The medical profession is in a muddle when it comes to the kneecap.

We all agree that the medical word for 'kneecap'is 'patella', but there is a great deal of confusion about many of the other words used to discuss patellar problems. So much so in fact that a group of top level knee surgeons - The International Patellofemoral Study Group - met to examine the problem. The outcome of their discussions was published online in French by Dr Jean-Yves DuPont and in the medical journals in English by Dr Ronald Grelsamer.

The Group began by asking the twenty specialists - from five countries - to define the term 'subluxation', a word used commonly when talking about patellar instability. Believe it or not, they got back twenty different definitions! They realised that there was a serious problem here and they set about examining its extent.



They began with 'luxation' - but problems were immediate. The French and German speakers were comfortable talking about 'luxation' but all the English speakers never used the term 'luxation' at all! They talked of 'dislocation', and felt that 'luxation' should be dropped altogether. Not surprisingly the French and German speakers thought that 'dislocation' should be dropped in favour of 'luxation'.

The experts then moved on to examine whether at least the terms were used in the same way, and whether all doctors would understand exactly what was meant when either term was used. But again no, not really.

There were three different usages -
  • If a doctor had said 'The patient has suffered a dislocation (or luxation)' all of the experts agreed that this meant that there had been a distressing incident where the kneecap had completely derailed (left the 'trochlear groove') and stayed there. This would be a sudden and painful event.
  • But it was also agreed that the term could be used, too, if the doctor during examination could make the kneecap derail (usually emphatically resisted by the patient) although it may never have derailed on its own.
  • And thirdly it could be used to describe the findings on X-ray when the kneecap looked derailed, although again the patient may never have suffered any sudden painful event.


The term 'subluxation' - a lesser form of kneecap instability, where the kneecap almost derails - was similarly used for different things -

  • something the patient suffers
  • something the doctor could elicit, even if the patient was not actually suffering from it
  • an X-ray finding, even if the patient had no symptoms

So, in other words, a patient can 'exhibit' subluxation, but not actually be symptomatic at all. Or may be labelled 'a subluxer' but suffer no symptoms. (Note that in contrast a 'dislocator' will always be symptomatic, except in the very, very rare case of permanent dislocation, which we have not discussed here).


Then the real 'biggie' muddles were put on the table - 'anterior knee pain', 'patellofemoral pain syndrome' and 'chondromalacia'. What did the experts make of these?

Anterior Knee Pain

What about 'anterior knee pain'? Like 'chondromalacia', this term is vague. The International Patellofemoral Study Group recommend that the term is best reserved to describe the patient who has yet to be evaluated.

Patellofemoral Pain Syndrome

'Patellofemoral Pain Syndrome' is used by some practitioners who find no identifiable cause of anterior knee pain. The Group agree the term should mean just this - it is NOT a diagnosis, merely an indication that the practitioner has not been able to identify the cause of the patient's pain.


On to a really big one - 'chondromalacia'. Thousands of articles on the web confidently talk of the condition of 'chondromalacia'. The USA even has a specific code for the condition (717.7).

But the twenty knee specialist from the five countries were all in accord that -

'the word chondromalacia should not be used as a diagnosis'

- it is simply a physical condition of the joint cartilage!

The word means literally 'cartilage softening'. If it has been shown that abnormal cartilage softening literally exists, then they agree it is valid to use the term, but even then the term should be clarified to avoid confusion. But they recommend instead that 'cartilage lesion' is a better term to use.

The terminological muddle goes further (see the reference), but I imagine you have already got the message - be very careful when you are given a patellar diagnosis that you understand exactly what you are being told because it's a minefield.


Grelsamer, R.P. Patellofemoral semantics. The Tower of Babel. The International Patellofemoral Study Group. Am J Knee Surg. 1997 Spring;10(2):92-5.


Patellar Instability - A continuum

Dr Lars Blønd explains -