Patellofemoral pain syndrome (PFPS) is the most common form of knee pain treated in physical therapy clinics. I made this series to help people better understand this condition, why it occurs and how to fix it.
In case you missed it:
Today we’ll be discussing the factors that influence the patellofemoral (PF) joint’s capacity and how that affects knee pain.
We have quite a bit of newer research coming out showing that a very large predictor of injury is training volume. If we go over a certain threshold of training volume, our risk of injury goes up (17, 18, 19).
One particularly promising area of injury prediction research is looking at spikes in an athlete’s training volume (20). Most of this research is coming from Tim Gabbett who has studied rugby and soccer (football) athletes. Spikes in training volume are defined as any event of training that far exceeds the typical volume of training.
It makes total sense, do way more then the body is accustomed to, we get hurt. Tim calls this the acute to chronic workload ratio.
Basically if the acute training load (the total volume of training performed in a given week) is much larger then the chronic training load (average training volume over the past several weeks) then we’re more likely to get hurt (17, 18, 19, 20).
A few examples:
Here’s the kicker, what Tim also found was that high levels of volume are actually predictive of lower risk of injury (20).
Tim found that athletes with higher VO2 max (a marker of cardiovascular fitness) and had longer preseasons were less likely to get hurt (17, 18, 19). Basically athletes who had greater fitness and longer periods of preparation before their competitive season began were less likely to get hurt.
Athletes who were accustomed to handling a large volume of training were less likely to be injured. This makes sense, athletes that train at a higher volume are potentially more adapted toward higher training volumes. They are potentially creating greater “capacity” to handle these training loads and less likely to be hurt when exposed to higher volume training environments (tournaments, multi-day competitions etc.). Remember the olympic lifting athlete described in the last article series. She was able to increase her capacity over time to handle much larger training volumes without getting hurt.
We can take these same concepts and apply it to our injury prevention tactics. Slowly increasing training volumes over time can increase our capacity and make us better able to handle larger and larger amounts of stress.
Far and away the greatest predictor of having future patellofemoral pain syndrome is having weakness with knee extension or weakness of the quads (2, 21, 22). People with PFPS have been shown to have a 6-12% deficit in strength compared to healthy controls without PFPS (2). This makes sense, if the quadriceps are not capable of handling the stress of a given activity, the knee becomes painful. It also seems that having PFPS creates (or increases) weakness.
Patients with PFPS tend to have weakness in the hip musculature (abduction, extension, external rotation (4). Patient with PFPS also present with reduced lateral core strength (9). These reductions in strength also tend to correlate with dynamic valgus seen in single leg squat tasks (4). What’s interesting is that weakness of the hips (abduction and external rotation) is NOT a predictor of future PFPS (21, 22). Some research actually shows those with great hip strength have an increased risk of PFPS (2). It seems that weakness of the hip only occurs after already acquiring PFPS (21, 22).
It makes sense that having weakness of the hip could create poor movement during squatting and jumping maneuvers and thus PFPS but just keep in mind that the research does not support this (21, 22, 2). Weakness of the hip is potentially not a cause but more of an effect after acquiring PFPS (2).
Side Note: Posterolateral hip strength is NOT a good indicator of frontal and transverse hip mechanics during running or step-down maneuvers in healthy individuals (2). In other words, having weakness in the hips doesn’t mean you’ll move poorly. Another interesting thing observed in our medical literature is that hip strengthening does NOT improve biomechanics during single leg squat and running activities (2, 4). These activities improve with cues and biofeedback (mirror feedback) during specific tasks and tend not to improve from task to task (improving a single leg squat does not improve running mechanics) (2, 4). This concept will become very important when we discuss rehabilitation.
Regardless, hip strengthening has been shown to be an effective treatment for PFPS and even more so when combined with quadriceps strengthening (2, 7, 8). Some authors theorize that hip strengthening improves the PF joint’s capacity indirectly, thus increasing the joint’s ability to handle stress and decrease pain (2, 4).
In the last article we took an in depth look into movements at the hip, femur, tibia, ankle and foot. We saw how these movements relate to the PF joint. Femoral internal rotation and tibial external rotation both lateralize the stress to the knee and decrease surface area within the joint to dissipate force. All of these things increase stress within the PF joint. Excessive pronation at the foot (4), lack of ankle dorsiflexion (26, 27) and contralateral hip drop during single leg squatting maneuvers and jumping can all drive abnormal femoral and tibial rotation as well.
People with PFPS had more ipsilateral (same side) trunk lean, contralateral (opposite side) pelvic drop, hip adduction and knee valgus (3). In individuals with PFPS, correcting these biomechanical faults can improve their symptoms (2, 10, 14). Having patients go into more knee valgus, hip adduction and foot pronation has been shown to provoke these patient’s knee pain (3). Basically, correcting these movements makes people feel better and worsening these movements creates more knee pain.
It makes sense then that keeping neutral alignment of the PF joint during movement can improve capacity of the knee.
Side Note: Only 50% of patients with PFPS present with these mal-alignment issues (4). This means that there are probably many other factors that contribute to pain besides just altered movement. This is also a potential reason why many athletes can have “poor” mechanics during running and never experience any knee pain. They may have built capacity in other ways and can handle the increased stress without trouble.
Also keep in mind that as we descend deeper into knee flexion (knee bending) and as the degree of quad contraction increases we increase stress within the PF joint. Having more knee flexion and stronger quad contractions will increase stress in the PF joint. This will become important during rehabilitation when PF joint capacity is limited and we’re attempting to apply the right dosage of exercise to reduce pain and restore homeostasis.
Dictionary.com describes psychosocial as:
Psychosocial factors are things like beliefs and automatic thoughts that can drive good or bad behaviors during rehabilitation. Social factors influence these thoughts and behaviors as well.
Patellofemoral pain syndrome is correlated with anxiety, depression, fear of movement and catastrophization (2, 25). These are known psychosocial factors that can complicate the rehabilitation process. These thoughts can decrease a patient’s desire to perform movements that improve pain and these negative thoughts can also sensitize our nervous system and create more pain. These negative thoughts and behaviors can derail our best attempts to rehabilitate.
One example of a catastrophization would be:
“I can’t believe my knee hurts when I try to squat. It will never get better and I’ll never be able to compete in weightlifting ever again”
An example of a negative belief contributing to perpetuation of pain would be:
“Having pain is a sign that my knee is not improving, is getting worse and is probably getting damaged further”
These thoughts and beliefs can be addressed through a combination of therapeutic neuroscience education and cognitive behavioral therapy. We’ll touch on these in the next article.
Lastly, conditions such as anxiety and depression perpetuate the release of stress hormones like cortisol. Cortisol is a hormone that can sensitize your nervous system and increase pain (28).
Obviously we know that anxiety and depression are just 2 cases that can bring a lot of stress. Stress comes in all forms and too much can exacerbate all pain issues (not just knee pain). Managing stress is obviously a part of this equation but so is:
This is an absolute behemoth of a topic that I’ll undoubtedly cover in future series but for now just keep in mind that this is all part of the capacity and pain equation.
Now, half of this is either good or bad news. We can’t really pick our parents. Genetically we’re given a specific shape to our patella and trochlear groove. As discussed in part 2, this is going to change from person to person. In some people, the fit of the patella and trochlear groove just isn’t great. In some people it is. Ce la vie (That’s life).
The other piece of the equation is body mass index (BMI). Body mass index is the ratio of your height to your weight. If you’re very heavy and short then you’ve got a higher BMI. This is something we can control. Having a higher BMI correlates with patellofemoral pain syndrome in adults only (23). For some reason BMI is not correlated with PFPS in adolescents (23). Either way, it makes sense. The heavier you are, the more stress will go through the PF joint every time you use your lower body.
Now let’s take this information and bring it back to our runner examples earlier in the article series. If you remember, “runner B” got injured. “Runner B” also had less capacity then runner A. Maybe “runner B”:
Any of these factors could have decreased her capacity and increased her risk of injury. Hopefully now you can see that getting injured is a multi-factorial process. It’s often not 1 single factor (technique, strength, mobility) that leads to an injury. All of these factors are probably relevant.
So to recap:
The other goal of this article series was to show you all of the factors that lead to a healthy homeostasis of the knee. When we have knee pain from patellofemoral pain syndrome the homeostasis of the knee is off. In order to get out of pain we’ll need to improve capacity again. In the next article we’ll go over how we can tweak these 5 factors to get out of pain and back to training.
Knee pain is the best pain,
Dan Pope DPT, OCS, CSCS, CF L1
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