Knock knees, known medically as genu valgum, describe a condition where the knees angle inward and touch, while the ankles remain separated when standing. This alignment can give the legs an “X-shaped” appearance.
Understanding Knock Knees
Knock knees, an inward angulation of the knees, are a common part of leg development in many children. Infants are born with a bow-legged appearance, where their knees curve outward. This alignment usually shifts to a knock-kneed alignment as children reach toddler age, often becoming noticeable between two and three years old.
The inward angle of the knees often peaks around three to four years of age. This physiological genu valgum is a normal and temporary stage, with the leg alignment gradually correcting itself as the child grows. In most instances, this natural correction occurs without intervention by the time a child reaches seven or eight years of age.
When Knock Knees Signal a Concern
While often a normal developmental stage, certain indicators suggest knock knees might be more than a temporary phase and could benefit from medical evaluation. These include persistence beyond age seven or eight, or a worsening severity of the inward angulation over time.
Asymmetry, where one knee is significantly more affected than the other or only one leg exhibits the inward tilt, is an important sign. Pain in the knees, hips, or ankles, or the development of a limp or unusual walking pattern, can signal an underlying issue. Difficulty participating in physical activities like running or walking, or a rapid progression of the deformity, are also reasons for medical consultation. Additionally, if knock knees appear before age two or after age seven, or if the distance between the ankles exceeds about eight centimeters when the knees are together, professional assessment is recommended.
Underlying Causes of Knock Knees
Knock knees can stem from various factors, broadly categorized into physiological and pathological causes. Physiological genu valgum is a common, self-correcting part of normal growth and development in children. The changing angles of the hip, thigh, knee, and foot during development contribute to this temporary alignment.
Pathological causes, which are less common, often involve underlying medical conditions. Metabolic bone diseases, such as rickets, result from deficiencies in vitamin D or calcium that affect bone formation. Genetic syndromes like skeletal dysplasias or lysosomal storage diseases can also lead to knock knees. Other causes include bone infections, trauma or injury to the growth plates around the knee, and conditions like obesity that place additional stress on the joints. Inflammatory diseases, renal failure, or benign bone tumors may also contribute to the development of knock knees.
Diagnosis and Treatment Approaches
Diagnosing knock knees begins with a physical examination where a medical professional observes the child’s standing posture and walking pattern. The distance between the ankles when the knees are touching may be measured to assess the severity of the alignment. If the child is older than seven, or if there is asymmetry in the legs or suspicion of an underlying condition, X-rays may be used to evaluate the bone structure and identify the source of the angulation. Blood tests might be performed to check for metabolic causes like vitamin D deficiency.
For most cases of physiological knock knees, observation and monitoring are the approaches, as the condition often resolves spontaneously with growth. If an underlying medical condition is identified, treatment focuses on addressing that cause, such as providing vitamin D and calcium supplements for rickets. Physical therapy exercises may be recommended to strengthen supporting muscles and improve posture. Bracing or orthotics are sometimes considered, particularly for cases involving leg length discrepancies.
For severe, progressive, or symptomatic knock knees that do not resolve naturally, surgical interventions may be necessary. Guided growth surgery, or hemiepiphysiodesis, is a minimally invasive option for growing children, involving the placement of a small metal plate to temporarily slow growth on one side of the bone, allowing the other side to catch up and straighten the leg. For older adolescents or adults, an osteotomy may be performed, which involves cutting and realigning the bone to correct the angular deformity and redistribute weight more evenly across the knee joint.