Knee hyperextension (locking back of knee) occurs in 50-70% of stroke victims, so it's common. Physios usually offer some relief in rehabilitation but often shrug their shoulders and hope it sorts itself out. Physios can place a slither of EVA under your heel, tie your legs in a rubber elastic strap, rely on AFO (ankle- foot orthosis), or build your leg stength through exercises (eg stand-up, sit-down, aquatherapy).
All help, but this knee brace pictured below, delivered by post at < $30 has never been recommended to me before, and has improved my walking gait and confidence enormously while negating hyper-extension of the knee. I've tried other knee braces, but they're useless and uncomfortable. The 4 little springs behind the knee really work, for me at least. Note that I use a walking stick, also. I will use it for long walks on occasion to make me walk faster; but not wear it indoors so I build up my muscles/strength. Same with AFO, or wear it even less, relying on my own leg strength to build and support me.
