26th July, 2016

malvernphysio

Function of the kneecap

With a recent spate of kneecap (patella) tracking issues, I thought I would explore this injury more and describe the reasons behind faulty patella-tracking.

Patella-tracking issues are one of the most common knee conditions due to the significant number of factors that affect the position of the patella. They usually occur at a time when the stresses placed on the knee change. This may be from an increase in activity, possibly from new or different shoes, or even from new exercises.

To understand this injury further, it’s helpful to understand the purpose of the patella. The patella is a sesamoid bone; a bone that lies within a tendon. In this case, it is the tendon that connects your thigh muscles (quadriceps) with the top of the shin (tibia). The quadriceps are a strong and powerful muscle group and perform the role of straightening the knee (and at times control bending of the knee). You can see from the pictures below that without the patella, the line of pull generated by the quadriceps, results in significant compression of the tibia into the thigh-bone (femur). With the patella present, the direction of pull is changed so that there is less compression between the tibia and femur, and more rotary force straightening the knee.

patella moment arm

As we can see any activation of the quadriceps creates some compression of the tibia into the femur. This is why the quadriceps are an important muscle in knee control. Along with this force, there is also a significant force compressing the patella into the lower part of the thigh-bone (femoral groove). This articulation is called your patello-femoral joint. It is where tracking issues occur and where pain is typically felt with patella-tracking problems.

PFJ

The ideal position of the patella in the femoral groove is one which creates even load from the underside of the patella into this groove when the quadriceps contract. Dysfunction and pain starts to arise as soon as the patella is pulled away from this position. One common reason for this malposition is an uneven pull on the patella. Another common reason is that poor technique or weakness around the hip and/or ankle, result in a change in position of the femoral groove relative to the patella. Often the change in position of the femoral groove is harder to assess and more likely to be missed by a less thorough therapist. An example of patella mal-positioning is shown in the picture below.

skyline view knee

It is obvious to see the difference here between the patella that sits evenly in the femoral groove, and the patella that is sitting imperfectly. The imperfectly aligned patella results in cartilage wear. This is evident in the knee on the left of the picture by the lack of space between the underside of the patella and the femoral groove beneath.

There are a multitude of other potential contributors to poor tracking. Some are based on strength, flexibility and tightness, others have to do with the shape of your body and your bones. Due to the vast number of contributing factors, it is only with a very thorough examination, as well as careful prescription of specific exercises and interventions, that we can fix these issues and keep you out there enjoying the things you like.

Book an appointment with one of the physio’s at Malvern Physiotherapy Clinic if you suffer from any of these knee pains. We will perform a thorough assessment, explain the reasons for your issues and show you exercises specific to your issues.

Written by Mark Fotheringham

Physiotherapist at Malvern Physiotherapy Clinic