Bow Legs and Knock Knees: What’s Normal and What Needs Treatment?

As parents, noticing unusual leg alignment in children, such as bow legs or knock knees, can be concerning. While these conditions are often part of normal development, it is important to understand what is normal and when treatment is necessary. Consulting a paediatric orthopaedic surgeon can provide clarity and guidance.

What Are Bow Legs and Knock Knees?

Bow legs occur when the legs curve outward, creating a noticeable gap between the knees when standing with feet together. In contrast, knock knees are when the knees touch while the ankles remain apart. These conditions are common in young children and typically change as they grow.

What Is Normal?

Leg alignment changes naturally during growth.

• Bow legs are common in babies and toddlers under two years old. This is because of their foetal position during pregnancy.
• By age 3 to 4, the bowing usually straightens.
• Knock knees become more noticeable around ages 4 to 6. This phase often resolves by age 7 to 8, with legs straightening into normal alignment.

In most cases, these changes do not require treatment as they are part of normal growth.

When Should You Be Concerned?

Although most children outgrow these conditions, some cases may need medical attention. Signs to look out for include:

• Severe bowing or knock knees that worsen over time.

• Unequal leg alignment on both sides.
• Persistent issues beyond age 8 years old.
• Pain.
• Underlying medical conditions, such as malnutrition, rickets or bone infections.

Causes of Abnormal Alignment

Abnormal bow legs or knock knees may result from:

• Rickets, caused by vitamin D deficiency.

• Blount’s disease, a growth disorder affecting growth plate in the shinbone.

• Bone fractures or injuries that healed incorrectly.
• Genetic conditions affecting bone development.

Treatment Options

When treatment is required, your paediatric orthopaedic surgeon may recommend:

• Observation and monitoring: Mild cases often improve with time.
• Physical therapy: Exercises may strengthen muscles and improve alignment.
• Surgery: Occasionally, some cases may need surgical correction to straighten the legs.

Guided growth surgery (Hemiepiphysiodesis)

Guided growth is a minimally invasive surgical procedure where a tension band plate (also called a guided growth plate / 8-plate) is applied to a crooked bone to gradually straighten it as a child or adolescent grows.  Guided growth is also sometimes called temporary hemiepiphysiodesis or growth modulation. 

• What are tension band plates?

These plates are about the size of a paper clip and are shaped like the number 8. It consists of a plate that is secured to the bone using two bone screws.

• What are growth plates?

Growth plates, also called physis, are responsible for bone growth in children.  They are located at each ends of the long bones and are made of a thin layer of specialized growth cartilage.  As children become adults or skeletally mature, the growth plates disappear and are replaced by bone. 

• How does guided growth work?

Most bone growth in the legs happen near the knees, so the 8-plate is typically applied to the growth plates that are closest to the knee.  The hardware is only applied on one side of the involved knee.  The position causes the bone growth to temporarily stop/slow on that side of the growth plate.  The other side of the growth plate continues to grow normally and this will gradually straighten out the crooked deformity over time. 

• What happens during guided growth surgery?

Typically the child is placed under general anaesthesia for this minimally invasive surgery.  An approximately 1 to 1.5- inch (2.5-3.5 cm) incision is made and the 8-plate inserted and secured with bone screws so that it is on each side of the growth plate. 

• What happens after guided growth surgery?

The patient can put weight on the leg immediately post surgery and should be able to return to normal daily activities within 3-4 weeks.  Contact sports should be avoided for 6 weeks.  There may be some swelling in the knee and physical therapy is recommended for a few weeks to prevent stiffness.   Follow up should happen regularly so the surgeon can monitor the gradual straightening of the bone.  These visits are very important.  If the plates remain in place for too long, the bone may be over-corrected (crooked in the opposite direction).  After the correction is achieved, the hardware is removed.  After removal the bone will continue to grow normally. 

• What is rebound?

After treatment is completed and the hardware is removed, the bone may grow crooked again.  This happens in some patients and is called a rebound.  When rebound is anticipated especially if the child is very young, the surgeon may recommend partial removal of the hardware so that it can easily be reinserted in the future if required.  This means that instead of removing the 8-plate and both screws, the surgeon will remove only one screw, leaving the 8-plate and the other screw in place. 

• Is the timing of guided growth important?

A child’s bone age may be different than the child’s chronological age.  Accuracy of timing may be improved by examining Xrays of the hand to determine the child’s bone age, which is an estimate of the maturity of the skeletal system.  The surgery is only done if the child has at least 2 years of growth left before skeletal maturity (estimated 14 for girls and 16 for boys).  The timing of correction, including removal of the growth modulation device is very important, as over-correction or under-correction can happen.  It is important to maintain follow up during the correction phase. 

• Does guided growth work in adults?

Guided growth does not work in adults (skeletally mature).  It only works in children while their bones are still growing / growth plate still open.

Bone osteotomy

In severe deformities or in skeletally mature bone, a bone cut (osteotomy) may be required.  Depending on the degree of correction required, the correction may be acute (internal fixation with a plate) or gradual (external fixator i.e. Ilizarov frame).

Early intervention ensures better outcomes and prevents future complications.

Conclusion

Bow legs and knock knees are often normal phases of development in children. However, persistent or severe cases may indicate underlying issues requiring medical attention. If you notice unusual leg alignment in your child, consult a paediatric orthopaedic surgeon for a professional assessment. Timely diagnosis and treatment can support your child’s healthy growth and mobility.

Understanding what’s normal and when to seek help provides peace of mind and ensures your child receives the care they need.