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