A knock knee occurs when the knees bend inward and touch or “knock” against each other even when the ankles are apart. The condition can cause pain, joint damage, poor posture, and difficulty walking, among other problems. Although knock knees can affect anyone, it is most common in children. By the age of seven or eight, it normally corrects itself because it is a normal part of growth and development. In some cases, it may persist or worsen over time, or it may be caused by a disease or condition that requires medical attention.
Knock knees are believed to be caused by a problem with the development of the bones and cartilage in the legs during pregnancy. Some risk factors include:
Genetic mutations in the genes GDF6, GDF3, or MEOX1
Metabolic diseases, such as rickets (a bone disease caused by lack of vitamin D) or renal (kidney) failure
Physical trauma, such as injuries, fractures, or infections that affect the growth plates or the bones in the legs
Arthritis, especially in the knees, that causes inflammation and damage to the joints
Congenital conditions, such as fetal alcohol syndrome, Goldenhar syndrome, or hemifacial microsomia, that affect the development of the face and body
Knock knees are characterized by the inward bending of the knees, which is visible when the legs are straight and the feet are together. There may be a gap between the ankles of several centimeters to more than 10 centimeters (4 inches). Other symptoms include:
Pain or stiffness in the knees, hips, ankles, or lower back
Difficulty walking, running, or jumping
Reduced range of motion in the legs
Abnormal gait or posture
Frequent falls or tripping
Problems with balance and coordination
Reduced self-esteem or confidence
Occasionally, an ultrasound can detect knock knees during pregnancy, but it is usually discovered after birth or in childhood. In order to diagnose the condition, the legs are examined and the angle between the thigh bone and the shin bone is measured. Adults normally have a Q-angle of less than 15 degrees and children typically have a Q-angle of less than 20 degrees. Children with a Q-angle of more than 30 degrees or adults with a Q-angle of more than 20 degrees have knock knees.
In addition to imaging tests, such as X-rays, CT scans, and MRI scans, genetic tests may also be conducted to identify any mutations in the genes associated with knock knees1.
In most cases, knock knees will resolve on their own as the child grows, so no treatment is required. However, some treatment options may include:
Medications and supplements to treat any underlying diseases or deficiencies, such as vitamin D, calcium, or anti-inflammatory drugs
Physical therapy to improve the strength and flexibility of the muscles and ligaments in the legs, and to correct the posture and gait
Orthotics, such as braces, splints, or shoe inserts, to support the legs and align the knees
Surgery to correct the deformity of the bones or joints, such as osteotomy (cutting and reshaping the bone), epiphysiodesis (stopping the growth of one side of the bone), or arthroplasty (replacing the joint with an artificial one)
When a child's condition is severe or cannot be treated with other means, surgery is usually reserved. As the bones are still growing and healing, surgery is less risky and more effective in children than it is in adults. A surgeon's preference will determine the type and timing of surgery.
As a genetic or developmental disorder, knock knees cannot be prevented. However, some steps can be taken to reduce complications and improve quality of life for people with knock knees.
Avoiding activities that can injure or strain the legs or knees, such as contact sports, diving, or heavy lifting
Wearing protective gear, such as helmets and seat belts, when riding a bike or a car
Following the doctor’s recommendations for medications, supplements, physical therapy, orthotics, or surgery
Having regular check-ups to monitor the condition and the growth of the legs
Seeking support from family, friends, or professional counselors to cope with the emotional and social challenges of living with knock knees
