An axial malalignment of the lower limb is present when the mechanical axis of the limb, which defines the load bearing, is not running through the middle of the knee.
If the mechanical axis is too medial to the middle of the knee (too much on the inner side), genu varum (bowleg deformity) is present. If the mechanical axis is too lateral to the middle of the knee (too far on the outer side), genu valgum (knock-knee deformity) is present. Each of these deformities frequently occurs in both limbs, which leads to the typical images that inspired the terms bowlegs and knock-knees.
Many children have bowlegs after birth, which then slowly develop into knock-knees. This is completely normal and does not require any treatment. The limbs usually grow straight until age 6 to 8 years.
However, if spontaneous correction does not occur and normal alignment is not reached, incorrect loading of the knee joint can lead to increased wear of the cartilage and subsequent arthritis and pain later in life. Sometimes bowlegs and knock-knees are hereditary (run in the family).
As such, if a bone deformity based on the joint angles at the knee cannot be corrected by other means, such as physical therapy, surgery might be warranted. If the axial malalignment exceeds a certain extent, different surgical options are available for correction.
In milder cases with a normal and healthy growth plate, growth can be guided. The growth plate can be blocked on one side, which results in asymmetric growth and change of the alignment of the leg. Therefore, a small 8-shaped plate with one small screw above and one below the growth plate is inserted during a short surgery.
Only in severe cases, such as congenital, metabolic, or syndromic disorders, or after trauma is external fixation used for correction. In those cases, a six-axis external fixation frame such as the Taylor spatial frame (Smith & Nephew, Memphis, Tennessee, USA) can achieve correct alignment in all planes.