1	Objective Outcome Measures in RA Eric Garling, Bart Kaptein, Paul de Bruin, Edward Valstar, Piet Rozing, Rob Nelissen Biomechanics and Imaging Research Group, Department of Orthopaedics Division of Image Processing, Department of Radiology (LKEB)
2	Outcome measures Objective performance measures of functioning may not be dependent on: Patient report Observer judgment Objective performance outcome measures that are valid, accurate and precise: Micromotion of implants Fluoroscopy EMG Gait analysis?
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4	Marker-based RSA Calibration box Tantalum markers in the bone as landmarks Tantalum markers attached to the implant as landmarks
5	Model-based RSA Not necessary to adapt prosthesis However, marking of bone remains necessary 3D surface model of prosthesis from manufacturer or by means of reversed engineering
6	Model-based RSA
7	Accuracy femoral component (SD)
8	Accuracy tibial component (SD)
9	Image-based RSA Practical issues of marker insertion: No need to place markers per-operatively Some locations are difficult to reach New opportunities: Retrospective studies (standard AP-Xray) Fluoroscopy on patients without prosthesis Validation of computer navigated prosthesis placement
10	Image-based RSA
11	Image-based RSA
12	Image-based RSA
13	Accuracy Image-based RSA
14	Summary RSA Marker-based RSA has a very high accuracy Model-based RSA has a slightly lower accuracy But Model-based RSA is much easier, faster and cheaper to set-up Sept 2007: implants form CE level 2b to CE level 3 Pre-market clinical data obligatory! Image-based RSA is a new approach to RSA Does not require markers Does require a CT Less accurate However, wider applicability
15	Periapatite May Not Improve Micromotion of Knee Prostheses in Rheumatoid Arthritis A prospective randomized RSA study Clin Orthop Relat Res; [Epub ahead of print], 2006
16	Coated implants in RA Acrylic bone cement golden standard Long-term structural integrity? (Hughes et al, 2003) Younger population Coated implants: Enhances bone ingrowth (Nelissen et al., 1998; Søballe et al., 1993) Sealing effect (Rahbek et al., 2001)
17	Study design Prospective randomised RSA study of 12 PA coated and 10 uncoated tibial components (Duracon, Stryker Howmedica)
18	Patients
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20	Tilting of Duracon tibal component
21	Conclusion PA coated Duracon tibial components A trend was seen that the cement less PA-coated Duracon prosthesis used in patients with RA provided improved fixation of tibial components compared with non-coated components
22	Micromotion of mobile bearing versus posterior stabilized total knee prostheses A prospective randomized RSA study Acta Orthop 76(3); 353-361, 2005
23	Mobile bearing knee
24	Study design Prospective randomised RSA study of 20 MB and 20 PS total knees (Interax, Stryker Howmedica)
25	Patients
26	Knee Society Score Function part
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33	Limited Rotation of the MB in a Rotating Platform Total Knee Prosthesis
34	Kinematics of mobile bearing (fluoroscopy) Broad range of kinematic patterns of tibia with respect to the femur (Banks; Dennis; Komistek; Stiehl) Unknown if and how the polyethylene bearing actually moves in MB TKA
35	Method Ten RA patients NexGen LPS MB prosthesis (Zimmer, Warsaw IN) Per-operative insertion of tantalum beads in bearing 6 months post-operatively ‘Good' Knee Society Score for function Perform 3 step-ups (18 cm) without bars
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37	Fluoroscopic set-up
38	Fluoroscopic analysis software (Model-based RSA)
39	Accuracy Marker-Based Fluoroscopic Analysis
40	Results: external rotation femoral component and bearing
41	External rotation mobile bearing
42	Difference in exo-rotation between femoral component and MB
43	Results Erratic movements All cases more axial rotation of femur than MB insert with respect to the tibia In three cases no rotation of the MB insert
44	Discussion Polyethylene on metal impingement due to the constraint of the locking screw ? Fibrous tissue formation? Wear rate comparable with fixed bearings? Loosening comparable with fixed bearing?
45	Electromyography (EMG) of mobile bearing and posterior stabilised total knee prostheses in RA patient group
46	External movement registration Optotrak EMG Extensors (RF, VM, VL) Flexors (BF, ST ) Force Plate
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48	Results No significant differences in co-contraction Higher peak activity of VM, VL and ST in MB group (p< 0.05) Earlier activation of the muscles in MB group (p< 0.05)
49	Discussion 'Best' RA patients of the original knee prostheses cohort Avoidance of pain during MVC Therefore new normalisation method for EMG signal
50	Isokinetic dynamometer Validation of EMG normalization method for TKA patients using isokinetic dynamometer Concentric isokinetic flexion and extension contractions at three different velocities (30, 60, 90, deg s-1) Compare active stabilization (co-contraction) MB and PS
51	Validation normalisation model
52	Co-contraction
53	Conclusions MB total knees are more demanding for patients and require better pre-operative and post-operative ligaments and muscles Rehabilitation programs should include: strength training elements of muscle-coordination training
54	Soft tissue artefact assessment in gait analysis using fluoroscopy and skin mounted markers Gait & Posture: submitted
55	Introduction External movement registration (gait analysis) Assessment of normal and pathological knee joint function External movement registration systems: Optotrac, Vicon, Flock of Birds etc. Individual skin mounted markers Clustered markers
56	Introduction Sources of error: Anatomical landmark misplacement Soft tissue movement artefacts: relative movement between markers and the underlying bone Cortical pins, CT, MRI: Displacement errors up to 23 mm Rotational errors up to 11 degrees (Lafortune et al., 1992; Hagemeister et al. 1999; Patel et al., 2004)
57	Skin motion artefact assessment using fluoroscopy
58	Method Plate mounted markers (n=5) Strap mounted markers (n=5)
59	Experimental set-up
60	Skin motion artefacts resulting in adduction-abduction movement
61	Skin motion artefacts resulting in internal-external rotation
62	Plate markers showing a paradoxical ‘screw-home mechanism’
63	Discussion skin motion artefacts Large influence of skin motion artefacts Difficult to interpret data Strap mounted markers are to be preferred above plate mounted markers Reliable estimation of 3D skeletal system kinematics using skin-mounted markers cannot be achieved and limits the contribution of human movement analysis to clinical practice and biomechanical research
64	Conclusion Accurate techniques Precise techniques Reproducible analyses Validated techniques What are you measuring?
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