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Lessons from
Retrieval Analysis of
Joint ReplacementsTim Wright, PhD
3rd ISOC Meeting - Bologna
Failure Analysis
Explain theunexpected
Retrieval Analysis as Failure Analysis
Strengths Direct assessment of in vivo “real life” performance Early warning of unanticipated problems Justification for rational design changes
Limitations “Failed” devices Clinical data sometimes unknown
Retrieval Analysis has Other Purposes
Implants: OR Pathology Biomechanics
Cleaned and cataloged: 77120601
Boxed and labeled (without patient identifiers)
Entered into password-protected searchable web-based database (IRB Approved/HIPAA Compliant)
Connected to TJR registries (CERT and CORRe)
Yr MoDay #
Retrieval Analysis at HSS
5
15
25
35
45
55
0 10
0
Wea
r Rat
e (m
m3
/mc)
Radiation Dose (Mrad)5 15
.. . .
.
Courtesy of Harry McKellop, PhD
Retrieval Analysis as Postmarket Surveillance
Crosslinking of Polyethylene
Fatigue Wear and Fracture
Cyclic crack driving force
Rate
of c
rack
gro
wth
Bradford et al, CORR 2004
Reliance on Preclinical Tests
Joint simulators
Standardized tests
ClinicalRelevance?
30% to 96% reduction at 2 – 5 yrs
THA Clinical Results
N = 37 in each group
Patient-matched: age, wt, sex
Dorr et al, JBJS 2005
Retrieval Analysis
• Examine cross-linked polyethylene acetabular liners for wear damage
• Compare wear damage to that in a conventional polyethylene liner with identical design and same manufacturer
Materials
79 conventional liners (Trilogy, Zimmer)78 cross-linked liners (Longevity, Zimmer)
Materials
79 conventional liners (Trilogy, Zimmer)78 cross-linked liners (Longevity, Zimmer)
15X
Fracture
Schroder, et al., 2010 ORS
Conventional Poly and Cross-linked Poly
1 Incipient Crack 5 Incipient Cracks, 1 Rim Fx
Reliance on Preclinical Tests
Joint simulators
Standardized tests
ClinicalRelevance?
PreclinicalTesting
Design
ClinicalUse
RetrievalAnalysis
Retrieval Analysis as a Design Tool
Posterior Stabilized TKA
• Assure femoral posterior translation (in flexion) • Prevent femoral anterior subluxation (at high flexion)• Provide large ROM
Anterior Impingement• Occurs at:
– hyperextension– low flexion angles
• Prevents posterior femoral translation– increases stability– causes wear & deformation
• Unintended articulation– large contact stresses– low contact area
Retrieval analysis of a modern PS design
103 Retrieved Optetrak Tibial Components
Examine all inserts for evidence of damage to the tibial post on each face
Methods
103 Retrieved Optetrak Tibial Components
Demographic Data Radiographic Analysis
– Age– Weight– Height– BMI– Length of implantation– Reason for revision
– Femoral and tibial varus-valgus angle– Femoral component
flexion-extension angle– Tibial posterior slope
Methods
Rational Design Change
• Determine stresses associated with box-post impingement in current design
• Examine design alternatives intended to reduce stresses
Model the Anterior Impingement
Apply a Load in Hyperextension
445 N
Finite Element Computer Model
UHMWPE (elastic-plastic)
Metal (rigid indenter)
Polyethylene Stresses
Polyethylene Deformation
Polyethylene Deformation
Polyethylene Deformation
Original versus New Design
Design Maximum Stress (MPa)
Original design 37
New design 2435%
Reduction to Practice
Rounded box to minimize bone resection
Direct assessment of in vivo “real life” performance
Early warning of unanticipated problems
Justification for rational design changes
The Importance of Retrieval Analysis
Thanks for your attention