• Specifications
• ExperimentationJointMechanics

TableOfContents

Target Outcome

• Measurements of six degree of freedom kinetics and kinematics of the tibiofemoral joint under quasi-static loading conditions
• Measurements of six degree of freedom kinetics and kinematics and contact pressures of the patellofemoral joint under quasi-static loading conditions

Prerequisites

Infrastructure

For more details see ["Infrastructure/ExperimentationMechanics"].

Prerequisite Protocols

• ["Specifications/Specimens"].
• ["Specifications/SpecimenPreparation"]
• ["Specifications/Registration"]
• ["Specifications/ExperimentationAnatomicalImaging"]
• ["Specifications/PressureCalibration"] (for patellofemoral joint testing)

Protocols

Tibiofemoral Joint Testing

Primary Conditions

• Joint laxity at 0°, 30°, 60°, and 90° flexion angles for three isolated degrees of freedom:
  1. internal­-external rotation,
  2. varus-valgus, and
  3. anterior-posterior translation.
• Combined loading; permutations of internal-external rotation moments, varus-valgus moments, and anterior-posterior drawer forces.

Secondary Conditions

• Joint stretching at various flexion angles, to potentially identify gross mechanical properties of the ligaments

Measurements

• Joint kinetics
  • reaction forces (anterior-posterior, compression-distraction, medial-lateral)
  • reaction moments (flexion-extension, internal-external rotation, varus-valgus)
  • provided in anatomical joint coordinate system
  • provided in a human-readable or openly accessible form with clear descriptions of data structures and file naming/storage conventions
• Joint kinematics
  • translations (anterior-posterior, compression-distraction, medial-lateral)
  • rotations (flexion-extension, internal-external rotation, varus-valgus)
  • provided in anatomical joint coordinate system
  • provided in a human-readable or openly accessible form with clear descriptions of data structures and file naming/storage conventions

Equipment Use Modes

• Refer to ["Infrastructure/ExperimentationMechanics"] for details of the equipment utilized in this specification.
• Tibiofemoral joint testing will be done via the six degrees of freedom robot (Rotopod R­2000, PRSCO, Hampton, NH) with a rotary stage mounted to the top to yield a seventh degree of freedom for increased range of motion.
• An Optotrak motion tracking system (NDI, Ontario, Canada) will used to digitize the robotic system hardware and specimen anatomy, to create and control motions and loads in an anatomical knee joint coordinate system specific to the specimen (Grood and Suntay, 1983).
• A universal force sensor (UFS) will be attached to the robot platform, or may be attached to the frame surrounding the robot depending on the range of motion considerations of the particular loading condition. The tibia will be fixed to the UFS.
• The robot will be operated in real-time force feedback control so that loading trajectories can be applied to determine the five degrees of freedom kinematics of the joint. Flexion will be prescribed, as in position control.

Operating Procedure

Coordinate System Optimization:

• A kinetics based neutral position (minimal loading) will be established once the femur is set to 0° flexion angle by operating the robot in force control mode.

• The tibiofemoral joint will be moved under a passive flexion from 0° to 90° flexion with a 100 N compressive load. The femur coordinate system will then be optimized to minimize the change in joint translations and off-axis rotations throughout the cycle. -- ["aerdemir"] DateTime(2013-11-19T11:20:33Z) What is the reasoning behind this protocol?

  • This process is intended to define a functional mechanical axis of the femur. Some limitations may exist in that the screw home mechanism may be 'optimized away'.
• The kinetics based neutral position will re-established with the refined coordinate system.

Preconditioning:

• The specimen will be preconditioned by manually loading the knee and by applying the terminal loads of the laxity loading protocols once for 30° flexion.

Testing of Primary Conditions:

• Testing protocols were adapted from Borotikar (2009).

• The data will be collected and stored based on filing naming conventions utilized by the BioRobotics Core of the Cleveland Clinic, see ["Infrastructure/ExperimentationMechanics"] and [attachment:Infrastructure/ExperimentationMechanics/simVitro%20-%20Data%20File%20Structure%20Quick%20Reference%20Guide_Rev02.pdf data storage conventions].

• -- ["aerdemir"] DateTime(2013-11-19T12:29:09Z) What are the file naming conventions and data structure for Optotrak measurements?

• Throughout all tests, a 20N axial compression will be included to maintain tibiofemoral joint contact.

• -- ["aerdemir"] DateTime(2013-11-19T12:10:08Z) Need details of what will be measured exactly. I assume UFS will measure the forces and moments and kinematics will come from the robot, and also from Optotrak markers, and at the background they are processed to provide the measurements in desired coordinate systems, right?

• The actions during the timeline of testing will be:
  1. Apply AP laxity loading at 30° flexion:
     • Anterior­/posterior force of 0 to ±100 N in steps of 10 N.
     • Note that this loading condition will be repeated throughout testing to ensure there was no injury or damage to any of the structures in the joint. It will also quantify small changes in joint laxity that may occur during testing due to repetitive loading.
  2. Set flexion angle to 0°.
  3. Apply laxity loading:
     1. Internal­-external rotation: 0 to ±5 Nm in steps of 1 Nm.
     2. Varus-valgus: 0 to ±10 Nm in steps of 2.5 Nm. 0 to ±100 N in steps of 10 N.
     3. Anterior-posterior translation: 0 to ±100 N in steps of 10 N.
  4. Apply combined loading:
     1. permutations of internal external rotation moments of -5, 0, 5 Nm, varus-valgus moments of -10, 0, 10 Nm, and anterior-posterior drawer force of -100, 100 N.
  5. Set flexion angle to 30°.
  6. Apply laxity loading.
  7. Apply combined loading.
  8. Apply AP laxity loading at 30° flexion.
  9. Set flexion angle to 60°.
  10. Apply laxity loading.
  11. Apply combined loading.
  12. Set flexion angle to 90°.
  13. Apply laxity loading.
  14. Apply combined loading.
  15. Apply AP laxity loading at 30° flexion.

Patellofemoral Joint Testing

Primary Conditions

• Patellofemoral mechanics under quadriceps loading at tibiofemoral flexion angles of 0°, 15°, 30°, 45°, and 60°.

Secondary Conditions

• Patellofemoral mechanics under quadriceps loading with perturbed tibiofemoral internal-external rotation.

  • -- ["hallorj"] DateTime(2013-10-10T14:14:18Z) Should we consider perturbing tibiofemoral IE at some/all of the fixed flexion angles? Both in vivo and in silico based studies suggest patellofemoral mechanics are sensitive to this degree of freedom.

• Patellofemoral mechanics under quadriceps loading with modified angle of pull.

  • -- ["colbrunn"] DateTime(2013-11-04T10:24:18Z) The folks at Wayne State also modify the angle of pull relative to the femur. They call it femur rotation.

Measurements

• Joint kinematics
  • translations (anterior-posterior, compression-distraction, medial-lateral)
  • rotations (flexion-extension, internal-external rotation, varus-valgus)
  • provided in anatomical joint coordinate system
  • provided in a human-readable or openly accessible form with clear descriptions of data structures and file naming/storage conventions
• Contact pressures
  • sensor location aligned with anatomical joint coordinate system
  • provided in a human-readable or openly accessible form with clear descriptions of data structures and file naming/storage conventions

Equipment Use Modes

• Refer to Infrastructure/ExperimentationMechanics for details of the equipment utilized in this specification. ["Specifications/SpecimenPreparation"] provides information on the state of the specimens before this testing starts.
• Tibiofemoral joint testing will placed and oriented via the six degrees of freedom robot (Rotopod R­2000, PRSCO, Hampton, NH) with a rotary stage mounted to the top to yield a seventh degree of freedom for increased range of motion.
• Quadriceps loading will be applied by a muscle actuator system.
  • A linear actuator will be used for this purpose, see (["Infrastructure/ExperimentationMechanics"]).
  • A freeze clamp will be used to attach the actuator to the tendon (["Specifications/SpecimenPreparation"]).
  • The line of action will be setup to approximate the sulcus defined (inferior-superior) direction of the trochlear groove and will be placed accordingly before testing.
    • The line of action of the actuator will be quantified in a known coordinate frame during robot initialization, see ["Specifications/Registration"].
• Joint kinematics will be measured using an Optotrak motion tracking system (NDI Corp., Ontario, Canada), which utilizes infrared emitting diode (IRED) markers:
  • Triad marker clusters will be attached to each bone using the developed protocol.
  • Kinematics will be described using a standard joint coordinate system, much like the tibiofemoral joint.
• Pressure measurements will be accomplished using a pressure sensor (K-Scan sensor 5051, Tekscan Inc., MA) placed between the cartilage surfaces of the patella and femur

  • The current sensor number might be 5101. -- ["aerdemir"] DateTime(2013-11-19T12:10:08Z) Might?

  • Measures contact pressure distribution, area, and total force.
  • Equivalencing and calibration will need to be performed before the testing, refer to ["Specifications/PressureCalibration"].

Operating Procedure

-- ["aerdemir"] DateTime(2013-11-19T12:29:09Z) Do we need to do any coordinate system optimization?

-- ["hallorj"] DateTime(2013-11-19T15:27:10Z) I assumed this testing would be performed after the tibiofemoral testing, which already has the "optimized" JCS for tibiofemoral control.

-- ["aerdemir"] DateTime(2013-11-19T12:29:09Z) Do we need to do any pre-conditioning?

-- ["hallorj"] DateTime(2013-11-19T15:27:10Z) We haven't performed conditioning in the past, though that doesn't mean we shouldn't. That said, previous results indicated patellofemoral kinematics were insensitive to the load magnitude. I would expect conditioning to have an even smaller effect (though this hasn't been explicitly tested).

-- ["aerdemir"] DateTime(2013-11-19T12:29:09Z) Any preparation to place the pressure sensor?

-- ["hallorj"] DateTime(2013-11-19T15:27:10Z) YES! We need to add a procedure to place the sensor. This was definitely a bit challenging in the past. Let's discuss what we previously did then I can explain it in the specimen preparation specifications

Testing of Primary Conditions:

• The data (tibiofemoral and patellofemoral) will be collected and stored based on filing naming conventions utilized by the BioRobotics Core of the Cleveland Clinic, see Infrastructure/ExperimentationMechanics and data storage conventions.

• -- ["aerdemir"] DateTime(2013-11-19T12:29:09Z) What are the file naming conventions and data structure for Optotrak measurements?

• Tekscan pressure measurements output in the proprietary .fsx format. Pressure measurement file names will be specified as Specimen#_surgicalState_flexionAngle_quadLoad_Trial#.fsx.
  • Specimen# = specimen identifying number as provided by the cadaveric supplier. Specimen demographics will be provided for each specimen.
  • surgicalState = This is the overall sate of the joint. This testing includes a cleaned yet structurally intact joint. As such, it will be described as "cleaned." Details related to specimen preparation can be found in ["Specifications/SpecimenPreparation"]
  • flexionAngle = tibiofemoral flexion angle
  • quadLoad = specified quadriceps loading value
  • Trial = trial number. This should correspond to the trial number in the kinematics file as well.
  • File naming conventions should allow for easy organizing of data with the robotic system data file structure conventions.
• The actions during the timeline of testing will be:
  1. Set tibiofemoral joint kinematics
     • 0° flexion
     • Minimize out of plane loads (representation of passive flexion)
     • Lock tibiofemoral joint pose and orientation
     • Various flexion angles will represent expected range of tibiofemoral joint flexion during gait .
  2. Apply incremental quadriceps loads of ~20, 100, 200, 300, 400, 500, and 600 N
     • To accommodate the necessity for manual acquisition of patellofemoral pressure maps, loading states will be manually controlled.

     • Once desired load is reached, data will be collected for a set duration. -- ["aerdemir"] DateTime(2013-11-19T12:29:09Z) How long?

     • Record relative bone positions and patellofemoral contact pressures at each increment.
  3. Set tibiofemoral joint kinematics with 15° flexion
  4. Apply incremental quadriceps loads and record bone positions and contact pressures
  5. Set tibiofemoral joint kinematics with 30° flexion
  6. Apply incremental quadriceps loads and record bone positions and contact pressures
  7. Set tibiofemoral joint kinematics with 45° flexion
  8. Apply incremental quadriceps loads and record bone positions and contact pressures
  9. Set tibiofemoral joint kinematics with 60° flexion
  10. Apply incremental quadriceps loads and record bone positions and contact pressures

References

Borotikar, Bhushan, Subject specific computational models of the knee to predict anterior cruciate ligament injury, Doctoral Dissertation, Cleveland State University, December 2009.

Grood ES, Suntay WJ. A joint coordinate system for the clinical description of three-dimensional motions: application to the knee. J Biomech Eng. 1983 May;105(2):136-44. [http://www.ncbi.nlm.nih.gov/pubmed/6865355 PubMed]