Kneecap Subluxation / Dislocation

This means the kneecap does not stay in its groove on the lower end of the thigh bone when the knee is actively bending. It may simply move out ‘a bit’ but not completely (Subluxation) or it may go out completely (Dislocation) and stay out until it is put back in! It is usually associated with some structural abnormality or weakness of the kneecap bones, ligament & muscles. There is sometimes a strong family history of this condition so it is OK to blame the folks for your crook knees. It can also occur as a result of a direct sideways knock to the kneecap.
It is usually a fairly dramatic and painful event and may follow a twist or a knock to the knee.
Sometimes subluxation can be less dramatic and be more of a chronic (longer) problem with pain after or during bending activity (maltracking).
Treatment for an acute injury will often involve draining blood from the joint if it is very swollen, as blood is very harmful if left it the joint. An X-ray will be essential to check for any chips or breaks to the kneecap. Further treatment may involve physiotherapy/taping/bracing to correct kneecap muscle/ligament weakness/imbalance.
Surgery by arthroscopic lateral release and/or electrothermal medial capsular shrinkage or capsular plication can be necessary depending on the structural abnormalities predisposing to the problem. A lateral release involves releasing (usually by electrosurgery) the tight ligament pulling the kneecap out of its groove laterally so that the kneecap can sit more normally in its groove. This is done in Day Surgery. Full recovery back to sport may take 6-12 weeks and require physio.
More complex open surgery such as tibial tubercle transfer (Roux-Elmslie-Trillat procedure) may be necessary to repair damage and/or reduce the risk of further troubles again by correcting structural abnormalities.
Sometimes the kneecap is ‘never the same again’ after this injury and can go on to later develop kneecap arthritis!