A valgus knee, commonly known as “knock-knee,” is an orthopedic condition defined by the inward angling of the knee joint. This misalignment causes the knees to touch or almost touch when standing, while the ankles remain separated. The condition affects the mechanical axis of the entire leg, disrupting the natural weight distribution across the joint. While often observed as part of normal growth in young children (ages three to six), a persistent valgus alignment in adolescence or adulthood may indicate an underlying issue that requires attention.
Defining the Valgus Knee Angle
The term “valgus” refers to a deformity where the bone segment furthest from the body’s center, or distal segment, is angled outward, away from the midline. In the knee, this results in the lower leg (tibia) splaying outward relative to the thigh bone (femur), creating the characteristic knock-kneed posture. This mechanical misalignment shifts the load-bearing axis of the leg to the outer side of the joint, placing excessive stress on the lateral compartment of the knee.
The degree of this inward angle is assessed using the Quadriceps Angle, or Q-angle, which is formed by two intersecting lines. One line connects the hip bone’s anterior superior iliac spine to the center of the kneecap, and the second line runs from the center of the kneecap down to the shin bone’s tibial tubercle. An increased Q-angle is directly associated with valgus knee alignment. While a natural valgus angle exists (around 14 degrees in males and 17 degrees in females), an excessive angle indicates a structural problem. A mechanical axis deviation of 1.1 degrees or more valgus is considered malalignment, and angles over 20 degrees are classified as severe.
Common Causes and Risk Factors
The development of a valgus knee stems from developmental, structural, and acquired causes. Physiological valgus is a normal developmental phase in young children that usually self-corrects by age seven; failure to correct past this point is considered pathological. Structural factors often relate to genetics or congenital conditions, such as bone dysplasias, which predispose an individual to alignment issues.
Acquired causes include systemic conditions affecting bone health, such as rickets (caused by Vitamin D deficiency) or kidney failure. Trauma, including fractures that heal improperly or prior knee surgery, can also lead to valgus deformity in adults by causing the outer knee compartment to collapse. Furthermore, mechanical imbalances originating outside the knee joint, such as chronic weakness in the hip muscles (gluteus maximus), can allow the knee to collapse inward during weight-bearing activities.
Associated Symptoms and Long-Term Complications
The inward angulation of the valgus knee disrupts the body’s natural biomechanics, leading to a number of immediate symptoms. Individuals may experience knee pain, often localized to the side of the knee due to excessive strain on the lateral structures, as well as joint instability. The altered alignment can also cause patellar tracking issues, where the kneecap is pulled laterally, contributing to pain at the front of the knee, known as patellofemoral pain syndrome. An abnormal gait pattern can develop, sometimes causing the knees to rub together during walking, which may lead to fatigue and reduced mobility.
The most significant long-term consequence of chronic valgus malalignment is the accelerated wear and tear on the knee joint surfaces. Because the mechanical load is shifted to the outer side of the joint, this excessive pressure causes the breakdown of the cartilage and the lateral meniscus, leading to early-onset osteoarthritis in the lateral compartment. Studies have shown that even mild valgus malalignment, defined as 1.1 to 3 degrees, is associated with a substantially increased risk of disease progression and lateral cartilage damage. This progressive joint degeneration can eventually result in debilitating pain and a significant reduction in the quality of life.
Non-Surgical and Surgical Management
Management of valgus knee depends heavily on the patient’s age, the severity of the deformity, and the presence of pain or arthritis. Non-surgical approaches are the initial focus for mild to moderate cases, aiming to reduce symptoms and improve biomechanics.
Non-Surgical Treatments
Physical therapy is frequently prescribed to strengthen the muscles that stabilize the knee and hip, specifically the gluteal muscles. This helps improve movement mechanics and correct an abnormal gait. Conservative treatments also include the use of custom orthotics or shoe inserts, which can help redistribute pressure in the lower leg and improve overall limb alignment. Bracing may be utilized to provide external support and stability to the joint during activity. Pain management techniques, such as anti-inflammatory medications, are often used concurrently to alleviate discomfort associated with the condition.
Surgical Intervention
For severe deformities, or when non-surgical treatments fail to control pain and the condition progresses to advanced arthritis, surgical intervention is considered. The gold standard for correcting valgus malalignment in younger or middle-aged patients is an osteotomy. This procedure involves surgically cutting and reshaping the bone, typically the femur just above the knee (distal femoral osteotomy), to realign the limb and shift the load-bearing axis back toward the center of the joint. For patients with advanced, debilitating arthritis, a total knee replacement may be necessary to restore function by replacing the damaged joint surfaces with an artificial implant.