Alignment and Arthroplasty

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Alignment and Arthroplasty 

 Justin Cobb Johann Henckel, Vijay Kannan, Farhad Iranpour,

Robin Richards 

Imperial College London

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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?

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Accuracy vs function

Better function

More accurate surgery

Type II error

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Our Aim

Preop plan for each individual Precise operation Documentation of position achieved Correlated with function

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This paper

Will show you how to measure Will talk about what to measure And suggest a way forward

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1 how to measure

Computerised Axial Tomography– Modality of choice in the skeleton

-Planning

-Outcome measurement

Dose optimisation vs image quality• Minimising dose

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X-rays Inaccurate

– Magnification• 8-20%

– Perspective distortion• Rotation in one plane creates compound errors

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CT

Virtual surgery– Accurate pre-op planning

Ability to measure outcome– And confirm the link

• between structure and function

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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

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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

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Methods

Phantom pelvis and limbs Varied the scan parameters Evaluated the image quality Effective dose measurements 2 commercial software packages

– CT DOSE & CT-EXPO

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Phantom

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Splint

Conventional trauma splint Stabilise leg and knee Distract the medial condyles Blind areas (Movement detection software)

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Splinting

Picture of splint note can open the joint

Motion detecting software

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Hip Centre

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Ankle

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Planning

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Post op analysis

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Post op analysis

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Planned ve achieved

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Tibia

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Results

0.50 0.760.74

Total effective

dose (worst case)

0.0054x2.5mm545120Ankles

0.124x1mm20100120Knees

0.640.370.564x5mm

0.640.370.614x2.5mm580120Hips

Female patientMale patient

Calculation using CT-EXPO programme

Calculation using CT DOSE programme

Effective Dose (mSv)CollimationScan length (cm)

mAskVpArea scanned

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Results

=

~ 0.7mSv ♀ 0.735mSv♂ 0.5mSv

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Scan Time

Actual scan time under 1 Min

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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

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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

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Our Protocol

451202.5mm5cm distal tib/fib & talus

Ankle

1001201.0mm10cm either side of joint line

Knee

801202.5mmFemoral headHip

80Mid pelvis to feetTopogram(Scout film)

mAskVCollimationAreaPROTOCOL