Knock Knees (Genu Valgum): Understanding Causes, Symptoms, and Treatment

What is a Knock Leg?

A knock leg, medically known as genu valgum, is a common lower limb alignment where the knees angle inward and touch, or nearly touch, when a person stands with their feet apart. This condition creates an "X" shape with the legs, often leading to altered biomechanics and potential issues throughout the kinetic chain.

Understanding Genu Valgum: A Deeper Dive

Genu valgum, or "knock knees," describes an angular deformity of the lower limb where the femurs (thigh bones) and tibias (shin bones) meet at the knee joint at an exaggerated valgus angle. This means the distal segment (the lower leg) is angled away from the midline of the body. In a healthy 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. In genu valgum, this line deviates significantly, with the knee falling inward.

Anatomical Description: The primary characteristic of genu valgum is the inward angulation of the femurs and tibias at the knee joint. This misalignment places increased stress on the lateral (outer) compartment of the knee and often leads to stretching of the medial (inner) collateral ligament and compression of the lateral meniscus. It can also influence the alignment and function of the ankle, foot, and hip joints.

Causes of Knock Knees

The etiology of genu valgum can range from normal physiological development in children to acquired conditions in adults.

Physiological/Developmental:

• Normal Childhood Development: It is common and often physiological for children between the ages of 2 and 6 years to exhibit some degree of genu valgum as part of their normal development. This typically resolves spontaneously by age 7 or 8 as the child grows and their bones mature.
• Rapid Growth Spurts: Adolescents undergoing rapid growth may temporarily develop knock knees.

Pathological/Acquired:

• Rickets: A condition caused by prolonged vitamin D deficiency, leading to softening and weakening of bones, which can result in bone deformities like genu valgum.
• Osteoarthritis: Particularly in the lateral compartment of the knee, leading to progressive cartilage loss and joint space narrowing that can shift the mechanical axis inward.
• Trauma or Injury: Fractures or injuries to the growth plates (epiphyseal plates) around the knee in children can disrupt normal bone growth, leading to angular deformities.
• Genetic Conditions: Certain genetic disorders, such as skeletal dysplasias, can cause genu valgum.
• Obesity: Excess body weight places increased stress on the knee joints, which can exacerbate or contribute to the development of knock knees, especially in children and adolescents.
• Ligamentous Laxity: Generalized joint hypermobility or specific laxity of the medial collateral ligament can contribute to the valgus alignment.
• Muscular Imbalances: Weakness in hip abductors (e.g., gluteus medius) and external rotators, combined with tightness in hip adductors and internal rotators, can pull the knees inward.
• Foot Pronation: Excessive pronation of the feet (flat feet) can sometimes contribute to a compensatory inward rotation of the tibia and femur, leading to genu valgum.

Recognizing the Symptoms

While the visual appearance is the most obvious sign, genu valgum can present with a range of symptoms depending on its severity and underlying cause.

• Visual Appearance: The most defining symptom is the inward angulation of the knees, where they touch or nearly touch while the ankles remain separated when standing with feet together.
• Pain: Individuals may experience pain in various areas, including the knees (medial aspect due to stretching, or lateral due to compression), hips, ankles, or feet. This pain is often exacerbated by prolonged standing, walking, or physical activity.
• Gait Abnormalities: A characteristic "waddling" gait may be observed as the individual attempts to clear their feet past each other due to the inward knee angle. This can lead to inefficient movement patterns.
• Functional Limitations: Difficulty with certain physical activities, such as running, jumping, or prolonged walking, may arise. There might also be challenges with balance and stability.
• Patellofemoral Pain: The altered alignment can increase stress on the kneecap (patella), leading to anterior knee pain.
• Foot and Ankle Issues: Compensatory pronation of the feet and associated foot pain or instability are common.

Diagnosis and Assessment

Diagnosis of genu valgum typically involves a combination of physical examination, imaging, and functional assessment.

• Physical Examination: A healthcare professional will visually inspect the alignment of the legs, assess the range of motion at the knee, hip, and ankle, and palpate for tenderness. They may measure the intermalleolar distance (IMD), which is the distance between the medial malleoli (inner ankle bones) when the knees are touching.
• Imaging:
  • X-rays: Standing long-leg X-rays are crucial to accurately measure the mechanical axis of the lower limb and quantify the degree of valgus deformity. They can also identify underlying bone abnormalities or signs of arthritis.
  • MRI: May be used to assess soft tissue structures like cartilage, ligaments, and menisci if there are concerns about associated injuries.
• Gait Analysis: Observational or instrumented gait analysis can reveal how the valgus alignment impacts walking mechanics, identifying compensatory movements and areas of excessive stress.

Management Strategies for Knock Knees

Treatment for genu valgum depends on the cause, severity, age of the individual, and presence of symptoms.

Conservative Approaches:

• Observation (for children): In young children with physiological genu valgum, observation is often the primary approach, as the condition frequently resolves with growth. Regular follow-up is important to monitor progression.
• Weight Management: For individuals who are overweight or obese, weight loss can significantly reduce the load and stress on the knee joints, potentially alleviating symptoms and preventing progression.
• Orthotics and Bracing:
  • Foot Orthotics: Custom or off-the-shelf orthotics can help support the arch of the foot and reduce excessive pronation, which may indirectly improve knee alignment.
  • Knee Braces: In some cases, specific knee braces might be used to provide support and encourage better alignment, particularly during activities.
• Physical Therapy & Exercise: A cornerstone of conservative management, focusing on:
  • Strengthening: Targeting weak muscles that contribute to valgus collapse, such as the hip abductors (gluteus medius, gluteus minimus), hip external rotators, and vastus medialis obliquus (VMO) of the quadriceps.
  • Stretching: Addressing tight muscles that pull the knees inward, including hip adductors, hamstrings, and the iliotibial band (IT band).
  • Proprioception and Balance Training: Improving neuromuscular control and stability around the knee and ankle joints.
  • Gait Retraining: Teaching more efficient and less stressful walking patterns to reduce dynamic valgus.

Surgical Intervention: Surgery is typically reserved for severe cases, those that do not respond to conservative treatment, or when the deformity is progressive and causing significant pain or functional limitation.

• Guided Growth Surgery (Hemiepiphysiodesis): For growing children with significant, progressive genu valgum, small plates or screws are placed on one side of the growth plate to temporarily slow growth on that side, allowing the other side to catch up and correct the deformity over time.
• Osteotomy: In adolescents or adults, an osteotomy involves surgically cutting and realigning the bone (usually the tibia or femur) to correct the angle and redistribute weight-bearing forces more evenly across the knee joint.

Exercise Science Perspective: Corrective Strategies

From an exercise science and kinesiology standpoint, addressing genu valgum involves understanding the interplay of muscular imbalances, joint mechanics, and kinetic chain considerations. The goal of exercise is to optimize joint alignment and function, reduce pain, and improve movement efficiency.

Muscular Imbalances: A common pattern associated with dynamic genu valgum (knock knees that appear or worsen during movement) is:

• Weakness: Gluteus medius, gluteus minimus (hip abductors), gluteus maximus (hip extensor/external rotator), and hip external rotators (e.g., piriformis, gemelli, obturators). Also, the vastus medialis obliquus (VMO) of the quadriceps.
• Tightness: Hip adductors (inner thigh muscles), tensor fasciae latae (TFL) / iliotibial band (IT band), hip internal rotators, and sometimes hamstrings.

Kinetic Chain Considerations: Genu valgum is rarely an isolated knee problem. Its effects ripple through the entire kinetic chain:

• Foot & Ankle: Often associated with excessive foot pronation (flat feet) as a compensatory mechanism.
• Hip: Inward rotation of the femur, often due to weakness in external rotators.
• Lower Back: Altered gait and pelvic alignment can lead to compensatory movements and potential stress on the lumbar spine.

Recommended Exercises: A comprehensive exercise program should include:

• Strengthening Exercises:

  • Hip Abductors: Side-lying leg raises, clam shells, band walks (lateral shuffles).
  • Hip External Rotators: Seated external rotations with resistance, fire hydrants.
  • Gluteus Maximus: Glute bridges, squats (with focus on knee alignment), deadlifts (with proper form).
  • Vastus Medialis Obliquus (VMO): Terminal knee extensions with a resistance band, leg presses with focus on quadriceps activation.
  • Core Stability: Planks, bird-dog, dead bug to improve trunk control and support proximal stability.

• Stretching Exercises:

  • Hip Adductors: Butterfly stretch, wide-leg straddle stretch.
  • IT Band/TFL: Standing IT band stretch, foam rolling.
  • Hamstrings: Standing or seated hamstring stretches.

• Proprioception and Balance Training:

  • Single-leg balance (progressing from stable to unstable surfaces).
  • Bosu ball squats or lunges.
  • Balance board exercises.

• Gait Retraining Cues:

  • Focus on "knees over toes" during squats and lunges.
  • Encourage slight external rotation at the hip during walking to prevent inward collapse.
  • "Drive the knees out" cue during exercises.
  • Mindful walking, focusing on foot strike and knee alignment.

When to Seek Professional Help

While mild, physiological genu valgum in young children often resolves, it is important to consult a healthcare professional, such as a pediatrician, orthopedic surgeon, or physical therapist, if:

• Genu valgum is severe or asymmetrical.
• It is present in children older than 7-8 years.
• It develops or worsens rapidly.
• There is associated pain, limping, or difficulty with walking or physical activity.
• It is accompanied by other symptoms such as short stature or bone deformities.
• It develops in adulthood.

Early assessment and intervention can help manage symptoms, prevent progression, and improve long-term outcomes for individuals with genu valgum.