Orthopedic Implant Testing Guide

Common Orthopedic Implants that Require Mechanical Testing

Bone Screws

Bone screws are used in surgical procedures to secure implants such as plates or rods, stabilize fractures, or facilitate bone fusion. They must be engineered with precise mechanical characteristics to enable secure fixation. Bone screws used in orthopedic applications undergo mechanical testing to assess their load-bearing capacity, pull-out strength, torque resistance, and fatigue behavior.

Dental Implants

A dental implant is a metal post, usually made of titanium, that replaces the root portion of a missing tooth. It serves as an anchor for artificial teeth and requires stringent mechanical testing to ensure stability and functionality. Dental implants are subjected to mechanical testing to evaluate their structural strength by calculating their load-bearing and bending capacity, and fatigue resistance.

Hip Implants

Hip implants are prosthetic devices used to replace a damaged or deteriorated hip joint. These orthopedic devices must be meticulously designed to mimic the natural movement of the hip and withstand long-term wear. Mechanical testing of hip implants is crucial to determine their load-bearing capacity, wear resistance and overall performance.

Knee Prosthesis

Knee prostheses are artificial substitutes for the knee joint used in knee replacement surgeries. These devices are designed to replicate the complex movements of the knee and provide durable functionality. Knee prostheses undergo mechanical testing to evaluate their durability, load-bearing capability, and fatigue resistance, showing the capability of the device to withstand the expected loads over a specified time.

Shoulder Implants

Shoulder implants are orthopedic prosthetic devices that are intended for use as a replacement to damaged shoulder joints. Shoulder implants must be designed to restore the full range of motion and bear the mechanical load associated with arm movement. Shoulder implants undergo mechanical testing to assess their load-bearing capacity, wear resistance, and overall stability.

Spinal Implants

Utilized in spinal surgeries to correct deformities or stabilize the spine, spinal implants may include rods, screws, plates, and cages. They must be designed to align with the complex biomechanics of the spine. Mechanical testing of spinal implants involves evaluating their fatigue resistance, stability, and load-bearing capacity.

Common Orthopedic Implant Test Types & Standards:

Axial-Torsion Testing

Axial torsion testing assesses the performance of orthopedic implants under combined axial (linear) and torsional (rotational) loads. Essential for devices like bone screws or hip implants, this testing ensures that they can withstand both twisting and compressive forces in the body. It plays a crucial role in determining the device’s functionality, reliability, and safety.

• • ASTM F543 Standard Specification and Test Methods for Metallic Medical Bone Screws
    • Four test methods to measure the vertical torsion (A1), the insertion/removal torque (A2), the pullout strength (A3), and the axial compression load force (A4) of self-tapping bone screws
  • ISO 6495 Implants for surgery — Metal bone screws with asymmetrical thread and spherical under-surface — Mechanical requirements and test methods
    • Torsion test methods to measure the breaking torque and rotation at failure of metal bone screw

Bend Testing

Orthopedic implants such as bone screws and dental implants require bend testing to evaluate their structural strength. Bend tests can be performed as static tests or dynamic (fatigue) tests. Bend test results include important mechanical properties such as bending (flexural) strength, flexural strain, bending moment, and bending stiffness.

• • ASTM F382 Metallic Bone Plates
    • Four-point bending fatigue test method to characterize and compare the fatigue performance of different bone plate designs
  • ISO 9585 Implants for surgery — Determination of bending strength and stiffness of bone plates
    • Bend test method for determining the bending strength and stiffness of bone plates
  • ISO 14801 Dynamic loading test for endosseous dental implants
    • Fatigue testing method to measure the maximum load and maximum bending moment of dental implants

Fatigue Testing

Fatigue testing simulates the repetitive loads or motions that medical devices experience in the body to evaluate their longevity and reliability. This is vital for devices like orthopedic implants and vascular stents that endure millions of cycles throughout their lifespans. The process involves applying controlled loads, stresses, or strains, mimicking physiological conditions.

Compliance with rigorous standards like ASTM and ISO ensures uniformity in evaluating durability and safety. Fatigue testing results include fatigue resistance, fatigue limit, fracture toughness and more. Analysis of fatigue testing results provides insights into lifespan, potential failure modes, and design improvements.

• • ASTM F382 Metallic Bone Plates
    • Four-point bending fatigue test to characterize and compare the fatigue performance of different bone plate designs
  • ASTM F1717 Spinal Implant Test Methods
    • Three static and one fatigue (compression bending) test methods on spinal implant specimens
  • ASTM F1800 Standard Practice for Cyclic Fatigue Testing of Metal Tibial Tray Components of Total Knee Joint Replacements
    • Fatigue test method to quantify the fatigue strength and lifetime of knee prostheses
  • ASTM F2028 Standard Test Methods for Dynamic Evaluation of Glenoid Loosening or Disassociation
    • Fatigue test methods to measure how much a prosthetic reverse glenoid component rocks or pivots following cyclic articulation with a mating humeral liner
  • ASTM F2077 Standard Test Methods for Intervertebral Body Fusion Devices
    • Static and dynamic in vitro test methods of different designs of intervertebral body fusion device assemblies
  • ISO 7206 – Determination of endurance properties and performance of stemmed femoral components
    • Fatigue test methods to measure the loads hip implant specimens can withstand over a number of cycles
  • ISO 14801 – Dynamic loading test for endosseous dental implants
    • Fatigue testing method to measure the maximum load and maximum bending moment of dental implants
  • ISO 14879-1 Implants for surgery — Total knee-joint prostheses — Part 1: Determination of endurance properties of knee tibial trays
    • Fatigue test method reporting the number of cycles applied and mode of failure to examine the defects caused by the loading on knee prostheses

In Vitro Testing

In vitro testing involves evaluating medical devices outside the human body, often in a controlled laboratory environment that simulates physiological conditions. This testing is crucial for understanding how devices like orthopedic implants, stents, or catheters will interact with biological tissues and fluids. It allows for thorough assessments of biocompatibility, functionality, and long-term performance.

• • ASTM F2077 Standard Test Methods for Intervertebral Body Fusion Devices
    • Static and dynamic in vitro test methods of different designs of intervertebral body fusion device assemblies

Shear Testing

Shear properties can be calculated via different test types including tension, flexion, and compression as well as different test set ups such as the V-notched rail method, short beam method, and more. The most common measurement obtained from a shear test is the shear strength, shear modulus, shear strain, and shear yield stress.

• • ASTM F1829 Static Evaluation of the Glenoid Locking Mechanism in Shear
    • Shear test method for evaluating the performance of metal or composite-backed anatomic glenoid prostheses’ locking mechanism
  • ASTM F2077 Standard Test Methods for Intervertebral Body Fusion Devices
    
    • Static and dynamic in vitro test methods of different designs of intervertebral body fusion device assemblies

Tensile Testing

Materials used in the making of orthopedic implants require tension testing to provide information on their strength, ductility and superelasticity. These attributes are vital for understanding how a material or device will perform under stretching or pulling forces in the body.

• • ASTM F2516 – Standard Test Method for Tension Testing of Nickel-Titanium Superelastic Materials
    • Tensile test method of superelastic nickel-titanium (nitinol) materials to determine the upper plateau strength, lower plateau strength, residual elongation, tensile strength, and elongation.