Axle misalignmentsWhile it is completely normal in childhood to have a temporary axial misalignment of the legs, the leg axis in adults is normally formed in such a way that an optimal load distribution on the knee joint is ensured. A bow leg (genu varum) or a knock-kneed leg (genu valgum) can lead to increased wear and tear (knee arthrosis) due to the asymmetrical load on the knee joint, depending on the degree of deformity.
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Children normally have a bow-leg position immediately after birth. In the course of growth, most children then temporarily develop a knock-kneed position, which develops into the normal physiological axis of the adult by the age of about eight to ten years. This shows an X-position (valgus position) of five to seven degrees.
A malalignment of the legs can occur due to a variety of causes. Growth disorders, accidents, inflammatory-rheumatic diseases, tumors, paralysis, overweight, congenital systemic diseases or metabolic diseases are possible reasons for this.
Symptoms and progression
While slight deformities are widespread and mostly harmless, more severe changes often lead to premature wear of the joint and thus to arthrosis .
The axial misalignment then increases over time, and it is not uncommon for the stabilizing ligaments of the knee joint to be affected as well. Pain as well as a feeling of instability when walking are common symptoms.
A simple test is to look at the legs in a standing position and check if the knee joint and the inner ankles touch each other. If this is not the case, there may be an axial malalignment: A gap between the knee joints indicates a varus leg axis (bow leg), while a gap between the medial malleoli indicates a valgus leg axis (knock-kneed). Patients can perform this test themselves, for example, in front of a mirror at home.
An exact diagnosis can be made by taking an x-ray of the leg axis with the aid of a so-called whole-leg x-ray. A special technique is used to record and analyze the entire length of the legs in a standing position. For the evaluation of the leg axis, the drawing of the so-called Mikulicz line has proven to be useful. This line runs from the center of the femoral head to the center of the upper ankle joint. Crosses the knee joint ideally a few millimeters inside related to the knee joint center. If the Mikulicz line runs further inwards, it is called a bow leg, if it runs further outwards, it is a knock-kneed leg.
Fig. 1: Whole-leg radiograph with the Mikulicz line drawn in; an knock-kneed leg is present. (Source: Prof. Markus Wunschel, Karlsruhe)
As mentioned above, slight axial deviations are harmless and do not need to be treated.
If a finding requiring therapy is present, the treatment depends on the stage of development of the skeleton.
Therapy in children and adolescents with open growth plates
As long as the skeleton is in growth, the desired correction of the axial malposition can be achieved with growth guidance. In this method, growth plates are closed temporarily or permanently (with the help of a so-called epiphysiodesis), so that the leg grows "by itself" in the desired direction and the leg axis corrects itself.
Fig. 2: Epipyhsiodesis on the inner femoral condyle (one of the two bony processes at the lower end of the femur, which is part of the knee joint) to correct a knock-kneed position in a child (source: Prof. Markus Wunschel, Karlsruhe)
Therapy for adults
In adults, axial malalignment can be corrected by what is known as an adjustment osteotomy. Depending on the technique used and the type of deformity, the lower leg and/or thigh bone is operated on to correct the axis. This procedure is often used in younger patients with joint arthrosis affecting only a part of the joint.
If the joint is already too worn, replacement of the knee joint by means of an endoprosthesis is usually necessary (knee prosthesis). Here the leg axis can also be corrected by appropriate techniques.
Fig. 3: Pronounced bow leg in a female patient with rheumatoid arthritis (Source: Prof. Fig. 4: Therapy of osteoarthritis. Malalignment by means of a prosthesis (Source: Prof. 4: Therapy of arthrosis. Axle malposition by means of prosthesis (source: Prof. Markus Wunschel, Karlsruhe)
Prevention / What patients can do themselves?
To prevent late effects such as early osteoarthritis, it is important to regularly check the leg axes of children and adolescents during growth. If abnormalities are detected, a pediatric orthopedic examination is recommended first, followed by surgical therapy if necessary.
Literature and further links
Pape, D. / Rope, R. / Adam, F. / Rupp, S. / Kohn, D. / Lobenhoffer, P.: Imaging and preoperative planning of tibial head osteotomy. The Orthopedist, 2004;33(2):122-34.
Duchow, J. / Kohn, D. /: The treatment of incipient gonarthrosis in middle age. The Orthopedist, 2003;32(10):920-29.
Vogt, B. / Schiedel, F. / Rodl, R.: Growth management in children and adolescents. The Orthopedist, 2014;43(3):267-84.
Westhoff, B. / Wild, A. / Krauspe, R.: Development of the leg axis in childhood and therapy options for malalignments near the knee joint. The Orthopaedist, 2002;31(12):1198-208.
Schmitt, E. / Heisel, J. / Jani, L. / Schumacher, G.: Knee joint near leg axis malalignments. Guidelines of orthopedics. German Society for Orthopedics and Orthopedic Surgery, Cologne: Deutscher arzteverlag, 2002. This dictionary entry contains only general information. Must not be used for self-diagnosis or self-treatment. It cannot replace a visit to the doctor.