Genu Valgum (Knock-Knee)

• Genu valgum, or knock-knee, is a normal phase of development in children 2-4 years old.
• Girls normally have slightly more valgus of the knee than do boys.
• The valgus straightens to achieve the adult position by 6-7 years of age.
• Rickets, trauma, and genetic disorders also may cause genu valgum.
• Some patients have an idiopathic valgus, not resulting from any of the foregoing disorders, that falls outside the normal limits and persists beyond 10 years of age.
• Areas affected include the distal femoral and proximal tibial growth plates.

Epidemiology

• Family history of genu valgum
• Proximal tibia metaphysic fracture in children (Cozen fracture); asymmetric overgrowth occurs and deformity is possible (parents should be warned about this possibility).

• Physiologic genu valgum
• Metabolic disorder
• Steroid dependence
• Proximal tibia fracture
• Skeletal dysplasias
• Chromosome disorders (e.g., Klinefelter syndrome)

• Proximal tibia fracture
• Pseudoachondroplasia
• Renal osteodystrophy
• Metaphyseal dysplasia
• Rickets
• Down syndrome

• Parental concern about the appearance of the child’s legs is the most common reason for presentation.
• It is usually asymptomatic.
• The knees usually are not painful in childhood but the physical appearance is sometimes bothersome; occasionally, valgus knees are associated with patellar discomfort.
• In adulthood, valgus knees are more likely to produce arthritic symptoms outside of the joint.

Tests

• The main differential diagnosis is to determine whether the condition is physiologic or pathologic.
• Physiologic genu valgum occurs without underlying rickets, dysplasia, or other known cause.
• The most common skeletal dysplasias causing valgus are metaphyseal dysplasia and pseudoachondroplasia, as well as multiple osteochondromas.

• Physiologic valgus:
  • No treatment is indicated for physiologic genu valgum in patients <7 years old.
  • If the deformity persists after 7 years of age, hemiepiphysiodesis (at age 11-12 years) may be considered to achieve normal alignment.
    • Epiphysiodesis consists of slowing or stopping the growth plate on the medial side to allow the lateral side to catch up.
    • This relatively simple procedure does not substantially weaken the bone and allows early weightbearing.
• Pathologic valgus:
  • For metabolic disorders, including renal osteodystrophy, the underlying condition should be treated.
  • Bracing has not been effective in preventing or reversing the deformity.
  • Single- or multiple-level osteotomy may be necessary to correct the deformity; medical control of the disease is needed first.
  • Usually, therapy is directed by a renal or endocrine specialist.
• Fracture:
  • Follow-up of proximal tibia fracture should extend for several years after the injury.
  • Early tibial osteotomy should be avoided because of the high incidence of recurrence of valgus deformity.
  • If an unacceptable degree of valgus remains after 1-2 years follow-up, hemiepiphysiodesis or osteotomy may be indicated.
• Dysplasia:
  • Children with pseudoachondroplasia and metaphyseal dysplasias are likely to develop genu valgum.
  • Osteotomy may be necessary to correct the deformity.

Special Therapy

• 2 types of surgery commonly are used to correct valgus deformity when it persists: Hemiepiphysiodesis and varus osteotomy.
  • Epiphysiodesis aims to achieve satisfactory mechanical alignment at the end of growth.
  • Proximal tibia osteotomy should be considered if epiphysiodeses is not feasible.
    • Osteotomy involves a more difficult recovery period than epiphysiodesis because, in the former procedure, the bone is divided completely.
• The overall success rate of surgery is >90%.

• Untreated genu valgum: If severe, the patient may develop patellofemoral pain and late degenerative arthritis from stresses on the lateral joint surface.
• Surgical complications:
  • Infection
  • Compartment syndrome
  • Recurrence of deformity or overcorrection and neurovascular injury