1. 25 iv 06 Alignment and Arthroplasty Justin Cobb Johann Henckel, Vijay Kannan, Farhad Iranpour, Robin Richards Imperial College London

2. 25 iv 06 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. 25 iv 06 Accuracy vs function  Better function More accurate surgery Type II error

4. 25 iv 06 Our Aim  Preop plan for each individual  Precise operation  Documentation of position achieved  Correlated with function

5. 25 iv 06 This paper  Will show you how to measure  Will talk about what to measure  And suggest a way forward

6. 25 iv 06 1 how to measure  Computerised Axial Tomography –Modality of choice in the skeleton -Planning -Outcome measurement  Dose optimisation vs image quality Minimising dose

7. 25 iv 06 X-rays  Inaccurate –Magnification 8-20% –Perspective distortion Rotation in one plane creates compound errors

8. 25 iv 06 CT  Virtual surgery –Accurate pre-op planning  Ability to measure outcome –And confirm the link between structure and function

9. 25 iv 06 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. 25 iv 06 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. 25 iv 06 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. 25 iv 06 Phantom

13. 25 iv 06 Splint  Conventional trauma splint  Stabilise leg and knee  Distract the medial condyles  Blind areas (Movement detection software)

14. 25 iv 06 Splinting Picture of splint note can open the joint  Motion detecting software

15. 25 iv 06 Hip Centre

16. 25 iv 06 Ankle

17. 25 iv 06 Planning

18. 25 iv 06 Post op analysis

19. 25 iv 06 Post op analysis

20. 25 iv 06 Planned ve achieved

21. 25 iv 06 Tibia

22. 25 iv 06 Results 0.500.76 0.74 Total effective dose (worst case) 0.0054x2.5mm545120 Ankles 0.124x1mm20100120 Knees 0.640.370.564x5mm 0.640.370.614x2.5mm580120 Hips Female patientMale patient Calculation using CT-EXPO programme Calculation using CT DOSE programme Effective Dose (mSv)CollimationScan length (cm) mAskVpArea scanned

23. 25 iv 06 Results = ~ 0.7mSv ♀ 0.735mSv ♂ 0.5mSv

24. 25 iv 06 Scan Time  Actual scan time under 1 Min

25. 25 iv 06 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. 25 iv 06 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. 25 iv 06 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