The phenomenon where hips or knees appear to collapse inward during movement is a common biomechanical issue known as dynamic valgus or medial knee collapse. This inward movement represents an uncontrolled shift of the leg that places increased stress on the joints, ligaments, and tendons of the lower body. Understanding the root cause is the first step, as this pattern is often a sign of underlying functional imbalances rather than a simple structural defect.
Defining the Mechanics of Inward Hip Movement
The inward movement is a complex, three-dimensional motion involving the entire leg, best understood through the concept of the kinetic chain. This chain describes how movement or lack of stability in one joint affects the joints both above and below it. When the hip appears to “go inward,” the femur simultaneously undergoes internal rotation and adduction.
The femur rotates inward while also moving closer to the center line of the body. This dual action forces the knee to drift toward the midline, often resulting in the foot flattening or over-pronating to compensate. This uncontrolled collapse is most visible during weight-bearing activities like walking, running, or squatting. The motion can be initiated from the hip (a top-down cause) or the foot (a bottom-up cause), but the hip is the primary controller.
Primary Functional Causes: Muscle Imbalances
The most common drivers of inward hip movement are specific weaknesses and imbalances within the hip musculature. The hip abductors and external rotators are the primary stabilizing muscles meant to prevent this inward rotation and adduction. When these muscles are weak or not activating efficiently, the femur is left unchecked, allowing the inward collapse to occur.
The Gluteus Medius, a powerful hip abductor, is important for maintaining pelvic stability during single-leg stance, such as walking or running. If the Gluteus Medius is weak, the pelvis on the non-weight-bearing side will drop. Alternatively, the stance leg will compensate by allowing the femur to internally rotate and adduct, translating hip weakness into the visible inward shift.
The deep external rotators, a group of smaller muscles including the piriformis and obturator group, are designed to counteract the internal rotation of the femur. These muscles provide rotational control to keep the thigh bone aligned within the hip socket. When these deep stabilizers fatigue or fail to activate quickly, the femur twists inward, contributing to the dynamic valgus pattern. Other muscles, such as the hip adductors and the Tensor Fasciae Latae (TFL), can become tight and overactive, pulling the leg inward and compounding the gluteal weakness.
Structural and Lifestyle Contributors
While functional weakness is modifiable, some individuals have underlying anatomical factors that predispose them to this alignment. One structural cause is femoral anteversion, a congenital condition where the neck of the femur is rotated slightly inward. This inward twist naturally increases the resting internal rotation of the leg, requiring greater muscular effort to maintain neutral alignment. Another factor is tibial torsion, a twist in the shinbone that can cause the feet to point inward and alter the mechanical axis of the leg.
Modern lifestyle habits are powerful contributors to muscular imbalance. Prolonged sitting is a major culprit, keeping the hip flexors in a shortened position and leading to chronic tightness of the iliopsoas muscle group. This tightness can inhibit the Gluteus Maximus and tilt the pelvis forward, encouraging the inward hip movement. Additionally, wearing unsupportive footwear that allows for excessive foot pronation can initiate the kinetic chain collapse from the ground up, placing increased rotational demands on the hip stabilizers.
Strategies for Correction and Management
Correcting this movement pattern requires a targeted, two-pronged approach focusing on strengthening and flexibility, alongside conscious movement pattern retraining. The solution is strengthening the weak hip abductors and external rotators to regain dynamic control over the femur. Specific strengthening exercises, such as the clamshell, lateral band walks, and single-leg bridges, effectively isolate the Gluteus Medius and deep rotators. These exercises should focus on quality of movement over quantity, ensuring the hip remains stable and the knee stays aligned.
Flexibility and Retraining
Tight muscles must be addressed to restore normal joint range of motion and pelvic posture. Stretching the hip flexors, such as a half-kneeling hip flexor stretch, helps to lengthen the iliopsoas and reduce the anterior pelvic tilt that contributes to the inward collapse. Stretching the hip adductors can also improve hip mobility, allowing the leg to move freely without being pulled toward the midline.
Integrating these exercises with movement pattern retraining is crucial. This involves consciously focusing on keeping the knee aligned over the second toe during functional tasks like climbing stairs or squatting. If the inward movement is accompanied by pain, or if dedicated exercises do not yield noticeable improvement, consulting a physical therapist is advised. A professional assessment can determine if the cause is structural or functional and create a specific rehabilitation plan.