My Mother needs help walking but currently she can't walk because her legs stay bent at the knee (frog-like). Anyone have any clues?

Is mom at home or in a skilled nursing facility? Neatly a year after my mom develooed contractures from being bedbound in the hospital due to pneumonia and sepsis, the PTs at her nursing home were able to get her walking again. Ask that the doctor order a pt evaluation and therapy

This is called a joint contracture and is a common problem in ALZ.

"A contracture is a chronic loss of joint motion caused by shortening of a muscle or tendon. In late stage Alzheimer’s disease, contractures of the knees, elbows, and hands form mostly from lack of movement- enhanced by neurologic changes in muscle tone making joints more resistant to passive movement.

"Many people in the later stages of Alzheimer’s disease sit… a lot. They stay in one position with their knees and elbows bent. Frequently, if they are seated in a wheelchair with sling upholstery and poor pelvic support, their thighs and knees touch. They may even pull their arms in tight against their chest if they feel cold. Sitting in this position for several hours, and then being transferred back to bed curled up in this same position, leads very quickly to limited joint movement. This makes it very hard to clean, feed, and dress someone whose limbs don’t move well." (thedementiaqueen)

Intense physical therapy can help.

What does her primary doctor says is the cause for your Mother's knees to stay bent?

I know personally for myself the lack of use of one's limbs will make the muscles freeze up, and one would need a lot of physical rehab to get them back to working order.