Limb Length Discrepancy

What is Limb Length Discrepancy (LLD)?

A limb length discrepancy (LLD) happens when one arm/leg is more elongated than the other leg/arm. A difference in leg lengths is more noticeable and can affect daily activities. There are various causes for a leg length discrepancy, but they generally fall into two main categories: 1) congenital conditions that result in slower growth of one leg, and 2) incidents during a person’s lifetime that impact bone length or growth centers, such as fractures, trauma, or infections. Often, parents observe a difference as their babies start standing or walking, prompting them to seek medical advice to determine the cause.

Leg length discrepancies are quite common, with many individuals having a minor difference without experiencing any noticeable effects or requiring treatment. Regardless, when the discrepancy calculates more than 1.5-2.0 cm (5/8 of an inch), most doctors suggest an evaluation. To assess a limb length discrepancy, a thorough physical examination is conducted, and standing X-ray films may be taken to obtain a precise measurement.

If the limb length discrepancy significantly impacts a child’s daily life, treatment may be necessary. Both non-surgical and surgical options exist. One non-surgical approach is the use of a shoe lift, which can be added to or inserted into the shoe to correct some leg length differences. However, this method only corrects the discrepancy while the lift is worn. While shoe lifts can be helpful, some children have leg length differences that are too substantial and may benefit from surgical intervention. Surgical treatments can involve either shortening the longer leg or lengthening the shorter leg, providing a permanent correction to the limb length. The choice between these techniques depends on the specific condition of the child.

There are two types of limb-length discrepancies:

1. Structural discrepancy: In this patient, a bone in one leg/arm is shorter than the affiliated bone in the other extremity.
2. Functional discrepancy: Here, bone lengths are equal in both legs or arms, but a joint contracture (reduced joint mobility) in the knee, hip, shoulder, elbow, or another joint disrupts symmetry between the limbs.

What causes Limb Length Discrepancy?

Limb-length discrepancies can be classified as congenital, meaning they are present at birth, or they can develop due to illness or trauma.

Congenital limb-length discrepancies:

Individuals are born with limb-length discrepancies (LLD) when one/more additional elongated bones in a leg/arm do not form during the gestation period. In most patients, the reason for this illness is unknown.

Leg-length discrepancies occur when a child is born with an illness that involves the alignment of their hip joints, for instance, coxa vara, and developmental dislocation of the hip joint.

Limb-length discrepancies related to injury or illness:

A complex fracture or a fracture that fails to heal properly can impede the growth of the affected bone. In some cases, certain fractures can lead to excessive bone growth during the healing process. This is particularly common in thighbone (femur) injuries.

Damage to the growth plate caused by injury or bone infections like osteomyelitis can disrupt normal growth. Growth plates are soft areas located at each end of the long bones in the arms and legs, where bone growth occurs. As a teenager or young adult reaches their adult height, the growth plates solidify into bone. If the growth plate in one limb is damaged, the other limb will continue to grow, resulting in a gradual difference in length over time.

Bone tumors and bone cysts can obstruct bone growth. Depending on the size and location of the tumor or cyst, its removal through surgery, radiation, or chemotherapy may slow down or completely halt bone growth.

For example, cerebral palsy and other neuromuscular issues can impact a child’s alignment and general posture, potentially leading to a limb-length discrepancy (LLD).

Signs and symptoms of Limb Length Discrepancy

Limb-length discrepancies can manifest in either the arms or legs, but when it affects a child’s legs, the symptoms tend to be more noticeable, often necessitating treatment.

The symptoms and effects of leg-length discrepancies can vary from one child to another and may include:

Most generally, discrepancies in the distances of the femur (thigh bone) and tibia (shin bone) are obeyed, even though the fibula (the shorter bone in the lower leg) can even be involved.

Difficulties with walking, such as limping, shuffling, or favoring the longer leg while walking on the tip-toes of the shorter leg.

Increased fatigue due to the additional effort required to move with an uneven gait.

Limb-length discrepancies can even boost the chance of developing affiliated situations, involving low-back pain, osteoarthritis, & scoliosis.

It is important to note that these symptoms and effects can vary depending on the severity of the limb-length discrepancy and the individual child. Consulting with a healthcare professional is essential to accurately diagnose and determine the appropriate treatment for each specific case.

Diagnosis of Limb Length Discrepancy

Limb-length discrepancies (LLD) are frequently originally doubted by parents who follow abnormal walking patterns in their child or by school nurses while routine scoliosis screenings. Once these early indications arise, it is crucial to seek a formal examination from experienced clinicians who specialize in diagnosing bone development issues in children.

A skilled pediatric orthopedic physician will conduct a comprehensive medical history review, physical examination, and visual assessment of your child. During the physical exam, the physician will observe your child’s sitting, standing, walking, and overall movement. Children may exhibit compensatory behaviors for a shorter leg, such as walking on their toes, flexing their knees, or limping.

To determine the measurement of the limb-length discrepancy (LLD), healthcare providers may ask the child to stand barefoot on the ground during establishing a series of wooden blocks beneath the shorter extremity until the child’s hips are level. The height of the blocks is then measured to calculate the difference between the two legs.

In most cases, additional imaging studies will be ordered to confirm the diagnosis, establish baseline measurements for both legs and guide treatment recommendations. These may include:

1. X-rays: These produce images of the bones. X-rays of the legs are typically taken, but additional X-rays of the hand and hip may also be required to assess skeletal maturity or remaining growth potential.
2. EOS imaging: This technology generates 3-dimensional models from two flat images. EOS images are captured while the child is standing upright, enabling improved diagnosis due to weight-bearing positioning.
3. Computed tomography (CT) scan: This imaging technique combines X-rays and computer technology to examine bones, producing cross-sectional images (“slices”) of the body.
4. Magnetic resonance imaging (MRI): Using strong magnets, radio frequencies, and computer processing, MRI delivers elaborate images of organs, soft tissues, muscles, ligaments, and other formats within the body. MRI poses no radiation disclosure to the child.

Imaging studies and physical examinations may need to be repeated every six to twelve months while your child is still growing. This periodic reassessment is necessary to monitor any changes in the limb-length discrepancy, determining whether it is progressing or remaining stable.

Measurement of Limb Length Discrepancies

Direct Methods

Measuring limb length using a tape measure between two defined points while standing is a common method. Two commonly used points are the anterior iliac spine and the medial malleolus, or the anterior inferior iliac spine and lateral malleolus.

However, it is important to be cautious as there is a significant amount of criticism and debate regarding the accuracy of tape measure methods. If you opt for this method, consider the following topics and potential errors:

• Always take the mean of at least two or three measurements.
• Whenever possible, compare measurements taken by two or more clinicians.
• Iliac asymmetries can either conceal or exaggerate a limb length inequality.
• Unilateral divagations in the elongated axis of the lower extremity, for example, genu varum, can mask or emphasize a limb length inequality.
• The asymmetrical position of the umbilicus can affect measurements.
• Joint contractures can also impact the accuracy of measurements.

Indirect Methods

The palpation of bony landmarks, such as the iliac crests or anterior iliac spines, while standing, is commonly used to assess limb length. These methods involve determining if the bony landmarks are at the same level horizontally or if there is a limb length inequality.

Among these processes, the mixture of palpation and illustrated analysis of the iliac crest or anterior superior iliac spine along with the usage of blocks or general-thickness book pages beneath the shorter extremity to adjust the level of the iliac crests (or ASIS) appears to be the most accurate and precise clinical approach for assessing limb inequality.

Regardless, it’s essential to regard that asymmetrical pelvic rotations in planes other than the frontal plane may be related to limb length imbalance. Therefore, it is recommended to palpate and compare multiple pelvic landmarks, including the greater trochanter, when using the block correction method.

To ensure the accuracy and reliability of limb length assessment, it is essential to follow these guidelines and consider the broader literature on the subject

The PALM (Pelvic Limb Alignment Method)

The PALM (Pelvic Limb Alignment Method) is an accurate and reliable tool for measuring pelvic height differences. It offers a convenient and cost-effective alternative to radiographic measurements.

Here is the correct and unique description of the measurement procedure:

1. Two tape strips are positioned on the ground, with a separation of 15cm between them. These tape strips serve as markers of where patients should place their feet.
2. Patients are instructed to take 10 steps while ensuring that the medial borders of their feet align with the outer edges of the tape strips.
3. Patients are required to stand in an upright position with no bending of the knees, hips, or spine.
4. The PALM device is then positioned on the most superior element of the iliac crest.
5. The distance between the caliper heads is measured, recording the measurement to the nearest millimeter.
6. Additionally, the inclinometer ball, which is designed to move towards the side of the shorter limb, is used to measure the angle of inclination. The inclination is documented to the closest half-degree.

By following this procedure, the PALM provides precise measurements of pelvic height differences. It is a reliable method that eliminates the need for radiographic measurements, offering a practical and cost-effective approach to assessing limb length discrepancies.

Measurement Using Blocks

The patient stands with their feet approximately 10 cm apart, knees extended, and equal weight distributed on both feet. The clinician places their hands on bilateral anatomical structures such as the posterior superior iliac spine, anterior superior iliac spine, or left and right iliac crest. The clinician visually assesses for any apparent limb length inequality. If a discrepancy is observed, a wooden board with a thickness of 0.5 cm is placed under the foot of the shorter side.

The process continues by gradually increasing the thickness of the plank under the shorter side until equal limb lengths are achieved. The final thickness of the plank corresponds to the measured leg length difference.

The reliability of this method largely depends on the accurate measurements taken by the clinician. However, studies have shown promising results regarding inter-examiner agreements between highly trained clinicians and medical students. It is important to consider confounding variables that can affect the accuracy of measurements, including pelvic asymmetry, incorrect foot positioning, obesity, joint contractures, scoliosis, and potential measurement errors.

While this method offers a practical approach to assessing limb length inequality, attention to detail and consideration of potential influencing factors are essential for obtaining reliable and accurate results.

How are limb-length discrepancies treated?

Limb-length discrepancies can be addressed through various treatment options, including both surgical and non-surgical approaches. The choice of treatment for your child will depend on several factors, such as their age, overall health, medical history, the affected limbs (legs or arms), the extent of the discrepancy, your child’s tolerance for specific interventions, and your preferences.

Non-surgical treatments for leg-length discrepancies:

1. Shoe lifts: Placing lifts inside the shoe of the shorter leg can help equalize leg lengths, improving walking and reducing back pain.
2. Physical therapy: Special stretches and exercises can be employed to alleviate pain and enhance overall function.
3. Occupational therapy: This therapy focuses on developing fine motor skills, such as handwriting.
4. Adaptive devices: Assistive devices can aid your child in performing everyday activities like tying shoes, buttoning shirts, or holding books.
5. Prosthetics: Custom-designed prosthetics can be utilized to fit over a shorter limb or replace a limb that has been amputated partially or entirely.

Surgical treatments for limb-length discrepancies:

1. Leg-shortening surgery: If the leg-length discrepancy is expected to be moderate (between two and six centimeters) when your child reaches an adult height, the longer leg may be shortened. This procedure slows down the growth of the longer leg, allowing the shorter leg to catch up.

• Epiphysiodesis: The growth plate is fused temporarily or permanently to control the growth in the longer limb.
• Epiphyseal stapling: Staples are surgically inserted on either side of the growth plate. Once the desired length is achieved, the staples are removed.
• Bone resection: A section of bone is surgically removed from the longer leg. This procedure is suitable for adults or adolescents who have reached their adult height.

2. Limb-lengthening surgery: This procedure stimulates new bone growth in the shorter leg or arm and is typically reserved for significant limb-length discrepancies that significantly impact daily activities. It is usually performed during late teens or early adulthood.

Limb-lengthening surgeries involve a multi-stage process. In the initial stage, an orthopedic surgeon performs an osteotomy, cutting the bone to be lengthened. A lengthening device is then attached, which your child will wear for several months. This device can be external (worn on the outside of the limb) or internal (surgically inserted within the bone).

During the lengthening period, adjustments are made to the device to gradually increase the gap between the bone ends, promoting the growth of new bone. Regular visits to the orthopedic surgeon are necessary to monitor progress and address any potential complications.

The 2 kinds of limb-lengthening instruments are external fixators & internal fixators. External fixators are worn on the outside of the limb, attached to the bone with pins. The device is adjusted by the patient or their family to increase the gap until the desired length is achieved. Once the bone has healed, the device is surgically removed. Internal fixators, such as the PRECICE Nail, are inserted into the bone and gradually expanded using an external magnet, allowing precise lengthening. Like external fixators, internal fixators are removed after lengthening and bone formation.

Left humerus: A. initial to lengthening; B. one year after prior elongation of ~4.5 cm utilizing a precise nail; C. instantly after 2nd elongation of ~4.5 cm; D. 6 months after 2nd elongation.

It’s important to note that the choice of treatment and specific procedures will be determined by your child’s healthcare team based on individualized assessments and discussions with you.

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Author: Dr.Mittal Vaghela