Rotational laxity increases the risk of anterior cruciate ligament (ACL) injuries and residual rotational laxity can result in inferior surgical outcomes and risk of retears. The dynamic rotatory knee stability can be assessed through manual examination, but it is limited to the surgeon's experience and it provides inaccurate measurements, highlighting the need for objective measurement of knee rotational laxity. The objective measurement of knee laxity can help to better identify patients that may benefit from conservative treatment or those that require surgical treatment with or without concomitant extra-articular procedures. We rely in Porto Knee Testing Device (PKTD®) to accurately measure sagittal and rotatory laxity of the knee, either individually or in a combined fashion. The PKTD® is safe and can be used in combination with CT or MRI, which allows to assess both the “anatomy” and the “function” in the same examination. By this way, we may have a total ACL rupture and a stable knee not requiring surgery or, on the other hand, the same injury scenario but with an unstable knee that requires surgical intervention (with or without lateral extra-articular tenodesis). In cases of partial ACL tears, it may be possible to identify some ligamentous fibers that remain functional, where the conservative treatment or augmentation techniques can provide satisfactory results. It can also identify when a posteromedial or posterolateral instability is associated. The PKTD® can also be used to follow-up the laxity results of conservative and surgical procedures and contribute to the decision-making of return to sports