The patella is the medical term for the knee cap. Dislocation is when it moves out of joint to the outside of the knee. It may pop back on its own, or may stay dislocated until someone puts it back. It can happen from a direct blow to the kneecap, or as a result of a twisting injury. It is a little more common in females and some people's leg shape makes them more prone than others. Once it has happened once it can become a recurrent problem happening again and again.
It causes immediate intense pain over the front of the knee. There is a sensation of the kneecap popping out and giving way. The dislocation is visible as a large lump on the outside of the knee, and the knee will quickly swell.
Immediate medical attention is required to get the patella back in joint. This may be done at the time of injury by a physio, by a paramedic or in accident and emergency. In hospital X-rays should be taken and the knee put in a brace or plaster. In the days after this you should get it checked out by Mr Willis-Owen. You will be out of action for several weeks.
After the initial emergency treatment of getting the knee cap back in joint Mr Willis-Owen will assess the knee for further damage often with an MRI scan. Usually the ligaments (medial patellofemoral ligament) on the inside of the knee have to tear at the time of the dislocation, and often there can be cartilage damage occurring on the back of the kneecap as this gets scuffed. Depending of the extent of the damage surgery may be needed. When surgery is not needed careful treatment with bracing, crutches, and physio is required to allow the ligaments to heal properly and prevent the problem becoming recurrent. If not treated properly the kneecap can easily pop out again. In these cases a medial patello-femoral ligament reconstruction may be needed. Lots of physio to strengthen the VMO muscle will be needed after this injury.