ASTM F2451-05

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Designation:F2451–05
Standard Guide for
in vivo Assessment of Implantable Devices Intended to
Repair or Regenerate Articular Cartilage
This standard is issued under the fixed designation F2451; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope F895 Test Method for Agar Diffusion Cell Culture Screen-
ing for Cytotoxicity
1.1 This guide covers general guidelines for the in vivo
F981 Practice forAssessment of Compatibility of Biomate-
assessment of implantable devices intended to repair or regen-
rials for Surgical Implants with Respect to Effect of
erate articular cartilage. Devices included in this guide may be
Materials on Muscle and Bone
composed of natural or synthetic biomaterials (biocompatible
F1983 Practice for Assessment of Compatibility of
and biodegradable) or composites thereof and may contain
Absorbable/Resorbable Biomaterials for Implant Applica-
cells or biologically active agents such as growth factors,
tions
synthetic peptides, plasmids, or cDNA.
F2150 Guide for Characterization and Testing of Biomate-
1.2 Guidelinesincludeadescriptionandrationaleofvarious
rial Scaffolds Used inTissue-Engineered Medical Products
animal models utilizing a range of species such as rabbit
2.2 Other Documents:
(lupine), dog (canine), pig (porcine), goat (caprine), sheep
ISO-10993 Biological Evaluation of Medical Devices—
(ovine), and horse (equine). Outcome measures based on
Part 5: Tests for in vitro Cytotoxicity
histologic, biochemical, and mechanical analyses are briefly
21 CFR Part 58 Good Laboratory Practice for Nonclinical
described and referenced. The user should refer to specific test
Laboratory Studies
methods for additional detail.
1.3 This guide is not intended to include the testing of raw
3. Terminology
materials, preparation of biomaterials, sterilization, or packag-
3.1 Definitions:
ing of product.ASTM standards for these steps are available in
3.1.1 cartilage regeneration—the formation of articular-
Reference Documents.
like cartilage that has histologic, biochemical, and mechanical
1.4 The values stated in SI units are to be regarded as the
properties similar to that of native articular cartilage (1, 2).
standard.
3.1.2 cartilage repair—the process of healing injured carti-
1.5 This standard does not purport to address all of the
lage or its replacement through cell proliferation and synthesis
safety concerns, if any, associated with its use. It is the
of new extracellular matrix (1, 2).
responsibility of the user of this standard to establish appro-
3.1.3 compact bone—classification of ossified boney con-
priate safety and health practices and determine the applica-
nective tissue characterized by the presence of osteons con-
bility of regulatory requirements prior to use.
taining lamellar bone.
2. Referenced Documents 3.1.4 femoral condyles—the anatomic site corresponding to
the distal end of the femur characterized by medial and lateral
2.1 ASTM Standards:
convex surfaces that are lined by cartilage and articulate with
F561 Practice for Retrieval and Analysis of Medical De-
the proximal tibia and medial and lateral menisci.
vices, and Associated Tissues and Fluids
3.1.5 fibrocartilage—disorganized cartilagenous tissue hav-
F565 Practice for Care and Handling of Orthopedic Im-
ing an abnormally high content of type I collagen.
plants and Instruments
3.1.6 growth plate—the anatomic location within the epi-
physeal region of long bones corresponding to the site of
This guide is under the jurisdiction of ASTM Committee F04 on Medical and
Surgical Materials and Devices and is the direct responsibility of Subcommittee
F04.44 on Assessment for TEMPs.
Current edition approved April 1, 2005. Published May 2005. DOI: 10.1520/ Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
F2451-05. 4th Floor, New York, NY 10036.
2 4
For referenced ASTM standards, visit the ASTM website, www.astm.org, or AvailablefromU.S.GovernmentPrintingOfficeSuperintendentofDocuments,
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM 732 N. Capitol St., NW, Mail Stop: SDE, Washington, DC 20401.
Standards volume information, refer to the standard’s Document Summary page on The boldface numbers in parentheses refer to the list of references at the end of
the ASTM website. this standard.
Copyright ©ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA19428-2959, United States.
F2451–05
growth of bone through endochondral bone formation. The testsonmaterialsordevices,orboth,priortoassessmentofthe
growth plate in skeletally mature animals is fused. in vivo models described herein.
3.1.7 hyaline articular cartilage—cartilagenous connective 4.4 It is recommended that safety testing be in accordance
tissue located in diarthrodial joints and characterized by its with the provisions of the FDA Good Laboratory Practices
localization to articulating surfaces. Regulations 21 CFR 58.
3.1.8 marrow—also called myeloid tissue; soft, gelatinous 4.5 Safety and Effectiveness studies to support IDE (Inves-
tissue that fills the cavities of the bones. It is either red or tigational Device Exemption), PMA (Premarket Approval), or
yellow, depending upon the preponderance of vascular (red) or 510K submissions should conform to appropriate FDA guide-
fatty (yellow) tissue. lines for development of medical devices.
3.1.9 matrix—a term applied to either the exogenous im- 4.6 Animal model outcomes are not necessarily predictive
planted scaffold or the endogenous extracelluar substance of human results and should, therefore, be interpreted cau-
(otherwise known as extracellular matrix) derived from the tiously with respect to potential applicability to human condi-
host. tions.
3.1.10 patella—the bone of the knee joint which articulates
5. Animal Models
within the trochlear groove of the femur.
3.1.11 residence time—the time at which an implanted
NOTE 1—This section provides a description of the options to consider
in determining the appropriate animal model and cartilage defect size and
material (synthetic or natural) can no longer be detected in the
location.
host tissue.
3.1.12 skeletal maturity—the age at which the epiphyseal 5.1 Joint Size and Load:
plates are fused. 5.1.1 A high proportion of hyaline cartilage injuries in
3.1.13 subchondral plate—the margin of compact bone in humans occur in the knee joint predominantly in the medial
direct apposition to the articular cartilage. compartment (that is, medial femoral condyle and tibial pla-
teau). Accordingly, the knee joint is commonly used for
3.1.14 synovial fluid—the fluid secreted by synovium pro-
viding lubrication and nutrition to the joint surfaces. assessing cartilage repair/regeneration in animal models.
5.1.2 The knee is a complex diarthrodial joint involving
3.1.15 synovium—the epithelial lining of synovial joint
cavities that produce synovial fluid. primarily two separate articulations; femoropatellar and femo-
rotibial.The articular surfaces of the distal femur and proximal
3.1.16 tidemark—the anatomic site in articular cartilage
corresponding to the margin between cartilage and the under- tibia are incongruent and contain wedge shaped fibrocartilag-
enous menisci separating the articular surfaces. Contact be-
lying calcified cartilage.
3.1.17 trabecular bone—classification of ossified boney tween the cartilage of the femoral condyles and that of the
tibial plateau occurs at the innermost central region of each
connective tissue characterized by spicules surrounded by
marrow space. medial and lateral meniscus. Mechanical load is distributed
directlyfromthefemurtothetibiaaswellasindirectlythrough
3.1.18 trochlear groove—the anatomic site on the distal end
of the femur corresponding to the region of articulation with the menisci. The patella articulates with the femoral condyle
the patella. within the trochlear groove.
5.1.3 Significant variability exists between animal species
4. Significance and Use
withrespecttotheweightoftheanimal,jointanatomy,andgait
4.1 This guide is aimed at providing a range of in vivo thereby influencing joint kinetics, range of motion, and me-
models to aid in preclinical research and development of tissue chanical forces on joint surfaces. These factors influence the
engineered medical products intended for the clinical repair or
thicknessanddistributionofarticularcartilagewithinthejoints
regeneration of articular cartilage. as well as macromolecular content, distribution, and collagen
4.2 This guide includes a description of the animal models,
architecture. These factors play a significant role in the
surgical considerations, and tissue processing as well as the responsetoinjuryordiseaseofarticularcartilage(seeTable1).
qualitative and quantitative analysis of tissue specimens. The user should consider carefully the animal model that is
4.3 The user is encouraged to utilize appropriateASTM and appropriate for the stage of investigation of an implanted
other guidelines to conduct cytotoxicity and biocompatibility device (3).
TABLE 1 Animal Models for the Assessment of Cartilage Repair
Critical
Cartilage Thickness
Breed Age of Weight at Defect Sites Size Defect
Species at Femoral
Commonly Used Adult Eqivalancy Adult Equivalancy Commonly Used (Diameter
Condyle (mm)
in mm)
A
Rabbit (Lupus or Lupine) New Zealand White 9 months 3–4 kg FC, TG, TP, P 0.25–0.75 3
B
Dog (Canine) Mongrel, Beagle >1–2 years 15–30 kg FC, TG, P 1.3 —
B
Pig (Porcine) Minipig 10 months– 20–40 kg FC, TG — —
1 year
B
Goat (Caprine) Spanish, Dairy, Boer Cross 2–3 years 40–70 kg FC, TG, TP, P 1.5–2 —
B
Sheep (Ovine) Suffolk or Texel 2–3 years 35–80 kg FC, TG 1.7 7
B
Horse (Equine) Mixed, Thoroughbred, Quarter Horse 2–4 years 400–500 kg FC, TG, RC 2–3 9
A
small animal.
B
large animal; FC, femoral condyle; TG, trochlear groove; TP, tibial plateau; P, Patella; RC, radial carpal.
F2451–05
5.1.4 Mechanical load has been shown to affect cartilage particular species should be chosen to exceed the age of
repair.Amongstthemechanobiologicalfactors,theintermittent skeletal maturity. The cohorts should have fused epiphyseal
hydrostatic pressure and shear stresses play an important role growth plates. Skeletal maturity varies between species and
in modulating cartilage development, and maintenance as well can be generally determined radiographically if necessary.
as cartilage degeneration (4, 5).The impact of mechanical load
5.4.2 Older animals have a higher propensity for osteopenia
extent or duration on the implanted device, surrounding native
and degenerative joint diseases such as osteoarthritis, and have
articular cartilage, and underlying bone varies depending on
a decreased capacity to repair articular cartilage defects. If
the anatomic site and the position of the joint (6). The defect
specific conditions are considered important for the intended
site chosen to evaluate implants should, therefore, factor the
device assessment, then an appropriate model should be used.
impact of mechanical load on the performance of the implant.
5.4.3 The mesenchymal stem cell pool, growth factor re-
5.1.5 It is suggested that the gait and stance of a particular
sponsiveness, and metabolic activity of cells generally de-
species be considered when factoring the extent of exposure of
creases with age (7). Thus, reparative processes that are
the implant site to stress during standing and motion.
dependent on the number and activity of native cells may be
5.1.6 The extent of compressive and shear forces in the
partially compromised in older animals.
femoral condyles, trochlear groove, and tibial plateau differ
5.5 Study Duration:
significantlyasdodifferinganatomicsitesofthesamearticular
5.5.1 The length of the study depends on the stage of device
surface.
development, the species used, the size of the defect, and
5.1.7 It is recommended that an appropriate species and
composition and design of implant.
anatomic site be chosen having articular surfaces and thickness
5.5.2 In small animals, small defects implanted for 6 to 8
sufficiently large to adequately investigate and optimize the
weeksprovideinformationregardingresidencetimeofimplant
formulation, design, dimensions, and associated instrumenta-
and fixation device as well as the type of repair.
tion envisaged for human use.
5.5.3 Using larger animals, study periods of 8 to 12 weeks
5.1.8 Larger animals are more appropriate for studying
are limited to providing information regarding the biocompat-
repairinjointsthathavegreaterarticularcartilagesurfaceareas
ibility, early cellular responsiveness, and the persistence and
andathicknessthatmorecloselyapproximatesthatofhumans.
condition of the implant within the defect.
5.1.9 Larger defect dimensions generally require a method
5.5.4 Periods of 6 to 12 months are generally necessary to
of fixation to secure the implant and thereby reduce implant
gain confidence in the extent of success in the repair or
dislocation. The method of implant immobilization can nega-
regeneration of articular cartilage based on histologic and
tivelyimpactboththesurroundinghosttissueandrepairtissue.
biochemical outcome measures, including the interface with
Accordingly, the difference in the design of the test device in
adjacent cartilage and subchondral bone, as well as the
smallanimalswhichgenerallydonotrequirefixationshouldbe
opposing articular surface.
factored into the interpretation of results with respect to
5.6 Rabbit Model—The femoral condyle and trochlear
predictability of outcomes in larger animal models and humans
groove are most frequently used as sites for evaluation of
requiring fixation.
implants in rabbits (8-14). The use of the patella has been
5.1.10 For each species, a critical size defect is defined as
investigated as well (15, 16).
the minimum defect dimension (in diameter) that the animal is
5.6.1 The use of rabbits is generally more economical
incapable of repairing without intervention. The diameter of
compared to larger species.
critical defects generally differ for each species and should be
5.6.2 Due to the small surface area and thickness of carti-
considered carefully when designing the implant dimensions
lage in rabbits, the dimensions of the defect are limited.
and method of fixation.
5.6.3 Evaluation of methods of device fixation in the defect
5.2 Handling:
is less feasible in the rabbit model. Accordingly, the rabbit
5.2.1 Exposure of implants to extreme and highly variable
model is best suited for assessing biocompatibility, materia
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