The standard “ASTM F1781-21 Standard specification for elastomeric flexible hinge finger total joint implants” developed by the American Society for Testing and Materials (ASTM) describes the requirements for elastomeric flexible hinge finger total joint implants with and without metal grommets for reconstruction of the metacarpophalangeal (MCP) and proximal interphalangeal (PIP) joints. This standard excludes implants that do not have an elastomeric connection across the joint. This standard is limited to implants made from a single material in a single molding procedure in a single step.
The prostheses described in this standard are designed for use in the proximal interphalangeal (PIP) and metacarpophalangeal (MCP) joints.
In terms of classification, a limited joint prosthesis is used for joint replacement and prevents displacement of the prosthesis in more than one anatomic plane and consists of a single, flexible, inter-joint component or multiple components connected or approximated together (21 CFR 888.6 standard).
Proper material selection is necessary, but not sufficient, to ensure proper operation of a device. All devices meeting this specification must be manufactured from materials with adequate mechanical strength, durability, and biocompatibility. All elastomeric components must comply with ASTM F2038-18 and ASTM F2042-18.
Test and evaluation parameters that can be considered for elastomeric implant materials are included in ASTM D813-07, ASTM D1052-09, ASTM D2240-15, ASTM D412-16, and ASTM D624-00 standards. Manufacturers must comply with this standard before implants are manufactured from other elastomeric materials.
For biocompatibility, devices made of materials with limited or no history of successful use for orthopedic implant applications should be determined to demonstrate acceptable biological response when tested in accordance with ASTM F748-16 or ASTM F981-04 or ISO 10993-1. Although no known surgical implant material has been shown to be completely free of adverse reactions in the human body, long-term clinical experience has shown that an acceptable level of biological response can be expected if materials that meet the specifications and guidelines are used. However, these specifications and guidelines apply to finished medical devices, not to raw materials where the design and manufacturing process of the device may affect the biological response. Therefore, for a device made of materials that meet these specifications and guidelines, biocompatibility should be verified in accordance with ASTM F748-16 or ASTM F981-04 or ISO 10993-1 unless it can be justified that the design and processing will not affect the biocompatibility of the final sterilized device.
Titanium used as a construction material for metal grommets shall comply with ASTM F67-13. Metal grommets shall conform to the shape of the implant and shall not interfere with the function of the flexible hinge implant. Fluorescent penetrant testing shall be performed in accordance with ASTM F601-18 when appropriate for metal grommets. Design and fabrication shall follow 21 CFR 820.
For in vitro laboratory testing, ASTM standards have not been developed for testing finger implants. Laboratory testing simulating the conditions of use using a joint function simulator is desirable to compare materials and designs and to provide an indication of clinical performance. Implant testing should be performed in accordance with the intended function of the implant.
Implants intended to completely or partially immobilize a joint must be subjected to the loads and kinematics expected to be experienced during activities of daily living.
In terms of fatigue testing, clinical failure modes such as fracture at the hinge and fracture at the junction of the distal body and hinge have been reported. The fatigue properties of the implant should be evaluated. Testing is conducted under high-cycle fatigue conditions for a minimum of 4 million cycles and under low-cycle fatigue conditions for a minimum of 1330 cycles or until failure to assess the implant's resistance to failure. The failure mode is reported for each specimen tested.
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