
Damage to the cruciate ligaments can cause feelings that the knee simply cannot be trusted. It may suddenly give way or feel unstable.
Cruciate instability is a feeling of abnormal movement in the knee joint consequent on damage to one or both cruciate ligaments. Page updated June 2024 by Dr Sheila Strover (Clinical Editor)

Damage to the cruciate ligaments can cause feelings that the knee simply cannot be trusted. It may suddenly give way or feel unstable.
It is a challenge for the surgeon to decide on surgery for the cruciate problem, as a delay may lead to the meniscus damage.
"....Information regarding the number of instability episodes should be obtained early in the history of patients with ACL injury, as this may influence the likelihood of having medial meniscal damage...." "....lateral meniscal damage...(is) more common in an acute ACL injury and medial meniscal damage...(is) more common in a chronic ACL injury...."
In the 1980's it was common to do an early reconstruction, but it was found that unsettled inflammation in the knee frequently led to stiffness from arthrofibrosis.
Practice, therefore, changed to allow a period of rehabilitation before any reconstructive surgery, and this also allowed an assessment of the degree of stability the patient had despite the cruciate injury.
So not everyone who has frequent instability episodes will end up with arthritis, but it is certainly more likely.
"....The long-term risk of osteoarthritis in ACL-deficient knees is high. It remains unclear whether reconstruction of the ACL significantly reduces this risk. The status of the meniscus at the time of ACL reconstruction is a strong predictor of the risk of osteoarthritis."