Knock Knee: Causes, Symptoms, Diagnosis and Treatment

What Is Knock Knee?

Knock knee, also known as "knock-knee deformity," "knock-knee syndrome," "knocked knee," or "genu valgum" is a condition that affects people of all ages. It is characterised by an incorrect alignment around the knee, which causes the knees to bend inward and touch or "knock" against each other, even when a person is standing with their ankles apart. This misalignment places excessive force on the knee's outer side, leading to pain, joint damage, and early onset of knee arthritis over time. The condition is usually bilateral, affecting both legs, but it may only affect one knee in some cases. Correcting the deformity can improve knee mechanics and walking ability, decrease pain, and stop the rapid progression of damage to the knee.

Is it Normal?

Most children go through a phase where their knees knock together. This is a normal part of growth and usually corrects itself as the child gets older. However, if the knock knees stay beyond six years of age, is severe, or it affects one leg more than the other, it may be a sign of knock-knee syndrome. It's common for children to have bow legs until they start walking, usually between 12 and 18 months of age. By the time they are two to three years old, their legs typically angle inward, making them knock-kneed. The child's legs will normally straighten out by age seven to eight. If knock knees continue after this age or worsen over time, or if they only affect one leg, it may be due to a disease, infection, or other condition. In such cases, it's advisable to consult an orthopaedic specialist for further evaluation, as surgery may be required to treat the condition.

What Causes Knock Knee?

Knock knee is a condition caused by different factors, such as an underlying congenital or developmental disease, infection, or traumatic knee injury. Knock knee syndrome is caused by:

• Congenital conditions

• Metabolic disease

• Fractures that heal with a deformity (malunion) 

• Renal (kidney) failure

• Bone infection (osteomyelitis)

• Growth plate injury

• Physical trauma (injury)

• Arthritis (particularly in the knee)

• Benign bone tumours

• Rickets (a type of bone disease caused by lack of vitamin D)

High BMI and obesity can increase the pressure on the knees and contribute to knock knees.

Symptoms of Knock Knee

Knock knee is a condition where a person's knees are closer together than their ankles. When standing with legs straight and toes forward, individuals with knock knees may experience discomfort and pain due to their gait. Knock-knee syndrome can trigger pain and abnormal overload on one or both knees. This can result in bone deformity, knee instability, and progressive degeneration of the knee joint. The most noticeable symptom of a knock knee is the visible separation of ankles when the knees are put together.

The most prominent symptoms include:

• Symmetric inward angulation of the knees

• Ankles remain apart while the knees are touching

• Unusual walking pattern

• Outward rotated feet

• Knee, foot or ankle

• Hip pain

• Progressive knee arthritis as adults

• Knee instability

• A limp while walking

• Difficulty walking or running

• Stiff or sore joints

• Reduced range of motion in hips

• Feet not touching while standing with knees together

How Is Knock Knee Diagnosed?

The diagnosis of knock knee involves a thorough examination of an individual's medical history, family history, pre-existing conditions, and current health status. A physical examination of the child's legs and gait is also performed. In addition, a standing alignment X-ray or EOS image is taken, which produces an image of the leg from hip to ankle. This helps the orthopaedist locate the mechanical axis of the deformity and determine its location. The X-rays also identify the magnitude and location of the deformity.

Treatment Options for Knock Knee

Most children do not need any treatment as knock knees usually gets better as the child grows and their legs straighten. But sometimes physiotherapy or treatment from a foot specialist (podiatrist) may be recommended. If knock knees cause problems such as pain or difficulty walking, you may be referred to a specialist for tests to see what might be causing it. Rarely, surgery to straighten the knees and legs may be recommended as this option is only for severe cases.

If a disease or infection causes knock knees, doctors will treat that condition before or during orthopaedic correction. Treatment for mild cases may include braces to help bones grow correctly. If the condition doesn't improve gradually, surgery may be recommended.

Guided growth minimal incision surgery is used in growing children to encourage the limb to grow straight. Osteotomy, a procedure in which the femur is cut and realigned, may be necessary.

Braces can be used to reposition the knees for mild cases of knock knees in children or adolescents. However, if this method does not work or if the patient is an adult, a knee-realignment osteotomy may be necessary to prevent or delay the need for knee replacement surgery.

External fixators may also be used, which involve inserting pins into the bone and attaching them to an external stabilising structure. Physical therapy is important, especially after surgery. In skeletally mature adolescents and adults, osteotomy is recommended to straighten the legs. X-rays are used to determine the location and severity of the deformity. The femur is usually treated, but in some cases, the tibia or both femur and tibia may need treatment. For moderate deformity, internal fixation (plate or rod) is typically used to stabilise the osteotomy. For severe mal-alignment, gradual realignment of the limb can be achieved through the use of an external fixator after an osteotomy.