Knock knees, medically termed Genu Valgum, is a common orthopedic concern where the knees touch while the ankles remain separated. This lower limb alignment issue involves an inward angling of the thigh and shin bones, altering the mechanical axis of the leg. While frequently observed in young children as part of normal growth, persistent or later-onset Genu Valgum can lead to pain and long-term joint strain.
What Defines Knock Knees (Genu Valgum)
Genu Valgum is defined by the inward angling of the knees toward the midline. The severity of the deformity is clinically measured by the intermalleolar distance—the space between the inner ankles when the knees are together. A distance of 8 centimeters or more often indicates a pathological condition requiring further evaluation.
A physician may also assess the Q-angle, which measures the alignment between the quadriceps muscle and the patellar tendon. An increased Q-angle, typically exceeding 17 degrees in females or 14 degrees in males, is associated with Genu Valgum. This increased angle indicates a greater lateral pull on the kneecap, which significantly impacts patellofemoral joint mechanics.
Developmental and Pathological Causes
The most frequent cause of knock knees in children is physiological genu valgum, a normal stage of lower limb development. Infants are typically bow-legged (genu varum) until about two years old, when the alignment reverses into a knock-kneed configuration. This inward angling usually peaks between three and five years old and spontaneously corrects itself to the final adult alignment by age seven or eight.
When the condition does not self-correct or appears later in life, it is classified as pathological genu valgum, often linked to an underlying medical issue.
Pathological Causes
Pathological causes include:
- Metabolic bone diseases, such as Rickets, caused by severe deficiency in Vitamin D, calcium, or phosphate. This systemic weakening softens bone tissue and leads to bilateral deformity requiring nutritional treatment.
- Trauma to the growth plates from a previous fracture or infection, which disrupts normal bone growth.
- Localized problems, such as a growth plate injury or a benign bone tumor, often resulting in unilateral genu valgum (affecting only one leg).
- Excessive mechanical stress from conditions like obesity, which increases the load on the knee joints and worsens the valgus angle.
- Certain genetic syndromes and skeletal dysplasias that affect the growth and development of bone and cartilage.
Associated Pain and Long-Term Joint Strain
The inward knee alignment significantly alters the biomechanics of the lower limb, leading to an abnormal distribution of forces across the knee joint. This misalignment shifts the mechanical axis of weight-bearing laterally, forcing disproportionate stress onto the outer compartment of the knee. This increased pressure on the lateral cartilage and meniscus causes localized pain and contributes to accelerated wear.
The altered gait pattern associated with Genu Valgum, which may include a waddling walk or foot pronation (flat feet), places strain on surrounding muscles, ligaments, and tendons. Individuals often experience patellofemoral pain syndrome (discomfort around the kneecap) due to the excessive lateral pull on the patella caused by the increased Q-angle. This abnormal loading can also strain ligaments, stretching the medial collateral ligament and tightening structures on the outer knee.
This persistent abnormal stress increases the likelihood of developing osteoarthritis, specifically targeting the lateral compartment. Since osteoarthritis involves the progressive breakdown of joint cartilage, the chronic overloading seen in Genu Valgum can accelerate this degenerative process. Addressing the misalignment is crucial for mitigating the long-term risk of severe joint deterioration.
Treatment and Management Strategies
Management depends highly on the individual’s age, the underlying cause, and the severity of the deformity. For physiological genu valgum in young children, the primary strategy is careful observation, as the condition is expected to resolve naturally by late childhood. Regular follow-up appointments monitor the alignment and ensure the intermalleolar distance is decreasing over time.
Non-Surgical Interventions
Non-surgical interventions are the first line of treatment for cases that persist, cause pain, or are linked to muscle weakness. Physical therapy focuses on strengthening muscles that stabilize the hip and knee, such as the hip abductors and internal rotators, to counter the mechanical forces pulling the knee inward. Custom orthotics or shoe inserts can address excessive foot pronation, improving overall leg alignment and reducing strain. Weight management is strongly recommended for overweight individuals, as reducing body mass significantly lowers the mechanical load on the knee joints.
Surgical Correction
Surgical correction is reserved for severe deformities that cause significant pain, functional limitation, or rapid progression. In growing children, guided growth (hemiepiphysiodesis) involves the temporary placement of a small metal plate on one side of the growth plate. This slows growth on the inner side of the knee, allowing the leg to gradually straighten over time. For adolescents or adults, a corrective osteotomy is typically used, involving surgically cutting and realigning the bone (femur or tibia) to restore the proper mechanical axis. This procedure aims to redistribute weight evenly across the joint, relieving pain and preventing further deterioration.