Knee Dislocation and Patella Alta

Knee Dislocation and Patella Alta

A lesser known cause of knee dysfunction and pain is called “patella alta”. It is not always symptomatic but it can predispose you to dislocation. Patella alta means that your kneecap is riding high in relation to the joint. Let’s look at a side by side comparison:

Normal                                       Patella Alta

Normal Patella Alta

The reason this can be a problem has to do with what is called the trochlear groove. The end of your femur or thigh bone, looks like the classic cartoon bone with two bulbs. These bulbs, called epicondyles, form the groove where the patella is supposed to reside. 

epicondyles

When you bend your knee, the patella descends in the groove, and as you straighten the knees, it ascends. 

patella biomechanics

You can imagine that if it is already resting in a higher than normal position and you straighten your knee, it becomes unstable as the trochlear groove becomes shallower. If you couple that movement with any rotation of the femur, the patella can easily dislocate. It can also wear away the cartilage on the back side of the patella which is called chondromalacia which can predispose you to knee replacement later in life. 

What is the cause? It’s not fully understood and it may be congenital, but there is an association between patella alta and Osgood Schlatter’s disease. Osgood Schlatter’s is a condition where a strong pull of quadriceps places repetitive strain on the insertion called the tibial tubercle. This causes microfracturing of the tibial tubercle. In response, the body lays down bone tissue and causes a pronounced bump on the top and front of your shin. 

Osgood Schlatter's

As always, correlation does not mean causation, but there is a proposed link. One common cause of Osgood Schlatter’s disease is a sudden growth spurt. The femur rapidly grows and outpaces the growth (or lengthening) of the quadricep muscle. The leads to a tight quadricep and/or a long patellar tendon. 

Considering that the patella lies embedded in the musculotendinous junction of the quadriceps, it would follow that a tight quadricep could pull the patella upwards. If this sounds like you, some guided stretching and soft tissue mobility by a physio may be all you need to improve your knee function. 


Christopher EllisComment