Knock Knees (Genu Valgum): Prevalence in Girls, When to Worry, and Management

Is knock knees common in girls?

Yes, a mild degree of genu valgum, or "knock knees," is physiologically common in young children, often peaking around ages 2-4, and can persist longer or be more pronounced in girls due to a combination of developmental, anatomical, and biomechanical factors.

Understanding Genu Valgum (Knock Knees)

Genu valgum, commonly known as knock knees, is a lower limb alignment condition where the knees angle inward, touching or nearly touching, while the ankles remain separated when standing with the feet together. This results in an "X" shape of the legs. Anatomically, it indicates an increased valgus angle at the knee joint, meaning the tibia (shin bone) deviates laterally relative to the femur (thigh bone).

Prevalence in Children, Especially Girls

It is indeed common for children to exhibit physiological genu valgum as a normal part of their growth and development. This typically follows a progression: infants are often born with a degree of genu varum (bow-legs), which naturally corrects and transitions into genu valgum, peaking around 2-4 years of age. By age 6-7, most children's legs naturally straighten to a neutral alignment or a slight valgus angle (around 5-7 degrees), which is considered normal.

While physiological genu valgum affects both boys and girls, there are reasons why it might be perceived or genuinely present more frequently, or with more concern, in girls:

• Pelvic Width: As girls mature, they typically develop a wider pelvis relative to their femur length compared to boys. This wider Q-angle (quadriceps angle) can naturally predispose them to a slightly greater valgus alignment at the knee.
• Ligamentous Laxity: Some individuals, more commonly girls, may exhibit greater generalized ligamentous laxity, which can contribute to joint instability and a tendency towards valgus alignment.
• Growth Spurts: Rapid growth during puberty can sometimes temporarily exacerbate or reveal underlying mild alignment issues.
• Activity Levels and Footwear: While not direct causes, certain activity patterns or footwear choices can influence biomechanics and potentially contribute to the presentation or progression of knock knees.

For the vast majority of children, this developmental genu valgum resolves spontaneously as they grow.

When to Be Concerned: Pathological Genu Valgum

While physiological genu valgum is benign and self-correcting, it's crucial to differentiate it from pathological genu valgum, which requires medical attention. Seek professional advice if:

• Asymmetry: Only one leg is affected, or there's a significant difference between the two legs.
• Persistence or Worsening: The condition persists beyond age 7-8, or it appears to be worsening rather than improving.
• Pain or Limping: The child experiences pain in the knees, hips, or ankles, or develops a noticeable limp.
• Interference with Activity: The knock knees impede walking, running, or participation in physical activities.
• Associated Symptoms: There are other symptoms like short stature, bone deformities elsewhere, or a family history of metabolic bone disease.

Pathological causes can include:

• Rickets: A condition caused by vitamin D deficiency, leading to softening and weakening of bones.
• Renal Osteodystrophy: Bone disease due to chronic kidney failure.
• Trauma: Injuries to the growth plates around the knee.
• Bone Dysplasias: Genetic disorders affecting bone growth.
• Obesity: Excessive weight can place increased stress on developing joints.

Biomechanical Implications and Risk Factors

Even mild, persistent genu valgum can have biomechanical implications over time, particularly in active individuals:

• Altered Gait Mechanics: Individuals with knock knees may exhibit a compensatory gait pattern, such as increased foot pronation (flat feet) or hip internal rotation.
• Uneven Joint Loading: The valgus alignment can lead to increased compressive forces on the lateral (outer) compartment of the knee and increased tensile forces on the medial (inner) compartment. This uneven loading can accelerate wear and tear.
• Muscular Imbalances: Often, genu valgum is associated with specific muscular imbalances:
  • Weak Hip Abductors: Muscles like the gluteus medius and minimus, which stabilize the pelvis and abduct the thigh, may be weak, allowing the knees to collapse inward.
  • Overactive Hip Adductors: Muscles on the inner thigh may be tight or overactive.
  • Weak Vastus Medialis Obliquus (VMO): A component of the quadriceps, the VMO is crucial for patellar tracking; its weakness can exacerbate knee instability.
  • Tight Hamstrings or Gastrocnemius: Flexibility limitations in these muscles can also influence knee alignment.
• Increased Risk of Injury: Over time, individuals with persistent genu valgum may be at a higher risk for patellofemoral pain syndrome (runner's knee), anterior cruciate ligament (ACL) injuries, and early-onset osteoarthritis in the lateral knee compartment.

Assessment and Diagnosis

A comprehensive assessment by a healthcare professional (pediatrician, orthopedic specialist, physical therapist) is crucial for accurate diagnosis. This typically involves:

• Physical Examination: Observing the child's posture, gait, and assessing range of motion, muscle strength, and flexibility. Measurement of the intermalleolar distance (distance between the ankles) when knees are touching is a common clinical measure.
• Medical History: Inquiring about family history, nutritional status, and any associated symptoms.
• Imaging Studies: X-rays may be used in certain cases, especially if pathological causes are suspected, to assess bone alignment and growth plates.

Management and Corrective Strategies

For physiological genu valgum that is expected to resolve, observation is often the primary approach. For persistent or pathological cases, management depends on the underlying cause and severity:

• Non-Surgical Interventions:

  • Exercise and Physical Therapy: This is a cornerstone for addressing muscular imbalances and improving biomechanics. Focus areas include:
    • Strengthening Hip Abductors: Exercises like side-lying leg raises, clam shells, and glute bridges.
    • Strengthening Gluteus Maximus: Squats, lunges, deadlifts (with proper form).
    • Strengthening Vastus Medialis Obliquus (VMO): Terminal knee extensions, step-ups.
    • Stretching: Addressing tightness in hip adductors, hamstrings, and gastrocnemius.
    • Core Stability: Improving trunk control to support lower limb alignment.
  • Orthotics: Custom or off-the-shelf shoe inserts can help address excessive foot pronation, which often accompanies genu valgum and influences the kinetic chain.
  • Bracing: In some cases, specific knee braces may be used, particularly in growing children, to guide alignment.
  • Weight Management: For children with obesity, weight loss can significantly reduce stress on the knee joints.
  • Nutritional Correction: If rickets is the cause, vitamin D and calcium supplementation, along with dietary changes, are essential.

• Surgical Interventions: For severe, progressive, or painful pathological genu valgum that doesn't respond to conservative measures, surgical options may be considered, especially in adolescents. These typically involve osteotomy procedures to realign the bone or guided growth techniques using plates or screws to correct the deformity over time.

Prognosis and Long-Term Outlook

The prognosis for genu valgum is generally excellent, especially for the common physiological type in children, which resolves spontaneously. For pathological cases, early diagnosis and appropriate intervention are key to preventing long-term complications such as chronic pain, degenerative joint disease, and functional limitations. With proper management, most individuals can achieve good functional outcomes.

Conclusion

While genu valgum is a common developmental phase in young children, and may appear more frequently or persist slightly longer in girls due to normal anatomical differences, it typically resolves naturally. However, understanding the distinction between physiological and pathological knock knees is vital. For persistent, painful, or progressive cases, a comprehensive assessment by a healthcare professional is essential to identify underlying causes and implement appropriate, evidence-based management strategies, often involving targeted exercise to address biomechanical imbalances.