Lying wall slides are knee rehabilitation exercises to improve flexion - 'facilitated' exercises use the good leg to help gain deeper flexion.
Use a helper
It is a simple exercise, but you may need a helper to help you get your legs into the starting position alongside the wall, perhaps next to a doorway.
Deconditioned Knee: The Effectiveness of a Rehabilitation Program that Restores Normal Knee Motion to Improve Symptoms and Function. Shelbourne KD, Biggs A and Gray T. N Am J Sports Phys Ther. 2007 May; 2(2): 81–89.
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