What is genu valgum (knock knees)?

Genu Valgum (Knock Knees)

Genu valgum is a lower limb deformity characterized by the distal part of the leg below the knee deviating outwards in relation to the femur, resulting in a knock-kneed appearance. 1

Definition and Clinical Presentation

• Genu valgum is characterized by an increased distance between the ankles (intermalleolar distance) when the knees are touching in standing position 1
• The condition can be assessed by measuring the intercondylar and/or intermalleolar distance, which varies with age 1
• Radiographically, it presents as a valgus alignment of the knee with an abnormal mechanical axis deviation 2

Etiology

Genu valgum can be:

• Physiological/developmental (common in children 3-7 years old) 3
• Pathological, associated with:
  • Metabolic bone diseases such as X-linked hypophosphataemia (XLH) 1
  • Glycogen storage diseases 1
  • Hereditary multiple exostoses (HME) 3
  • Obesity (particularly in adolescents) 4, 5
  • Idiopathic lateral distal femoral physeal growth suppression 5
  • Genetic disorders (some cases may be inherited in an autosomal dominant pattern) 6

Diagnostic Evaluation

• Clinical assessment includes measurement of:

  • Intercondylar and/or intermalleolar distance 1
  • Alignment of the lower limbs in standing position 1
  • Gait analysis 1

• Radiographic evaluation:

  • Weight-bearing anteroposterior (AP) and lateral radiographs are essential 2
  • Standing long-leg (hip-to-ankle) views provide optimal assessment of alignment 2
  • AP views obtained in 10 degrees of internal rotation improve interpretation of valgus alignment 2
  • Key measurements include mechanical axis deviation (MAD), mechanical lateral distal femoral angle (LDFA), and medial proximal tibial angle (MPTA) 3

Management

Conservative Treatment

• Physical therapy interventions:

  • Exercises to strengthen muscles around the knee joint 7
  • Gait training to improve biomechanics 7
  • Custom-molded foot orthoses may improve distal alignment at feet and ankles and secondarily decrease genu valgum 1
  • Taller orthotic intervention with ankle foot orthoses may be recommended for more severe malalignment or instability 1

• Bracing options:

  • Realignment knee braces can be used to induce a valgus or varus torque on the knee 1
  • Various designs include double upright with hinge, single upright with strap, single upright with hinge, and cloth sleeve with hinge 1
  • Valgus bracing can reduce the external knee adduction moment by up to 20% 1

Surgical Treatment

• Temporary hemiepiphysiodesis using eight-plates is an effective procedure for treating genu valgum in children with remaining growth potential 4
• Guided growth techniques must be carried out at least 2-3 years before skeletal maturity 2
• Corrective osteotomy may be necessary in severe cases or when growth modulation is not possible 4, 5
• Mechanical axis deviation Zone 2 or greater despite optimized medical treatment may require surgical intervention 2

Complications and Prognosis

• If left untreated, genu valgum may lead to:

  • Abnormal gait 1
  • Joint pain and instability 7
  • Premature osteoarthritis of the knee 3
  • Functional limitations in daily activities 7

• Treatment outcomes:

  • Conservative treatment can improve symptoms and function in mild to moderate cases 7
  • Surgical correction with temporary hemiepiphysiodesis has shown good results with low complication rates (2.8%) 4
  • Slight overcorrection is desirable due to the rebound phenomenon, especially in young patients with high growth potential 4

Special Considerations

• Obesity is a significant risk factor and may complicate both the progression and treatment of genu valgum 4, 5
• In adolescents with low growth potential (older than 14 years), surgical correction may have limited success 4
• Regular monitoring is essential, especially during periods of rapid growth 1
• Multidisciplinary approach involving orthopedic surgeons, physical therapists, and other specialists may be necessary for optimal management 1