Genu varum and genu valgum in children are frontal plane deformities of the knee angle. The range of normal for knee angle changes with age. Lateral bowing of the tibia in children is common during the first year, bowlegs are common during the second year, and knock-knees are most prominent between ages 3 and 4 years. Varus or valgus deformities are classified as either “focal,” as seen in tibia vara, or “generalized,” as occurs in rickets.
History Inquire about the onset. Was there an injury or illness? Is the deformity progressing? Are old photographs or radiographs available for review? Is the child’s general health good? Does the family provide a normal diet? Are other family members affected?
Physical examination Start with a screening evaluation. Does the child have normal height and body proportions? Short stature is common in rickets and various syndromes. Are other deformities present? Is the deformity symmetrical? Is the deformity localized or generalized? Are the limb lengths equal? Shortening and knee angle deformity may be due to epiphyseal injuries or some developmental problems such as fibular hemimelia. Measure the rotational profile. Frontal and transverse plane deformities often coexist; make a clear separation. Measure the deformity. With the patella directly forward, measure the knee angle with a goniometer. Measure the intermalleolar or intercondylar distance. Does the deformity increase when the child stands? If the collateral ligaments are lax, such as in achondroplasia, the varus deformity is worse in the upright position.
Laboratory If the child has a generalized deformity, order a metabolic screen, including calcium, phosphorus, alkaline phosphatase, and creatinine, plus a hematocrit.
Imaging If findings suggest the possibility of a pathological basis for the deformity, order a single AP radiograph of the lower limbs. If knee ligaments are loose, make the radiograph with the infant or child standing. Position the child with the patella directly forward. Use a film large enough to include the full length of femora and tibiae. A 36-inch film is often required. Study the radiograph for evidence of rickets, tibia vara, or other problems. Measure the metaphyseal-diaphyseal angle of the upper tibia. Values above 11° are consistent with but not diagnostic of tibia vara. Measure the hip-knee-ankle angle. Complete the evaluation with other imaging studies if necessary. For knee deformities, a lateral radiograph is useful. CT or MRI studies may be useful in identifying and measuring a physeal bridge. Document the deformity by photography. A sequence of photographs provides a graphic record of the change with time.
Mechanical axis Obtain a long, standing radiograph of the lower limbs. Be certain the child is positioned with the patella directly anterior when the exposure is made. Draw the axis of the femur and tibia connecting the center of the femoral head to the center of the distal femoral epiphysis. Construct a second line between the midpoint of the upper and lower tibial epiphyses. Mark the articular surfaces. Measure the degree of valgus or varus.
Zone system On a full-length radiograph, draw a line between the femoral head and ankle. Note the position of the knee relative to this axis
Follow a plan. First make the differentiation between physiologic and pathologic forms. If a pathologic form is present, consider the different categories of causes. Causes are varied, and usually the diagnosis is not difficult.
The vast majority of children have bowlegs or knock-knees that will resolve spontaneously. Document these physiological variations with a photograph and see the child again in 3–6 months for follow-up. No radiographs are necessary. If the problem is pathological, establish the cause. Then consider treatment options.
Nonoperative treatment with shoe wedges is not effective and should be avoided. Long-leg bracing may be used for early tibia vara, but its effectiveness is uncertain. Avoid long-term bracing for conditions such as vitamin D–resistant rickets because the effectiveness of bracing is unclear and considerable disability results from brace treatment.
Operative correction options include osteotomy, or hemiarrest procedures either by hemiepiphysiodesis or unilateral physeal stapling. The objectives of operative treatment are to
- (1) correct knee angle,
- (2) place the articular surfaces of the knee and ankle in a horizontal position,
- (3) maintain limb length equality,
- (4) correct any coexisting deformities.
To achieve these objectives, preoperative planning is required.
Make cutouts Before undertaking any osteotomy, make tracings of the bone and perform the intended osteotomy on the paper. This allows previsualizing the outcome and making necessary modifications beforehand.
Make corrective osteotomies as close to the site of deformity as practical.
Translation of the osteotomy may be necessary to position the joint within the mechanical axis.
Mulilevel osteotomies are often necessary in generalized deformities from metabolic conditions and osteochondrodystrophies. Balance the number of osteotomies with risks.
Recurrent deformity is likely in certain conditions, so delay each correction as long as possible to reduce the number of procedures required during childhood.
Idiopathic Genu Valgum and Valgum
Valgus deformity with an intermalleolar distance exceeding 8–10 cm is most common in obese girls. This deformity seldom causes functional disability; the problem is primarily cosmetic. If severe, with an intermalleolar distance of >15 cm, consider operative correction by hemiepiphysiodesis or stapling. Make a standing radiograph and construct the mechanical axis. Determine the site(s) of deformity. The distal femur is most deformed near the appropriate site for correction.
Varus deformity is most common in Asians. The varus deformity may be familial. Whether it increases the risk of degenerative arthritis is uncertain. This deformity seldom requires operative correction. Manage severe deformity by stapling or hemiepiphysiodesis.
Posttraumatic Genu Valgum
Posttraumatic genu valgum results from overgrowth following fracture of the tibial metaphysis.
Natural history The deformity develops during the first 12 to 18 months due to tibial overgrowth following the fracture. This is followed by a very gradual reduction of the valgus over a period of years. In the majority, this correction is adequate and no operative procedure is necessary.
Management Manage proximal tibial fractures by correcting any malalignment, and immobilize with a long-leg cast applied with gentle varus molding. Document reduction and position with a long film that includes the entire tibia. Advise the family of the potential of this fracture to cause a secondary deformity, which cannot be prevented. Avoid early osteotomy because recurrence is frequent and the deformity usually resolves spontaneously with time. Reassure the family that the knee will not be damaged by the deformity. Should the deformity persist, correct by osteotomy or by hemiepiphysiodesis or stapling near the end of growth.