Knock Knees (Genu Valgum): Causes, Pain, and Treatment Options

Why do knock knees hurt?

Knock knees, or genu valgum, cause pain primarily due to altered biomechanics that unevenly distribute forces across the lower limb joints, leading to increased stress, wear, and inflammation in specific tissues of the knees, hips, and ankles.

Understanding Genu Valgum (Knock Knees)

Genu valgum, commonly known as "knock knees," is a lower limb anatomical alignment where the knees angle inward, touching or nearly touching, while the ankles remain separated when standing with the feet together. This creates an "X" shape with the legs. While a mild degree of valgus is normal, particularly in young children, persistent or excessive genu valgum can lead to significant biomechanical issues and pain.

Causes of Genu Valgum:

• Physiological Genu Valgum: Common in children aged 2-6 years, often resolving naturally.
• Developmental Factors: Can persist from childhood due to genetic predisposition or growth plate abnormalities.
• Acquired Causes:
  • Muscle Imbalances: Weakness in hip abductors (gluteus medius/minimus) and external rotators, combined with tightness in hip adductors and internal rotators.
  • Ligamentous Laxity: Looseness in the medial collateral ligament (MCL) or other knee ligaments.
  • Bone Deformities: Rickets, osteomalacia, or fractures that heal improperly.
  • Obesity: Increased load on the knee joint.
  • Arthritis: Degenerative changes can sometimes lead to or exacerbate valgus deformity.

The Biomechanical Cascade: How Knock Knees Lead to Pain

The fundamental reason knock knees cause pain lies in the altered mechanical axis of the lower limb. Instead of the weight-bearing line passing through the center of the knee, in genu valgum, this line shifts laterally, placing disproportionate stress on the inner (medial) compartment of the knee and causing a cascade of compensatory movements throughout the kinetic chain.

Key Biomechanical Effects:

• Increased Medial Compartment Loading: The inward angulation of the knees forces more of the body's weight through the medial condyles of the femur and tibia. This excessive compression wears down articular cartilage and meniscus on the inside of the knee.
• Lateral Compartment Overstretching: Conversely, the outer (lateral) structures of the knee, including the lateral collateral ligament (LCL) and lateral meniscus, are subjected to excessive tensile (stretching) forces.
• Patellofemoral Maltracking: The inward knee angle often pulls the patella (kneecap) laterally, causing it to track abnormally in the trochlear groove of the femur. This leads to uneven loading and friction beneath the kneecap.
• Compensatory Foot Pronation: To maintain balance and absorb shock, the foot often compensates by excessively pronating (flattening of the arch), which further internally rotates the tibia and exacerbates the knee's valgus alignment.
• Altered Hip Mechanics: The body attempts to compensate for the knee's alignment by internally rotating the hips and increasing adduction, placing stress on hip abductors and external rotators.

Common Painful Conditions Associated with Knock Knees

The chronic abnormal loading and compensatory movements resulting from genu valgum can lead to a variety of painful conditions:

• Knee Pain:
  • Medial Compartment Osteoarthritis (OA): Chronic compression of the medial knee leads to degeneration of articular cartilage and bone spurs, causing pain, stiffness, and reduced mobility.
  • Patellofemoral Pain Syndrome (PFPS): Lateral maltracking of the kneecap causes irritation and pain behind or around the patella, especially during activities like squatting, climbing stairs, or prolonged sitting.
  • Medial Collateral Ligament (MCL) Strain/Overload: While the MCL is on the medial side, it can be stretched or overloaded due to the constant valgus stress.
  • Meniscal Tears: The increased compressive forces on the medial meniscus make it more susceptible to tears.
  • Iliotibial Band Syndrome (ITBS): Although often associated with genu varum (bow legs), compensatory internal rotation of the femur can sometimes contribute to increased tension in the IT band, leading to lateral knee pain.
• Hip Pain:
  • Greater Trochanteric Pain Syndrome (GTPS) / Trochanteric Bursitis: Weakness in the hip abductors (gluteus medius/minimus) and excessive hip adduction/internal rotation can overload the hip abductor tendons and bursa, causing pain on the outside of the hip.
  • Hip Impingement (FAI): While not directly caused by knock knees, altered hip mechanics can exacerbate or contribute to symptoms in individuals with underlying FAI.
• Ankle and Foot Pain:
  • Plantar Fasciitis: Compensatory foot pronation can excessively stretch the plantar fascia, leading to heel pain.
  • Posterior Tibial Tendon Dysfunction (PTTD): The increased demand on the posterior tibial muscle to support the arch in an overpronated foot can lead to inflammation or degeneration of its tendon.
• Lower Back Pain:
  • The altered alignment and compensatory movements throughout the lower kinetic chain can lead to imbalances in the pelvis and spine, potentially contributing to lower back discomfort or pain.

Contributing Factors and Muscle Imbalances

Addressing muscle imbalances is crucial for managing pain and improving alignment in individuals with knock knees.

Common Muscle Weaknesses:

• Gluteus Medius and Minimus: These hip abductors are critical for stabilizing the pelvis and preventing excessive hip adduction and internal rotation, which contribute to valgus collapse.
• Vastus Medialis Obliquus (VMO): This quadriceps muscle helps stabilize the patella and can become weakened with maltracking.
• Core Stabilizers: A weak core can lead to poor pelvic control, impacting lower limb alignment.

Common Muscle Tightnesses:

• Hip Adductors: Tightness in these inner thigh muscles pulls the knees inward.
• Tensor Fasciae Latae (TFL) and Iliotibial Band (ITB): Tightness in these lateral hip/thigh structures can contribute to lateral knee pain and affect patellar tracking.
• Hamstrings: Tight hamstrings can alter pelvic tilt and affect knee mechanics.
• Gastrocnemius/Soleus (Calf Muscles): Tightness here can limit ankle dorsiflexion, potentially increasing compensatory pronation at the foot.

Diagnosis and Assessment

A thorough assessment by a healthcare professional (e.g., orthopedic surgeon, physical therapist, kinesiologist) is essential to determine the cause and extent of pain related to genu valgum.

Diagnostic Steps:

• Clinical Examination: Visual assessment of alignment, gait analysis, range of motion testing, and palpation of painful areas.
• Muscle Strength and Flexibility Assessment: Identifying specific muscle imbalances.
• Imaging: X-rays (standing weight-bearing views are crucial to assess mechanical axis and joint space), MRI (for soft tissue evaluation like meniscus or ligaments), or CT scans may be used.

Management and Treatment Strategies

Treatment for painful knock knees focuses on reducing pain, improving alignment, and restoring proper biomechanics.

Conservative Management:

• Physical Therapy/Exercise Prescription:
  • Strengthening: Targeting weak muscles such as hip abductors (e.g., clam shells, side-lying leg raises), gluteus maximus (e.g., glute bridges, squats with proper form), VMO, and core muscles.
  • Stretching: Addressing tight muscles like hip adductors, hamstrings, TFL/ITB, and calf muscles.
  • Neuromuscular Re-education: Training proper movement patterns during functional activities (e.g., squats, lunges, walking).
• Orthotics and Footwear: Custom or over-the-counter orthotics can help support the arch and reduce excessive foot pronation, thereby influencing knee alignment.
• Bracing: In some cases, specific knee braces may be used to provide support and improve alignment.
• Pain Management: NSAIDs, ice, or heat may be used for symptomatic relief.
• Weight Management: Reducing excess body weight significantly decreases the load on the knee joints.

Surgical Intervention:

• In severe cases, or when conservative measures fail, surgical options may be considered, particularly for growing children or adults with significant pain and functional limitations.
  • Guided Growth (in children): Using small plates or screws to temporarily slow growth on one side of the bone, allowing the other side to catch up and correct the alignment.
  • Osteotomy (in adults): A surgical procedure to cut and realign the bone (usually the tibia or femur) to shift the weight-bearing axis and reduce stress on the painful compartment.

Prevention and Long-Term Outlook

Early identification and intervention are key to preventing or mitigating pain associated with knock knees. Maintaining strong hip abductors, glutes, and core muscles, coupled with appropriate flexibility, can help support proper lower limb alignment. While some degree of genu valgum may persist, consistent adherence to rehabilitation exercises and lifestyle modifications can significantly reduce pain, improve function, and slow the progression of degenerative joint changes, allowing individuals to lead active, pain-free lives.