What causes a knee to buckle and feel unstable? i just had fluid removed and now my knee feels unstable is this normal? please explain and help

Uncertain whhy: The bucking is due to the reason why the knee swelled in the first place and you will need an evaluation. I suspect arthritis or a cartilage lesion.

Osteo arthritis: Can happen as a result of injury or Osteoarthritis Can happen as a result of injury to Tendons,Ligaments or cartilage inside Knee Joint Torn meniscus or a fragment of bone or cartilage gets trapped Tearing of any of ligaments can result in buckling

Mechanical problems : Is usually caused by mechanical problems which cause instability. They can be a torn or worn out meniscus and partial or complete tears of the ligaments that structurally hold the need together