The term “bow-legged” describes a condition where the legs curve outward at the knees, creating a noticeable, wide space between the knees when a person stands with their feet and ankles together. Medically, this alignment is known as Genu Varum, where the lower leg bones angle inward relative to the thigh bones. This configuration gives the legs an “O” shape appearance, often visible during walking. The causes of Genu Varum differ significantly between infants, children, and adults.
Understanding Physiological Bowing: The Normal Curve
The most frequent occurrence of outward leg curvature is physiological genu varum, a normal part of skeletal development. Nearly all infants are born with some degree of bowing, resulting from the tightly flexed position maintained inside the uterus before birth. This positioning causes the lower leg bones to naturally rotate and bow slightly.
This physiological curvature is typically symmetrical, affecting both legs equally, and does not cause pain. The bowing usually becomes more pronounced when a child begins to stand and walk, placing weight on the curved bones. For most children, the condition corrects itself naturally as they grow and their bones mature. The legs usually straighten completely by the age of two or three years.
After the bowing resolves, the legs often transition into a period of knock-knees (genu valgum) between the ages of three and five years. The legs typically settle into normal adult alignment by the time a child reaches seven or eight years old. Physiological bowing resolves without medical intervention, unlike pathological causes which are often asymmetrical, worsen, or persist past the age of three.
Pathological Conditions Causing Bowing in Children
When Genu Varum does not resolve naturally or is severe, it indicates a pathological condition affecting bone growth or structure. One common underlying cause is Rickets, a bone growth disorder resulting from a prolonged deficiency of Vitamin D, calcium, or phosphate. These nutrients are necessary for bone mineralization; a shortage leads to soft, weak bones that bend under the pressure of standing and walking. Rickets causes the growth plates to widen and the leg bones to bow, though it is less common in developed nations due to fortified foods.
Another specific condition is Blount’s disease (tibia vara), which involves an abnormal growth of the inner part of the shinbone (tibia). This irregular growth plate development causes the bone to angle sharply just below the knee joint, leading to progressive bowing that worsens over time. Blount’s disease can manifest in toddlers (infantile) or adolescents, often linked to excess body weight or early walking. It is frequently asymmetrical, affecting one leg more than the other, and requires targeted treatment to prevent permanent deformity.
Bowing can also be caused by rare skeletal dysplasias, which are genetic disorders affecting the development of cartilage and bone. Achondroplasia, a form of dwarfism, is a well-known example where bowing is a common feature. Additionally, bone infections or fractures near the knee’s growth plate that heal improperly can disrupt normal alignment, leading to a fixed varus deformity.
Adult-Onset Bowing and Treatment Options
Bowing in older individuals often results from an untreated childhood condition that worsened, or it can develop later in life. The most common cause of adult-onset bowing is advanced osteoarthritis of the knee joint. Cartilage loss is often more pronounced on the inside (medial) compartment of the knee. The resulting collapse of the joint space shifts the mechanical load to the inner side of the leg, gradually pushing the limb into a bow-legged position.
Trauma can also be a factor, particularly if a severe fracture of the thigh bone (femur) or shin bone (tibia) near the knee heals with a misalignment. Diagnosis typically begins with a physical examination, measuring the distance between the knees, and observing the gait. X-rays are used to accurately measure the angle of the deformity and determine the source of the mechanical axis deviation. Blood tests may be necessary to rule out metabolic conditions like osteomalacia (the adult form of rickets).
Treatment varies based on the cause and severity, starting with observation for mild, non-progressive cases in young children. Pathological bowing, especially early Blount’s disease, may be managed with bracing to guide bone growth. For severe deformities, pain, or functional limitation in older children and adults, surgical correction is often necessary. The procedure of choice is frequently a high tibial osteotomy, where the shinbone is cut and realigned to shift the weight-bearing axis away from the damaged inner compartment of the knee. This realignment reduces pain and slows the progression of arthritis.