Angular deformities of the lower extremities

Angular deformities of the lower extremities occur when the legs are in a nonneutral alignment. Types include genu valgum (knock-knees) and genu varum (bow legs). Angular deformities are part of physiologic development, but pathologic deformities (e.g., due to trauma, metabolic disease, skeletal dysplasias, neoplasms) may also occur. Evaluation includes a history, physical examination, and manual measurements of leg alignment. Physiologic causes are diagnosed clinically. Further evaluation with imaging and/or laboratory studies is reserved for individuals with suspected pathologic angular leg deformities. Physiologic deformities are typically self-limited and managed with watching waiting. Management of pathologic deformities includes treatment of the underlying cause and surgery when indicated.

This article covers genu valgum and genu varum; genu recurvatum is covered separately.

• Angular misalignment of the legs is seen in all children during physiologic development. ^[1]
  • Most children are born with a varus alignment that persists through 2 years of age.
  • Leg alignment then briefly becomes neutral before proceeding to valgus alignment from 3 to 6 years of age.
  • From 7 or 8 years of age, alignment is neutral or mildly valgus (∼ 6 degrees).
• Suspect pathologic causes of angular leg deformities in patients with either of the following:
  • Persistent deformity
    • Genu varum ≥ 3 years of age ^[2]
    • Genu valgum ≥ 8 years of age ^[1][2]
  • Clinical features of pathologic angular leg deformities

All patients ^[2]

• Misalignment of the lower extremity/extremities
  • Genu varum: medial deviation of the mechanical axis
  • Genu valgum: lateral deviation of the mechanical axis
• Additional features depend on the cause of angular deformity.

Physiologic angular leg deformities ^[2]

• Symmetric and bilateral misalignment
• No associated symptoms
• Age consistent with physiologic age ranges
  • Genu varum: birth to 2 years of age
  • Genu valgum: 3–7 years of age

Pathologic angular leg deformities ^[2]

Any of the following features may indicate a pathologic cause:

• Limping or frequent tripping or falling
• Fever, pain, or swelling
• Asymmetric or unilateral deformity
• Severe deformity
• Gait abnormalities, e.g., lateral thrust or medial thrust ^[6][7]
• Short stature
• Signs of underlying disease, e.g., metabolic disease, skeletal dysplasia
• Progression or persistence beyond the expected age of physiologic resolution ^[2]

Individuals with obesity are at an increased risk for severe and/or progressive genu valgum. ^[8]

Blount disease ^[9][10]

Blount disease is an acquired disorder where abnormal development of the medial proximal tibial physis leads to a progressive varus deformity.

• Epidemiology
  • Infantile age of onset: 1–3 years
  • Juvenile age of onset: 4–10 years
  • Adolescent age of onset: > 10 years
• Clinical features
  • Genu varum
  • Procurvatum of the medial aspect of the proximal tibial metaphysis
  • Shorter limb on the affected side
• Risk factors
  • Genetic susceptibility
  • Mechanical overload due to excessive body weight

Approach ^[1][2][3]

• Assess for features of pathologic angular leg deformity.
• Clinically measure leg alignment.
• Proceed to diagnostic studies, including imaging, for:
  • Equivocal or pathologic clinical measurements
  • Clinical features of pathologic angular leg deformities
• No further studies are recommended for patients with physiologic deformities.

Clinical measurements of leg alignment ^[1][3][6]

Perform measurements while the patient is supine or standing. ^[1][2][6]

• Genu varum
  • Femoral intercondylar distance > 6 cm ^[1][6]
  • Tibiofemoral angle > 15 degrees from neutral ^[1][11]
• Genu valgum
  • Intermalleolar distance > 8 cm
  • Tibiofemoral angle > 12 degrees from neutral ^[12]

Perform imaging when manual measurements are equivocal or abnormal. ^[1]

Measurements of leg alignment can also be made from radiographs. ^[13]

Diagnostic studies ^[1][2][6]

• Imaging
  • Initial modality: bilateral standing full-length hip to ankle x-ray with patellas facing forward ^[7]
  • Findings: affected bone(s), precise measurements of leg alignment, pathologic causes of angular leg deformities ^[5]
• Laboratory studies: to identify the suspected pathologic cause of angular leg deformity, e.g., diagnostics for vitamin D deficiency

Management is based on the underlying cause.

Physiologic angular leg deformities ^[1][2]

• Provide reassurance that most physiologic deformities are self-limited. ^[3]
• Monitor at subsequent visits. ^[1][14]
• Refer patients with worsening or persistent deformities to orthopedics ^[2]

Pathologic angular leg deformities ^[1][2]

• Treat underlying pathologic causes of angular leg deformity; consider specialist referral.
• Refer to orthopedics for surgical evaluation.

Complications of pathologic angular deformities include: ^[7]

• Ligamentous knee laxity
• Patellar instability or patellar maltracking
• Early-onset osteoarthritis ^[1][2]
• Growth plate involvement

Varus deformities overload the medial knee joint; valgus deformities overload the lateral knee joint. ^[7]

We list the most important complications. The selection is not exhaustive.