Introduction
Knee valgus is a topic that raises concerns, especially regarding ACL and MCL injuries during sports activities. However, it is important to understand that knee valgus, often visually noticeable by significant medial knee displacement in the frontal plane, isn’t always inherently dangerous.
It is crucial to differentiate between apparent knee valgus, which often serves a functional purpose, and true knee valgus, which appears more likely to lead to injury. This helps us to understand whether knee valgus is contextually good or bad, so that we avoid installing unnecessary fear avoidant movement when it is not...
What is 'Apparent Knee Valgus'?
Apparent knee valgus is a functional movement that aids in force absorption and movement efficiency. It is often characterised by internal hip rotation and pronation of the foot, particularly in the context of a barbell back squat. It is very commonly displayed by some of the best lifters in the world coming out of the hole of a heavy squat or clean. This creates the impression of large amounts of true knee valgus due to the medial knee displacement in the front plane but is actually largely due to inwards rotation in the transverse plane in the hips, ankles and foot complex.
What is 'True Knee Valgus'?
Conversely, true knee valgus involves a structural misalignment of the knee joint, increasing the risk of ACL injuries. Research suggests that ACL injuries occur when the lower body joints are not properly aligned to absorb the forces applied or we are too contextually weak to absorb said forces at specific joint angles, leading to disproportionate stress on the ACL and MCL ligaments in relation to the forces put on them and their acute or chronic capacity levels, which can cause a tear of the MCL and ACL.
What do the ACL and MCL do in relation to True Knee Valgus?
Our understanding indicates that both the MCL and ACL serve crucial roles in preventing valgus instability, although their anatomical mechanisms differ. The MCL functions by preventing the opening of the medial joint space, thereby averting valgus instability.
Conversely, the ACL's function involves preventing internal rotation of the tibia, contributing to the overall stability of the knee joint. These distinct mechanisms highlight the complementary nature of the ligaments' roles in maintaining proper alignment and stability, safeguarding against high magnitudes of True Valgus.
ACL Injuries in a variety of positions: What do they have in common?
ACL injuries can happen in a variety of positions, for example, during a cutting motion, a landing or heavily planting a foot in front of the centre of mass. The inherently dangerous thing they have in common is unlikely to be medial knee displacement in the frontal plane, but instead what is going on away from the knee that means that forces can’t be appropriately absorbed enough to avoid dangerous magnitudes of true knee valgus.
For example, heel-first landings have often been described as a higher risk landing position, likely because it removes any force absorption abilities away from the foot and ankle complex, unlike a landing further into the forefoot.
*Sourced from Carlson et al. (2016)*
The Role of Joint Alignment in Reducing ACL Injury Risks
Proper joint alignment may play a crucial role in mitigating ACL injury risks associated with true knee valgus. By focusing on force absorbing movement patterns and foot positioning, individuals can redistribute forces away from the ACL and MCL ligaments. Strategies such as encouraging foot pronation, hip internal rotation, and inward knee tracking during activities like heavy squats can optimize force absorption and may minimize stress on the knee joint, avoiding high magnitudes of true knee valgus.
The Caveat:
During sporting actions like fast cutting, to be more affective, we WANT stiff and explosive redirection. It is therefore likely also beneficial to expose athletes to stiff landings and cutting movements in isolated settings, so they have greater capacity and stamina for quick decelerations and accelerations when they do inevitably happen in a functional setting, without excessive load being absorbed through true valgus, but instead through the muscles and tendons surrounding the major joints in the movement strategy that is utilised.
Apparent and True Knee Valgus: A Holistic Approach
Understanding the distinction between apparent and true knee valgus allows us to take a holistic approach to knee health and injury prevention. While apparent knee valgus can be functional and beneficial for force absorption and production, true knee valgus requires attention and corrective measures to attempt to reduce ACL injury risks.
Therefore, it may be appropriate to encourage and allow athletes to display apparent knee valgus during exercises like barbell back squats or jumping. Conversely, we still want to avoid true knee valgus and continually work on landing positions that don’t display true knee valgus to reduce to potential for dangerous landing positions when a motor pattern is disrupted.
Conclusion
It may be better to view knee valgus as primarily a force absorption strategy rather than inherently good or bad. Whether it is then considered favourable or unfavourable depends on whether it manifests as apparent or true knee valgus.
In field sport, neuromuscular factors, such as a disrupted motor pattern causing a poor landing position, largely influence the occurrence of true knee valgus and such related issues. Similarly, in closed-chain exercises like back squats, neuromuscular factors probably play a significant role in reducing true valgus. but the benefits of range of motion and strength in force-absorbing positions, like internally rotated hip positions, remain promising, given the degree to which the elite squatters of the world utilise them, but would benefit from further research validation.
References and readings:
Matsumoto, H., Suda, Y., Otani, T., Niki, Y., Seedhom, B.B. and Fujikawa, K., 2001. Roles of the anterior cruciate ligament and the medial collateral ligament in preventing valgus instability. Journal of orthopaedic science, 6(1), pp.28-32.
Hogg, J.A., Waxman, J.P. and Shultz, S.J., 2022. Examining the effects of femoral anteversion and passive hip rotation on ACL injury and knee biomechanics: a systematic review and meta-analysis. Journal of Experimental Orthopaedics, 9(1), pp.1-16.
Dischiavi, S.L., Wright, A.A., Hegedus, E.J. and Bleakley, C.M., 2019. Rethinking dynamic knee valgus and its relation to knee injury: normal movement requiring control, not avoidance. journal of orthopaedic & sports physical therapy, 49(4), pp.216-218.
Carlson VR, Sheehan FT, Boden BP. Video analysis of anterior cruciate ligament (ACL) injuries: a systematic review. JBJS reviews. 2016 Nov 11;4(11):e5.
Montgomery, C., Blackburn, J., Withers, D., Tierney, G., Moran, C. and Simms, C., 2018. Mechanisms of ACL injury in professional rugby union: a systematic video analysis of 36 cases. British Journal of Sports Medicine, 52(15), pp.994-1001.
Della Villa, F., Buckthorpe, M., Grassi, A., Nabiuzzi, A., Tosarelli, F., Zaffagnini, S. and Della Villa, S., 2020. Systematic video analysis of ACL injuries in professional male football (soccer): injury mechanisms, situational patterns and biomechanics study on 134 consecutive cases. British journal of sports medicine, 54(23), pp.1423-1432.
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