Knee Bowing (Genu Varum): Causes, Symptoms, Diagnosis, and Treatment

What is Knee Bowing?

Knee bowing, medically known as genu varum, describes a condition where the legs curve outwards at the knees, causing the knees to remain wide apart even when the ankles are touching. This misalignment can be a normal developmental stage in young children or a pathological condition stemming from skeletal abnormalities, metabolic disorders, or degenerative joint disease.

Understanding Genu Varum: An Anatomical Perspective

Genu varum, commonly referred to as "bow-leggedness," is a lower limb deformity characterized by an outward angulation of the tibia and/or femur relative to the knee joint. In an ideal, neutral mechanical alignment, a straight line should pass from the center of the hip joint, through the center of the knee, and down to the center of the ankle joint. In genu varum, this line shifts medially (inward) relative to the knee, causing increased compressive forces on the medial (inner) compartment of the knee and tensile forces on the lateral (outer) structures.

Key Anatomical Considerations:

• Tibiofemoral Angle: This angle, measured between the long axis of the femur and the long axis of the tibia, is crucial for assessing knee alignment. In genu varum, the tibiofemoral angle demonstrates a varus (inward) deviation.
• Weight-Bearing Axis: The altered alignment in genu varum shifts the primary weight-bearing axis towards the medial compartment of the knee, leading to uneven stress distribution across the joint surfaces.

Causes and Risk Factors

The causes of knee bowing vary significantly with age and can range from benign physiological variations to serious underlying medical conditions.

Physiological Bowing:

• Infants and Toddlers: It is very common and considered normal for infants and toddlers (up to 2-3 years of age) to exhibit mild genu varum. This is often due to their position in the womb and typically corrects spontaneously as they grow and begin weight-bearing.

Pathological Causes:

• Rickets: A leading cause globally, rickets is a bone-softening disease due to prolonged vitamin D deficiency, which impairs calcium and phosphate absorption, leading to weak, flexible bones that bow under weight.
• Blount's Disease (Tibia Vara): A growth disorder affecting the growth plate (epiphysis) of the medial proximal tibia. It causes the tibia to grow abnormally, leading to progressive bowing of one or both legs. It can occur in early childhood (infantile Blount's) or adolescence (adolescent Blount's).
• Osteoarthritis: Particularly medial compartment osteoarthritis, where cartilage loss on the inner side of the knee can cause the joint space to narrow, leading to an acquired varus deformity.
• Fractures and Trauma: Poorly healed (malunion) fractures of the femur or tibia, especially those involving the growth plates in children, can result in angular deformities.
• Skeletal Dysplasias: Genetic disorders affecting bone and cartilage development, such as achondroplasia, can lead to various limb deformities, including genu varum.
• Metabolic Bone Diseases: Conditions like Paget's disease of bone can cause bone remodeling abnormalities and bowing.
• Obesity: Excessive body weight can place increased stress on developing growth plates, potentially contributing to or worsening genu varum, especially in conditions like Blount's disease.
• Infection or Tumors: Rarely, infections or tumors near the knee's growth plates can disrupt normal bone growth and lead to bowing.

Signs, Symptoms, and Associated Conditions

The presentation of genu varum can range from a purely cosmetic concern to a debilitating condition with significant pain and functional limitations.

Common Signs and Symptoms:

• Visible Outward Curvature: The most obvious sign is the noticeable outward bend of the legs at the knees.
• Wide Gait: Children and adults with significant genu varum may walk with a wider stance or a "waddling" gait to maintain balance.
• Asymmetrical Bowing: One leg may be more bowed than the other, which is often a red flag for pathological causes.
• Pain: Medial knee pain is common due to increased compression and stress on the inner compartment of the joint. Pain can also manifest in the hips or ankles due to compensatory biomechanical changes.
• Stiffness or Instability: Some individuals may experience knee stiffness or a feeling of the knee "giving way."
• Functional Limitations: Difficulty with prolonged standing, running, or participating in sports due to pain, fatigue, or altered mechanics.

Associated Conditions:

• Accelerated Medial Compartment Osteoarthritis: The uneven weight distribution significantly increases the risk and progression of cartilage degeneration on the inner side of the knee.
• Meniscal Tears: The increased stress can predispose individuals to medial meniscal tears.
• Ligamentous Strain: Chronic varus stress can lead to stretching or laxity of the lateral collateral ligament (LCL) and increased tension on the medial collateral ligament (MCL).
• Patellofemoral Pain Syndrome: Altered lower limb alignment can affect patellar tracking, leading to anterior knee pain.

Diagnosis

Accurate diagnosis is crucial to differentiate between physiological bowing and pathological conditions, guiding appropriate management.

Diagnostic Steps:

• Medical History and Physical Examination:
  • Gait Analysis: Observing how the individual walks to identify any abnormalities.
  • Alignment Assessment: Visual inspection of the lower limbs, measuring the distance between the knees when the ankles are together.
  • Range of Motion: Assessing knee, hip, and ankle flexibility and strength.
  • Palpation: Checking for tenderness, swelling, or bony deformities.
• Imaging Studies:
  • Standing Long-Leg Radiographs (X-rays): This is the gold standard. Full-length X-rays of both legs, taken while standing, allow for precise measurement of the mechanical axis (hip-knee-ankle axis) and the femorotibial angle. This helps quantify the degree of bowing and identify the level of deformity (femoral, tibial, or both).
  • MRI/CT Scans: May be used in complex cases to assess soft tissue structures (meniscus, ligaments, cartilage) or detailed bone morphology, especially if a tumor or complex growth plate issue is suspected.
• Blood Tests: If rickets or other metabolic bone diseases are suspected, blood tests for vitamin D levels, calcium, phosphate, alkaline phosphatase, and parathyroid hormone may be ordered.

Treatment and Management Strategies

Treatment for knee bowing depends heavily on the underlying cause, the patient's age, the severity of the deformity, and the presence of symptoms.

1. Observation and Monitoring:

• For physiological bowing in young children, regular monitoring by a pediatrician is often sufficient. Most cases resolve spontaneously by age 3-4.
• Children are typically re-evaluated periodically with physical exams and sometimes repeat X-rays to track progression or resolution.

2. Conservative Management:

• Physical Therapy:
  • Strengthening Exercises: Focusing on quadriceps, hamstrings, glutes, and core muscles to improve stability and support.
  • Stretching: Addressing any muscle imbalances or tightness (e.g., tight hip adductors or IT band).
  • Gait Training: Improving walking patterns to optimize weight distribution.
  • Proprioception and Balance Training: Enhancing joint awareness and stability.
• Orthotics and Bracing:
  • Knee-Ankle-Foot Orthoses (KAFOs): For young children with progressive Blount's disease, custom braces may be used to guide growth and prevent worsening of the deformity.
  • Shoe Inserts/Orthotics: Can sometimes help with pain by subtly altering foot mechanics and reducing stress on the knee, though they do not correct the underlying bony alignment.
• Weight Management: For overweight or obese individuals, weight loss can significantly reduce the load on the knees and slow the progression of degenerative changes.
• Nutritional Supplementation: For rickets, vitamin D and calcium supplementation, along with dietary changes, are essential to correct the underlying deficiency and allow bones to remineralize.
• Pain Management: Over-the-counter pain relievers (NSAIDs) and activity modification can help manage symptoms.

3. Surgical Interventions:

Surgery is typically considered for progressive pathological bowing, significant pain, functional limitations, or when conservative measures fail.

• Guided Growth (Hemiepiphysiodesis): For growing children with moderate bowing, a small plate or screw is temporarily placed on one side of the growth plate (physis) of the tibia or femur. This slows growth on that side, allowing the other side to catch up and gradually correct the alignment over time.
• Osteotomy (High Tibial Osteotomy - HTO): For adolescents and adults, particularly those with symptomatic medial compartment osteoarthritis and varus alignment. A wedge of bone is removed or added from the tibia (or sometimes the femur) near the knee, and the bone is realigned and fixed with plates and screws. This shifts weight-bearing to the healthier lateral compartment of the knee.
• Total Knee Arthroplasty (TKA): In severe cases of genu varum with advanced, end-stage osteoarthritis and significant joint destruction, knee replacement surgery may be the most appropriate option. The surgeon corrects the alignment during the procedure.

Prevention and Prognosis

Preventing pathological knee bowing often involves addressing underlying risk factors.

Prevention Strategies:

• Adequate Nutrition: Ensuring sufficient intake of vitamin D and calcium, especially during childhood and adolescence, is crucial for bone health and preventing rickets.
• Healthy Weight Management: Maintaining a healthy body weight can reduce stress on growth plates and joints, potentially mitigating the risk or progression of conditions like Blount's disease and osteoarthritis.
• Early Detection: Regular pediatric check-ups are vital for identifying physiological bowing that persists or worsens, or any signs of pathological conditions.

Prognosis:

The prognosis for genu varum varies widely:

• Physiological Bowing: Excellent prognosis, almost always resolves spontaneously.
• Rickets: Generally good with appropriate vitamin D and calcium supplementation, though severe cases may require bracing or surgery.
• Blount's Disease: Prognosis depends on age of onset and severity. Early diagnosis and treatment (bracing or guided growth) in infantile Blount's generally lead to good outcomes. Adolescent Blount's may be more challenging and often requires surgery.
• Osteoarthritis-related Bowing: Management focuses on slowing progression and alleviating symptoms. Surgical correction (osteotomy or TKA) can provide significant relief and improve function.

When to Seek Professional Help

It's important to consult a healthcare professional, such as an orthopedic surgeon or a pediatrician, if you or your child exhibit any of the following:

• Persistent bowing: If bowing continues beyond age 2-3 years, or worsens after age 4.
• Asymmetrical bowing: When one leg is significantly more bowed than the other.
• Associated symptoms: Any pain, limping, stiffness, or difficulty with walking or physical activity.
• Rapid progression: If the bowing appears to be worsening quickly.
• Unusual height or weight: If a child is significantly taller or heavier than average for their age, which can sometimes be associated with certain growth plate disorders.