Bow Knee Syndrome (Genu Varum): Understanding Causes, Symptoms, and Treatment

What is a bow knee syndrome?

Bow knee syndrome, clinically known as genu varum, is a condition characterized by an outward curvature of the lower legs, causing the knees to remain apart even when the ankles are touching. This misalignment can shift weight-bearing forces, potentially leading to increased stress on the inner compartment of the knee joint.

Understanding Genu Varum: The "Bow Knee" Deformity

Genu varum, commonly referred to as "bow legs" or "bandy legs," describes a physical deformity where the femurs (thigh bones) and tibias (shin bones) angle outward at the knees, creating a bow-like appearance. While a mild degree of bowing is a normal physiological variation in infants and toddlers, often resolving spontaneously by age two or three, persistent or progressive genu varum, especially beyond this age, can indicate an underlying pathological condition. This alignment issue affects the mechanical axis of the lower limb, altering the distribution of forces across the knee joint.

Anatomy and Biomechanics of Genu Varum

The knee joint is designed to bear and distribute body weight efficiently. In a healthy, neutral alignment, a straight line can be drawn from the center of the hip through the center of the knee to the center of the ankle. This ensures even loading across the medial (inner) and lateral (outer) compartments of the knee.

In genu varum, the mechanical axis deviates laterally. This means that when a person stands, more of their body weight is channeled through the medial compartment of the knee. Over time, this chronic overload can lead to:

• Increased stress on the medial meniscus: The C-shaped cartilage shock absorber on the inner side of the knee.
• Accelerated wear of articular cartilage: Leading to medial compartment osteoarthritis.
• Stretching of the lateral collateral ligament (LCL): While the medial collateral ligament (MCL) may become compressed or shortened.
• Altered muscle mechanics: Specific muscles around the hip and knee may become overstretched or tightened in an attempt to compensate for the misalignment, impacting gait and overall lower limb function.

Common Causes and Risk Factors

While physiological genu varum in early childhood is common and typically self-correcting, several factors can lead to pathological bow knee syndrome:

• Blount's Disease (Tibia Vara): A growth disorder affecting the growth plate near the top of the tibia, causing the bone to grow abnormally and bow outward. This can occur in early childhood (infantile Blount's) or adolescence (adolescent Blount's).
• Rickets: A bone-softening disease caused by severe and prolonged Vitamin D deficiency, leading to impaired bone mineralization. This makes bones weak and prone to bowing under body weight.
• Osteoarthritis: Particularly medial compartment osteoarthritis, where cartilage loss on the inner side of the knee can lead to collapse of the joint space and subsequent varus deformity.
• Bone Fractures or Trauma: Injuries to the growth plates in children or malunion (improper healing) of fractures in adults can result in angular deformities.
• Metabolic Bone Diseases: Conditions like Paget's disease or renal osteodystrophy can affect bone strength and structure.
• Bone Infections (Osteomyelitis): Can damage bone and growth plates.
• Genetic Syndromes: Certain rare genetic conditions can predispose individuals to skeletal deformities.
• Obesity: Excessive body weight can exacerbate the stresses on the knee joint, particularly in individuals with a predisposition to genu varum or those with developing Blount's disease.
• Occupational or Sporting Stresses: Repetitive high-impact activities or prolonged weight-bearing in certain positions can contribute to or worsen knee alignment issues over time, especially in predisposed individuals.

Recognizing the Symptoms

The primary symptom of bow knee syndrome is the visible outward curvature of the legs, where the knees do not touch when the ankles are together. Other symptoms can include:

• Gait Abnormalities: A characteristic "waddling" gait or an altered walking pattern to compensate for the misalignment.
• Knee Pain: Often localized to the medial (inner) side of the knee, especially during activity or weight-bearing.
• Joint Stiffness: Particularly after periods of inactivity.
• Reduced Range of Motion: Difficulty fully straightening or bending the knee.
• Instability: A feeling of the knee "giving way."
• Increased Risk of Injury: Higher susceptibility to medial meniscus tears, medial collateral ligament (MCL) strain, and accelerated development of medial compartment osteoarthritis.
• Compensatory Pain: Pain in the hips, ankles, or feet due to altered biomechanics and compensatory movements.

Diagnosis of Bow Knee Syndrome

Accurate diagnosis is crucial to differentiate between physiological bowing and pathological conditions, and to determine the underlying cause. The diagnostic process typically involves:

• Medical History and Physical Examination: The healthcare provider will ask about the onset of symptoms, family history, and perform a thorough physical assessment. This includes observing the leg alignment, measuring the distance between the knees when the ankles are together, assessing gait, and evaluating joint range of motion and stability.
• Imaging Studies:
  • X-rays: Full-length standing X-rays of the lower limbs are essential. These allow for precise measurement of the mechanical axis and assessment of bone morphology and joint space.
  • MRI (Magnetic Resonance Imaging): May be used to evaluate soft tissue structures like cartilage, menisci, and ligaments, especially if pain or internal knee pathology is suspected.
  • CT Scan (Computed Tomography): Provides detailed images of bone structure and can be helpful in complex cases or surgical planning.
• Blood Tests: If metabolic causes like rickets are suspected, blood tests to check Vitamin D levels, calcium, phosphorus, and other bone markers may be ordered.

Treatment and Management Strategies

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

Conservative Management

For mild cases, physiological bowing, or when surgery is not indicated:

• Observation: Especially for physiological bowing in young children, where regular monitoring is often sufficient as the condition typically self-corrects.
• Weight Management: Reducing excess body weight can significantly decrease the load on the knee joints.
• Orthotics and Braces:
  • Knee-Ankle-Foot Orthoses (KAFOs): In children with progressive Blount's disease, bracing may be used to guide bone growth.
  • Offloading Braces: For adults with medial compartment osteoarthritis, custom knee braces can help shift weight away from the painful inner compartment.
• Pain Management: Over-the-counter pain relievers (e.g., NSAIDs), ice, and heat can help manage discomfort.
• Physical Therapy: Focuses on strengthening supporting musculature and improving biomechanics.

Surgical Intervention

Surgery is considered for severe, progressive, or symptomatic cases, particularly when conservative measures fail:

• Osteotomy (High Tibial Osteotomy - HTO): A common procedure for adults with genu varum and medial compartment osteoarthritis. A wedge of bone is either removed or added to the tibia just below the knee to realign the leg, shifting weight-bearing to the healthier lateral compartment.
• Guided Growth (Epiphysiodesis): In children with Blount's disease or other growth plate abnormalities, small plates or screws can be strategically placed to temporarily slow growth on one side of the bone, allowing the other side to catch up and correct the deformity as the child grows.
• Total Knee Replacement (TKR): In older adults with severe genu varum and extensive knee joint degeneration, a total knee replacement may be necessary to restore alignment and alleviate pain.

Exercise and Rehabilitation Considerations

Physical therapy and a tailored exercise program are integral components of both conservative management and post-surgical rehabilitation for bow knee syndrome. The goals include:

• Strengthening Key Muscles:
  • Gluteal Muscles (Gluteus Medius and Minimus): To improve hip stability and control, which influences knee alignment.
  • Quadriceps and Hamstrings: For overall knee stability and strength.
  • Hip Abductors and Adductors: To ensure balanced strength around the hip.
• Stretching: Addressing muscle imbalances and tightness, particularly in the hip adductors, IT band, and calves, which can contribute to altered gait.
• Gait Retraining: Teaching proper walking mechanics to reduce stress on the knee.
• Proprioceptive Exercises: Balance and stability exercises (e.g., single-leg stands, wobble board) to improve neuromuscular control around the knee.
• Low-Impact Activities: Encouraging exercises like swimming, cycling, and elliptical training, which provide cardiovascular benefits without excessive impact on the knee joint.
• Activity Modification: Advising against or modifying high-impact, repetitive activities that exacerbate medial knee stress.

When to Seek Professional Medical Advice

It is important to consult a healthcare professional, such as an orthopedic surgeon or a sports medicine physician, if you or your child exhibit any of the following:

• Persistent or Worsening Bowing: If the bowing does not improve or appears to worsen, especially after age two or three.
• Asymmetrical Bowing: If one leg is significantly more bowed than the other.
• Pain, Swelling, or Stiffness: In the knees or other joints, particularly if it interferes with daily activities.
• Difficulty Walking or Running: Or any noticeable change in gait.
• Bowing that Develops Later in Childhood or Adulthood: This is more likely to indicate a pathological cause.
• Associated Symptoms: Such as short stature, muscle weakness, or bone tenderness.

Prevention Strategies

While not all cases of genu varum are preventable, certain measures can reduce the risk or severity of some forms:

• Adequate Nutrition: Ensuring sufficient intake of Vitamin D and calcium, especially in children, is crucial to prevent rickets.
• Early Diagnosis and Management: Prompt identification and treatment of conditions like Blount's disease or rickets can prevent or minimize severe deformity.
• Maintaining a Healthy Weight: Reducing excess body weight significantly decreases the load on the knee joints, potentially mitigating the progression of osteoarthritis-related genu varum.
• Proper Exercise Technique: Engaging in physical activity with correct form and progressive loading can help maintain joint health and muscle balance.

Conclusion

Bow knee syndrome, or genu varum, is a condition ranging from a common physiological variation in toddlers to a significant orthopedic deformity in children and adults. Understanding its causes, from growth disorders and metabolic diseases to osteoarthritis, is key to effective management. While surgical correction may be necessary in severe cases, conservative approaches, including weight management and targeted exercise, play a vital role in alleviating symptoms, improving function, and slowing progression. Early diagnosis and a comprehensive, individualized treatment plan are essential for optimizing outcomes and maintaining long-term knee health.