Dynamic valgus refers to a lower limb movement pattern where the knee collapses inward, moving towards the body’s midline, particularly during activities that involve single-leg support or landing. This inward movement of the knee, often described as “knock-kneed” during motion, is a combination of several biomechanical actions occurring simultaneously in the hip, knee, and ankle. It is a dynamic alignment, meaning it appears during movement rather than being a static anatomical feature.
Understanding Dynamic Valgus
Dynamic valgus is a complex movement pattern involving the femur’s (thigh bone) internal rotation and adduction, along with knee abduction, anterior tibial translation, and external tibial rotation. This combination of movements results in the knee moving inward, beyond the alignment of the foot and thigh. This pattern is most noticeable during functional activities such as landing from a jump, performing a squat, or running.
The interplay of the hip, knee, and ankle joints contributes to dynamic valgus. For instance, excessive pronation of the foot (flattening of the arch) can influence tibial (shin bone) rotation, which affects knee alignment. Similarly, movements at the hip, such as internal rotation and adduction of the femur, directly contribute to the knee’s inward collapse. The degree of dynamic knee valgus can vary, with ranges reported as 1-9 degrees for males and 5-12 degrees for females during a single-leg landing task.
Common Causes
Dynamic valgus results from a combination of muscle imbalances, restricted joint mobility, and suboptimal motor control. Weakness in the hip abductor and external rotator muscles, particularly the gluteus medius and gluteus maximus, is a common cause. These muscles stabilize the pelvis and prevent the femur from excessively rotating inward. When weak, they allow the hip to adduct and internally rotate, leading to the knee’s inward collapse.
Overactivity or tightness in opposing muscle groups, such as the hip adductors, can also pull the thigh inward, exacerbating valgus alignment. Limited ankle dorsiflexion can force the knee to compensate by moving inward during squatting or landing activities. Poor motor control means that even with adequate strength and flexibility, the body may not adopt optimal alignment. This can be observed as a “skill issue” in untrained individuals performing movements like squats.
Associated Risks and Injuries
Dynamic valgus is associated with various lower limb injuries. Patellofemoral pain syndrome (PFPS), or “runner’s knee,” involves pain around the kneecap. Increased valgus loading during dynamic activities raises lateral forces on the patellofemoral joint, contributing to PFPS.
Another injury linked to dynamic valgus is a non-contact anterior cruciate ligament (ACL) tear. The rapid inward movement and rotation of the knee, often occurring within milliseconds of initial ground contact, place excessive stress on the ACL, leading to rupture. Iliotibial band syndrome (ITBS), characterized by pain on the outside of the knee, is also commonly associated with dynamic valgus due to increased tension and friction on the iliotibial band. Ankle sprains, particularly those involving excessive pronation of the foot, can also occur due to altered biomechanics.
Assessment and Management Strategies
Dynamic valgus is identified through observation during functional movements. Healthcare professionals assess this movement pattern by observing individuals perform tasks such as squats (single-leg or double-leg), single-leg landings, or lateral step-down tests. During these assessments, the inward movement of the knee is noted, and measurements like the frontal plane knee projection angle (FPPA) are used to quantify the degree of valgus.
Management strategies for dynamic valgus focus on addressing underlying biomechanical deficiencies. Strengthening exercises target weak muscles, particularly the hip abductors and external rotators like the gluteus medius and gluteus maximus, to improve hip stability and control. Flexibility and mobility interventions address tight areas, such as improving ankle dorsiflexion and hip flexor mobility, to allow for a more natural movement path. Motor control retraining involves consciously practicing correct movement patterns, often with real-time feedback, to improve neuromuscular coordination. Professional consultation with physical therapists or other healthcare providers is recommended for proper diagnosis and a personalized exercise program.