HOL has three AMTI 12-station hip simulators and two AMTI 6-station displacement controlled knee simulators. We offer device wear testing services with acetabular liners, tibial inserts, patellae components and certain spine and shoulder implants. We also have access to AMTI’s latest testing technology e.g. force controlled knee simulators and six DOF VIVO joint simulators.

  • Implant pre-conditioning (e.g., accelerated aging per ASTM F2003, pre-soaking in serum per ISO 14242 and 14243)
  • Wear and fatigue testing of the components
  • Wear particle isolation and size/shape analysis per ASTM F561

Case Studies

Patellae wear testing

In the absence of any standard patellae wear testing protocols, we modified one of our knee simulators to investigate the wear behavior of a specific patellae design using both conventional and highly-crosslinked UHMWPE. We demonstrated the important role of patellar component oxidative stability in preventing failure during high-stress activities, such as stair climbing.

Wear testing of kinematically advanced TKR

We evaluated the long-term wear performance of a kinematically advanced TKR design. However, standard ISO/ASTM displacement profiles were not appropriate for this particular device. We conducted dynamic computer simulations to predict the kinematic waveforms, which we used to conduct extended wear testing of the device on the knee simulator.

Aggressive hip wear testing

We designed an aggressive Mode 3 hip wear testing to address a question posed by the FDA for the clearance of a highly crosslinked, vitamin-E stabilized UHMWPE acetabular liner. We developed a method to reproducibly roughen femoral heads and completed a 5 million cycle aggressive testing. The testing results contributed toward achieving FDA clearance for the product.

Assessment of hip wear after in vivo damage

Component damage can occur during implantation. Damage can come from either surgical instruments or third-body particles. Some novel femoral head designs use a relatively thin surface coating that can get damaged during the implantation process. We investigated the change in wear response of acetabular liners between fresh, undamaged femoral heads and surgically retrieved damaged femoral heads. The results suggested that the head damage described previously would not lead to catastrophic runaway wear of highly-crosslinked UHMWPE.

Spine wear testing

We helped assess a new lumbar intervertebral spacer's wear behavior. We leveraged our expertise in joint simulators and knowledge of the unique kinematics of the spine to design test fixtures that allowed use of our existing simulator as a lumbar spine simulator in accordance with ISO 18192.

  • HOL has seven MTS servo-hydraulic load frames and one MTS electromechanical load frame with load capacities ranging from 100N to 100kN. These are used for mechanical, fatigue, and custom device testing, including:
    • Locking mechanism integrity, static strength and dynamic fatigue testing
    • Post fatigue test (PS Knee)
    • Femoral head burst strength and fatigue testing per ASTM 2345
    • Modular component assembly strength:
      • Pull-out, push-out, torque out and lever-out testing of modular implant assemblies such as femoral head-stem assemblies; acetabular liner-shell assemblies, tibial insert-tibial base plate assemblies, dual mobility head-liner assemblies etc.
    • Rim impingement fatigue strength: repeatedly impinging the femoral neck on to the rim of the component under clinically relevant conditions to determine the resistance to crack initiation and propagation or failure.
    • Frictional torque: determining if different designs, materials, and component sizes affect the frictional behavior of a hip bearing couple. Differences in torque may affect the wear of the material as well as trunnion corrosion in the head/neck femoral junction.