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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. ? 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

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  1. Alignment and Arthroplasty Justin Cobb Johann Henckel, Vijay Kannan, Farhad Iranpour, Robin Richards Imperial College London

  2. 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?

  3. Accuracy vs function • Better function Type II error More accurate surgery

  4. Our Aim • Preop plan for each individual • Precise operation • Documentation of position achieved • Correlated with function

  5. This paper • Will show you how to measure • Will talk about what to measure • And suggest a way forward

  6. 1 how to measure • Computerised Axial Tomography • Modality of choice in the skeleton -Planning -Outcome measurement • Dose optimisation vs image quality • Minimising dose

  7. X-rays • Inaccurate • Magnification • 8-20% • Perspective distortion • Rotation in one plane creates compound errors

  8. CT • Virtual surgery • Accurate pre-op planning • Ability to measure outcome • And confirm the link • between structure and function

  9. 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

  10. 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

  11. Methods • Phantom pelvis and limbs • Varied the scan parameters • Evaluated the image quality • Effective dose measurements • 2 commercial software packages • CT DOSE & CT-EXPO

  12. Phantom

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

  14. Splinting Picture of splint note can open the joint • Motion detecting software

  15. Hip Centre

  16. Ankle

  17. Planning

  18. Post op analysis

  19. Post op analysis

  20. Planned ve achieved

  21. Tibia

  22. 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

  23. Results ♀ 0.735mSv ♂ 0.5mSv ~ 0.7mSv =

  24. Scan Time • Actual scan time under 1 Min

  25. 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

  26. 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

  27. 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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