Alignment and Arthroplasty

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
Effective Dose (mSv)
Collimation
Scan length (cm)
mAs
kVp
Area scanned
Calculation using CT-EXPO programme
Calculation using CT DOSE programme
Female patient
Male patient
0.64
0.37
0.61
4x2.5mm
5
80
120
Hips
0.64
0.37
0.56
4x5mm
0.12
4x1mm
20
100
120
Knees
0.005
4x2.5mm
5
45
120
Ankles
0.50 0.76
0.74
Total effective dose (worst case)
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
mAs
kV
Collimation
Area
PROTOCOL
80
Mid pelvis to feet

• Topogram
• (Scout film)

80
120
2.5mm
Femoral head
Hip
100
120
1.0mm
10cm either side of joint line
Knee
45
120
2.5mm
5cm distal tib/fib talus
Ankle