When I had my knee joint replaced the doctor told me both ligaments inside the joint were missing. Is this something I've had from birth?

Not likely or you would probably have had knee problems at a young age. There are two ligaments that criss-cross inside the knee joint--the anterior cruciate ligament (ACL) and the posterior cruciate ligament (PCL). Together, these ligaments help hold the joint together and keep it stable during movement.

Torn or damaged knee ligaments can occur with trauma, injury, or age. Many patients having a total knee replacement have a deficient ACL. An earlier injury and torn ligament often lead to knee arthritis. Less commonly, the PCL is involved.

It's rare to have both ligaments missing at the same time. This is a sign of severe injury, probably more than one--since the mechanism of injury is different for each one.