Fig. 1
Patellofemoral pain (PFPS) is a pain/discomfort felt on or around the kneecap (patella). (Fig. 1)
It is also called Runner’s Knee because it is more prevalent among runners. However, it can occur in any active individual. The pain worsens with activities such as running, climbing stairs, prolonged sitting, and squatting.
The kneecap glides along the bony groove along the thigh bone (femur) when we bend and straighten our knees. When doing activities that involve the knee, the quadriceps are often involved in these actions. The pulling force of the muscles exerts a compressive force on the kneecap i.e., patellofemoral joint (PFJ), which is also known as the patellofemoral joint reaction force (PFJRF).
In February 2022, an article [¹] in the British Journal of Sports Medicine analysed and compared the compressive force that goes through the kneecap i.e. the PFJRF, in different activities and physical interventions by reviewing results from 71 articles.
The table below shows the approximate PFJRF in healthy individuals across various activities, which is a gauge of how much pressure is exerted on the knee.
The table above shows that the pressure on the kneecap differs during daily activities. More stress is felt on the kneecap when we run as compared to ascending and descending stairs.
What causes the pain?
There can be many different factors that can cause PFPS. Some common factors include:
- weak or tight lower limb muscles which lead to poor muscular control and alignment of the lower limbs;
- bony or structural anomaly; and/or
- ill-fitting footwear.
Let’s take a look at how the alignment of the lower limb joints will affect the pressure exerted on the kneecap.
Fig. 2 and Fig. 3
In an ideal alignment, the joints of the lower limbs should be nicely in line on top of each other. If seen from above, the kneecap should glide effortlessly within the groove of the thigh bone.
Fig. 4 and Fig. 5
However, when they are not, the patella is unable to slide smoothly along in the grove. Instead, it tracks toward the outer side. This is known as maltracking of the kneecap, or patella maltracking.
For individuals with maltracking of the kneecap, the kneecap moves out from its normal position and moves to its sides, and starts to rub against the thigh bone. (Fig. 2 and Fig. 3) This increases the pressure between the kneecap and the thigh bone, thereby irritating the soft tissues around them and causing pain. (Fig. 4 and Fig. 5)
Proper lower limb joint alignment is maintained when there is adequate hip control and ankle stability. When the outer muscles of the hip are strong , they will be able to prevent the thigh bone from turning inwards in relation to the hip/knee joint. With good ankle stability, forces that go through the leg during weight-bearing activities are well-absorbed, thus, reducing the stress in the knee joint.
Alteration in the hip-knee and ankle joint alignment will affect the line of pull from the quadricep muscles to the kneecap. As a result, the kneecap glides to the side and the pressure in the kneecap increases.
How can I prevent PFPS?
1) Proper conditioning:
Strengthening the outer hip muscles (gluteal muscle group, refer to Fig. 6) and improving ankle stability can help maintain proper alignment in the knee when we move.
Fig. 6
2) Increased flexibility of our lower limb muscles:
This is to prevent excessive overloading on the kneecap.
3) Avoidance of excessive training or sudden increase in activities:
Warming up and cooling down are essential every time you work out. Know your own body’s limits!
4) Proper footwear:
Ensure your shoes are not worn out and can provide adequate support and shock absorbance. Choose the correct shoe with a suitable fit for your foot type!
If you think you might be having PFPS, don’t worry, we’ve got you covered! Keep an eye out for our next article where we will be going through some stretches and exercises to improve the mobility and strength of your lower limbs!
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In the meantime, you can check out our previous articles on ankle sprains and flat feet!