I need a partial knee replacement & also i have spinal stenosis. would possibly any of these two cause my legs occasionally to buckle when i walk?

Depending upon the severity of the "spinal stenosis", neurogenic claudication when ambulating can occur. Progressive walking can result in increased leg numbness and weakness, usually painless, resulting in potential collapse and need to rest. The knee problem would be associated with pain. Surgical procedures for lumbosacral stenosis are available.