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Chapter 596IntroductionRisk factors for ACL injury are multifactorial and, next to gender-related, genetic, and hormonal factors, include anatomical and biomechanical factors.14,25 One anatomical factor that has been of interest in recent studies is the amount of posterior tibial slope (PTS). From cadaveric experiments it is known that increased PTS leads to more forward-directed forces on the tibia and increases strain on the ACL.3 Dejour and Bonnin showed that every increase of 10° in PTS leads to a 6mm increment of passive anterior tibial translation (ATT) in ACL deficiency.10 More recent studies confirm the correlation between PTS and passive ATT in both ACL-deficient and ACLintact knees.8,9,13Increased PTS is related to increased risk of primary ACL injury and increased risk of graft failure after ACL reconstruction.6,30,32 For this reason it has been suggested that, in revision cases, altering the amount of PTS by an anterior closing-wedge osteotomy could reduce strain on the ACL graft and prevent another re-injury.17 It should be noted that past studies have evaluated passive ATT either using instrumented Lachman or in a cadaveric setting, both of which eliminate muscle tone. The influence of PTS on dynamic ATT is less extensively studied. As clearly as the relation between PTS and passive ATT is demonstrated, less is known about the relation between PTS and tibial rotation. The ACL is known to restrict ATT, but also plays a role in limiting tibial rotation.12Due to the anatomical features of the tibial plateau, axial load transfers into an anteriorly directed force on the tibia.10 This force increases with PTS.10 As the medial and lateral tibial plateaus differ in congruency with the femur, as well as in mobility, we argue that the translation in the lateral compartment is more susceptible to changes in PTS. Due to this difference between the medial and the lateral compartment, axial load would not only be transferred into ATT, but also into rotation of the tibia relative to the femur. We hypothesized that this difference (referred to as ΔPTS) might be of more importance than the actual amount of slope itself, with respect to rotation.Mark Zee.indd 96 03-01-2024 08:56