Knee Alignment: Understanding Varus and Valgus Knees, Causes, and Management

What is the difference between a varus and valgus knee?

Varus and valgus knee alignments describe the angular deviation of the lower leg relative to the thigh, specifically at the knee joint, with a varus knee presenting as "bow-legged" and a valgus knee as "knock-kneed."

Understanding Knee Alignment

The human knee joint, a complex hinge joint, is designed to facilitate movement while bearing significant loads. Optimal knee alignment is crucial for efficient biomechanics, distributing forces evenly across the joint surfaces and minimizing stress on ligaments, tendons, and cartilage. When we refer to knee alignment, we are primarily concerned with the frontal plane relationship between the femur (thigh bone) and the tibia (shin bone) as they meet at the knee.

Normally, a healthy knee exhibits a slight valgus angle of approximately 5-7 degrees, meaning the femur angles slightly inward from the hip to the knee, and the tibia then descends vertically to the ankle. This slight "physiological valgus" helps ensure the mechanical axis (the line of weight bearing from the hip through the knee to the ankle) passes optimally through the center of the knee joint. Deviations from this normal alignment can lead to increased stress on specific compartments of the knee and contribute to various musculoskeletal issues.

Varus Knee Alignment (Genu Varum or "Bow-Legged")

A varus knee, often referred to as "bow-legged," is characterized by an outward angulation of the tibia relative to the femur. In this alignment, the knees appear to be excessively separated when the ankles are together, creating an arch-like shape with the legs.

Definition: Genu varum describes a condition where the distal (far) part of the tibia deviates medially relative to the proximal (near) part, resulting in the knees pointing outward.

Biomechanics and Forces:

• Weight-Bearing Axis: In a varus knee, the mechanical axis of the lower limb shifts medially, placing increased compressive forces on the medial (inner) compartment of the knee joint.
• Ligamentous Stress: The lateral collateral ligament (LCL) on the outside of the knee may experience increased tensile stress, while the medial collateral ligament (MCL) may become lax.
• Muscle Imbalances: Often associated with increased activity of the hip abductors and external rotators, and potentially weaker hip adductors and internal rotators.
• Gait Mechanics: May present with an exaggerated external rotation during gait or an inability to fully extend the knee.

Potential Implications/Risks:

• Medial Compartment Osteoarthritis: The most common long-term consequence due to chronic overload of the medial tibial and femoral condyles.
• Meniscal Tears: Increased risk of tears to the medial meniscus.
• LCL Strain/Injury: Due to increased tension on the outside of the knee.
• Patellofemoral Pain Syndrome: Altered patellar tracking can occur.
• Tibial Stress Fractures: Potentially due to altered load distribution.

Valgus Knee Alignment (Genu Valgum or "Knock-Kneed")

Conversely, a valgus knee, commonly known as "knock-kneed," is characterized by an inward angulation of the tibia relative to the femur. When a person with valgus knees stands with their knees together, their ankles remain separated.

Definition: Genu valgum describes a condition where the distal part of the tibia deviates laterally relative to the proximal part, causing the knees to touch or nearly touch while the ankles are apart.

Biomechanics and Forces:

• Weight-Bearing Axis: In a valgus knee, the mechanical axis of the lower limb shifts laterally, placing increased compressive forces on the lateral (outer) compartment of the knee joint.
• Ligamentous Stress: The medial collateral ligament (MCL) on the inside of the knee may experience increased tensile stress, while the lateral collateral ligament (LCL) may become lax.
• Muscle Imbalances: Often associated with overpronation of the feet, weakness in hip abductors (like gluteus medius), and tightness in hip adductors and internal rotators.
• Gait Mechanics: May present with an "in-toeing" gait or a dynamic knee valgus during movements like squatting or jumping.

Potential Implications/Risks:

• Lateral Compartment Osteoarthritis: Less common than medial OA, but still a risk due to chronic overload of the lateral tibial and femoral condyles.
• Patellofemoral Pain Syndrome: Very common due to altered patellar tracking, often causing the patella to track laterally.
• MCL Strain/Injury: Due to increased tension on the inside of the knee.
• ACL Injury Risk: Dynamic knee valgus during athletic movements is a significant risk factor for anterior cruciate ligament (ACL) tears, especially in female athletes.
• IT Band Syndrome: Increased tension on the iliotibial band due to altered alignment.

Key Differences Summarized

Causes of Varus and Valgus Deformities

Both varus and valgus deformities can be influenced by a combination of factors, including:

• Genetic Predisposition: Some individuals are simply born with a predisposition to certain knee alignments.
• Developmental Factors: Often seen in children (e.g., physiological bowing in toddlers, or knock-knees in early childhood that typically self-correct). Persistent or severe cases may indicate underlying issues.
• Rickets: A bone-softening disease caused by vitamin D deficiency can lead to significant deformities.
• Trauma: Fractures around the knee, especially involving the growth plates in children, can lead to altered growth and alignment.
• Osteoarthritis: Degenerative joint disease can cause or exacerbate alignment issues as cartilage wears unevenly.
• Obesity: Increased body weight places greater stress on the knees, potentially worsening or contributing to deformities.
• Muscle Imbalances and Weakness: Weakness in key stabilizing muscles (e.g., gluteus medius for valgus, hip adductors for varus) or tightness in opposing muscle groups can contribute to dynamic alignment issues.
• Foot and Ankle Mechanics: Excessive pronation (flat feet) can contribute to dynamic knee valgus, while supination can sometimes be linked to varus.

Assessment and Diagnosis

Diagnosis of varus or valgus knee alignment typically involves:

• Visual Inspection: Observing the standing posture, gait, and alignment of the lower limbs.
• Physical Examination: Assessing range of motion, joint stability, muscle strength, and flexibility.
• Radiographic Imaging: X-rays (especially standing full-length limb radiographs) are crucial to accurately measure the mechanical axis and degree of angular deformity. This helps differentiate between physiological and pathological alignment.

Management and Corrective Strategies

Management approaches depend on the severity of the deformity, the presence of symptoms, and the underlying cause.

Conservative Approaches:

• Exercise and Rehabilitation:
  • For Valgus: Focus on strengthening hip abductors (gluteus medius), external rotators, and quadriceps (VMO emphasis). Stretching tight hip adductors and internal rotators. Addressing foot pronation with arch support exercises.
  • For Varus: Focus on strengthening hip adductors and internal rotators. Stretching tight hip abductors and external rotators.
  • Proprioception and Balance Training: Crucial for improving dynamic knee control.
  • Gait Retraining: Modifying walking or running patterns to reduce adverse loading.
• Orthotics and Bracing:
  • Foot Orthotics: Custom or off-the-shelf orthotics can help manage excessive pronation (for valgus) or supination (for varus) and improve overall lower limb alignment.
  • Knee Braces: Offloader braces can be used to shift weight away from the more stressed compartment of the knee, particularly in cases of unicompartmental osteoarthritis.
• Weight Management: Reducing excess body weight can significantly decrease the load on the knee joints.
• Activity Modification: Adjusting activities that exacerbate pain or stress on the knees.

When to Seek Medical Advice:

It is important to consult a healthcare professional (e.g., orthopedic surgeon, physical therapist, sports medicine physician) if:

• The deformity is severe or progressing.
• There is persistent pain, swelling, or instability.
• It impacts daily activities or athletic performance.
• It is suspected to be related to an underlying medical condition (e.g., rickets, growth plate issues).

In some severe cases, or when conservative measures fail, surgical interventions such as osteotomy (cutting and realigning the bone, e.g., high tibial osteotomy for varus or distal femoral osteotomy for valgus) may be considered to correct the alignment and redistribute forces across the knee joint.

Conclusion

Understanding the distinction between varus and valgus knee alignments is fundamental for anyone involved in fitness, rehabilitation, or healthcare. These structural deviations significantly alter knee biomechanics, predisposing individuals to specific patterns of stress, injury, and degenerative changes. While some degree of alignment variation is normal, pronounced varus or valgus can have serious long-term consequences. Through careful assessment, targeted exercise, and appropriate interventions, it is often possible to manage symptoms, improve function, and mitigate the risks associated with these common knee presentations.