Robot-based experimental in vitro investigation to evaluate the influence of tibial slope and lateral extra-articular tenodesis on the rotational instability of the knee (Tibiaslope)

Anterior cruciate ligament (ACL) injuries are among the most common sports injuries and impose a significant societal burden. Surgical treatment is considered the gold standard, yet failure still occurs in a substantial proportion of cases. Two modifiable risk factors are strongly associated with ACL reconstruction failure: anterolateral rotatory instability (ALRI) and increased posterior tibial slope (PTS).

ALRI, typically identified by a high-grade pivot-shift test, is associated with inferior clinical outcomes, higher graft failure rates, and earlier development of osteoarthritis. Increased PTS is likewise strongly linked to ACL injury and reconstruction failure, as shown in clinical, biomechanical, and simulation studies. Severe ALRI can be addressed with lateral extra-articular tenodesis (LET), while increased PTS can be reduced by an anterior closing-wedge high tibial osteotomy (ACW-HTO). However, optimal indications for these procedures remain controversial, and the interaction between ALRI and PTS has largely been neglected, despite emerging evidence that increased PTS exacerbates ALRI in both ACL-deficient and ACL-reconstructed knees.

This study aims to investigate the effects of modifying PTS via ACW-HTO and adding LET on ALRI under simulated sports loading conditions and established laxity tests (anterior translation, internal rotation, and pivot-shift). Three knee conditions are analyzed:

1. ACL-deficient knee,
2. ACL reconstruction without LET, and
3. ACL reconstruction with LET.

To assess the influence of tibial slope, each test is performed with both a low posterior tibial slope (5°) and a high posterior tibial slope (15°).