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3 rd ISOC Meeting - Bologna. Lessons from Retrieval Analysis of Joint Replacements. Tim Wright, PhD. Failure Analysis. Explain the unexpected. Retrieval Analysis as Failure Analysis. Retrieval Analysis has Other Purposes. Strengths
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3rd ISOC Meeting - Bologna Lessons from Retrieval Analysis of Joint Replacements Tim Wright, PhD
Failure Analysis Explain the unexpected
Retrieval Analysis has Other Purposes 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 at HSS 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 Mo # Day
. Retrieval Analysis as Postmarket Surveillance 55 /mc) 45 . Crosslinking of Polyethylene . 35 . . Wear Rate (mm3 25 15 5 0 5 15 0 10 Radiation Dose (Mrad) Courtesy of Harry McKellop, PhD
Fatigue Wear and Fracture Rate of crack growth Cyclic crack driving force Bradford et al, CORR 2004
Clinical Relevance? Reliance on Preclinical Tests Joint simulators Standardized tests
THA Clinical Results 30% to 96% reduction at 2 – 5 yrs 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 Conventional Poly and Cross-linked Poly 1 Incipient Crack 5 Incipient Cracks, 1 Rim Fx Schroder, et al., 2010 ORS
Clinical Relevance? Reliance on Preclinical Tests Joint simulators Standardized tests
Retrieval Analysis as a Design Tool Preclinical Testing Design Clinical Use Retrieval Analysis
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
Methods 103 Retrieved Optetrak Tibial Components Examine all inserts for evidence of damage to the tibial post on each face
Demographic Data Radiographic Analysis Methods • Age • Weight • Height • BMI • Length of implantation • Reason for revision • Femoral and tibial varus-valgus angle • Femoral component flexion-extension angle • Tibial posterior slope
Rational Design Change • Determine stresses associated with box-post impingement in current design • Examine design alternatives intended to reduce stresses
Finite Element Computer Model UHMWPE (elastic-plastic) Metal (rigid indenter)
Reduction to Practice Rounded box to minimize bone resection
The Importance of Retrieval Analysis Direct assessment of in vivo “real life” performance Early warning of unanticipated problems Justification for rational design changes