Leg Length Discrepancy: Types, Causes, Diagnosis, and Treatment

What is Shortening of a Leg?

Shortening of a leg, medically known as Leg Length Discrepancy (LLD) or anisomelia, refers to a condition where one lower limb is noticeably shorter than the other. This difference can range from subtle to significant, potentially impacting biomechanics, posture, and overall musculoskeletal health.

Understanding Leg Length Discrepancy (LLD)

Leg Length Discrepancy (LLD) is a common musculoskeletal condition characterized by an inequality in the length of the lower limbs. While a minor discrepancy (typically less than 5mm) is common in the general population and often asymptomatic, larger differences can lead to a cascade of compensatory mechanisms throughout the kinetic chain, from the feet up to the spine. Understanding the nature and cause of the discrepancy is crucial for effective management.

Types of Leg Length Discrepancy

LLD is broadly categorized into two main types, each with distinct underlying causes and implications:

• Structural (True) LLD: This type refers to an actual anatomical difference in the bone length of the femur (thigh bone) or tibia (shin bone). It is a fixed, measurable difference in the skeletal structure itself.
• Functional (Apparent) LLD: This type occurs when the legs are actually of equal length, but one appears shorter due to issues elsewhere in the body. These issues can include pelvic rotation, muscle imbalances, joint contractures, or spinal deformities that cause an asymmetry in the lower limb positioning, making one leg effectively "shorter" during weight-bearing.

Causes of Leg Shortening

The causes of leg shortening are diverse and depend on whether the discrepancy is structural or functional.

• For Structural LLD:
  • Congenital Conditions: Present at birth, such as fibular hemimelia (absence or shortening of the fibula), congenital coxa vara (hip deformity), or hemihypertrophy (overgrowth of one side of the body).
  • Developmental Conditions: Occurring during growth, including Perthes disease (hip joint disorder), Slipped Capital Femoral Epiphysis (SCFE), or growth plate injuries (epiphyseal fractures) that prematurely close or damage the growth plates.
  • Traumatic Injuries: Severe fractures, especially those involving the growth plates in children, can lead to shortening if the bone heals incorrectly or if growth is impaired.
  • Degenerative Conditions: Advanced osteoarthritis in the hip or knee can lead to significant loss of joint cartilage and bone, effectively shortening the limb.
  • Surgical Interventions: Complications from surgeries like hip or knee replacements, or procedures involving bone resection (removal), can sometimes result in leg shortening.
  • Neuromuscular Conditions: Conditions like polio, cerebral palsy, or spinal cord injuries can cause muscular weakness or spasticity that affects bone growth or joint alignment over time.
• For Functional LLD:
  • Pelvic Obliquity/Rotation: An anterior or posterior pelvic tilt, or pelvic rotation, can elevate one side of the pelvis, making the corresponding leg appear shorter.
  • Muscle Imbalances: Tightness in muscles such as the hip flexors, adductors, or piriformis, or weakness in gluteal muscles, can pull the pelvis out of alignment.
  • Joint Contractures: Limited range of motion in the hip, knee, or ankle due to injury, arthritis, or prolonged immobility can restrict full extension and create an apparent shortening.
  • Scoliosis: A lateral curvature of the spine can lead to an uneven pelvis and functional LLD.
  • Foot Pronation: Excessive pronation in one foot can lower the arch and effectively shorten that limb.

How Leg Shortening is Measured and Diagnosed

Accurate diagnosis of LLD is critical for determining the appropriate treatment.

• Clinical Examination: A healthcare professional will visually inspect posture, gait, and perform physical measurements.
  • Tape Measure Method: Measuring from the anterior superior iliac spine (ASIS) to the medial malleolus (ankle bone) while the patient is supine. This can detect both structural and significant functional discrepancies.
  • Block Test: Placing blocks of varying thicknesses under the shorter leg to level the pelvis, which helps estimate the magnitude of the discrepancy.
• Imaging Studies: These are crucial for confirming structural LLD and precisely quantifying the difference.
  • Scanogram (Orthoroentgenogram): A specialized X-ray technique that takes images of the hip, knee, and ankle joints on a single film or stitched images, allowing for direct measurement of bone lengths.
  • CT Scan (Computed Tomography): Provides highly accurate measurements of bone length, especially useful for complex cases.
  • MRI (Magnetic Resonance Imaging): Can assess soft tissue involvement and growth plate status in children.

Potential Biomechanical and Health Implications

Even small leg length discrepancies can have significant biomechanical consequences over time, leading to various musculoskeletal issues.

• Spinal Pain: Most commonly, chronic low back pain due to compensatory spinal curves (functional scoliosis) or disc compression.
• Hip Pain: Increased stress on the hip joint of the longer leg or the sacroiliac joint.
• Knee Pain: Altered loading mechanics can lead to patellofemoral pain syndrome, osteoarthritis, or meniscal issues.
• Foot and Ankle Problems: Excessive pronation in the longer limb or supination in the shorter limb, leading to plantar fasciitis, Achilles tendinopathy, or bunions.
• Gait Deviations: A noticeable limp, reduced stride length on one side, or compensatory movements like "hip hiking" on the shorter side.
• Increased Energy Expenditure: The body expends more energy to maintain balance and ambulate efficiently.
• Increased Risk of Injury: Chronic asymmetrical loading can predispose individuals to stress fractures or overuse injuries.

Management and Treatment Approaches

Treatment for leg shortening depends on the type, magnitude, and cause of the discrepancy, as well as the individual's symptoms and age.

• Conservative Management:
  • Shoe Lifts/Heel Lifts: For structural LLD, external shoe lifts or internal heel inserts can be used to equalize leg lengths, reduce compensatory mechanisms, and alleviate symptoms. The lift amount is typically determined by the measured discrepancy.
  • Physical Therapy & Exercise: Crucial for functional LLD. This includes:
    • Stretching: To address muscle tightness (e.g., hip flexors, hamstrings, adductors, piriformis) contributing to pelvic rotation or joint contractures.
    • Strengthening: To correct muscle imbalances (e.g., gluteal muscles, core stabilizers) that support proper pelvic alignment.
    • Gait Training: To re-educate movement patterns and reduce compensatory limping.
    • Manual Therapy: Joint mobilizations or manipulations to address restrictions in the spine, pelvis, or lower extremity joints.
  • Orthotics: Custom foot orthotics can address foot biomechanics (e.g., excessive pronation) that may contribute to functional LLD or help distribute pressure evenly with a lift.
• Surgical Interventions: Reserved for significant structural LLD (typically >2-2.5 cm) or when conservative measures fail.
  • Epiphysiodesis: In children with significant growth remaining, this procedure involves surgically arresting the growth plate of the longer limb to allow the shorter limb to catch up.
  • Limb Lengthening: A complex procedure involving osteotomy (cutting the bone) and gradual distraction using external fixators or internal motorized rods to stimulate new bone growth.
  • Limb Shortening: Involves resecting a segment of bone from the longer limb, less common but an option in certain cases.

Conclusion

Shortening of a leg, whether structural or functional, is a condition that warrants careful assessment due to its potential to disrupt normal biomechanics and lead to chronic pain and disability. An accurate diagnosis by a qualified healthcare professional, often involving a combination of physical examination and imaging, is the first step. Management strategies range from simple shoe lifts and targeted physical therapy to complex surgical interventions, all aimed at restoring balance, improving function, and enhancing quality of life.