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Knock Knees

What is Knock Knees?

In order to understand knock knees, also called genu valgum, it is important to first understand “normal” alignment of the legs. In the normal situation, when standing, the hips, knees and ankles all fall on a straight line. In other words, when you draw a line from the hip to the ankle, that line passes directly through the center of the knee. If that line passes to the outside of the knee (externally), this is called knock knees (genu valgum). If that line passes to the inside of the knee (internally), this is called bowlegs (genu varum).

Three color illustrations showing alignment from the hip to the ankle in an AP view. Images show normal alignment, knock knee alignment and bow leg alignment.

How is knock knees diagnosed?

On physical appearance, with the patient standing upright, the knees touch each other, but there is a wide space between the ankles. The best way to diagnose knock knees is by taking a standing X-ray, and drawing the straight line on the image from the hip to the ankle. If that line passes to the outside of the knee, there is genu valgum present. Additional diagnostic lines can be drawn to determine if the source of the angular deviation is coming from the femur (thigh bone) or the tibia (shin bone).

When looking at children’s X-rays, we also pay attention to the quality of the bone and the width of the growth plates. (Growth plates are responsible for children’s arms and legs getting longer as they mature.) Children with nutritional vitamin D deficiency, vitamin D-resistant rickets (disorder in which the bones become painfully soft and bend easily), or with kidney failure, for example, have widened, irregular growth plates and can present with genu valgum. In children where vitamin D deficiency, vitamin D-resistant rickets, or kidney failure are suspected as the cause of knock knees, additional blood tests (e.g., complete blood count, phosphorus, vitamin D level, creatinine, calcium) can be done to specifically look for those issues.

How is knock knees classified?

Knock Knees can be described as mild, moderate and severe. However, a more useful way to look at knock knees by etiology (cause). The following may be causes of knock knees:

  1. Idiopathic (no known cause) usually appears in adolescence
  2. Renal rickets (associated with kidney failure and renal osteodystrophy—a bone disease that occurs when your kidneys fail to maintain proper levels of calcium and phosphorus in the blood)
  3. Nutritional (vitamin D-resistant rickets)
  4. Hypophosphatemic rickets (vitamin D-resistant rickets)
  5. Normal developmental knock knees (peak incidence at age three -four years)

What is the recommended treatment for knock knees?

Many children will present with knock knees in their toddler years. This can be a normal tendency in children and typically does not require any treatment. However, if X-rays look abnormal (i.e., excessively wide or irregular growth plates) or the child looks pale and sickly, then further work up (i.e., blood tests) is needed. If there are abnormalities of metabolism or kidney function, then special medical treatment is needed. For example, nutritional rickets is treated with vitamin D replacement. Vitamin D-resistant rickets (X-linked hypophosphatemic rickets) is treated with vitamin D and phosphorous replacements, and more recently, the drug Berosumab (Crysvita). If medical treatment is not successful in getting the legs to straighten, then surgery may be required. In idiopathic cases (where the cause is unknown), treatment can be done surgically.

When is surgery needed for knock knees?

In growing children, it is possible to do very small, minimally invasive surgeries that will modulate the growth of the legs, getting them to grow straight over a period of 6-18 months. This is done by implanting a staple or plate with screws next to the growth plate, on the convex side of the limb deformity (i.e., the inner knee for genu valgum). These treatments generally don’t require limited weight bearing or much physical therapy. For more information on this treatment, please see Guided Growth (Hemiepiphysiodesis).

In older children with less than two years of growth remaining until maturity, or in adults, this system of guided growth is not an option. Instead, we must go to more invasive surgical techniques, in which the affected bones are cut (osteotomy), straightened, and fixed with either some form of internal fixation (bone plate) or an external fixator. Any of these more invasive surgical options require restricted weight bearing for at least 6-8 weeks and physical therapy for longer periods of time.

Why come to the International Center for Limb Lengthening for treatment of knock knees?

Your doctor at the International Center for Limb Lengthening will take the time to make sure you understand all of your options and then will customize your treatment to meet your specific needs. Our patients benefit from our team-centered approach with world-renowned pediatric and adult orthopedic surgeons and specialized physician assistants, nurses and physical therapists. We help patients with knock knees achieve their best possible result.

Doctors Who Treat Knock Knees