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1Introduction15Biomechanical Outcome after Modern ACL reconstructionBiomechanical studies show that ACL reconstruction in its current form does not restore normal knee kinematics.11,22,33 Gait analysis evidences that during level walking the ACL-reconstructed knee is less internally rotated 26,33 and during downhill running it is more externally rotated.30Although these studies indicate that rotational kinematics are not restored after ACL reconstruction, the question remains of whether tibial rotation is also abnormal during pivoting sports activities, as this may be a reason why patients do not return to their preinjury level of sports. The rotational laxity of the knee is determined by the range of motion that is allowed in the axial plane. This is why it’s important to measure the range of tibial rotation rather than the relative position of the tibia.Several factors may influence or relate to the range of tibial rotation – first and foremost the ACL itself: although cadaveric studies show that the ACL is an important constrainer for internal and external rotation,17 in vivo studies evidence conflicting results.27,30 Therefore the exact role of the ACL, and of the ACL graft after reconstruction, in limiting in vivo range of tibial rotation remains unknown. The role of the surrounding muscles with respect to the range of tibial rotation and whether this may be different during low- and high-demand activities has not yet been determined either. Excessive range of tibial rotation may affect clinical outcome after ACL reconstruction. And there are many different ways to assess clinical outcome after this procedure. On the one hand there is the technical success of the operation in terms of knee stability, graft survival and the occurrence of complications, yet there is also the patient’s perception of the success of the operation. In recent decades, patient-reported outcomes have received increasing attention in the evaluation of orthopaedic care. In assessing value-based healthcare, the added value for the patient is an important determinant. Many constructs can be assessed using patient-reported measures. Most commonly used constructs in ACL reconstruction outcomes assess patient satisfaction, subjective knee function, and psychological factors like fear of reinjury, kinesiophobia, and psychological readiness to return to sports. Mark Zee.indd 15 03-01-2024 08:56