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General Discussion1759Improving Functional and Biomechanical Outcome after ACL reconstruction Despite the rise in the number of ACL reconstructions being performed worldwide, return to sports rates are still poor. For instance, it is estimated that 175,000 ACL reconstructions are performed in the US annually.5With only 55% of patients returning to sports,1 the estimation is that 70,000 patients will quit competitive sports annually in the US alone. As return to sports is a complex concept, the general aim of this thesis is to improve functional and biomechanical outcome after ACL reconstruction, by generating a better understanding of these factors that are known to influence return to sports rates. In this General Discussion, the results of these studies are summarised and implications for clinical practice and future research are presented. Summary of the main findingsThe aim of the first part of the thesis was to study the influence of the ACL on the range of tibial rotation and to study the association between range of tibial rotation in sport-related activities on one hand and subjective knee function, psychological readiness and slope of the tibial plateau on the other. Persistent rotational laxity could be a key factor in poor returnto-sports rates. In Chapter 2 we reviewed the literature for studies investigating the purely mechanical influence of an ACL graft on the range of tibial rotation. Several studies conducted in anaesthetised patients show that the passive range of tibial rotation in ACL-deficient subjects is higher than that of intact knees, and that the passive range of tibial rotation decreases by 17-32% (average 25%) after ACL reconstruction.6,37,38 It should be noted that the methodological quality of the included studies was low and the level of the evidence was low-to-very-low due to heterogeneity in the design of these studies. The findings are nonetheless generally accepted, as they match the biomechanical role of the ACL and underline that ACL reconstruction can control the passive rotational movement of the tibia. Mark Zee.indd 175 03-01-2024 08:56