Lessons from Retrieval Analysis of Joint Replacements Tim Wright, PhD 3 rd ISOC Meeting - Bologna

Failure Analysis Explain the unexpected

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: 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 at HSS

Wear Rate (mm 3 /mc) Radiation Dose (Mrad) Courtesy of Harry McKellop, PhD Retrieval Analysis as Postmarket Surveillance Crosslinking of Polyethylene

Fatigue Wear and Fracture Cyclic crack driving force Rate of crack growth Bradford et al, CORR 2004

Reliance on Preclinical Tests Joint simulators Standardized tests Clinical Relevance?

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 Clinical Relevance?

Preclinical Testing Design Clinical Use Retrieval Analysis 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

Original versus New Design Design Maximum Stress (MPa) Original design 37 New design 24 35% 

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