Physiological bowing and knocked knees

Physiological bowing (genu varum) and physiological knocked knees (genu valgum) are common developmental variations of lower limb alignment in children. These conditions are part of normal skeletal growth and usually resolve spontaneously without treatment. Physiological genu varum is most prominent from birth to approximately 18–24 months of age, after which the legs gradually straighten. Physiological genu valgum develops between 2 and 4 years of age, reaches a maximum around 3–4 years, and gradually corrects to the normal adult alignment by approximately 7–8 years of age.

Persistent, progressive, asymmetrical, or severe deformity may indicate an underlying pathological condition such as Blount disease, rickets, skeletal dysplasia, trauma, infection, or metabolic bone disease and requires further evaluation.

Pathophysiology

Lower limb alignment changes predictably during childhood as the skeleton matures. Infants are born with physiological genu varum due to intrauterine positioning. As weight bearing begins, remodelling of the proximal tibia and distal femur gradually corrects the bowing. Between 2 and 4 years of age, the mechanical axis shifts laterally, producing a temporary physiological genu valgum. Continued skeletal growth subsequently restores normal lower limb alignment.

Abnormal or persistent deformity occurs when normal growth plate development is disrupted. In Blount disease, excessive compressive forces across the medial proximal tibial physis suppress normal growth, resulting in progressive tibial varus deformity. In rickets, defective mineralization of growing bone weakens the growth plate, leading to progressive angular deformities under normal weight-bearing forces.

Normal developmental alignment

Risk factors for pathological deformity

• Obesity

• Early walking

• Vitamin D deficiency

• Rickets

• Blount disease

• Skeletal dysplasia

• Previous trauma

• Previous physeal injury

• Bone infection

• Family history of skeletal disorders

Clinical presentation

Physiological deformity

• Symmetrical bow legs or knock knees

• Normal growth and development

• Normal gait

• No pain

• No limp

• No functional limitation

• Normal height for age

Features suggesting pathological deformity

• Progressive deformity

• Asymmetrical deformity

• Persistent genu varum beyond 2 years

• Persistent genu valgum beyond 7 years

• Intercondylar distance or intermalleolar distance greater than expected for age

• Limb-length discrepancy

• Pain

• Limp

• Short stature

• Widened wrists or ankles

• Features suggestive of rickets

• Family history of skeletal dysplasia

Diagnostic approach

Diagnosis is primarily clinical and should distinguish physiological variants from pathological conditions.

Clinical examination

Assess:

• Limb alignment

• Gait

• Symmetry

• Intercondylar distance (genu varum)

• Intermalleolar distance (genu valgum)

• Knee range of motion

• Limb-length discrepancy

• Rotational profile

• Height and growth pattern

Laboratory investigations (when pathology is suspected)

• Serum calcium

• Serum phosphate

• Alkaline phosphatase

• Serum 25-hydroxyvitamin D

• Parathyroid hormone

• Renal function tests

Imaging

Not routinely required for physiological deformity.

Indications include:

• Persistent deformity outside the normal age range

• Progressive deformity

• Asymmetry

• Suspicion of Blount disease

• Suspicion of rickets

• Limb-length discrepancy

Investigations:

• Standing long-leg radiographs (preferred)

• Plain knee radiographs

• Bone age assessment when indicated

Differential diagnosis

• Physiological genu varum

• Physiological genu valgum

• Blount disease

• Nutritional rickets

• Skeletal dysplasia

• Osteogenesis imperfecta

• Physeal injury

• Bone tumours

• Renal osteodystrophy

Non-pharmacological management

Physiological genu varum or genu valgum

Treatment is observation and parental reassurance.

• Explain the normal pattern of lower limb development.

• Routine activity restriction is unnecessary.

• Encourage maintenance of a healthy body weight.

• Encourage age-appropriate physical activity.

• Review every 6 months until spontaneous correction occurs.

Braces, corrective shoes, wedges, and splints are not recommended for physiological deformities because they do not accelerate correction.

Pharmacological treatment

Routine drug therapy is not indicated in physiological bowing or physiological knocked knees.

If vitamin D deficiency or nutritional rickets is confirmed, treat according to current vitamin D deficiency or rickets guidelines.

Example:

Calcium 600 mg + Vitamin D 800 IU (PO) once daily for 3 months (adjust according to age and nutritional status).

Surgical management

Surgery is not indicated for physiological genu varum or genu valgum.

Children with persistent or pathological deformities should be referred to an orthopaedic surgeon.

Temporary hemiepiphysiodesis (guided growth)

Temporary hemiepiphysiodesis is the preferred treatment for skeletally immature children with significant angular deformity and adequate remaining growth.

Indications

• Persistent genu valgum after approximately 7–8 years of age

• Persistent genu varum after approximately 2–3 years when physiological causes have been excluded

• Mechanical axis deviation causing functional impairment

• Progressive deformity

• Angular deformity generally exceeding 10–15°

• Deformity secondary to Blount disease or skeletal dysplasia with remaining growth potential

Procedure

• A tension-band plate ("eight-plate") or transphyseal screw is placed across one side of the growth plate.

• Continued growth on the opposite side gradually corrects the deformity.

• Clinical and radiographic review is recommended every 3–6 months.

• The implant is removed once neutral mechanical alignment is achieved to avoid overcorrection.

Corrective osteotomy

Corrective osteotomy is indicated when:

• Skeletal maturity has been reached.

• The deformity is severe.

• Guided growth is no longer possible.

• Blount disease presents late with established deformity.

• There is multiplanar deformity requiring immediate correction.

Common procedures include:

• Proximal tibial valgus osteotomy for severe genu varum.

• Distal femoral varus osteotomy for severe genu valgum.

• Combined femoral and tibial osteotomy when deformity involves both bones.

Internal fixation with plates, screws, or external fixation may be used depending on the deformity and surgeon expertise.

Follow-up

Children should be reviewed every 6 months to assess:

• Degree of deformity

• Limb alignment

• Growth

• Gait

• Functional status

Repeat standing radiographs are recommended only when progression or pathological deformity is suspected.

Prognosis

Physiological genu varum and genu valgum have an excellent prognosis. Most children achieve normal lower limb alignment without intervention. Early recognition of pathological causes such as Blount disease or rickets allows timely treatment and prevents permanent deformity, gait abnormalities, and early osteoarthritis.