ASTM F814-15 Standard Guide for Evaluating Modular Hip and Knee Joint Components

The American Society for Testing and Materials (ASTM) standard, “ASTM F814-15 Standard guide for evaluating modular hip and knee joint components,” describes a procedure to assist the developer of a modular joint replacement implant in selecting the tests and evaluations used to determine device safety. This guide does not attempt to describe all test methods associated with modular device evaluation. Additionally, this guide does not cover intentional intraoperative disassembly; it is designed only to suggest tests necessary to determine accidental disassembly loads.

For the purposes of this standard, the following terms and definitions apply:

• A modular femoral hip implant is any device consisting of two or more matching parts designed for implantation into the femur for the purpose of replacing the femoral hip joint.
• Bolts/screws are a fastener used to secure modular parts of the femoral or tibial component.
• Distal sheaths are modular accessories used to increase the length or distal diameter of the femoral component.
• The collar is the medial platform located just distal to the femoral neck.
• The femoral head is a spherical modular bearing that mates with the femoral component.
• The neck extension is the intermediate modular pair between the femoral component and the femoral head. The connections (e.g., threads and tapers) may vary.
• Proximal sleeves/pads are modular accessories to modify the geometry of the femoral component in the metaphyseal region.
• A modular knee implant is any device consisting of two or more matching parts designed for implantation into the femur or tibia for the purpose of replacing the knee joint.
• The metal-cut patella is a modular patella replacement consisting of an articulating piece secured to a metal support by means of a locking mechanism.
• The metal tibial tray is a metal component that is fixed to the proximal tibia, providing mechanical support to the modular tibial inserts and mating directly with them.
• A stem extension or sleeve is a modular extension to the knee-femoral or knee-tibial component that extends into the medullary canal. A stem extension can be attached to the femoral or tibial component by a variety of means, including a taper, screw, or stud.
• A tibial insert is a modular bearing element of a tibial component, usually constructed in accordance with the ASTM F648 standard, that is secured to a knee tibial tray by means of a locking mechanism.
• A wedge is a modular addition to a total knee replacement that functions to fill the gaps left by missing bone stock.

The tests recommended in this guide cover many different, but all possible areas of research and concern regarding modular hip stems and modular knee components. Due to the limitless possible modular designs, this guide should be used as a guide to what to consider regarding device safety testing. There may be situations where alternative testing methods may be useful.

When testing, during the assembly phase, the static assembly parameters should be evaluated to determine the minimum required loads (axial or torsional) that guarantee adequate assembly strengths. This testing can be performed in conjunction with disassembly to determine how various assembly loads affect disassembly.

The axial joint force is the force required to connect components (for example, to connect a tapered joint). Consideration should be given to: the procedure for applying the joint force (clinical significance) and the environment in which the components are connected (contamination).

Torsion is the torque required to connect components (e.g. bolts or screws). This may only apply to threaded connections. The procedure for applying the torsional force (clinical significance) must be considered.

In the disassembly process, static disassembly parameters should be evaluated to assess the minimum design requirements to prevent unintentional in vivo disassembly:

• Axial: The axial force required to disassemble mating components (for example, the force required to separate a tapered joint).
• Shear: The shearing force required to remove mating components (for example, the force required to cut a wedge from a tray).

Bending is the possibility of static separation under combined loading. It is necessary to consider the load deflection bending.

Torsion is the torque required to separate components (e.g. bolt or screw). This may only apply to threaded connections.

The nature of live loading creates the need for cyclic fatigue evaluation. Tests should be designed to examine pre- and post-cycling characteristics to understand how the design withstands and is affected by cyclic loading.

Fracture is the probability that a modular structure or connections will fail under fatigue loading. The following should be considered: a loading representative of the live loading applied to the component, a PN curve to determine the load levels at which the structure can withstand cyclic loading without failure, and test methods described in ASTM F1800, ISO 7206-4, ISO 7206-6, and ISO 7206-10.

Stripping is the possibility of modular components to disassemble under fatigue loading. It is necessary to consider: loading representative of the loading applied live to the component and measuring the stripping force after fatigue loading and comparing this with static values.

The effects of sterilization on the fatigue integrity of the modular connection. Sterilization may cause material changes that may affect the performance of the modular connection. Sterilization should be carried out according to the manufacturer's specifications. It is necessary to consider the effect of sterilization of plastic components.

In terms of corrosion, the environment in which the modular connection will be used can affect the ability of the connection to resist separation or fracture. Consideration should be given to: corrosion of dissimilar metal connections, corrosion of dissimilar metal connections, fluid environment, elevated temperature, cyclic loading frequency, dwell time (if any) used in the loading profile, and the ATSM F897 standard test method.

From a frictional perspective, micromotion between the two components of a modular joint can cause adverse effects (i.e. wear debris, increased risk of separation). Consideration should be given to: wear of tapered joints, wear of mating, non-jointed surfaces, environmental testing, and ASTM F1875 and ASTM F897 standards.

Our organization has a strong staff that closely follows the developments in the world in the field of science and technology and constantly improves itself. Among the numerous test, measurement, analysis and evaluation studies provided for businesses in various sectors, there are also testing services in accordance with the "ASTM F814-15 Standard Guide for Evaluating Modular Hip and Knee Joint Components" standard.