Patellofemoral malalignment: looking beyond the viewbox.

Post WR, Teitge R, Amis A. Clin Sports Med 2002;21;521-546.

This is the editor's interpretation of a paper published in the orthopaedic literature in 2002 - our attempt to make relevant medical articles accessible to lay readers. If you wish to read the original it is easy to ask your librarian to obtain a reprint for you from any medical library.


The article focuses on the point that the term 'patellofemoral malalignment' is overused and poorly defined. Drs Post and Teitge (surgeons) and Dr Amis (bioengineer) explain that sometimes the term is offered as a discrete clinical diagnosis, while at other times the term is used to describe on an X-ray (or other type of imaging such as MRI) the relationship in position of the patella to the underlying trochlear groove.

knee from above

The finding of an abnormal relationship on an imaging study may furthermore be improperly used to define a clinical diagnosis of malalignment even in the absence of symptoms. The authors feel that the great danger lies in the surgeon then believing that such a diagnosis is in itself a licence to offer corrective surgery - often leading to an unsuccessful outcome which may lead to further surgery to try and resolve the new problems!

The authors feel that no 'corrective' surgery should be undertaken on the basis of the imaging findings alone. They point out that imaging is only part of the evaluation of the patella, and that other elements need to be taken into account. X-ray findings need to be correlated with symptoms, and also with the way the patella moves with walking and the status of the nerves and muscles associated with the patella. 

Their definition of patellofemoral alignment is "where bony alignment, joint geometry, soft-tissue restraints, neuromuscular control, and functional demands combine to produce symptoms as a result of abnormally directed loads that exceed the physiologic threshold of the tissues. Malalalignment means malalignment of forces. Malalignment is not a specific image on a radiograph, nor is it a specific diagnosis. It is a concept of imbalance that helps explain patellofemoral disorders. The symptoms of this imbalance may be pain or patellar instability".

 

Defining patellar position in different planes

The authors highlight the importance of imaging the patella in different planes to fully understand any abnormal positioning -

  • medial/lateral translation (coronal or axial plane) - ie the patella has slid sideways to the inner or outer side of the groove

     
  • tilt (rotation in the axial plane) - ie the patella has tilted rather than slid, so that one edge is tilted closer to the groove and the other edge consequently tilted further away

     
  • spin (internal/external rotation in the coronal plane) - ie the patella has not slid nor tilted, and it basically in the right position but has rotated

     
  • flexion rotation (rotation in the sagittal plane - ie this is like 'tilt' but the tilt is from top to bottom, rather than side to side.

They point out that in order to fully describe patellar alignment it should be with reference to all these variables, and not just one of them, as is commonly the case.

After thus determining the patella's position relative to the underlying femur bone, the surgeon then needs to look at how it moves relative to the femur bone, assess the involved structures around the patella, and then evaluate all the information in relation to the symptoms the patient is suffering, and when and how the symptoms began.

Once having correctly assessed the patellar alignment, the clinician then needs to try and work out why the patellar is where it is, for example whether the person was born and developed that way or whether there is damage to the normal soft tissue supporting structures, maybe following an injury.

This article goes into much more detail about the evaluation of the patella and the editor recommends that the interested reader should obtain a copy, but these are the pertinent principles.

 

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