hamstring lengthening surgery

[Matilde Tomasi]

Hi everyone!
I'm pretty new on OpenSim. I'm trying to simulate the effect of an hamstring lengthening surgery. I have preoperative and postoperative kinematic and kinetic data of a patient with cerebral palsy (crouch gait). Through the CMC and FD I'd like to compare experimental postoperative kinematic data with my simulated kinematic data after having lengthened such muscles. I have a crucial question: observing hamstring lengths during the crouch, obviously they are shorter than those of an unimpaired subject. But if an unimpaired subject walked in crouched posture his hamstrings would be shorter too. This because such lengths depends on the limb configurations. So, do I need to simulate hamstring contracture (by reducing the optimal fiber length as I've seen in a Tutorial) before doing the CMC and then performing the FD with lengthened muscles (increasing tendon slack length)? Otherwise would it be correct without simulating contracture too?

Thanks for help!
Matilde