Angular deformities of the lower limbs occur when the legs deviate inward or outward from the body’s midline. The condition commonly known as “bow-legged” is medically termed Genu Varum, where the knees angle away from each other. The direct opposite of this alignment is Genu Valgum, often called “knock-kneed,” where the knees angle inward and touch or overlap. Understanding these conditions requires first grasping what constitutes a typical, or neutral, lower leg alignment.
Defining Normal Lower Leg Alignment
A healthy lower limb alignment is defined by the mechanical axis, an imaginary line extending from the center of the hip joint to the center of the ankle joint. In neutral alignment, this axis passes directly through or very near the center of the knee joint. This positioning ensures that weight-bearing forces are distributed evenly across the medial (inner) and lateral (outer) compartments of the knee. Normal adult alignment actually exhibits a slight outward angle, or valgus, where the mechanical axis runs slightly medial to the knee center. This small physiological valgus angle is a natural result of the wider human pelvis.
Genu Varum (Bow-Legged) Explained
Genu Varum, or bow-leggedness, is an alignment where the knees curve visibly outward, creating a gap between the knees when the ankles are touching. In this condition, the mechanical axis of the leg shifts medially, falling on the inner side of the knee joint. This medial displacement concentrates the weight-bearing load on the medial femoral condyle and the medial tibial plateau. This pathological loading on the inner knee compartment can lead to uneven cartilage wear and potential discomfort, especially as a person ages.
Genu Valgum (The Opposite Condition)
Genu Valgum, commonly known as knock-knees, is the anatomical opposite of Genu Varum, characterized by an inward angling of the knees. When a person with this condition stands with their knees touching, their ankles and feet are visibly separated. This alignment causes the mechanical axis to shift laterally, falling on the outer side of the knee joint. The weight-bearing stress is then concentrated on the lateral (outer) femoral condyle and tibial plateau.
Genu Valgum is a normal developmental stage in children, typically beginning around age two and peaking between three and four years old. The condition generally corrects itself spontaneously as the child grows, moving toward the slight valgus alignment considered normal in adults by about age seven.
Causes and When to Consult a Doctor
The most frequent cause of angular deformities in childhood is a normal developmental process called physiological bowing or knocking. Babies are born with Genu Varum, which naturally progresses to Genu Valgum before settling into a neutral alignment. Pathological causes, which signify an underlying disease, include rickets, a bone growth disorder caused by a deficiency in Vitamin D or calcium, and Blount’s disease, which affects the growth plate of the tibia.
A medical evaluation is warranted if the angular deformity is asymmetrical, meaning one leg is affected more than the other. Consultation is also advised if Genu Varum persists after age two, or if Genu Valgum is still present or worsening after age seven. Other concerning signs include pain, a persistent limp or unsteady walking, or if the child’s height is significantly below average.