Background <p>Dynamic valgus is a well-known risk factor for ACL injury. To date, there are no studies on the question of whether patients after harvesting of a semitendinosus tendon for reconstruction of the ACL are more likely to have a valgus knee movement than patients after harvesting of a quadriceps tendon graft.</p> Hypothesis/Purpose <p>Hypothesis of the present study is that patients with a semitendinosus tendon graft land a drop jump with more in valgus than patients with a quadriceps tendon graft.</p> Study design <p>Controlled Laboratory Study.</p> Methods <p>Patients who underwent ACL reconstruction were divided into 2 groups: Group 1 received the semitendinosus tendon, and Group 2 received the quadriceps tendon with bone block as a graft. Approximately 8 months post-surgery, various jump tests and strength tests were conducted. The primary outcome was the maximum valgus during landing.</p> Results <p>In the vertical drop jump, the maximal valgus angle was – 2.4° (IQR–11.3°–3.4°) in the ST group in comparison to 3.5° (IQR–9.1°–6.3°) in the QT group. This difference was statistically significant (p = 0.027). In both groups there was no significant difference in the maximal valgus angle between the operated and the contralateral side.</p> Conclusion <p>The results of the present study confirm our hypothesis, that patients with quadricps tendon graft land with a lower valgus angle than after harvesting the semitendinosus tendon.</p> Clinical relevance <p>The study demonstrates for the first time that patients with a semitendinosus graft exhibit a higher valgus angle during drop jump landings compared to patients with a quadriceps tendon graft. This represents a potential increased risk factor for recurrent ACL ruptures.</p> What is known about the subject <p>Previous studies have explored the outcomes associated with quadriceps and hamstring tendons in ACL reconstruction. While both graft types have shown favorable outcomes in terms of knee stability and functional recovery, there have been discussions regarding the potential risk factors for graft failure or re-rupture between these graft types. Previous research has suggested that the hamstring tendons play an important role for the stabilization of the knee joint against valgus stress and it has been shown that the dynamic valgus is an important risk factor for ACL injury. However, the existing literature has not provided conclusive evidence regarding differences in dynamic valgus of the knee during single leg jump tasks between both graft types. Thus, the current study aims to address this gap in knowledge by directly comparing the valgus angles during drop jump landings between patients who received a semitendinosus tendon graft and those who received a quadriceps tendon graft with a bone block. By elucidating any potential differences in biomechanical parameters between these graft types, the study contributes to a better understanding of the factors influencing the risk of ACL re-rupture following reconstruction surgery.</p> What this study adds to existing knowledge <p>By focusing on the valgus angle during drop jump landings, the study sheds light on a critical aspect of knee biomechanics that may influence the risk of ACL re-rupture. Previous research has explored various factors contributing to graft failure or re-rupture, but there has been limited understanding of how specific graft choices affect dynamic knee stability during functional activities like jumping and landing. The finding that patients with a semitendinosus tendon graft exhibit a higher valgus angle during drop jump landings compared to those with a quadriceps tendon graft provides valuable information for clinicians and surgeons. It highlights a potential biomechanical difference between these graft types that may have implications for post-operative rehabilitation protocols, patient counseling, and surgical decision-making.</p>