Limb Length Discrepancy

Summary

In this educational video, Mahesh Tapa discusses the importance of limb length measurements in pediatric radiology, a critical yet often overlooked aspect. He explains the goal of these studies is to identify discrepancies that may affect a patient's vertical alignment. Tapa demonstrates how to accurately measure limb lengths using an Eos imaging device, emphasizing the need for a weight-bearing approach and proper use of blocks to prevent self-compensation. He details the process of measuring the femur and tibia, and how these measurements can indicate where the discrepancy lies, whether in the long bones, pelvis, or foot. The video concludes with a clear example of reporting findings, aiming to simplify and clarify this essential procedure for radiologists and clinicians.

Takeaways

• 📚 The video is about limb length measurements, an essential aspect of pediatric radiology.
• 🤝 Dr. Vince Moscow from the orthopedic department provided insights and much of the understanding of the topic.
• 🎯 The goal of limb length studies is to identify any barriers to having a vertical spine during standing or weight-bearing.
• 🏥 Adequate images are crucial, with the block height under the shorter limb clearly labeled and the tops of both iliac crests visible.
• 🔍 Limb length discrepancy can occur not only in the femur and tibia but also in the ilium and foot, though the latter are not routinely measured.
• 📐 Limb length measurements should be done weight-bearing on an EOS device or using three short pelvis, knee, and ankle radiographs with rulers.
• 📏 A horizontal line is drawn through the tops of the iliac crests to measure the difference in height, ensuring accuracy in limb length discrepancy.
• 👟 A lift or block is used under the shorter limb to prevent self-compensation by the patient, which could lead to inaccurate measurements.
• ⚖️ The true limb length discrepancy is calculated by considering the difference in iliac crest height after applying the lift.
• 🦿 Measurements of the femur and tibia are made through their mechanical axis, not the anatomical axis, using specific landmarks.
• 📊 The video explains how to calculate the lengths of the femur and tibia and how these measurements contribute to understanding the overall limb length discrepancy.
• 📝 The final report includes the limb length discrepancy, the equal lengths of the tibias, and the shorter right femur, providing a comprehensive assessment.

Q & A

What is the primary goal of limb length measurements in pediatric radiology?

The primary goal of limb length measurements is to evaluate any barriers that may exist to having a vertical spine when standing or weight-bearing.

Why is it important to achieve parody of the iliac crests on weight-bearing radiographs?

Achieving parody of the iliac crests ensures that they are at a similar level and parallel to the ground, which is necessary for accurate limb length assessment and to determine if lifts under the shorter limb are needed.

What are the two key points to consider when ensuring adequate images for limb length studies?

The two key points are: 1) the height of the block used under the shorter extremity should be clearly labeled, and 2) the tops of both iliac crests should be visible on the image.

Why do radiologists also consider the ilium and foot in limb length discrepancy, aside from the femur and tibia?

The ilium and foot can also contribute to limb length discrepancy, and considering them provides a more comprehensive assessment of the patient's condition.

What is the standard method for limb length measurements as described in the script?

Limb length measurements should be done weight-bearing, either on an EOS device or using three short pelvis, knee, and ankle radiographs with rulers.

How can one ensure a horizontal line is drawn accurately on an image for measurement purposes?

By using a tool that allows for horizontal lines and ensuring the line is drawn away from the anatomical structure being assessed before moving it precisely to the top of the iliac crest.

Why is it necessary to use a block under the shorter foot during measurements instead of just having the patient stand?

Using a block prevents the patient from self-compensating for the limb length difference by bending the knee of the longer extremity, which would result in inaccurate measurements.

How does the clinical team estimate the size of the lift necessary during the physical exam?

The clinical team estimates the size of the lift necessary based on observations and assessments made during the physical examination of the patient.

What is the significance of the difference in iliac crest height after using a lift block?

The difference in iliac crest height after using a lift block helps determine the true limb length discrepancy by accounting for any compensation made by the patient.

How are the lengths of the femur and tibia measured in the context of limb length discrepancy?

The lengths are measured through their mechanical axis, from the top of the capital femoral epiphysis to the middle of the tibial plephone for the femur, and then the tibia length is calculated by subtracting the femur length from the total limb length.

What does the script suggest about the role of the iliac bone and foot in the overall limb length discrepancy?

If the tibias are of equal length and there is still a limb length discrepancy, it suggests that the difference may be due to the iliac bone or foot length, although these are not typically measured.

What is the conclusion of the report mentioned in the script regarding the patient's limb length discrepancy?

The conclusion is that with a 2.5 cm lift under the right foot, the right iliac crest is 5 mm higher, indicating the right limb is 2 cm shorter, with equal tibia lengths and the right femur being 1.1 cm shorter.