There is a growing appreciation in both medicine and in manual therapy (osteopathy, chiropractic, physiotherapy) of the role that excessively flexible ligaments can play in spinal and joint issues, and even in general health.
Most patients are convinced that there is a link between weather patterns and how their muscles and joints feel. This belief almost certainly pre-dates the ancient Greeks (one of whom, Hippocrates, believed it too).
Any change in the functioning of the knee stemming from the lumbar spine might cause knee pain.
If your feet and ankles stiffen up, the amount of information going to the brain (proprioception) drops dramatically.