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[[File:Knee pain.jpg|right|thumb|400px300px|Knee pain is the most common injury for runners. This illustration shows the relationship between the kneecap and leg bones.]]A pain behind the kneecap (Patellofemoral pain syndrome or PFPS) is one of the most problems for runners<ref name="RunningInjuries"/>. There is no well-established cure for this problem<ref name="PPConcepts"/>, but there are a number of things you can try and some treatments to avoid. ('''This article is under construction and incomplete!''')
=Causes=
There are a number of possible root causes of knee pain.
* '''Excessive stress'''. The kneecap is an amazing structure, but like all body parts, it has limits in the load it can take. This overload may be due to a number of factors. [[File:Knee Stress.png|center|thumb|300px|The stress on the knee can be a single heavy overload, or it can be a lighter stress applied many times. The green area is the area of safe functioning, and its upper limit is the blue line. The yellow area is where damage will occur to the knee, and the red area is where the damage becomes catastrophic. Note the gray area in the lower left where inactivity also causes knee damage.]]
** '''Low [[Cadence]]'''. Having a low [[Cadence]] results in more vertical movement, and thus higher landing forces.
** '''Highly cushioned shoes'''. Counterintuitively, the more cushioned your shoes are, the greater the loading force on your knees<ref name="ref9"/><ref name="ref10"/>.
** '''Obesity'''. Obviously being overweight puts more stress on the knees and is linked to knee pain<ref name="KneeObesity"/>.
** '''Bad running form'''. Problems with running form, such as overstriding (can increase the landing forces and cause injury.*** '''Overstriding. '''Overstriding is''' '''landing with the foot ahead of the hip), can increase the landing forces and cause injury<ref name="KneeOverstride"/>. (See [http://runningtimes.com/Print.aspx?articleID=23217 http://runningtimes.com/Print.aspxSee Are You Overstriding?articleID=23217] and [http://runningtimes.com/Article.aspx?ArticleID=20271 http://runningtimes.com/Article.aspx?ArticleID=20271An Analysis of Running Technique] for details on overstriding.)*** '''Heel strike. '''Landing with the weight on the heel of the foot creates a far greater peak force than landing so the weight is taken by the midfoot or forefoot <ref name="KneeForefoot"/>. * '''Inactivity'''. The human body needs activity to remain healthy, and the knee is a prime example of this. Animal studies have shown than complete immobilization of the knee can result in a 50% reduction in the cartilage thickness within weeks<ref name="KneeInactivity"/>. Thankfully this damage appears to be reversible.<br style="clear: both" />* '''Maltracking/malalignment. '''[[File:Kneecap.png|rightcenter|thumb|200px|A cross section of the kneecap and femor (thigh bone) showing how the kneecap fits in a groove.]] The kneecap moves in a groove in the thigh bone (see imagefemur), and it is widely believed<ref name="KneeRW"/> that if the kneecap does not track in this grove it will rub on the sides and cause knee pain. However, this belief is not well supported by the evidence<ref name="patellaralignment"/>. ** '''Weak Quads.''' The alignment of the kneecap is not related to the overall strength of the quads, but rather an imbalance of the muscles that make up the quads. [[File:Vastus medialis muscleshort.pngjpg|rightcenter|thumb|200px|The Vastus Medialis Obliquus or VMO, which is often blamed for mistracking of the kneecap.]] The quads consist of four muscles, and a relative weakness in a subdivision of one muscle, the Vastus Medialis Obliqus Obliquus or VMO (see image), has been linked to kneecap alignment<ref name="KneeLinTomo"/>. A study suggested that people suffering from knee pain (PFPS) has a delay in the activation of the VMO compared with the main quad muscles<ref name="KneeVMODelay"/> and another study noted that people with knee pain had a weaker (atrophied) VMO<ref name="KneeVMOAtrophy"/>. (Remember that the weakness could be caused by the knee pain, with people avoiding exercise and stress rather than the weakness causing the knee pain.)** '''Weak Hips.''' A weakness in the hip muscles has been linked to knee pain<ref name="KneeHip"/>. Weak hip muscles result in the leg rotating so the foot points towards the midline of the body (internal rotation), so when the leg bends extra stress is placed on the knee. <br style="clear: both" />** '''Q angle'''. The thigh bone and lower leg are not in a straight line, but form an angle at the knee called the 'Q angle'. A large Q Angle is often thought to cause or contribute to knee pain, but a high Q angle was only seen in 6% of knee pain (PFPS) cases<ref name="RunningInjuries"/> and a high Q angle is not associated with biomechanical knee stress<ref name="KneeQAngle"/>. [[File:Q Angle.png|noneright|thumb|500px200px|If you draw an imaginary line from the [http://en.wikipedia.org/wiki/Anterior_superior_iliac_spine front of the pelvis] to the kneecap and from the lower leg to the kneecap, the angle between the lines is the Q Angle.]]
** '''Over Pronation'''. Pronation is the natural movement of the foot where the arch flattens to absorb landing forces. If the foot pronates too much, the foot will lean towards the midline of the body and the lower leg and knee will follow this motion, moving towards the midline. Like weak hips, the movement of the knee towards the midline creates extra stress on the knee.
* '''Arthritis'''. Arthritis is an inflammation of the joints and can affect the knee. There are various types of arthritis, and diagnosis requires X-Ray, testing the fluid around the joint or inserting a viewing scope into the joint. Arthritis is outside of the scope of this article.
=Treatments=
* '''Ice'''. The use of ice will not remove the underlying cause of knee pain, but it can help with recovery and healing. See [[Cryotherapy]] for more details.
* '''Cadence'''. If you're cadence is too low it can cause various problems, and should be optimized to around 180 steps per minute (90 steps/min for each leg). See [[Cadence]] for more details.
* '''Massage the VMO'''. While the evidence for weak quads and VMO is marginal, massaging the VMO is easy and reasonably risk free. While the [[Foam Roller] is good for massaging most of the quads, it tends not to get to the VMO, and if the [[Foam Roller]] is your only quad massage technique then it's possible that your VMO is suffering from neglect. I would recommend using [[The Stick]] as well as using your elbow on the VMO. I've also found that using an electronic muscle stimulator on the VMO can help. See main article on [[Massage]] for more details.
* '''Massage the glutes.''' Weak glute muscles have been linked to knee pain<ref name="KneeHip"/><ref name="Glutes"/>, so massaging them may help them recover their strength and functionality.
* '''Electrical Muscle Stimulation'''. Strengthening the quad muscles using normal resistance training tends to put extra stress on the kneecap aggravating the injury. Resistance training the quad muscles tends to equally train all parts, rather than focusing on the VMO. Electrical muscle stimulation by contrast can directly target the VMO while putting relatively little stress on the kneecap. See [[Electrical Muscle Stimulation]] for more details.
* '''Minimalist shoes'''. There is good evidence that running shoes increase the stress on the knee<ref name="ref14"/>, and that a more minimalist approach to footwear may be appropriate. See '[[Are your running shoes injuring you]]?' for more details.
* '''Orthotics'''. Studies have shown that orthotics reduce knee pain, with a greater benefit shown in those that have greater pronation<ref name="KneeOrthWedge"/><ref name="KneeOrthIm"/><ref name="KneeOrthWAS"/>. However, there are concerns that orthotics may also increase the stress on the knee<ref name="KneeFootware"/>. Personally, I am concerned that Orthotics may help with knee pain but cause other problems, and the use of orthotics goes against the evidence for minimalist footwear
* '''Running form'''. Good running form has many benefits, but changing form tends to be difficult and can easily result in new injuries if done [[Too Much Too Soon|too quickly]]. I would recommend looking at [http://www.chirunning.com/ Chi Running] or the [http://posetech.com/ Pose Method], though personally I don't agree with their approach of pure forefoot running (your heal not touching the ground) and prefer a midfoot strike.
* Knee brace?
* Ice * Cadence* Minimalist shoes* Downhill running* Running form* Glutes<ref name="Glutes"/>Supplements
=Anti-treatments=
* '''Surgery to correct mistracking'''. A study of knee pain indicated that this type of surgery has the second highest failure rate<ref name="PPConcepts"/>.
* '''NSAIDs'''. Using NSAIDs does not generally improve healing, can mask symptoms and is considered a cause of cartilage damage<ref name="KneeNSAID"/>. An animal study showed that Asprin resulted in greater cartilage degeneration<ref name="KneeAsprin"/>. More at [[NSAIDs and Running]].
=References=
<ref name="KneeHip">Hip strength and hip and knee kine... [J Orthop Sports Phys Ther. 2008] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/18349475 </ref>
<ref name="KneeQAngle">Greater Q angle may not be a ri... [Clin Biomech (Bristol, Avon). 2011] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/21177007 </ref>
<ref name="KneeOrthIm">The immediate effects of foot orthoses on fu... [Br J Sports Med. 2011] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/20647297 </ref>
<ref name="KneeOrthWedge">Application of wedged foot orthosis effectively reduces pain in runners with pronated foot: a randomized clinical study http://cre.sagepub.com/content/early/2011/07/16/0269215511411938.abstract </ref>
<ref name="KneeOrthWAS">A randomised control trial of short term eff... [Br J Sports Med. 2012] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/21930514 </ref>
<ref name="KneeForefoot">Landing Pattern Modification to Improve Patellofemoral Pain in Runners: A Case Series - JOSPT – Journal of Orthopaedic & Sports Physical Therapy http://www.jospt.org/issues/articleID.2653/article_detail.asp </ref>
<ref name="KneeFootware">Effect of footwear on the external knee adduction momen... [Knee. 2012] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/21733696 </ref>
<ref name="ref14">The Effect of Running Shoes on Lower Extremity Joint Torques http://www.pmrjournal.org/article/S1934-1482(09)01367-7/fulltext </ref>
<ref name="KneeVMODelay"> http://rsi.aip.org/resource/1/rsinak/v82/i10/p105101_s1?isAuthorized=no </ref>
<ref name="KneeVMOAtrophy">Vastus Medialis Obliquus Atrophy: Does It Exist in Patellofemoral Pain Syndrome? http://ajs.sagepub.com/content/early/2011/04/12/0363546511401183 </ref>
</references>