Guidance Document For Testing Orthopedic Implants With Modified Metallic Surfaces Apposing Bone or Bone Cement

Guidance Document For Testing Orthopedic Implants With Modified Metallic Surfaces Apposing Bone or Bone Cement
April 28, 1994
This guidance was written prior to the February 27, 1997 implementation of FDA's Good Guidance Practices, GGP's. 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 GGP's
Orthopedic Devices Branch
Division of General and Restorative Devices
Office of Device Evaluation
Center for Devices and Radiological Health
U.S. Food and Drug Administration
I. PREFACE
For a number of years there has been increasing interest in surface treating orthopedic devices in an attempt to improve implant fixation. The purpose of this document is to recommend to manufacturers of orthopedic devices and sponsors of future premarket notifications (510k), Investigational Device Exemptions (IDE) applicatons, Premarket Approval (PMA) applications, reclassification petitions, and master files, important information that should be provided to the Food and Drug Administration (FDA) in order to evaluate the substantial equivalence and/or safety and effectiveness of modified orthopedic implant surfaces that are in contact with tissue or bone cement (e.g., porous coatings).
Based on currently available data, the Orthopedic Devices Branch (ORDB) proposes to now greatly limit the scope of this document for the following three types of coatings:
beaded, sintered cobalt-chrome coatings on a cobalt-chrome substrate;
beaded, vacuum-sintered titanium coatings on a titanium substrate; and
vacuum-sintered titanium fiber mesh pads on a titanium substrate.

Numerous test reports describing the physical characteristics and mechanical performance of the above three coating types have been submitted to and reviewed by ORDB. These reports indicate that the integrity of these coatings can be determined with a limited description of the mechanical properties when the materials of the coating and substrate are known, and, in the case of titanium implants, when the manufacturing method is known.
For porous coated hips (the only cementless, porous coated, Class II devices), the properties of the porous coating itself (e.g., average pore size) must be determined because they are indicators of the ability of the coating to allow biologic fixation.
ORDB proposes that items 1-3 below now adequately characterize these types of porous coatings:
the materials used and any standards to which they conform;
the static shear strength of the coating to the substrate (ASTM F1044); and
the average bead size; average pore size; overall pore volume; number of bead layers; and thickness of the coating.
The remainder of this document pertains to modified surfaces different from the above three types of porous coatings. Note: this document does not address interfaces between prosthetic parts, articulating surfaces, calcium phosphate coatings or biodegradable materials, which are described in separate documents.
Complete report can be viewed online.