Bow legs, medically known as genu varum, describe a condition where the legs curve outward, causing the knees to remain wide apart even when the ankles are together. This article explores the factors contributing to this condition, from normal childhood development to underlying medical issues in children and adults.
Defining Bow Legs and Normal Development
Genu varum is characterized by an outward bowing of the leg, where the lower leg angles inward in relation to the thigh’s axis, creating a visible space between the knees when the feet are aligned. This differs from “knock knees” (genu valgum), where the knees touch but the ankles are separated. Bow legs are a common and temporary occurrence in infants and toddlers, referred to as physiological bowing.
Physiological bowing is a normal part of development, stemming from the cramped fetal position in the womb. This natural bowing is present from birth, usually peaking around 18 months. The legs gradually straighten, and the condition often resolves naturally by two to three years as the child grows and bones align. If bowing persists beyond this age or worsens, it may indicate an underlying medical issue.
Underlying Reasons in Children
While many cases of bow legs in children are physiological, some signal an underlying medical condition. Rickets is a cause, involving the softening and weakening of bones due to a prolonged deficiency of vitamin D, calcium, or phosphorus. Without sufficient vitamin D, the body struggles to absorb these minerals, leading to impaired bone development and bowing of the legs. Rickets can also manifest with bone pain, growth delays, and weakened muscles.
Another cause of pathological bow legs in children is Blount’s disease, or tibia vara. This growth disorder affects the growth plate of the shinbone (tibia) just below the knee, causing the leg to bow outward. Blount’s disease can affect one or both legs and often progresses as the child grows, potentially worsening if untreated. It is more common in children who begin walking early or are overweight, and it can also have a genetic component.
Less common factors include certain bone dysplasias, which are genetic conditions causing abnormal bone and cartilage growth. Conditions like achondroplasia, a common form of dwarfism, can lead to bow legs. Trauma to growth plates from injuries or poorly healed fractures can also disrupt normal bone development, resulting in a bowed appearance.
Underlying Reasons in Adults
In adults, bow legs can develop or persist due to various factors, often differing from childhood causes. A common reason is osteoarthritis, particularly when it affects the inner (medial) compartment of the knee. This degenerative joint disease leads to cartilage breakdown and bone changes, which can cause the knee to collapse inward and result in a bow-legged alignment. Increased stress on the inner knee due to this misalignment can accelerate arthritis progression.
Previous injuries or poorly healed fractures to the leg bones can also contribute to bow legs. If a fracture heals in an incorrect position, known as a malunion, it can lead to a visible deformity and potentially affect leg length, causing symptoms like pain in the back, hip, or knee. Such malaligned healing can occur in the tibia or femur, impacting overall limb alignment.
Certain metabolic bone diseases can also lead to bone deformities, including bowing, in adults. Paget’s disease of bone is one such condition, where the body’s normal bone recycling process is disrupted, causing bones to become fragile, enlarged, and misshapen. This can affect leg bones, leading to a bowed appearance. In some cases, bow legs present in childhood due to conditions like Blount’s disease or rickets may persist or worsen into adulthood if untreated.
Identifying and Addressing Bow Legs
Diagnosing bow legs involves a physical examination by a medical professional, who assesses leg alignment. The doctor observes the space between the knees when the patient stands with feet and ankles together. Imaging tests, particularly X-rays, confirm the degree of bowing and identify underlying causes like growth plate abnormalities, rickets, or joint degeneration. These images help determine bone involvement and guide treatment decisions.
Treatment for bow legs varies based on the underlying cause, severity, and patient’s age. For physiological bowing in young children, observation is the primary approach, as the condition resolves naturally without intervention. If an underlying condition like rickets is diagnosed, treatment focuses on addressing that issue, such as providing vitamin D and calcium supplementation.
In cases of Blount’s disease or other pathological bowing in children, bracing may guide the legs into a straighter position as they grow. For more severe or progressive bowing, or when other treatments prove ineffective, surgical intervention may be necessary.
Corrective osteotomy, a procedure involving cutting and realigning the bone, is a common surgical option to straighten the leg and improve alignment. Another surgical technique, guided growth, involves placing a small plate or staple to temporarily slow growth on one side of the bone, allowing the other side to catch up and gradually correct the deformity. Consulting a medical professional is essential for proper diagnosis and to determine the most appropriate course of treatment.