The kneecap is integral in the structures allowing extension of the knee, and small anatomical variations can affect it.
First published in 2013, and reviewed August 2023 by Dr Sheila Strover (Clinical Editor)
What are the common kneecap problems?
Kneecap (or patellar) problems tend to cause a lot of misery.
These are the more common kneecap problems:
Excessive lateral pressure syndrome
Excessive lateral pressure syndrome is when the kneecap is abnormally tilted over to one side, generally the outer (lateral) side, causing pain. This is generally due to the kneecap restraints on that side (the 'lateral retinaculum') being too tight and pulling the kneecap over.
Maltracking
When the kneecap tends to ride too much to the outer side of the knee. This may lead to pain, crunching sounds and joint surface damage.
Mal-alignment
When the kneecap tends to ride too much to the outer side of the knee. This may lead to pain, crunching sounds and joint surface damage.
Subluxation of the patella
When the kneecap suddenly tracks out of its usual groove (trochlear groove) and jumps up onto the groove's edge. Causes sudden painful 'catching', possibly followed by some temporary discomfort. It is a progression of maltracking.
Patellar dislocation
With a severe injury the kneecap restraints may tear, no longer constraining it in its groove and allowing it to fully 'dislocate' out of the groove. The joint will look deformed.
It can also occur if the kneecaps are positioned too high up (patella alta) or if the groove is too shallow (trochlear dysplasia. It may be extremely painful and usually eventually requires restorative surgery. May become recurrent if inadequately treated.
Each episode predisposes to later arthritis.
Hoffa's syndrome
When the fat pad (which is normally present under the patella) is too big, it can get nipped between the femur and tibia, or between the femur and patella. This is painful and the fat pad may become scarred.
Plica syndrome
When a plica (a fold of the joint lining) is nipped between the kneecap and other structures in the knee, it may become damaged, painful and thicken into a tight band which 'catches' when the knee is in a certain position. Where it catches on bone, the joint surface may become damaged.
Patellar joint surface damage
Any of the conditions on the left can weaken and damage the white cartilage joint surface (gristle). At an early stage of damage the cartilage may soften and become boggy (chondromalacia). When damage extends down to the bone it becomes 'arthritis'.
Chondromalacia of the patella
This means 'softening' of the joint cartilage. Although people are often offered this name as a 'diagnosis', it is more correctly a descriptive term to indicate cartilage softening, which may occur in any of these patellar disorders.
Arthritis of the patella
Arthritis is established when the joint surface damage progresses to the point where the underlying bone is exposed. This may cause a gnawing pain, especially at night, and the knee may become swollen after activity. Chondromalacia is an early step in the development of arthritis.
Referred pain
Pain experienced around the kneecap is quite often not originating there, but from other damaged structures like the hip.
