The patella is a fascinating bone, it is the largest Sesamoid bone in the body. It acts as a fulcrum by increasing the angle at which the Quadriceps muscles act and therefore increasing the leverage that the quadriceps tendon can exert on the femur, we literally couldn't run without it. It isn't there when we are born... this bone forms as we start to walk and runs centrally along the leg within a grove designed just for it; the patello femoral / trochlear groove .
So what happens when this bone mal-tracks, or doesn't run straight? 🤔 Well let's start by thinking about the positions we often see a patella sitting in.
When the four quadriceps muscles are balanced and working together, they ensure the patella remains central to the leg, they also ensure the leg extends in a linear fashion. Clearly, if one side is stronger than another, this will create a slight rotational force on the patella, which will cause damage of the articular surface as it runs through the groove and therefore pain over time. 🙈
Let's look at two of the muscles that may cause the mal-tracking presentations we often see.
The Vastus Lateralis attaches through the lateral side of the patella and can therefore affect the patella position, dragging it into a lateral position. Vastus Medialis, however, as its name suggests, is the medial muscle of the four Quadriceps muscles. If overly tight, it will cause the patella to track medially. Let's add another complication in and think about the Vastus Medialis Oblique (VMO) muscle which is part of the Vastus Medialis muscle. There has been much debate over whether it functions separately to what is known as the Vastus Medialis Longus (VML) muscle or whether they are the same muscle. 🤓
Whether a separate muscle or not, it is implicated in patella position. A study by Sakai et al., (2000), investigated whether a weak VMO portion of the VM muscle group would lead to a patella shift, they looked only at zero and 15 degrees of knee flexion and did indeed find that a weak VMO area lead to a shift in patella position during extension. The Vastus Lateralis (VL) muscle has been shown to have a larger cross sectional area and a higher percentage of high threshold fibres than the VMO, meaning this muscle is likely to contract faster than the VMO potentially overpowering it and therefore leaving the patella laterally tracking. 😟
A study by Witvrouw et al,. (1996) hypothesised that a patella tap could test the contractile speed of the VMO relative to the VL and that pain might inhibit the speed of the contraction. Using EMG testing they found that in healthy individuals the MVO contracted faster than the VL, but in those with patello-femoral pain the MVO contracted after the VL, showing a reversal in firing patterns. If VL fires before VMO, this will cause the patella to track laterally over time, causing possible dysfunction
So what can we do about a mal-tracking patella? 🤔 Well, we can look at the position the patella is in and strengthen the muscles needed to return it to a central position. We can also feel the muscles to check which order they are firing when our client extends their leg. If the VMO is firing after the VL on initiation of movement, we need to address this by strengthening the medial part of the Quadriceps while restricting the lateral side. A simple way to do this is to use a band for resistance and twist the foot medially putting the lateral side under slight stretch to restrict it and allowing the medial side to do the main body of work....
If using this for CPD try this question:
Your client in the gym is staring to complain of knee pain, especially when performing squats. You look at his knees and notice the patellas laterally twist. His exercise regime includes sumo and goblet squads, how could you modify their program in the gym or clinic to encourage the patella back to a more neutral position?
Then write it all up in your CPD logbook for reflective learning. For your FREE CPD log click here and sign up to our newsletter.🤗