Post-Traumatic Knee Osteoarthritis Following Anterior Cruciate Ligament Reconstruction

Inclusion Criteria (healthy volunteers): * Age: 18-35 years * No previous anterior cruciate ligament (ACL) injury * Body Mass Index (BMI) between 18-30 * Regular physical activity (active during work or practicing sports regularly) * Signed informed consent to participate Exclusion Criteria (healthy volunteers): * Major injuries to the lower extremities with absence from sports or daily life activities longer than 2 weeks or that required surgery, less than 6 months before participation * Pre-existing arthritic disease including inflammatory or infectious arthritis Inclusion Criteria (ACL patients): * Age: 18-35 years * ACL tear which is recently reconstructed or will be reconstructed after enrollment in the current study (the reconstruction will take place within 6 months after injury) with a Hamstring autograft * BMI between 18-30 * Regular physical activity (active during work or practicing sports regularly) * Signed informed consent to participate Exclusion Criteria (ACL patients): * Major injuries to the lower extremities with absence from sports or daily life activities longer than 2 weeks or that required surgery, less than 6 months before participation * Pre-existing arthritic disease including inflammatory or infectious arthritis * Image based confirmation of local cartilage lesion grade 4 or major cartilage damage (Kellgren \& Lawrence \> 2) * Medial collateral ligament damage (\> grade 2) * Intra-articular knee fractures * Menisectomy with \<80% remnant