One of the most common diagnoses of the kneecap or patella is referred to as 'patellofemoral syndrome'. Patellofemoral syndrome is not a discrete condition but a collection of symptoms characterised by pain at the front of the knee related to the alignment and tracking of the kneecap in the underlying groove of the femur bone. An understanding of the conditions affecting alignment and tracking will give you a thorough background to the issues relating to the kneecap.
Another syndrome - the plica syndrome - is important to understand. The plica syndrome is a collection of symptoms related to a fold of the joint lining in the knee. Although these plica folds are normal structures, they may lead to symptoms that are mistaken as originating elsewhere, and inappropriate treatment may be offered.
More serious kneecap problems may include kneecap dislocation or fracture. Dislocation of the kneecap - and especially if it recurs - implies more significant structural problems than in patellofemoral syndrome, either as a cause of the dislocation or as a consequence. Such problems may include a high-riding kneecap (patella alta) or an abnormally shaped kneecap or groove (patella dysplasia and trochlear dysplasia). Surgery is also more likely to be necessary in the management of dislocation than in the management of patellofemoral syndrome.
Patella fracture often needs surgery and requires that the surgeon do his best to restore contiguity of the broken edges. Failure to pull the pieces together accurately may leave the patient with painful arthritis.
Another important kneecap condition to know about is arthrofibrosis - scarring and tethering behind the kneecap may the unfortunate consequence of injury or surgery affecting this region. This complication can usually be successfully managed if identified early, but if not it may result in stiffness and pulling down of the kneecap into an abnormally low position (patella baja) that results in severe pain and arthritic damage.
Kneecap arthritis may in fact be a consequence of any of the conditions already mentioned. Arthritis may affect the cartilage surface at the back of the kneecap or it may also affect the groove of the femur bone along which the kneecap slides as the knee is bent and straightened. Options for management include a variety of biological cartilage repair techniques as well as patello-femoral resurfacing using artificial components.
Patellectomy or removal of the kneecap for problems like these is nowadays rarely performed. Once the patella is removed there are consequences both for knee function and for future management.