In posterior compartment syndrome which passive movement causes pain?
It is possible to stretch the affected muscles by passively moving the joints in a direction opposite to that of the damaged muscle action:-

Passive extension of fingers produces pain in flexor compartment syndrome of the forearm.
Dorsiflexion of foot produces pain in the posterior compartment of the leg
Plantar flexion produces pain in the anterior compartment of the leg.
Dorsiflexion of foot
Foot inversion
Toe dorsiflexion
Toe planter flexion