According to the Children's Hospital Boston, knock knees are a normal part of the growth process in children 2 to 4. It describes it as "A standing child whose knees touch but ankles do not." The legs are aligned outward, and the knees are together. By age 6, this configuration should have disappeared and developed into a more adult-looking alignment. If it persists or develops afterward, underlying causes should be examined.
Osteomyelitis
The University of Maryland Medical Center describes osteomyelitis as a bacterial or fungal infection of any bone of the body. Rare in the United States, it's seen mostly in children and adults older than 50. Men appear to be affected more than women. Infection can occur from direct trauma or from infection traveling from another area of the body. It can be acute--lasting two or three months--or chronic. If the leg bone is infected, knock knees may occur.
Rickets
Rickets are the result of a vitamin D deficiency. Vitamin D helps regulate the calcium and phosphate in the blood. According to the University of Maryland Medical Center, if this is absent, the body takes these minerals from the bones, causing a softening and weakening of the bones. Also known as osteomalacia,
rickets involves the the growth plates. Because adults no longer have growth plates, rickets are seen only in children.
Injury
An injury to the knee affecting the anterior cruciate ligament or ACL causes instability to the knee in children or young adults. The University of Washington Medicine describe the ACL as crucial in preventing the slipping of the tibia bone at the knee. An injured or deficient ACL may cause the knee to slip forward and give the appearance of knock knees. Trauma to the growth plates of the tibia also results in knock knees in children.
