Knee Alignment: Genu Valgum (Knock-Knees) vs. Genu Recurvatum (Hyperextended Knees)

What is genu valgum vs genu recurvatum?

Genu valgum, commonly known as "knock-knees," describes an inward angulation of the knees, causing them to touch or nearly touch while the ankles remain apart. Genu recurvatum, or "hyperextended knees," refers to an excessive backward bending of the knee joint, beyond its normal anatomical extension limit.

Understanding Normal Knee Alignment

To appreciate deviations, it's crucial to understand optimal knee alignment. In a healthy standing posture, with feet hip-width apart and pointing straight ahead, a vertical line drawn from the hip joint should pass through the center of the knee and ankle. The femur (thigh bone) and tibia (shin bone) typically meet at a slight valgus angle (knee angled slightly inward) of approximately 5-7 degrees in adults, which is considered physiological. This alignment allows for efficient load bearing and biomechanical function during movement.

Genu Valgum (Knock-Knees)

Definition: Genu valgum is an angular deformity of the knee characterized by an increase in the physiological valgus angle, causing the knees to angle inward toward the midline. When an individual stands with their knees together, their ankles remain separated.

Characteristics and Appearance:

• Inward Knee Angle: The most prominent feature is the inward bowing of the knees.
• Ankle Separation: Despite the knees touching or nearly touching, there's a noticeable gap between the ankles.
• Patellar Tracking: The patella (kneecap) may appear to track more laterally or externally rotated.
• Gait Alteration: Individuals may exhibit a "waddling" gait as they compensate for the altered knee mechanics.

Common Causes:

• Developmental/Genetic: Often seen in young children as a normal developmental stage, usually resolving by age 7-8. Persistent cases can be genetic.
• Metabolic Bone Diseases: Conditions like rickets (vitamin D deficiency) can lead to bone deformities.
• Obesity: Excess weight places increased stress on the developing knee joints.
• Muscle Imbalances: Weakness in hip abductors (e.g., gluteus medius) and external rotators, coupled with tightness in hip adductors and tensor fascia latae (TFL).
• Foot Pronation: Excessive pronation (flat feet) can contribute to a compensatory inward rotation of the tibia, leading to dynamic valgus at the knee.
• Trauma or Injury: Growth plate injuries in children.

Associated Symptoms and Risks:

• Medial Knee Pain: Increased compression on the medial (inner) compartment of the knee.
• Patellofemoral Pain Syndrome: Abnormal patellar tracking can lead to pain around the kneecap.
• IT Band Syndrome: Increased tension on the iliotibial band due to altered mechanics.
• Ankle and Foot Issues: Compensation patterns can lead to pain or dysfunction in the lower leg.
• Increased Risk of ACL Injury: Dynamic valgus (knee collapsing inward during movement) is a significant risk factor for anterior cruciate ligament tears, especially in athletes.
• Osteoarthritis: Long-term altered load distribution can accelerate wear and tear on the joint cartilage.

Exercise Considerations:

• Strengthening: Focus on hip abductors, external rotators, and gluteal muscles (e.g., clam shells, lateral band walks, glute bridges). Strengthen vastus medialis obliquus (VMO) for patellar stability.
• Stretching: Address tightness in hip adductors, TFL, and hamstrings.
• Proprioception and Motor Control: Emphasize exercises that promote controlled knee alignment during functional movements (e.g., squats, lunges with focus on "knees over toes" or slight outward tracking).
• Foot Support: Consider orthotics for excessive foot pronation.

Genu Recurvatum (Hyperextended Knees)

Definition: Genu recurvatum is an extension deformity of the knee joint, where the knee extends beyond its normal anatomical limit of 0-5 degrees of hyperextension. This results in a "back-knee" appearance, with the knee joint bowing backward.

Characteristics and Appearance:

• Backward Bowing: The most noticeable feature is the knee joint extending excessively backward, creating a noticeable curve.
• Locked-Out Stance: Individuals often stand with their knees "locked out" into hyperextension, placing significant stress on the posterior knee structures.
• Altered Gait: During walking, there may be a noticeable "snap" or "pop" as the knee hyperextends at terminal stance.

Common Causes:

• Ligamentous Laxity: Loose ligaments, either congenital (e.g., Ehlers-Danlos syndrome) or acquired due to previous injury (e.g., ACL or PCL tear leading to instability).
• Muscle Imbalances:
  • Quadriceps Dominance/Overactivity: Strong quadriceps that pull the tibia into excessive extension.
  • Hamstring Weakness: Inadequate strength of the hamstrings to counteract quadriceps pull and control knee extension.
  • Calf Weakness: Weakness in gastrocnemius and soleus muscles, which help control ankle dorsiflexion and knee flexion.
• Proprioceptive Deficits: Poor awareness of knee joint position.
• Habitual Standing Posture: Standing with knees locked out can stretch the posterior capsule and ligaments over time, perpetuating the deformity.
• Neurological Conditions: Conditions affecting muscle tone or control (e.g., stroke, cerebral palsy).

Associated Symptoms and Risks:

• Posterior Knee Pain: Stress on the posterior knee capsule, popliteal fossa structures, and hamstrings.
• Patellofemoral Pain: Altered patellar mechanics due to hyperextension.
• Hamstring Strains: Hamstrings may be overstretched and weakened in this position.
• Increased Risk of Ligament Injury: Chronic hyperextension can predispose to tears of the ACL, PCL, or posterior capsule.
• Osteoarthritis: Abnormal load bearing can lead to cartilage degeneration.
• Nerve Impingement: Potential for irritation of nerves in the popliteal fossa.

Exercise Considerations:

• Strengthening: Focus on hamstrings (e.g., hamstring curls, RDLs), glutes, and calf muscles (e.g., calf raises).
• Proprioception and Motor Control: Teach conscious control to avoid locking out the knee during standing and dynamic movements. Emphasize "soft knees" or maintaining a slight knee bend.
• Eccentric Control: Train eccentric control of the quadriceps and hamstrings to absorb force effectively.
• Balance Training: Improve overall balance and stability.

Key Differences and Similarities

While both genu valgum and genu recurvatum represent deviations from ideal knee alignment, they affect the joint in distinct ways:

Similarities:

• Both can lead to altered gait mechanics.
• Both can increase the risk of various knee pathologies, including pain and osteoarthritis.
• Both are often influenced by muscle imbalances and habitual postures.
• Both can benefit from targeted exercise interventions and professional guidance.

When to Seek Professional Advice

While mild variations in knee alignment are common, it's advisable to seek professional medical or physical therapy evaluation if you experience:

• Persistent knee pain or discomfort.
• Functional limitations during daily activities or exercise.
• Rapid onset or progression of the deformity.
• Noticeable changes in gait or balance.
• Concerns about injury risk, especially for athletes.

A thorough assessment can identify the underlying causes, assess the severity, and recommend appropriate interventions, which may include physical therapy, orthotics, bracing, or in rare severe cases, surgical correction.

Conclusion

Genu valgum and genu recurvatum are distinct knee alignment deviations, each with unique biomechanical implications. Understanding their characteristics, causes, and associated risks is crucial for fitness professionals and individuals alike. Through targeted strengthening, stretching, and motor control exercises, coupled with appropriate professional guidance, it is often possible to manage these conditions, alleviate symptoms, and improve long-term knee health and function.