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ASTM F2777 knee bearing (tibial insert) endurance fatigue test and deformation under high flexion

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ASTM F2777 knee bearing (tibial insert) endurance fatigue test and deformation under high flexion


Used to evaluate the durability and deformation performance of knee joint pads under high bending load conditions. It simulates the stress and deformation of the knee joint during daily activities, such as walking, running, and the impact and pressure experienced during sports. During the tests, specific testing equipment and simulated physical movements are used to apply continuous and high-frequency loads to the knee joint, mimicking actual usage scenarios. By assessing the performance variations of knee joint pads under different bending cycles, such as deformation resistance, rebound performance, and durability, it is possible to determine the quality and lifespan of the pads, providing a basis for the design and improvement of knee protection products. This testing method is of great significance for the research and development as well as quality control of knee protection devices and sports goods.


Core Purpose:

  • Evaluate durability of tibial inserts under high flexion conditions (like squatting or kneeling)

  • Simulate posterior edge loading - a critical failure mode in high-flexion knee designs

  • Provide a standardized benchmark for comparing different implant designs

  • Support regulatory submissions by documenting mechanical performance

Scope:

  • Applies specifically to bicompartmental or tricompartmental knee prostheses with UHMWPE bearing components

  • Designed to test fixed-bearing and mobile-bearing knee systems

  • Focuses on worst-case loading scenarios that occur during extreme flexion


For this mechanical test, a maximum bending angle and a rotation of the tibial insert (internal rotation of 20°) around the superior-inferior axis must be selected. 

The yield performance in the worst-case scenario is determined after a dynamic load of 220,000 N for 2,275 cycles.To assess the creep performance, the change in play between the tibial base plate and the insert is measured before and after the high flexion fatigue test. 

Additionally, before and after the fatigue test, the "AP Pull Test" and the "Rotational Play Test" (according to ASTM F1223) are carried out and compared to each other.The values expressed in SI units should be accepted as standard. No other units of measurement are included in this standard.

ASTM F2777 knee bearing (tibial insert) endurance fatigue test and deformation under high flexion

UnitedTest UTDS series electromagnetic equipment provides precise sine wave load control, offering comprehensive testing tooling to meet the experimental condition requirements in the standards, as well as accurate and effective experimental plans (SOP), helping in the mechanical performance analysis of tibial braces.


Related Standards

  • ASTM F2083: Specification for knee replacement prostheses, references F2777 for mobile bearing evaluation

  • ASTM F2003: Practice for artificial aging of UHMWPE materials

  • ASTM F1223: Test methods for knee joint simulation, referenced for laxity measurements

  • ASTM F2722/F2723: Additional tests for mobile bearing stability and dislodgement resistance


Test Method and Fixtures

1 Test Setup and Conditions

Sample Preparation:
  • UHMWPE components must undergo artificial aging according to ASTM F2003 unless manufacturer can demonstrate aging has no detrimental effect

  • Metallic components follow complete manufacturing processes (machining, surface treatment) up to sterilization

  • Minimum of 5 specimens required for statistical significance

2 Loading

Cyclic Loading Parameters:
  • Peak Load: 2,275 N (approximately 232 kgf) - representative of high flexion activities

  • Load Ratio (R): 0.1 (minimum force = 227.5 N)

  • Frequency: 0.5 to 2.0 Hz (cycles per second)

  • Test Duration: 220,000 cycles or until failure (whichever occurs first)

  • Load applied through femoral component centerline to ensure even distribution

  • For mobile bearings, tibial tray rotated 20° internally relative to femoral component to simulate worst-case posterior contact

  • Fixed-bearing designs: After 20° internal rotation, only one femoral condyle contacts at maximum posterior point

3 Test Sequence

  1. Conditioning:
    • 37°C water bath immersion until thermal equilibrium

  2. Test Execution:
    • Apply cyclic load with femoral component flexed to manufacturer's maximum recommended angle

    • Maintain precise alignment throughout 220,000 cycles

  3. Post-Test Evaluation:
    • Repeat initial measurements to quantify deformation

    • Inspect for cracks, fractures, or dissociation from tibial tray

    • Measure creep recovery after 90+ minutes at room temperature

Success/Failure Criteria

The test passes if:
  • No catastrophic failure (fracture or complete dissociation) occurs before 220,000 cycles

  • Deformation measurements remain within manufacturer's specifications

  • No evidence of progressive damage that would compromise clinical performance


Essential Fixture Components


Fixture ElementFunctionDesign Requirements
Tibial Tray HolderFixes tibial baseplate at specified posterior slope angleCorrosion-resistant material, adjustable to manufacturer's recommended slope
Femoral Component MountPositions femoral component at maximum flexion angleAllows precise angle adjustment and maintains alignment during loading
Force Application SystemDelivers cyclic 2,275 N load through femoral centerlineRigid connection to testing machine, self-aligning to prevent bending moments
Water ChamberContains 37°C deionized water for test environmentSealed enclosure to maintain temperature and full immersion
Measurement SystemTracks vertical distraction and bearing tiltNon-contact methods preferred (e.g., laser sensors) to avoid interference




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