Malalignment of the lower limb can be present since childhood or can be acquired due to a fracture which has healed in a mal-aligned position. Degenerative (wear and tear) changes in the knee joint can also contribute to the deformity.
Deformities include abnormal angulation when viewed from the front or the side, abnormal rotation in the axis of the bone (torsion), and a discrepancy in length of the bone. Malalignment can lead to problems with function, or result in an uneven distribution of load through the joints.
Limb realignment following trauma
Limb malalignment after severe lower limb trauma is often multiplanar (made up of a combination of angulation in different planes, rotation, length discrepancy and translation). Minor deformity is amenable to non-operative treatment with physiotherapy, activity modification and the use of specialist footwear including heel raises. If there is malalignment causing problems which are refractory to non-operative management then surgery may be indicated.
Sometimes in individuals who are bow-legged, as a consequence of uneven load distribution, there may be arthritis affecting the inner (medial) side of the knee joint whilst the outer (lateral) side has much lower loads passing through it and the cartilage is unaffected. Wear on the cartilage in the medial compartment can exacerbate bow-legged (varus) malalignment and result in further loading of the inner (medial) side. The converse is true in some individuals who have knock-knees (valgus deformity).
By realigning the knee joint the body weight is shifted away from the damaged side, onto the healthy side. This relieves the pain that is due to arthritis in the knee by offloading the damaged side and can delay the need for knee replacement in young active individuals.
Osteotomy can also help with symptoms of instability: By altering the slope of the tibia it is possible to reduce the dependence of the knee on the anterior or posterior cruciate ligament.