Definition
Knock knees, medically termed genu valgum, is a lower limb alignment condition where the knees angle inward and touch each other when the legs are straightened, while the ankles remain apart. This can be a normal part of growth in young children or a pathological condition in older children and adults.
Physiological Development
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Normal growth pattern:
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Infants are often bow-legged (genu varum).
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By ages 2–4, knees naturally angle inward (physiological genu valgum).
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Usually self-corrects by age 7–8, leaving mild valgus alignment in adulthood (5–7 degrees in females, slightly less in males).
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Persistence beyond expected age or progression indicates possible pathology.
Causes
Physiological
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Common in children aged 2–4 years; resolves naturally.
Pathological
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Nutritional rickets (vitamin D deficiency).
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Renal osteodystrophy.
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Post-traumatic malunion after fractures.
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Genetic or metabolic bone diseases (e.g., skeletal dysplasias).
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Obesity (increased load on growth plates).
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Ligament laxity.
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Infections or tumors affecting growth plates.
Risk Factors
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Family history of bone alignment disorders.
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Poor nutrition and low vitamin D/calcium intake.
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Chronic illness affecting bone metabolism.
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Childhood obesity.
Clinical Features
Symptoms
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Most cases are asymptomatic in children.
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In symptomatic cases:
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Knee or hip pain.
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Limping or gait abnormalities.
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Difficulty running or participating in sports.
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Signs
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Intermalleolar distance: gap between ankles when knees are touching (measured with patient standing straight).
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Bilateral or unilateral deformity.
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Associated features of underlying disease (e.g., rachitic rosary, bone tenderness in rickets).
Diagnosis
History
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Age of onset, progression, pain, functional limitations.
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Family history and dietary history.
Examination
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Measure intermalleolar distance (normal <8 cm after age 7).
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Assess gait and lower limb alignment.
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Look for signs of systemic disease.
Investigations (if pathological suspected)
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X-rays (standing anteroposterior view of lower limbs) to measure mechanical axis and tibiofemoral angle.
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Blood tests: serum calcium, phosphate, alkaline phosphatase, vitamin D levels.
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Renal function tests if kidney disease suspected.
Management
1. Observation and Reassurance
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For physiological cases in children <7 years, with no pain or functional impairment.
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Regular monitoring every 6–12 months.
2. Non-Surgical Management
a) Correction of Underlying Cause
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Rickets:
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Vitamin D3 (cholecalciferol): 1,000–5,000 IU orally daily for 6–12 weeks depending on severity, then maintenance 400–800 IU/day.
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Calcium carbonate: 500–1,000 mg orally daily.
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Renal osteodystrophy: Manage per nephrology guidance.
b) Physiotherapy
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Quadriceps and hip abductor strengthening.
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Gait training and balance exercises.
c) Weight Management
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Diet and activity interventions for overweight/obese patients to reduce joint load.
d) Orthotic Support
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Lateral wedge insoles or custom knee braces in mild symptomatic cases, especially in adults with early osteoarthritis.
3. Surgical Management
Indications
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Persistent or progressive deformity after age 10.
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Intermalleolar distance >8–10 cm.
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Symptomatic cases with pain or gait disturbance.
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Significant cosmetic concern.
Procedures
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Guided growth surgery (temporary hemiepiphysiodesis):
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Placement of small plates/screws on one side of growth plate to gradually correct alignment in growing children.
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Osteotomy:
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Cutting and realigning the bone (distal femoral or proximal tibial osteotomy) in skeletally mature patients.
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Complications
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Altered biomechanics leading to knee osteoarthritis.
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Patellofemoral instability.
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Gait disturbances and reduced athletic performance.
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Psychological impact due to cosmetic appearance.
Prognosis
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Physiological genu valgum resolves spontaneously in most children.
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Pathological cases require early intervention to prevent long-term joint damage.
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Surgical correction usually yields good outcomes if performed at the right time.
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