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.

Outlines

00:00

📏 Understanding Limb Length Measurements in Pediatric Radiology

Mahesh Tapa introduces the topic of limb length measurements, a fundamental aspect of pediatric radiology. He acknowledges the topic's complexity and credits Dr. Vince Moscow for his insights. The primary goal of these measurements is to identify any hindrances to achieving a vertical spine during weight-bearing positions. Tapa emphasizes the importance of proper imaging, including the visibility of iliac crests and the correct labeling of block heights under the shorter limb. He also discusses the potential locations of limb length discrepancies, not only in the femur and tibia but also in the ilium and foot, although the latter are not routinely measured. The use of a standing EOS image is recommended for these measurements, and a detailed explanation of how to assess the adequacy of the image and measure the discrepancy between iliac crests is provided. Tapa also explains the rationale behind using a block to prevent self-compensation by the patient during the measurement process.

05:01

🦿 Measuring Femur and Tibia Lengths for Accurate Limb Discrepancy Assessment

This paragraph delves into the specifics of measuring the femur and tibia to determine the source of limb length discrepancies. Tapa explains the importance of using the mechanical axis for these measurements, rather than the anatomical axis, and describes the process of measuring from the capital femoral epiphysis to the tibial plateau and then to the medial femoral condyle. The method chosen by Seattle Children's Hospital, after consultation with the orthopedics department, is to calculate the femoral length and then subtract this from the total length to find the tibial length. Tapa provides a brief overview of the measurement process and then reports the differences in tibia and femur lengths, noting that while the tibias are of equal length, the right femur is slightly shorter than the left. This indicates that the overall limb length discrepancy may also involve the foot or iliac bone. The paragraph concludes with a summary of the findings and a reminder of the clinical implications for orthopedic surgeons, who may opt to lengthen the shorter limb's long bones or arrest the growth of the longer limb's bones.

Keywords

💡Limb Length Measurements

Limb length measurements refer to the process of determining the length of a limb, typically to identify discrepancies that may affect a person's posture or gait. In the video, this concept is central to understanding how pediatric radiologists assess and manage conditions that could lead to an uneven spine or limbs. The script mentions the goal of these measurements is to evaluate any barriers to having a vertical spine when standing or weight-bearing.

💡Pediatric Radiology

Pediatric radiology is a subspecialty of radiology that focuses on medical imaging of children. The video script emphasizes its importance in the context of limb length discrepancies, as it is a fundamental aspect of diagnosing and treating orthopedic issues in pediatric patients. Dr. Vince Moscow, an orthopedic specialist mentioned in the script, collaborates with radiologists to understand limb length discrepancies better.

💡Iliac Crests

The iliac crests are the uppermost parts of the hip bones that form the top of the pelvic girdle. In the script, they are important landmarks for assessing limb length discrepancies. The video explains that on weight-bearing radiographs, the iliac crests should be at a similar level and parallel to the ground, which helps in determining if there is a need for lifts under a shorter limb.

💡Weight-bearing Radiographs

Weight-bearing radiographs are X-ray images taken while the patient is standing and bearing weight on the limbs. The script describes the importance of these images in accurately assessing limb length, as they provide a realistic view of the spine and limbs under load, which is crucial for diagnosing and correcting limb length discrepancies.

💡Lifts

In the context of the video, lifts refer to the additional height placed under the shorter limb to level the iliac crests during imaging. The script explains that lifts are necessary to achieve a proper comparison of limb lengths and to prevent inaccurate measurements due to the body's natural compensation for limb length discrepancies.

💡Eos Imaging

EOS imaging is a type of low-dose, full-body, biplanar X-ray imaging system that provides a comprehensive view of the skeletal system. The script mentions using an EOS device for limb length measurements, emphasizing its utility in obtaining weight-bearing images that are essential for accurate diagnosis.

💡Mechanical Axis

The mechanical axis refers to the line that runs through the center of the long bones, such as the femur and tibia, and is used to assess the alignment of the limbs. The video script describes how measurements should be taken along the mechanical axis, rather than the anatomical axis, to accurately determine the length of the femur and tibia.

💡Femur

The femur, or thigh bone, is the longest and strongest bone in the human body. In the script, the femur's length is measured from the top of the capital femoral epiphysis to the medial femoral condyle as part of the limb length discrepancy assessment. Understanding the length of the femur is crucial for identifying the source of limb length discrepancies.

💡Tibia

The tibia, or shin bone, is the larger and stronger of the two bones in the lower leg. The video script discusses measuring the tibia's length to determine if it contributes to the limb length discrepancy. The script mentions that in this case, the tibia lengths were equal, indicating that the discrepancy was due to other factors.

💡Orthopedic Surgeon

An orthopedic surgeon is a specialist who diagnoses, treats, and manages musculoskeletal conditions. In the context of the video, the script explains that the orthopedic surgeon would not typically lengthen or shorten the pelvis or foot but would address limb length discrepancies by lengthening the long bones of the shorter limb or arresting the growth of the long bones of the longer limb.

Highlights

Introduction to limb length measurements as a fundamental aspect of pediatric radiology.

The importance of evaluating barriers to vertical spine alignment in limb length studies.

Achieving parody of the iliac crests on weight-bearing radiographs for accurate measurements.

Ensuring adequate images for limb length measurements, including visible iliac crests and labeled block height.

Exploring the potential locations of limb length discrepancy, including the femur, tibia, ilium, and foot.

Routine measurement practices and the rationale behind not measuring the ilium or foot heights.

Demonstration of a standing EOS image for limb length measurements, emphasizing weight-bearing conditions.

Technique for drawing horizontal lines to measure the difference in iliac crest levels.

The significance of using a block under the shorter limb to prevent inaccurate self-compensation by the patient.

Calculating the true limb length discrepancy by accounting for the difference in iliac height.

Clinical estimation of the necessary lift size during the physical exam for accurate measurements.

The decision-making process for limb length discrepancy reporting, including the use of a 2.5 cm block.

Measurement techniques for the femur and tibia through their mechanical axis for accuracy.

The collaboration between radiologists and orthopedic departments in determining measurement landmarks.

Interpretation of measurement results, including the significance of equal tibia lengths and femur length discrepancy.

Understanding the implications of limb length discrepancy on potential orthopedic interventions.

Conclusion summarizing the findings and the process of limb length measurement reporting.

Invitation for feedback and subscription for more pediatric radiology content.

Transcripts

hi i'm mahesh tapa and in this video i

want to talk to you about

limb length measurements it may not be a

very sexy topic but it's bread and

butter pediatric radiology

much of what i'm about to discuss began

with a simple discussion

with our orthopedic department dr vince

moscow in particular

really walked me through no pun intended

this topic

and much of my understanding the subject

matter

comes from him so a huge thanks to dr

moscow

first what's the goal of doing limb

length measurements

the purpose of doing limb length studies

is to evaluate

any barriers that may exist to having a

vertical spine

when standing or weight-bearing now

unless there is some sort of

segmentation or fusion anomalies or some

masses

of the lower spine or sacrum we should

be able to achieve

parody of the iliac crests on

weight-bearing radiographs

such that the iliac crests are at a

similar level

and parallel to the ground we may need

lifts under shorter limb but it should

be

achievable that brings me to two points

making sure that we have adequate images

one the height of the block being used

under the shorter extremity

should be clearly labeled and two the

tops of both iliac crests

should be visible on the image

let's step back a little and talk about

where along the limb

the length discrepancy might be

occurring as radiologists we

instinctively think of the femur and

tibia

however we can't forget about the ilium

and the foot they too can contribute to

limb length discrepancy as a routine we

don't

measure the ilium typically from the

iliac crest to the acetabular tectum

or the foot heights and i'll explain why

in a little bit

with that preamble out of the way let's

take a look

at a standing eos image by the way

limb length measurements should be done

weight bearing

on an eos device or using the three

short pelvis knee ankle radiographs

with rulers first let's see if this

image is adequate

indeed the tops of the iliac crests are

visible and the height

of the lift under the shorter limb is

clearly labeled

good now let's zoom to the top and see

if the iliac crests

are at the same level not quite

the right iliac crest is just a bit

higher how much higher

we need to draw horizontal lines through

the tops of the iliac crests

and measure the difference here's a pro

tip

make the line long and draw it

away from the anatomical structure being

assessed

and then move that line to that

anatomical structure

on this pax if i hold the shift key down

the line is completely horizontal now

move the line precisely to the top of

the iliac crest

do the same on the other side

now measure the difference between the

two sides

it looks like there is about a five or

six millimeter difference

let's zoom back out to get the full

picture

and again discuss our findings so far

why did we use a 2.5 centimeter block

under the right foot

how did we know that 2.5 centimeters was

the correct size lift to use

the clinical team will estimate the size

of lift

necessary during the physical exam and

that's how we decide on what block to

use

but why use a block at all can't we just

have the patient stand

and then make the measurements well we

can't

that's because the child will often try

to self-compensate

for the difference in limb length when

standing

by bending the knee of the longer

extremity

which will of course result in

inaccurate measurements

the 2.5 centimeters was a good estimate

however in this case the lift resulted

in the right iliac crest

being about five millimeters higher

so the true limb length discrepancy is

actually

two centimeters because we have to take

that difference in iliac height into

account

if the iliac crests were perfectly level

then the limb length discrepancy would

be

2.5 centimeters now let's say the right

iliac crest

was still five millimeters lower than

the left

despite the 2.5 centimeter block this

means the true

limb length discrepancy is actually

three centimeters

i hope this makes sense there are two

ways of stating the limb length

discrepancy for this child

we could simply say the right limb is

two centimeters shorter

or we could say with a 2.5 centimeter

lift under the right foot the right

iliac crest is five millimeters higher

indicating the right limb is two

centimeters shorter

i think the second way may sound a bit

more convoluted

but it gets the point across that a

block was used under the right lower

extremity

which resulted in that side being

slightly taller

now let's go on to make our measurements

of the femurs and tibias

we want to make the measurements of

these through their mechanical axis

and not their anatomical axis for

example

this is the anatomical axis of the right

femur

this is the mechanical axis vertically

down

from the top of the capital femoral

epiphysis to

the medial femoral condyle be sure to

describe

the landmarks you are using to make the

measurements

after discussing with our orthopedics

department

we decided to do the following make a

measurement from the top

of the capital femoral epiphysis to the

middle

of the tibial plephone then

measure from the top of the capital

femoral epiphysis

to the medial femoral condyle

this will give you the femoral length

then subtract the two numbers

and that will give you the tibia length

some institutions measure the tibia

directly

or choose the middle of the femoral head

but this

is how we decide to do it at seattle

children's hospital

after discussing with our orthopedics

department

now that you know the landmarks i'm

going to just fast forward through all

these measurements

for the sake of brevity we report the

differences

in the tibia and femur lengths let's

take a closer look at what the numbers

are actually telling us

looks like there wasn't any appreciable

difference in the tibia lengths

and the right femur is about a

centimeter or so

shorter than the left femur what does

this mean exactly

because we said earlier that the limb

length discrepancy

was 2 centimeters well it just means

that the difference in the femur lengths

can only account for part of the overall

discrepancy

since the tibias are equal lengths it

must mean

that either the foot or the iliac bone

is also shorter we could measure these

heights but we typically don't

the orthopedic surgeon isn't going to

lengthen or shorten the pelvis or foot

he or she will either lengthen the long

bones of the shorter limb

and or arrest the growth of the long

bones of the longer limb

in conclusion for this report my

impression would be

with a 2.5 centimeter lift under the

right foot

the right iliac crest is 5 millimeters

higher

indicating the right limb is two

centimeters shorter

the tibias are of equal lengths and the

right femur is

1.1 centimeters shorter so i hope

this video has made limb length

measurements a little easier and a

little bit more

understandable if you like what you see

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bell i'll see you next time