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Why does my knee hurt sometimes and not others?

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The patellofemoral joint (PFJ), the joint between the knee cap and thigh bone underneath is affected by many different structures. Many patients have a structurally sound knee, but yet have pain, (for more on this see my blog on why does my knee hurt when my MRI scan is normal?). The relative position of the knee cap, (patella) and thigh bone underneath will alter how pressure is distributed across this joint, and excessive pressure in any one place has the potential to cause pain. Therefore there are many factors in day-to-day life that can alter the pressure and hence the pain. Let’s take muscle length. If certain muscles are tight this can alter the patella and/or thigh bone position. Factors as subtle as ambient temperature, whether you are cardiovascuarly warmed up from exercise and even how stressed you are can all impact on muscle length. (If you want to know more on this, see my blog on why has it been suggested that I should stretch to help my PFJ pain.)


Your position during all activities during the day can alter the pressure in your PFJ. Let’s take your car seat position. A change of a few cm back or up will alter the pressure which may explain more pain in some cars than others. Similarly the height of stairs will alter your PFJ mechanics, and hence some stairs may be more pain provoking than others.


The foot is known to play a big part in the functioning of the PFJ. You may notice that different shoes, or indeed the absence of shoes makes a difference to your pain. Understanding this and being strategic about your footwear can be a pragmatic tactic to help. For example, high heels commonly increases PFJ pain. Reserve wearing them for situations where you are not on your feet for prolonged periods.