I suffered knee cap dislocation at the age on 11. I'm now 36 years old. After plaster for a month and few physiotheraphy sessions at home, the knee was back to functional. In the interim years i've suffered few jerks like slipping etc and suffer knee stiffness but the knee becomes normal after few weeks. A month back my knee suddenly got locked, although it was normal after a couple of hours. However this has happened 4 times over last one month. An MRI of the knee shows near full cartilage loss.