The phenomenon commonly described as “knees caving in” during movement is clinically known as dynamic knee valgus. This movement fault occurs when the thigh bone (femur) internally rotates and the knee tracks inward toward the body’s midline. Dynamic knee valgus is frequently observed during functional tasks like squats, lunges, running, or jumping. It is a recognized risk factor for injuries, including patellofemoral pain and non-contact anterior cruciate ligament (ACL) tears. Understanding the mechanical reasons behind this misalignment, which involves the kinetic chain from the foot up to the hip, is the first step in correction.
Muscle Imbalances Driving Knee Valgus
The most common functional cause of dynamic knee valgus originates at the hip and pelvis. The primary issue involves weakness or inhibited function of the lateral hip stabilizers, particularly the gluteus medius and gluteus maximus muscles. These muscles control the position of the femur by performing hip abduction and external rotation.
When these stabilizers cannot adequately control the femur during weight-bearing activities, the thigh bone drops into adduction and internal rotation. This uncontrolled inward rotation of the femur pulls the knee joint out of alignment, causing it to collapse inward. Research indicates that individuals exhibiting dynamic knee valgus often display a diminished capacity to absorb impact through the hip joint, shunting that stress to the knee.
This hip weakness is often compounded by tightness in opposing muscle groups. Overactive inner thigh muscles (adductors) can physically pull the leg toward the center line of the body. Tightness in the hip flexors can also contribute to an anterior pelvic tilt, which further compromises the mechanical advantage of the gluteal muscles and worsens the imbalance.
Ankle and Foot Mechanics
While hip control is a major contributor, issues lower down the leg can also exacerbate the knee-caving pattern. The foot and ankle act as the foundation for the entire leg, and their mechanics directly influence the knee joint position. A common factor is excessive foot pronation, which is the flattening or collapsing of the arch.
When the arch collapses, the foot rolls inward, causing the shin bone (tibia) to rotate internally. Since the knee is a hinge joint that sits between the femur and the tibia, this inward rotation of the tibia forces the knee joint to follow suit. This mechanical link translates the fault upward to the knee.
Another factor is limited ankle dorsiflexion, the ability to flex the foot upward toward the shin. When dorsiflexion is restricted during movements like a squat, the body compensates to maintain balance and depth. This compensation often involves the tibia rotating internally or the foot pronating, both leading to the knee tracking inward. Improving ankle joint mobility is an indirect way to improve knee alignment during dynamic movements.
Corrective Movements and Strengthening
Addressing dynamic knee valgus requires a two-pronged approach: strengthening weak muscles and retraining the movement pattern itself. The focus must be on strengthening the lateral hip stabilizers, which include the gluteus medius and gluteus maximus. Exercises that specifically target these muscles in a controlled manner are effective for building the necessary strength and endurance.
Foundational strengthening exercises include the single-leg glute bridge and the side-lying clam shell exercise. These movements help activate the external rotators of the hip, teaching them to fire independently. As strength improves, functional movements incorporating resistance, such as banded lateral step-outs or squats performed with a resistance band looped just above the knees, can be introduced to force the hips to work against the inward pull.
Movement pattern correction is necessary to retrain the brain’s control over the limb. During activities like squats or lunges, consciously cueing the knees to track outward, keeping them aligned over the middle of the foot, helps establish a new motor pattern. Using visual feedback, such as performing exercises in front of a mirror, helps monitor alignment and prevent the inward collapse. Consistency is required, as overwriting faulty movement habits takes time and repetition.
When to Consult a Specialist
While many cases of dynamic knee valgus improve with focused self-correction and exercise, certain signs indicate the need for professional guidance. If the inward knee collapse is accompanied by persistent pain in the knee, hip, or lower back that does not improve after several weeks of corrective exercise, seek a professional assessment. Pain that interferes with daily activities or simple movements like walking is a clear signal that the issue may be more complex than a simple muscle imbalance.
A Physical Therapist can perform a detailed biomechanical analysis to pinpoint the exact contributing factors, which may involve structural issues or complex movement dysfunctions. If the knee alignment issue appears to be structural, meaning the “caving” is present even when standing still (static genu valgum), an Orthopedist should be consulted. They can evaluate the bony alignment and rule out underlying conditions that might require medical or surgical intervention.