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Alignment and Arthroplasty. Justin Cobb Johann Henckel, Vijay Kannan, Farhad Iranpour, Robin Richards Imperial College London. Function is what really matters. ? The relationship with alignment ? We know that they are related But how directly? The rules are different For osteotomy

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Alignment and arthroplasty

Alignment and Arthroplasty

Justin Cobb

Johann Henckel, Vijay Kannan, Farhad Iranpour,

Robin Richards

Imperial College London


Function is what really matters
Function is what really matters

  • ? The relationship with alignment ?

  • We know that they are related

    • But how directly?

  • The rules are different

    • For osteotomy

      • overcorrect 62%

    • For uka

      • Undercorrect leave varus

    • For tka

      • ?undercorrect? or neutral

  • We also know that everyone is different

    • So does everyone deserve a unique plan?


Accuracy vs function
Accuracy vs function

  • Better function

Type II error

More accurate surgery


Our aim
Our Aim

  • Preop plan for each individual

  • Precise operation

  • Documentation of position achieved

  • Correlated with function


This paper
This paper

  • Will show you how to measure

  • Will talk about what to measure

  • And suggest a way forward


1 how to measure
1 how to measure

  • Computerised Axial Tomography

    • Modality of choice in the skeleton

      -Planning

      -Outcome measurement

  • Dose optimisation vs image quality

    • Minimising dose


X rays
X-rays

  • Inaccurate

    • Magnification

      • 8-20%

    • Perspective distortion

      • Rotation in one plane creates compound errors


CT

  • Virtual surgery

    • Accurate pre-op planning

  • Ability to measure outcome

    • And confirm the link

      • between structure and function


Dose measurements
Dose measurements

  • Assumed Linear relationship

    • between radiation dose and malignancy.

  • Effective dose mSv

    -Weighted Dose received by the key dose sensitive organs.

  • 10mSv gives a 1 in 2000 risk of radiation induced malignancy.

  • 2.5mSv is annual background in UK


Risks
Risks

  • CXR – 0.02 mSv

  • Transatlantic flight 0.04mSv

  • Long leg measurement film – 0.7 mSv…

  • Lumbar spine x-ray – 1.3 mSv

  • CT abdo/pelvis – 10mSv

  • Upper recommended limit – 5 mSv / year

  • Perth protocol - 2.5 mSv (Chauhan et al JBJS 2004 86 – B) kV 140, mAs 85 2.5mm slices


Methods
Methods

  • Phantom pelvis and limbs

  • Varied the scan parameters

  • Evaluated the image quality

  • Effective dose measurements

  • 2 commercial software packages

    • CT DOSE & CT-EXPO



Splint
Splint

  • Conventional trauma splint

  • Stabilise leg and knee

  • Distract the medial condyles

  • Blind areas (Movement detection software)


Splinting
Splinting

Picture of splint note can open the joint

  • Motion detecting software









Results
Results

Area scanned

kVp

mAs

Scan length (cm)

Collimation

Effective Dose (mSv)

Calculation using CT DOSE programme

Calculation using CT-EXPO programme

Male patient

Female patient

Hips

120

80

5

4x2.5mm

0.61

0.37

0.64

4x5mm

0.56

0.37

0.64

Knees

120

100

20

4x1mm

0.12

Ankles

120

45

5

4x2.5mm

0.005

0.50 0.76

Total effective dose (worst case)

0.74


Results1
Results

♀ 0.735mSv

♂ 0.5mSv

~ 0.7mSv

=


Scan time
Scan Time

  • Actual scan time under 1 Min


New ct scanners
New CT scanners

  • 16/64 slice – 256

  • More Detectors (Use more of the dose)

  • Artifact reduction

  • Speed

  • Volume data

    in 3 planes

  • Standing CT

  • Segmenting MRI


Summary 1
Summary 1

  • How to measure

  • Imperial Protocol:

  • CT can be rapidly acquired 40s

  • 2D and 3D post operative analysis

  • Real measurements of implant position

    can be obtained

  • We are now able to fully measure the

    accuracy of CAOS systems well within

    the envelope of +/- 2mm & 2

  • For the same dose as a standing film


Our protocol
Our Protocol

PROTOCOL

Area

Collimation

kV

mAs

Topogram

(Scout film)

Mid pelvis to feet

80

Hip

Femoral head

2.5mm

120

80

Knee

10cm either side of joint line

1.0mm

120

100

Ankle

5cm distal tib/fib & talus

2.5mm

120

45


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