TKA detailed patella model - stiff patella tendon problem

Main Forum
1

Hello, AnyBody

I am trying to make a TKA squat model with accurate patella kinematics during 0-120 degree knee flexion.

My model is based on TKA-KneeBendDemo

My model looks fine with 15-120 degree knee flexion, but not for 0-120.

Patella was over flexed at 0-15 degree, which doesn’t looks stable. And I think this is affected by stiff patella tendon, pushing the patella component superiorly.

If my opinion is right, how should I overcome this problem?

I tried to make the patella tendon as stiffness string component, but it failed (overloaded muscle configuration).

Maybe when patella tendon length lower than slack length transfers zero load, which means no load transfer between quadriceps and tibia.

Thank you.

Regards,
Jaehun Ro

Corentec Co., Ltd.

2

Hello Jaehun,

Possibly the length of patellar tendon is not scaled well in your case. This correction below might solve it:


  AnyKinEqSimpleDriver PatellaMovement = {
    AnyKinPLine &Jnt = .KinematicMeasures.Patella;
    
    // Scale patella tendon length based on the over all leg length
    AnyVar lengthScale = vnorm(..Seg.Shank.KneeJoint.sRel - ..Seg.Shank.Insertion_patella_tendon.sRel)
                / vnorm(..Seg.Shank.StdPar.Insertion_patella_tendon-..Seg.Shank.StdPar.KneeJoint);
 

      
 
           
    AnyVar TendonLength =  lengthScale *..ModelParameters.PatellarLigamentLength; 



    DriverPos = {TendonLength};
    DriverVel = {0.0};
    Reaction.Type = {On};  // The muscles must do the work
  };

Please change it in AMMR\Body\AAUHuman\LegTLEM\Jnt.any and let us know if this helped.

Kind regards,
Pavel

1 Like
3

Hello, Pavel

Thanks for your reply.

I thought that I’ve done the tendon scaling in my model but there were some mistakes.

I corrected my mistakes and scaled my model’s patellar tendon but it didn’t worked well.

It seemed too short in the model view, so I added some value to elongate it.

After adding constant (5mm), the model worked well.

However, I’m still not sure about the stiff patellar tendon. It still seems to push the patella upward, at early flexion.

Is there any idea to make patellar tendon to be elastic spring element?
Or is my opinion of stiff patellar tendon wrong?

Best regards,
Jaehun Ro

Corentec Co., Ltd.