This guidance was written prior to the February 27, 1997 implementation of FDAs Good
Guidance Practices, GGPs. It does not create or confer rights for or on any person and does not
operate to bind FDA or the public. An alternative approach may be used if such approach
satisfies the requirements of the applicable statute, regulations, or both. This guidance will be
updated in the next revision to include the standard elements of GGPs.
GUIDANCE DOCUMENT FOR TESTING NON-ARTICULATING,
"MECHANICALLY LOCKED", MODULAR IMPLANT COMPONENTS
DRAFT
PLEASE FORWARD YOUR COMMENTS TO:
Orthopedic Devices Branch
Division of General and Restorative Devices
Center for Devices and Radiological Health
U.S. Food and Drug Administration
9200 Corporate Blvd.
Rockville, MD  20850
301-594-2036   2
PREFACE
Many orthopedic devices are designed with modular or multiple components which are locked together.  The
purpose of this document is to recommend to the device manufacturer or sponsor of a premarket notification (510k),
Investigational Device Exemption (IDE), Premarket Approval (PMA) application, reclassification petition, and master
file; important information that should be provided to the FDA so that the FDA will be able to determine the substantial
equivalence and safety and effectiveness of devices that are made of separate parts, have nonarticulating interfaces
between implant components and are assembled by the manufacturer or surgeon, e.g.:
morse taper in a femoral ball on stem;
threaded nut-bolt interface in a spinal implant;
crimping in a bone anchor;
lock and key between porous metal pads and hip stem; and
interference fit between a bone screw and intramedullary rod.
This information includes important issues and concerns, properties that should be evaluated, summaries of
possible test methods, rationale/purpose of each test, pass/fail criteria or typical results for each test, literature citations,
and a format for organizing data for submission to FDA.
The development of this guidance document is based on an evaluation of the literature and on the experience of
the Orthopedic and Rehabilitation Devices Branch (ORDB) and is primarily intended to be a scientific position paper. 
Therefore, it suggests some important evaluation criteria, test procedures, and end points that FDA feels are necessary to
provide reasonable assurance of substantial equivalence and/or safety and effectiveness of modular orthopedic devices. 
Although this guidance document contains certain administrative requirements, it does not replace the requirements of
the 21 CFR 801 or 807 or the statue.
FDA may require information in addition to what is contained in this document if circumstances require it.  In
other  instances,  the  sponsor  may  be  able  to  sufficiently  justify  the  omission  of  some  tests.    Suggestions  and
recommendations presented in this document are not mandatory requirements, but reflect data and methodologies which
ORDB has determined to be acceptable.  Therefore, the words "should", "must" and "shall" are not used in a regulatory
sense and should not be construed as such.  They express FDA's current feeling as to what constitutes good scientific
decision making. 
The guidance document should be viewed as a living document.  As scientific knowledge changes and
scientific techniques are improved, FDA will revise the document.  Nonetheless, the basic objectives will remain the
same.
MATERIALS AND DESIGN DESCRIPTION
Each part of each component of the implant system should be listed along with the following information:
1  the name of the component and each its parts;
2  a description of the function of each major design feature
3  the names of all other components and tissues that are expected to contact the component
and the type of interface (i.e., articulating, fixed mating part, coating, tissue fixation);   3
4  the material composition of each component to include:
a  the document number of any previous submission to FDA or other reference which
fully characterized the material (e.g., a master file, 510k, literature article);
b  a brief description of the material or the name and number of the voluntary
standards that applies to the material (any difference in the final product and the
requirements in the referenced standard must be itemized and justified);
c  any trade names for the materials; and
d  the names of establishments which process the material.
5  the major processing methods which determine the material microstructure and hence, its
properties; and
6  details about the design (e.g., engineering drawings, model numbers, sizes, photographs)
which should include the ball and liner design tolerances and manufacturing variability for
interfaces. 
STRENGTH, ASSEMBLY AND DISASSEMBLY
Static strength may determine the load to fracture, deformation or the relationship between assembly load and
disassembly load.  A measure of the loads applied to the device to assemble and disassemble components may provide
information about the:
1  ease of assembly by the surgeon,
2  ease of disassembly by the surgeon,
3  ease of inadvertent disassembly in the patient,
4  possibility of high induced stresses in the assembled device, and
5  possible relationship between loosening and assembly loads.
DEVICE RIGIDITY
The long term effects of the device rigidity on bone should be addressed.  Too much rigidity may cause stress
shielding (e.g., larger and stiffer intramedullary rod or hip stem) while too little rigidity may result in poor healing (e.g.,
greater movement at an interface of a modular device compared to the same device made of a solid body). 
STRESS ANALYSIS
High stresses leading to deformation, fracture or increased wear of the components may be due to:
1.  poor tolerances
2.  inadequate instructions for attachment (e.g., excessive use of force);
3.  local stress risers (e.g., corners);
4.  thermal expansion of parts during sterilization; and
5.  thin cross-sections.   4
These parameters may be evaluated in a stress analysis with mechanical testing to justify assumptions made in
the analysis.
FATIGUE PROPERTIES
Cyclic fatigue testing should be considered if the device has the same design as a predicate device except for
differences in features which may affect the fatigue life.  Whether evaluated separately or in a single test, the   wear,
corrosion and fatigue properties of the device assembly should be examined in any test performed, where possible.
CYCLIC WEAR, DEGRADATION AND CORROSION
Cyclic testing should be considered for a device which has the same design as a predicate device except for
differences in features which may affect loosening, cracking, deformation, corrosion, degradation and wear at interfaces.
 To simulate actual clinical mechanisms as much as possible, the following test method and measurement parameters
should be considered:
DEVICE CHARACTERIZATION
The dimensions and tolerances that would be expected to result in the highest stresses (i.e., worst
case) must be tested.
Test samples must be the final product to be shipped for clinical use.
In addition to the information listed in the MATERIALS AND DESIGN DESCRIPTION section of
this documents, the exact composition and microstructure of the substrate and any modified surface
present must be fully characterized quantitatively from a representative sample of the test specimens. 
The tolerances for the analyses must be reported.  Surfaces exposed to wear must also include the
following:
total number of physically and/or chemically distinct surface layers;
thickness of each layer;
drawing or photographs showing the locations of the modified surfaces on the implant and
any variation in the modified surface thickness; and
roughness.
TEST METHODS
At least three identical test specimens and three identical controls must be tested.  The number of
samples depends on the standard deviation and the desired levels of statistical significance and
difference in results between test and control specimens.
Polymer samples should be presoaked until a steady state fluid absorption (determined by weighing)
is approached (about 30 days for UHMWPE).  Samples must be stored and tested in isolation within a
noncorrosive chamber. 
Three polymer controls which are soaked as are the wear specimens but not wear tested, should be
weighed to correct for ongoing fluid sorption by the wear tested components during the wear test. 
The soak controls should be agitated and cyclically loaded (except for tangential wear motions) as are
the wear test specimens. 5
The volume and concentration of surrounding fluids shall be maintained during testing by avoiding
evaporation or by replacing water loss.
Other test parameters should also be included in the methods if the in vitro results will more closely
duplicate the in vivo results. 
Specimens must be cyclically loaded in a joint simulator or other appropriate instrumentation.  The
device orientation and loading profile must simulate worst case fretting motions, cyclic stresses, three
body wear and corrosion/degradation environment which could occur during clinical use.
Interpretation of the results may be simpler using a 37 +- 1 C, aerated saline test solution having a pH
of 7.3 +- 0.5 (carbonate buffered).  This is because saline leaves no deposits and the solution
composition does not change with time.  Ringer's or Hanks solutions may better simulate physiologic
conditions and may be appropriate if corrosion is not an issue, but control of the composition,
measurements of surface deposits and interpretation of the results must be more stringent than if saline
is used.  A 0.2% sodium azide or other suitable antibiotic may also be used.  A 37 C temperature is
preferred, though room temperature may be used if this has no effect on mechanisms (e.g., polymer
deformation or creep).  Solution temperature and pH must be monitored throughout the test. 
Accelerated testing (e.g., change in temperature, pH, P , electric potential) must be validated with a
O2
real time control. 
The surfaces exposed to solution should be the same for all specimens and simulate corrosion as it
might occur clinically.  Corrosion testing of modular devices requires that corrosion is induced at
appropriate interfaces and not at the outer surface.  It is not enough to merely pit the outer surface of
the material because this does not represent the corrosion that occurs as a result of the geometry and
wear occurring at the crevice (Buckley, C.A.; et al. 1992). 
Corrosion test specimens should be electrically insulated from the test apparatus to avoid galvanic
corrosion effects (Higo, Y.; Tomita, Y. 1994, page 152).
MEASUREMENTS
Wear particles, wear markings, material transfer and corrosion (e.g., pitting, etched dendritic surface
structure, discoloration) should be quantified after components are disassembled, and before and after
cleaning if necessary.  Material transfer that may occur while assembling or disassembling parts, prior
to fretting, should be taken into account (Bhambri, S.K.; Gilbertson, L.N. , page 123).
Roughness and appropriate dimensions of each test specimen must be measured before and after
testing to assess the effects of wear and deformation. 
Weight changes of device components should be made if the test samples are small enough compared
to the losses due to wear and corrosion.  Samples shall be cleaned prior to weighing as outlined in
McKellop, H.A.; Lu, B.; Benya, P.: 'Friction, Lubrication and Wear of Cobalt-Chromium, Alumina
and Zirconia Hip Prostheses Compared on a Joint Simulator'. Trans. Orthop. Res. Soc., pp. 401,
1992. The weight loss of each wear component shall be adjusted for the change in weight of the soak
controls.  The room temperature and humidity during weight measurement shall be reported.  The
volume of wear debris shall be calculated by dividing by the density of the material.
Test methods should be validated by comparing in vitro results to in vivo results to determine if in
vitro test methods are realistically simulating what occurs in patients (e.g., three body wear).  This
may be determined by comparing wear particles of in vitro test samples to those of explanted devices
of similar design as well as in vivo and in vitro wear and corrosion rates.   6
After noting their location on all surfaces, wear particles should be washed off implant surfaces into
the test solution.  A sample of the wear particles should be characterized, then all metal particles in
solution dissolved with an acid (e.g., HCl), and the total metal content in the solution, including
particles, measured by AAS (atomic absorption spectroscopy) (Kovacs, P.; et al. 1992).  Care should
be taken to remove all particles from the test specimen surface and to completely dissolve particulate
or oxidized metal (Margevicius, R.W.; et al. 1989).
Complimentary methods of monitoring fretting corrosion may be used in addition to those listed
above.  For example:  fretting corrosion currents measured during cyclic loading or crack formation
and fatigue strength before and after fretting.
BIOCOMPATIBILITY
Materials with limited or no history of successful use in orthopedic implants must be determined to exhibit an
acceptable biological response equal or better than predicate or substantially equivalent devices when tested by the
following methods:
ASTM F 748;
ASTM F 981; and
an  animal  implant  model  in  which  particles  are  introduced  into  the  medullary  canal  (simulating  stem
micromotion).  The study should include histological examination of the:
1.  adjacent tissues, and                             
2.  regional lymph nodes.
CLINICAL DATA
All available clinical data involving the modified surface described above should be summarized in a table. 
This data should include, but is not limited to information regarding loosening between parts of the device and at the
bone-implant interface, frank surface coating failure or other indications of success or failure.
MANUFACTURING
The manufacturing process of the final product and test samples must be described in enough detail to give a
clear understanding of the origin of significant differences between the properties of currently marketed devices.
REPORTING
To help FDA in its review and facilitate a determination of substantial equivalence and/or safety and
effectiveness,  a  very  brief  summary  of  all  information  should  be  organized  in  the  order  shown  in  part  VII.
ORGANIZATION OF REPORTED INFORMATION.  Any additional and important information not specifically
mentioned in the above guidance document should be inserted into this organization where appropriate.  Detailed test
reports from which the summarized data originated should be organized in a similar manner (as much as possible) and
included in the submission to FDA.  The detailed reports should include, but are not limited to, the following:
1.  Report title
2.  Investigators' names
3.  Facility Performing the test
Name
Address
Phone Number   7
4.  Dates
Test initiation
Test completion
Final report completion
5.  Objectives/Hypothesis
6.  Test and control samples
Sample selection criterion
Design
Materials
Processing methods
Differences between test samples, control samples and marketed device
7.  Methods and Materials
Test setup schematic or photograph
Description of grips or potting medium interfacing with samples
Test equipment calibration schedule, methods and data
Discussion of dependent, independent and uncontrolled variables, e.g.:
Test and control sample parameters
Environment composition, pH, volume, flow, temperature, replacement
Electromagnetic fields, applied charge, irradiation
Load directions, points of application and magnitudes
Times (e.g. rates, frequencies, number of cycles)
Other
Rationale for choices of parameters, values, etc.
Methods of specimen examination (e.g., failure analysis)
Statistical justification for the number of samples
Chronological description of the test procedures
Deviations from referenced protocols and standards
8.  Results
Time from manufacturing till testing commences
Discussion of the data and possible mechanisms
List of conclusions
Discussion of the objective/hypothesis
Simplifications and assumptions and their clinical implications
9. Appendices
Experimental data
Calculations
Bibliography of all references pertinent to the report 8
ORGANIZATION OF REPORTED INFORMATION
PROPERTY  CONCERNS OR ISSUES  POSSIBLE TESTING
1.STRENGTH,           1.EASE OF ASSEMBLY LOAD VS DEFLECTION TO FAILURE
ASSEMBLY &          2.EASE OF DISASSEMBLY FOR VARIOUS ASSEMBLY LOADS
DISASSEMBLY 3.DISASSEMBLY IN THE PATIENT
4.HIGH INDUCED STRESSES (# 5)
5.LOOSENING (# 3)
6.FRACTURE & DEFORMATION
2.DEVICE RIGIDITY  HIGH RIGIDITY/BONE PLOT LOAD VS DEFLECTION
RESORPTION OR LOW
RIGIDITY/BONE FRACTURE
3.CYCLIC FATIGUE    FRACTURE, DEFORMATION, WEAR "S-N" CURVE
  PROPERTIES & LOOSENING
4.IMPROPER            EFFECT OF HIGH STRESS ON THE INSTRUCTIONS FOR ATTACHMENT &
CONNECTIONS ENDURANCE OF THE DEVICE COMPONENT MATCHING IN LABEL
5.INDUCED EFFECT OF HIGH STRESS ON THE STRESS ANALYSIS &/OR
STRESSES    AT ENDURANCE OF THE DEVICE MECHANICAL TESTING (# 1-3)
CONNECTIONS
6.LOCAL STRESS        EFFECT OF HIGH STRESS ON THE STRESS ANALYSIS &/OR
RISERS ENDURANCE OF THE DEVICE MECHANICAL TESTING (# 1-3)
7.THERMAL             EFFECT OF HIGH STRESS ON THE STRESS ANALYSIS &/OR
EXPANSION OF        ENDURANCE OF THE DEVICE MECHANICAL TESTING (# 1-3)
PARTS DUE TO       
STERILIZATION
8.INSUFFICIENT        EFFECT OF HIGH STRESS ON THE STRESS ANALYSIS &/OR
MATERIAL TO         ENDURANCE OF THE DEVICE MECHANICAL TESTING (# 1-3)
SUPPORT LOADS
9.WEAR, CORROSION MORE CREVICES & FRETTING CREVICE CORROSION STUDY
    & DEGRADATION
DISSIMILAR METALS IN CONTACT GALVANIC CORROSION STUDY
AMOUNT, SIZES & TYPES OF IONS FRETTING CORROSION (E.G.,
& PARTICULATE MATERIAL ASTM F 897) OR DEGRADATION
RELEASED
10.BIOCOMPAT- BIOCOMPATIBILITY OF:
   ABILITY 1.PARTICLES
2.BREAKDOWN PRODUCTS
3.METAL IONS
4.BULK MATERIAL
11.OTHER  NEW FAILURE MECHANISMS
LOOK FOR & EVALUATE NEW FAILURE
MECHANISMS
CLINICAL STUDY