Genu Valgum and Genu Varum in Children

Definitions. Genu varum, "bow-legs", is a tibiofemoral angle in varus: with the ankles together the knees stand apart. Genu valgum, "knock-knees", is the reverse: with the knees together the ankles stand apart. Both are coronal-plane malalignments of the knee, and the first job in clinic is to decide whether the one in front of you is a stage of normal development or a disease.

View larger

The physiological arc. Newborns are bowed, about 10-15° of varus, from intrauterine positioning. The legs straighten to neutral by 18-24 months, swing into a maximum valgus of 10-15° at 3-4 years, and then settle gradually to the adult alignment of 5-7° valgus by 6-7 years. Physiological deformity is symmetric and keeps to this timetable, and that is the whole of its definition.

Who has the pathological forms. Physiological angular deformity is extremely common and usually normal. Infantile Blount disease is more common in children of African descent, early walkers and the obese. The nutritional form of rickets is rare in developed countries; renal osteodystrophy is its counterpart in chronic kidney disease.

The mechanical axis. The mechanical axis of the limb is the line from the centre of the femoral head to the centre of the ankle, assessed on a standing long-leg radiograph. Normally it passes through or just medial to the centre of the knee, the reference figure being about 8 to 10 mm medial; the distance from the axis to the knee centre is the mechanical axis deviation (MAD). In genu varum the knees bow apart and the axis passes further medial to the knee, overloading the medial compartment. In genu valgum the knees touch with the ankles apart and the axis passes lateral to the knee, overloading the lateral compartment.

View larger

Where the growth is. The proximal tibial physis provides 55% of tibial growth. The distal femoral physis provides 70% of femoral growth and 37% of the length of the leg. The distal femur contributes more to angular correction than the proximal tibia because it grows faster. Asymmetric loading affects physeal growth according to the Hueter-Volkmann law, compression retarding growth and tension stimulating it.

Guided growth. Hemiepiphysiodesis retards growth on one side of the physis and lets the other side, still growing, bring the limb back into line. The 8-plate does this by creating a tension-band effect; screw and staple methods are also used. Overcorrection is a risk if the hardware is not removed promptly. When planning surgery, consider the site of maximum deformity, the centre of rotation of angulation (CORA).

History. The story tells you whether the deformity is keeping to the physiological timetable, and it screens for the systemic causes before you examine a single joint. Ask about:

• Age of onset - when the parents first noticed the deformity
• Progression - improving, stable or worsening
• Walking age - early walkers are at risk of Blount disease
• Family history - skeletal dysplasia, rickets
• Diet and sun exposure - vitamin D intake, the risk of nutritional rickets
• Medical history - renal disease, gastrointestinal malabsorption

Gait. Watch the knee in stance for a lateral thrust, the knee appearing to "pop out" laterally as the limb loads. In-toeing or out-toeing may coexist with an angular deformity, so assess the overall gait pattern and the foot progression angle as well.

Standing examination. With the ankles together, measure the intercondylar distance for varus; with the knees together, measure the intermalleolar distance for valgus. Compare the two sides, and record the rotational profile, because internal tibial torsion may coexist.

Systemic examination. Short stature suggests skeletal dysplasia or rickets. Feel the wrists for the physeal widening of rickets and the chest for a rachitic rosary, and look for the dysmorphic features of a skeletal dysplasia.

Red flags. Physiological deformity corrects; pathological deformity persists. Suspect pathology when there is:

• Asymmetry between the two sides
• Rapid progression beyond the expected pattern
• An extreme angle: varus over 15° after age 2, valgus over 15° after age 5
• Short stature
• A lateral thrust in gait
• Deformity persisting or worsening after the age at which it should have corrected

When to image. Request radiographs for the child with any of the red flags, asymmetry, an extreme angle, a pattern that is not physiological, a lateral thrust or short stature, and for the child who simply concerns you clinically. The film to ask for is a standing AP long-leg radiograph, for accurate assessment of the mechanical axis. Bilateral deformity earns bloods as well.

The metaphyseal-diaphyseal angle. Described by Levine and Drennan with an original threshold of over 11°; the higher cut-off of over 16° popularised by Feldman and Schoenecker is the modern working value suggesting Blount disease, with an indeterminate grey zone between 9° and 16°. Use the two thresholds for opposite purposes, because the test is asymmetric. Feldman found that only one Blount limb measured under 11°, so an MDA below 11° effectively rules Blount out and is the number to reassure with. But 37% of physiologically bowed limbs (66 of 179) also exceeded 11°, so that threshold cannot rule it in; on its own it would label more than a third of normally bowed toddlers. Above 16° the separation is real (means 9° physiological versus 19° Blount). And Feldman's own conclusion stands: the MDA "should not be the sole criterion", so combine it with age, symmetry, progression and the rest of the radiograph.

Other measurements. The tibial metaphyseal angle assesses the severity of tibia vara. Gordon's epiphyseal-metaphyseal angle is an adjunct that may improve early discrimination of Blount disease from physiological bowing.

After guided growth. Wound care, weight-bearing as tolerated immediately, no immobilisation, and discharge on day 0 or 1. Normal activities resume quickly; the first follow-up radiograph at 6-8 weeks assesses early correction.

Monitoring. Every 3 months, a clinical and radiographic assessment with the mechanical axis measured on long-leg films, continued until the correction is achieved.

At correction. Once the alignment has normalised or is slightly overcorrected, the 8-plate is removed as day surgery. The limb may rebound slightly after removal, so a post-removal radiograph is taken at 3-6 months.

After osteotomy. Protected weight-bearing for 6-8 weeks with knee range-of-movement exercises, then progression to full weight-bearing and activity.

Physiological deformity. Near-universal spontaneous resolution; no intervention is needed in the vast majority.

Guided growth. A high success rate in appropriate candidates, with predictable correction, low morbidity, and reversibility if overcorrection occurs.

Blount disease. Infantile disease has a better prognosis when treated early; adolescent disease shows higher recurrence and often needs osteotomy. Residual malalignment carries a long-term risk of medial compartment osteoarthritis.

Global Epidemiology:

• Physiological angular variation is near-universal in toddlers and is the single commonest reason for paediatric orthopaedic referral for "bent legs"; the vast majority require only reassurance.
• Infantile Blount disease shows a higher reported prevalence in populations of African ancestry, in early walkers, and with rising childhood obesity; late-onset (adolescent) Blount tracks closely with the global obesity epidemic.
• Nutritional rickets remains an important and preventable cause worldwide, concentrated in infants with darker skin, limited sun exposure, exclusive prolonged breastfeeding without supplementation, and low dietary calcium; X-linked hypophosphataemic rickets and renal osteodystrophy are the main non-nutritional metabolic causes.

Guidelines, Side by Side:

There is broad international agreement on the principles (observe physiological deformity, screen for metabolic causes in bilateral deformity, prefer guided growth while the physis is open) and no major society-level disagreement on the core algorithm — the genuine debates are technical (thresholds, timing) rather than national.

Angular knee deformity is a high-volume but evidence-thin area: most data are retrospective single-centre series, and several practical questions remain genuinely unsettled. Examiners reward a candidate who can state what is established versus what is debated.

The MDA threshold and its grey zone. The original Drennan threshold (over 11°) over-calls Blount disease; the over 16° cut-off improves specificity but leaves a 9-16° grey zone where physiological bowing and early Blount overlap. Serial measurement and adjunct angles (for example Gordon's epiphyseal-metaphyseal angle) are more reliable than any single number.

Bracing, real or placebo? Reported bracing success in early infantile tibia vara is confounded by the fact that many young, low-stage cases would resolve spontaneously. There is no randomised evidence; brace type, dose and the true threshold for abandoning bracing remain debated.

Guided growth versus osteotomy in Blount disease. Guided growth is attractive but has a higher failure and recurrence rate in advanced Blount disease (Langenskiöld IV and above) and in obese adolescents, where many surgeons favour acute or gradual osteotomy. The optimal crossover point is not defined by high-level evidence.

Rebound and the timing of removal. Rebound after plate removal is common, over 40% of segments in long-term series. Whether to deliberately overcorrect, when to remove hardware, and whether to leave the plate in situ in younger children are all unresolved trade-offs against iatrogenic deformity.