The experience of knees collapsing inward when standing, squatting, or moving is a common biomechanical issue. This inward movement, often described as “knock knees,” signals an alignment problem in the lower body that extends beyond the knee joint itself. Understanding the causes behind this posture is the first step toward correcting it and preventing potential long-term discomfort or injury. This alignment issue typically results from a combination of muscle weaknesses, structural factors, and poor movement patterns.
What Is Knee Valgus?
Knee valgus is the clinical term used to describe the inward angle of the knee toward the midline of the body, a position that resembles “knock knees.” The condition can be static, where the knees angle inward even when standing still, or dynamic, where the collapse is only visible during movement or when bearing a load. Dynamic valgus collapse is the greater concern, as it indicates a loss of muscular control during functional activities like squatting or running.
You can check for dynamic knee valgus by performing a shallow squat in front of a mirror. If your knees drift inside the line of your feet as you descend, you are demonstrating this collapse. This alignment issue involves the thigh bone rotating inward and the shin bone twisting outward. The degree of this inward angle is sometimes quantified by the Q-angle, which relates the pull of the quadriceps muscle to the patella and tibia.
Functional Causes: Muscle Imbalances and Weakness
The most common and correctable cause of knees caving in is functional weakness in the muscles surrounding the hip and core. The hip muscles, particularly the gluteal group, are responsible for externally rotating and stabilizing the thigh bone. When the gluteus medius and gluteus maximus muscles are weak, they cannot effectively counteract the forces that pull the femur into internal rotation.
This weakness allows the thigh bone to excessively adduct and rotate inward, forcing the knee to collapse toward the center. The resulting misalignment places the knee joint in a compromised position during any weight-bearing activity. Similarly, tightness in opposing muscle groups, specifically the hip flexors and adductors (inner thigh muscles), can contribute to this problem. Tight adductors physically pull the leg toward the midline, further exacerbating the knee valgus position.
Structural Factors and Kinetic Chain Effects
While muscle weakness is often the primary driver, structural and distal factors also play a significant role in knee valgus, impacting the entire kinetic chain. The alignment of the foot and ankle can initiate a chain reaction that travels up the leg. Excessive foot pronation, or “flat feet,” causes the arch to collapse and the foot to roll inward.
This inward rolling of the foot forces the tibia to internally rotate, subsequently driving the knee inward. Limited ankle dorsiflexion, the ability to move the shin forward over the foot, can also cause the body to compensate by pronating the foot and collapsing the knee. Beyond these functional compensations, some individuals are anatomically predisposed to this alignment.
Natural variances in hip width, often greater in women, can lead to a slightly larger Q-angle. This wider hip structure changes the angle at which the thigh bone meets the knee, predisposing some people to an inward knee angle. If this poor alignment is left unaddressed, the rotational stress on the knee joint can lead to several long-term issues. These risks include patellofemoral pain syndrome, increased strain on the anterior cruciate ligament (ACL), and accelerated joint wear.
Next Steps: Corrective Strategies and Professional Guidance
Addressing the issue of inward-caving knees involves a targeted approach focused on strengthening weak muscles and improving movement control. Corrective strategies center on strengthening the hip abductors and external rotators to stabilize the femur and prevent its internal rotation. Specific exercises are highly effective in activating the gluteus medius and maximus:
- Clam shells
- Single-leg bridges
- Lateral band walks
These movements help the body learn to maintain proper knee-over-foot alignment during weight-bearing activities. Stretching exercises for tight muscles, particularly the hip flexors and adductors, are also beneficial for restoring a more neutral hip position. Alongside strengthening, it is important to practice movement awareness, focusing on consciously keeping the knees aligned with the feet during daily movements like squatting and standing up from a chair.
If the inward collapse persists despite consistent self-correction, or if you experience pain, consulting a physical therapist or orthopedic specialist is the recommended next step. A professional can provide a personalized assessment to determine whether the cause is primarily muscular, structural, or a combination of both. In cases where significant foot pronation contributes to the issue, a specialist may recommend custom orthotics to provide better arch support and correct the biomechanics from the ground up. Targeted physical therapy helps re-educate the nervous system and build the specific strength needed to maintain proper alignment and reduce the risk of injury.