Varum - singular. Varus - plural

Genu varum in achondroplasia has a complex and multifactorial aetiology, being a common deformity. It is first noticed at the standing age in 40% of all achondroplastic children and progresses rapidly at the age of three to four years, and again at six to seven years. The final progression of this deformity takes place during the pubertal growth spurt.

Already in 1970!, Ponsetti suggested that deformity of the lower limbs in achondroplasia was due to a failure of enchondral ossification leading to undergrowth of the tibia and relative overgrowth of the fibula. (Development of genu varum in achondroplasia, S. Lee et al, 2007)

To know more about endochondral ossification, please read here

Radiograph showing the method of measuring the lengths of the tibia and the fibula (A, tibial length; B, fibular length; fibular to tibial ratio = B:A). At “Development of genu varum in achondroplasia”, S. Lee et al. http://www.bjj.boneandjoint.org.uk/content/89-B/1/57/F1

Radiograph of a leg of a helathy child – two positions. Imagen from Children Hospital of Chigado. http://www2.luriechildrens.org/ce/images/content/radiology-photos1.jpg

There is little mention in the literature of the role of fibular overgrowth, but S. Lee research team showed that the fibular to tibial length ratio showed significant connection with the medial proximal tibial angle and the mechanical axial deviation in the skeletally-immature child with achondroplasia.

A very interesting clinical case, with a bilateral genu varus in a 5 year-old boy with achondroplasia described by Dr. Feldman here

Five year-old boy with bilateral genu varus (with deviation angles) Image taken from case study

The angle described in the radiograph is the metaphyseal-diaphyseal angle, measured by drawing a line along the long axis of the tibia, creating a perpendicular to this line, and drawing another line through axial plane of the proximal tibial metaphysis. The angle created between the perpendicular line shown in green, and the metaphyseal line shown in blue is the metaphyseal diaphyseal angle.

imagen taken from Radiopedia

3-Proximal Tibial Hemiepiphysiodesis

Percutaneous closure of the lateral aspect of the proximal tibial epiphysis can be effective in correcting persistent physiologic genu varum in adolescents. The indications are essentially the same as for stapling. However, once complete correction has been achieved, a second procedure may be necessary on the medial side to prevent overcorrection. The proximal fibular epiphysis is usually closed concomitantly. This procedure will not correct any medial tibial torsion (further reading here)

Right Femoral Osteotomy with Lengthening & Application of EBI External Fixator. Image from case study A: Syndemosis screw inserted into the left tibiofibular joint. B: Taylor Spatial Frame in place over the left fibula and tibia osteotomy sites. C: Fixator in place and the right femoral osteotomy and lengthening site.

The opposite problem is genus valgum, when knees touch.