sagittal plane motion. There was no significant difference in the total variation score under any condition. Furthermore, our participants have symmetry in both objective and subjective measurements. In conclusion, the introduced NormSumVar objectively quantifies pathological movement in the knee.