The etymology of this medical term comes from latim: genu –knee andvarus-bentoutward.
It reflects a deformity in whichone or bothlegsarebentoutward at theknee and it also known by bowleg.
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.
1- Proximal Tibial Valgus Osteotomy and Diaphyseal Fibular Osteotomy
An osteotomy is a surgical operation when a bone is cut to shorten, lengthen, or change its alignment. In thin approach of surgery, a diaphyseal fibular osteotomy is performed too because the fibula is usually too long and may be contributing to the deformity. Internal or external fixation to maintain alignment is necessary and usually supplemented by a long-leg cast until complete healing has occurred.
2-Proximal Tibial Hemiepiphyseal Stapling
Temporary retardation of growth in the lateral aspect of the proximal tibial epiphysis with staples is an effective method for correction of persistent physiologic genu varum. If the deformity is severe or there is limited remaining growth, a combined lateral stapling of the distal femoral and the proximal tibial epiphyses may need to be performed. This procedure will not correct any coexistent medial tibial torsion.
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.