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Genu Valgum (Knock-Knee)

Basics
Description
  • 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
Incidence
  • The condition is rare.
  • Pathologic valgus occurs in <1 per 1,000.
Prevalence
  • It occurs in young children, usually 3-11 years old.
  • Physiologic genu valgum is more common in females than in males.
Risk Factors
  • 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).
Genetics
  • Many forms of rickets are transmitted genetically.
  • Idiopathic valgus may be transmitted in families.
Etiology
  • Physiologic genu valgum
  • Metabolic disorder
  • Steroid dependence
  • Proximal tibia fracture
  • Skeletal dysplasias
  • Chromosome disorders (e.g., Klinefelter syndrome)
Associated Conditions
  • Proximal tibia fracture
  • Pseudoachondroplasia
  • Renal osteodystrophy
  • Metaphyseal dysplasia
  • Rickets
  • Down syndrome
Diagnosis
Signs and Symptoms
  • 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.
Physical Exam
  • Measure the ROM of the knee.
  • Determine and plot height and weight percentiles for the patient’s age.
  • Measure the angle between the tibia and the femur with a goniometer.
  • Measure the distance between the ankles when the knees are touching (intermalleolar distance).
  • Assess the alignment and ROM in the adjacent hip and ankle.
  • Check the rotation of the limb and the gait.
  • Check the collateral ligaments of the knee for laxity.
Tests
Lab
  • Serum levels of calcium, phosphate, alkaline phosphatase, urea nitrogen, and creatinine should be measured if rickets or a metabolic problem is suspected.
  • The most common type of rickets in developed countries is familial hypophosphatemic rickets.
  • If rickets is to be evaluated, check vitamin D levels (25-hydroxy and 1,25-dihydroxy) as well as the other parameters.
Imaging
  • Imaging of genu valgum, which is thought to be physiologic, is unnecessary for children <6 years old unless the patient has an asymmetric deformity or a pathologic condition is suspected.
  • An AP view of the lower extremity from the hip to ankle obtained while the patient is standing should be the 1st imaging study.
    • The knee should be pointing straight ahead.
    • The film cassette should be long enough to accommodate the entire extremity.
    • The femorotibial angle should be measured, and the site of the deformity should be identified as femoral, tibial, or both.
Differential Diagnosis
  • 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.
Treatment
General Measures
  • 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.
Activity
No activity restrictions are necessary.
 
Special Therapy
Physical Therapy
Not indicated, because therapy and exercises cannot affect the growth of the limb
 
Surgery
  • 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%.
Follow-up
Prognosis
Physiologic genu valgum resolves by age 7-10 years as long as it is mild (<15°) and no metabolic problems are present.
 
Complications
  • 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
Patient Monitoring
Children with idiopathic genu valgum may be followed every 12-24 months to determine whether the deformity is improving before a treatment decision is made.
 
Miscellaneous
Codes
ICD9-CM
736.41 Genu valgum
 
Patient Teaching
Inform parents that most cases of physiologic genu valgum begin to resolve spontaneously by 7 years of age.
 
FAQ
Q: Is bracing indicated in genu valgum?
A: Bracing for valgus has never been shown to be effective. It is very cumbersome because the knee cannot bend in a corrective brace.
 
Q: Is valgus a cosmetic problem or a functional one?
A: In the more severe degrees, it can impair running and increase the risk of arthritis.

Related posts:

  1. Blount Disease
  2. A Patient’s Guide to Blount’s Disease in Children and Adolescents
  3. A Patient’s Guide to Quadriceps Tendonitis of the Knee
  4. A Patient’s Guide to Revision Arthroplasty of the Knee
  5. Our Services
May 20th, 2010 | Tags: | Category: Dictionary

1 comment to Genu Valgum (Knock-Knee)

  • Vivian
    31 July, 2013 at 10:11 pm

    Hi. I have a knock knee but not both side , only left knee of leg.
    How to do my leg can be straight?
    Please email me. I would appreciate your help. Thanks!