Pediatric Genu Valgum Workup
- Author: Peter M Stevens, MD; Chief Editor: Jeffrey D Thomson, MD more...
When an underlying syndrome is suggested by the physical findings and history, consultation with a geneticist and workup are warranted. If metabolic bone problems are a concern, relevant hematologic and urine studies are warranted, along with consultation with an endocrinologist. In a select few patients, bone densitometry studies may be warranted.
The criterion standard for documentation of genu valgum is a standing anteroposterior (AP) radiograph of the lower extremities, taken with the patellae facing forward. This study permits direct visualization of both the true and the apparent limb lengths and alignment. The length of each femur and tibia is measured, and any diaphyseal deformities (which would be missed on a scanogram) are clearly visible.
The mechanical axis is a line drawn from the center of the head of the femur to the center of the ankle; this line should bisect the knee. In normal variations, this line is still in the central 50% of the knee. Genu valgum is defined by lateral deviation of the axis or deviation toward or beyond the joint margin. The deformity may be in the femur, the tibia, or both. The normal lateral distal femoral angle is 84° (6° of valgus), and the medial proximal tibial angle is 87° (3° of varus).
When physeal abnormalities are suspected, obtain AP and lateral radiographs of the hip or knee (or fluoroscopy) to have better visualization of the physis. If a skeletal dysplasia is suggested, a skeletal survey is warranted.
A sunrise or Merchant view of the patellae may reveal tilt, subluxation, and, occasionally, osteochondral defects or loose bodies. Finally, it may be helpful to obtain an AP radiograph of the left wrist for bone age, to ensure remaining growth (ideally ≥12 months) is adequate to allow for correction of a deformity by growth manipulation.
Depending on the underlying etiology of genu valgum, epiphyseal, physeal, or metaphyseal histologic abnormalities may be present. However, biopsy of the bone rarely is necessary or helpful. Such invasive procedures may have an adverse effect upon physeal growth and the outcome of treatment.
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