Biomechanical and Neuromuscular Contributors to Knee Valgus and ACL Injury Risk

Abstract

Anterior cruciate ligament (ACL) injuries are the most common injuries in athletes while also being non-contact. One key factor associated with these injuries is knee valgus—an inward collapse of the knee during movement that increases strain on the ACL and other knee ligaments. This paper review compiles and current research to identify the primary biomechanical contributors to knee valgus and ACL injury. Findings across studies consistently highlight deficits in hip and trunk strength, poor neuromuscular control, and limited ankle mobility. By accounting for evidence from various reviewed studies the review aims to clarify the biomechanical mechanisms underlying knee valgus and inform injury-prevention strategies for athletes and doctors.

Introduction

Anterior cruciate ligament (ACL) injuries are a major concern in sports medicine due to their frequency, severity, and long-term consequences. They often occur through non-contact mechanisms, such as landing from a jump, decelerating, or changing direction rapidly. the research will look to see the relationship between dynamic knee valgus—an excessive inward collapse of the knee joint—and the significance of ACL injury risk. Understanding the biomechanical contributors to knee valgus is essential for both injury prevention and performance optimization. Past research has pointed to several factors, including hip abductor and external rotator weakness, poor neuromuscular control, deficient trunk stabilization, and restricted ankle dorsiflexion. Each of these factors can heavily change lower-limb alignment, leading to greater knee valgus moments during high-impact tasks. However, variations in research populations and testing methods make it difficult to draw consistent conclusions across studies. This paper seeks to compile and analyze existing research on the biomechanical determinants of dynamic knee valgus and ACL injury risk. By synthesizing current findings.

Methods

This review was conducted using publicly available peer-reviewed research articles retrieved from databases including PubMed, Google Scholar, and ScienceDirect. Keywords used in the search included “dynamic knee valgus,” “ACL injury biomechanics,” “hip strength knee valgus,” “landing mechanics ACL,” and “neuromuscular control ACL risk.”

The qualifications of the studies are listed below:

• Examined biomechanical factors related to knee valgus or ACL injury risk,

• Involved healthy or athletic human subjects, and

• Were published within the last 10 years (2015–2025).

Review papers and experimental biomechanical analyses were all considered. Data from each source were compiled to identify recurring biomechanical themes and consensus findings among researchers.

1. Hip and Trunk Mechanics

Weakness in the hip abductors and external rotators is one of the most frequently cited contributors to dynamic knee valgus. When these muscles fail to stabilize the femur, the thigh tends to internally rotate and adduct during landing or cutting, promoting valgus collapse. Additionally, the femur is attached to the pelvis by a ball and socket joint giving the most range of motion (ROM) but also giving more opportunities for injury. Research by Myer et al. (2019) and Claiborne et al. (2020) demonstrated a strong correlation between hip strength deficits and increased knee valgus angles during jump-landing tasks. In addition, poor trunk stability can amplify lower-body misalignment. Excessive trunk lean toward the stance leg increases medial knee loading, further stressing the ACL. These findings emphasize the need for core and proximal hip strengthening in injury-prevention programs.

2. Neuromuscular Control and Movement Patterns

Even when muscle strength is sufficient, impaired neuromuscular coordination can lead to poor landing mechanics and valgus loading. Athletes with delayed gluteal activation or asymmetrical ground reaction forces often demonstrate higher valgus angles upon impact. Studies using motion capture and EMG analysis have shown that females, in particular, tend to rely more on quadriceps-dominant strategies and exhibit reduced hamstring coactivation—both of which elevate anterior tibial shear forces on the ACL. Training interventions focusing on jump technique, proprioception, and rapid stabilization have been shown to mitigate these risks.

3. Ankle and Foot Contributions

Limited ankle range of motion can indirectly increase knee valgus by altering landing kinematics. When the ankle lacks mobility, athletes need to compensate by pronating the foot or collapsing the knee inward. Bell et al. (2018) found that athletes with restricted dorsiflexion exhibited greater knee displacement during squatting and landing. Proper ankle mobility, combined with stiffness and reactive strength training, may therefore be an essential factor in maintaining stable knee alignment under load.

4. Interaction of Multiple Factors

The development of dynamic knee valgus is rarely caused by a single deficit. Rather, it emerges from interactions across the lower-extremity chain—from the hip to the ankle. Weak proximal control, and limited ankle mobility amplifying the stress placed on the ACL. Integrated prevention programs such as FIFA 11+ and neuromuscular training protocols have shown measurable reductions in knee valgus angles and ACL injury rates, emphasizing the importance of multi-dimensional approaches.

Conclusion / Future Directions

Dynamic knee valgus is a complex, multifactorial movement pattern strongly associated with non-contact ACL injury risk. It is consistently highlighted that hip and trunk weakness, impaired neuromuscular control, and ankle mobility restrictions are the primary biomechanical contributors. While the exact degree of influence for each factor varies across each study, the interaction among them appears to be the most critical determinant of injury risk.

Future research should explore individualized screening tools and targeted interventions that address these interconnected factors on its own. Looking at the issues as individuals may help understand what each person may be needing specifically. For athletes and practitioners, incorporating hip and core strengthening, neuromuscular coordination training, and ankle mobility work has shown evidence-based strategy for reducing knee valgus and preventing ACL injuries.