Limb Length Discrepancy
Summary
TLDRIn 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
📏 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.
🦿 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.
Mindmap
Keywords
💡Limb Length Measurements
💡Pediatric Radiology
💡Iliac Crests
💡Weight-bearing Radiographs
💡Lifts
💡Eos Imaging
💡Mechanical Axis
💡Femur
💡Tibia
💡Orthopedic Surgeon
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
please give me a thumbs up and if you
want to see
more pediatric radiology related content
please subscribe to my channel
and be sure to ring that notification
bell i'll see you next time
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