Introduction: Assessment of anterior knee laxity with arthrometers is a method of evaluating the integrity of the anterior cruciate ligament (ACL). It represents an important part of the clinical examination. Purpose: The purpose of this master's thesis was to determine the intra-rater reliability of the knee arthrometer GNRB® for measuring anterior knee laxity in athletes of different ages. Methods: We performed 2 measurements on 97 subjects using a GNRB® arthrometers. All male subjects were tested 2 times within 1 week, while female subjects were tested within 24 hours. Measurements were performed with a tibial force of 134N, 134N, 150N, 200N, and 200N. An intraclass correlation coefficient was calculated to evaluate the reliability of the measurements. Differences between the categories of gender, level of sport, regular menstrual cycle and oral contraception were tested with a t-test, and differences between age groups and sports were analyzed with a one-way analysis of variance (ANOVA). Results: Intra-rater reliability is good at 134 N on the right (ICC = 0.788) and left leg (ICC = 0.848) and at 200 N on the right (ICC = 0.756) and left leg (ICC = 0.805). Recreational athletes have statistically significantly greater anterior laxity than soccer and handball players. There is no significant difference in anterior knee laxity between women with regular and irregular menstrual cycles. The same goes for women who use oral contraceptives as compared to women who do not use oral contraceptives. Discussion and Conclusion: The intra-rater reliability of a GNRB® knee arthrometer is good for measurements with 134N and 200N forces. To improve the reliability, it is necessary to standardize the position of the subject, the stabilization of the patella and the measurement protocol. There is a tendency that a sport involving more changes of direction could have an influence on the anterior laxity of the knee joint. For future research, it is necessary to compare men and women in separate age groups, as the results of our and previous research contradict each other in terms of characteristic differences.
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