Knees that visibly angle outward are medically termed Genu Varum, commonly known as bow-leggedness. This alignment issue affects how the body distributes weight and moves. Genu Varum is characterized by the legs resembling an archer’s bow. Understanding the nature of this condition, its causes, and potential long-term effects is the first step toward effective management.
Describing Outward Knee Alignment
Genu Varum is an angular deformity of the knee joint where the lower leg angles inward relative to the thigh bone, creating an outward curve at the knee. When an individual stands with their ankles touching, a noticeable space remains between the knees, which is the defining characteristic of this alignment. In a properly aligned leg, a straight mechanical axis line should pass from the center of the hip joint, through the center of the knee, and down to the center of the ankle joint.
In Genu Varum, this mechanical axis is displaced toward the inner side of the knee, meaning the weight-bearing line falls medial to the center of the joint. The severity of the alignment is often measured using imaging techniques like full-length standing X-rays, which quantify the hip-knee-ankle angle.
Underlying Causes of This Alignment
The reasons for the development of an outward knee alignment are broadly categorized as either developmental or acquired. In infants and toddlers, a condition called physiologic Genu Varum is common and considered a normal variation of growth, typically resolving spontaneously by the age of three. If the bowing persists or worsens past this age, it is often a sign of pathologic Genu Varum.
Developmental Causes
One of the most common pathologic causes is Blount’s disease, a growth disorder affecting the inner part of the upper shinbone’s growth plate, which can appear in early childhood or adolescence. Nutritional deficiencies, particularly Rickets caused by a lack of Vitamin D, calcium, or phosphate, soften the bones and lead to progressive bowing due to body weight. Skeletal dysplasias, which are genetic bone growth disorders like achondroplasia, can also contribute to this alignment.
Acquired Causes
For adults, the outward alignment is frequently an acquired condition resulting from joint deterioration or trauma. Severe osteoarthritis that disproportionately affects the inner (medial) compartment of the knee can cause a gradual collapse and subsequent bowing of the leg. Previous fractures or injuries to the bones around the knee that healed improperly can also lead to a persistent angular deformity.
Potential Long-Term Health Consequences
The outward angulation of the knee alters the biomechanics of the lower limb, causing a redistribution of forces across the knee joint. The primary concern is the excessive mechanical loading placed onto the inner compartment of the knee. This medial compartment overload accelerates the wear and tear on the cartilage and menisci, increasing the risk of developing premature osteoarthritis.
This uneven weight distribution can lead to chronic knee pain, especially during weight-bearing activities or prolonged standing. The altered alignment also affects gait, potentially causing a lateral knee thrust, where the knee visibly shifts outward with each step. These functional changes can further stress the ligaments and muscles, leading to instability and secondary effects on the hip and ankle joints. If the condition is unilateral, a functional leg-length discrepancy can result, compounding walking difficulties and placing unequal strain on the spine. Untreated, the resulting joint degeneration can necessitate complex surgical interventions later in life.
Treatment and Management Options
The approach to managing outward knee alignment depends heavily on the patient’s age, the underlying cause, and the severity of the deformity.
Pediatric Treatment
For young children with physiologic Genu Varum, no intervention is typically needed beyond observation, as the condition often corrects itself with normal growth. If the bowing is due to Rickets, treatment focuses on correcting the nutritional deficiency with supplements, which may allow the bones to remodel and straighten. In children with progressive bowing due to conditions like Blount’s disease, non-surgical options may include bracing or corrective orthotic devices, although their effectiveness is limited in more severe cases. A minimally invasive surgical technique called guided growth may be used, which involves temporarily slowing growth on the outer side of the growth plate to allow the inner side to catch up and straighten the leg.
Adult Treatment
For adolescents and adults with a fixed angular deformity, surgical realignment is often necessary to prevent or slow the progression of arthritis. A procedure known as a High Tibial Osteotomy involves cutting and reshaping the tibia (shinbone). This shifts the weight-bearing axis away from the damaged inner compartment toward the healthier outer compartment. In cases where advanced osteoarthritis has already severely damaged the joint surfaces, a total or partial knee replacement may be the final option to restore function and relieve pain.