Patellofemoral Pain Syndrome (PFPS) is common, in fact one study that looked into its prevalence estimated that as many as 2.5 million runners will be diagnosed with the condition in a given year. It is characterised by a gradual onset of pain in the front of the knee that feels like it is deep under the knee cap. It is often made worse by activities that include running, walking, stair climbing, squatting and sitting for prolonged periods. It is rare that it leads to significant swelling within the knee, however a small swelling is not uncommon.
How do I know I have this condition?
Based on a number of tick boxes alone, you cannot say for certain that this is the problem you have. In addition, it is not unheard of that you may well have several things wrong with structures in and around your knee and this is just one of them.
Typically however this problem presents with;
- Insidious onset of symptoms (came on gradually, and was not associated with a specific injury e.g. fall, twisting etc)
- Pain localised to behind the knee cap
- Pain with two or more of the following; prolonged sitting, running, stairs, squatting or jumping
What will a clinician look to exclude through examination;
- Ligament injury
- Absence of tendon pathology
- Irritation to the bursa (fluid filled sacs that act as anti friction devices often between tendons and bone)
- Irritation of the fat pad (highly sensitive structure that sits below the knee cap and behind the patella tendon)
We cannot yet prove what the source of the pain is in this condition, but the evidence out there is growing to suggest that abnormal loading patterns to the undersurface of the knee cap can start the process of pain generation off.
In Feburary last year I wrote a guest blog which discussed the possible mechanism through which increased loading might occur. I pulled together some of the evidence that looked at the influence that the foot and hip have on this process.
Head to the Clinical Journal of Sports Medicine website to read what I wrote….
Tissue homeostasis is what will underpin whether the cartilage will remain healthy, or start to breakdown. Scott Dye in the early 00’s proposed that altered loading patterns on the retropatellar surface lead to an inability of the cartilage to maintain tissue homeostasis. This was proposed to reduce its capacity to dissipate load, resulting in increased focus to the force. Despite the cartilage being aneural (without a nerve supply), the underlying, sub-chondral,bone is highly innervated. If patterns of loading become more focused, this sub-chondral bone could start to complain and give you pain.
As discussed earlier, many other structures around the front of the knee could be the source of pain. Some which include; The infrapatella fat pad (hoffa’s fat pad) is extremely highly innervated, and may become inflamed due to the altered biomechanical loading that was discussed in section 2’s article. The patella tendon can mimic PFPS by its location of pain, however the symptoms do tend to be more superficial, and can often be localised with a fingertip (this pathology is discussed further on the tendinopathy page).