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

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?

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

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

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

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

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

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

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

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 mSv (Chauhan et al JBJS – B) kV 140, mAs mm slices

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

25 iv 06 Phantom

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

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

25 iv 06 Hip Centre

25 iv 06 Ankle

25 iv 06 Planning

25 iv 06 Post op analysis

25 iv 06 Post op analysis

25 iv 06 Planned ve achieved

25 iv 06 Tibia

25 iv 06 Results Total effective dose (worst case) x2.5mm Ankles 0.124x1mm Knees x5mm x2.5mm Hips Female patientMale patient Calculation using CT-EXPO programme Calculation using CT DOSE programme Effective Dose (mSv)CollimationScan length (cm) mAskVpArea scanned

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

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

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

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

25 iv 06 Our Protocol mm5cm distal tib/fib & talus Ankle mm10cm either side of joint line Knee mmFemoral headHip 80Mid pelvis to feetTopogram (Scout film) mAskVCollimationAreaPROTOCOL