ISO 16436-1

Purpose of the test
Wear testing supports the evaluation of bearing materials and implant designs used in anatomic total shoulder replacements. ISO 16436-1 provides a reproducible loading and motion profile intended to approximate a shoulder movement from 10° to 90° of elevation while lifting a 2 kg load. Rotation of ±10° about the glenoid component axis is superimposed to create multidirectional articulation. This profile represents one standardized movement pattern and does not reproduce every possible clinical activity.

Test specimens and worst-case selection
A minimum of three wear test specimens and one soak control specimen are required for each type of prosthesis. The humeral and glenoid components should be selected to represent the expected worst case for wear. More than one configuration may be necessary when the conditions associated with adhesive wear differ from those associated with fatigue or delamination.
Test components and the soak control are manufactured and sterilized as intended for clinical use. Component combinations, interlocks and modular interfaces should also represent the clinical configuration wherever practical. Limited adaptations are permitted when an articulating component must be removed repeatedly for wear measurement, but the original interlock features should be reproduced as closely as possible and all adaptations must be justified.

Simulator configuration and alignment
Testing may be performed using a dedicated shoulder wear simulator or an appropriately adapted knee-joint simulator meeting the relevant requirements of ISO 14243-1. The test system applies time-varying axial and shear forces together with controlled rotations about two simulator axes.
In the reference position, the implant is set at zero rotation and 10° of elevation. The axial force acts normal to the glenoid plane, while the shear force axis is oriented 20° relative to the superior-inferior axis of the glenoid component. Stemmed, stemless, asymmetric and augmented designs require configuration-specific alignment. For non-spherical heads, the selected orientation should create an appropriate worst-case condition and must be justified.

Loading and environmental conditions
The prescribed waveform reaches an axial force of approximately 1.11 kN and includes synchronized shear force and angular movement. The simulator operates at 1.0 Hz ± 0.1 Hz for a total of 5 million load cycles.
The articulating surfaces are completely immersed in bovine serum diluted to a protein concentration of 30 g/l ± 2 g/l. The fluid is maintained at 37 °C ± 2 °C. It is replaced completely at least every 500,000 cycles, with losses caused by evaporation replenished during testing.

Soak control
The soak control is used to account for changes in polymer mass caused by fluid absorption. A passive control is immersed under the same environmental conditions without loading or movement. Alternatively, a loaded control receives the same time-varying axial force as the wear specimens but no shear force or articulating motion. The selected control method is documented in the test report.

Wear measurement and inspections
Polymeric articulating components are cleaned, desiccated and weighed according to ISO 14243-2. Pre-soaking is recommended before the wear test. Initial optical or electro-optical examination provides a baseline for comparison with the surfaces after testing.
The test is stopped for measurement after at least:

• 500,000 cycles
• 1 million cycles
• Every subsequent 1 million cycles until completion at 5 million cycles

At each measurement interval, the applicable components are removed, cleaned and measured before being reinstalled in the same configuration. The articulating surfaces are inspected and photographed throughout the test. Final examination evaluates findings such as fracture, cracking, deformation, delamination and other changes to the bearing surfaces.

Evaluation and reporting
Results include the cumulative mass loss for each specimen, wear as a function of cycle count, and the individual and mean gravimetric wear rates with standard deviation. The report also documents the applied forces and rotations, resulting shear motion and torque, specimen identity and configuration, soak control method, surface condition and the interfaces of modular components.
Any early termination caused by specimen damage or test system failure must be explained. Deviations from the prescribed configuration or method also require justification, particularly when they affect implant alignment or the transformation of anatomical movement into simulator motion.