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Knee Pain

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[[File:Knee pain.jpg|right|thumb|300px|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"/>, so much so that it is sometimes referred to as 'runners knee'<ref name="KneeRunnersKnee"/>. 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. (Note that there are other types of pain in and around the knee, but this article only looks at pain behind the kneecap, more properly called Patellofemoral pain syndrome or PFPS,)

=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|centerright|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.]]*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. * '''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 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 See Are You Overstriding?] and [http://runningtimes.com/Article.aspx?ArticleID=20271 An 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" />* '''Weak Quads.''' It is common for people with knee pain to have weak quads<ref name="PFClinical"/>. However, I have found no research to suggest that weak quads are a cause of knee pain, a rather than a result of knee pain. I believe that it is more reasonable to conclude that knee pain results in less exercise as the patient avoids activities that cause pain, and thus the quads become weaker through inactivity.* '''Maltracking/malalignment. '''[[File:Kneecap.png|center|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 (femur), 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 [[VMO]].''' 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 muscle short.jpg|center|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 Obliquus or [[VMO]], has been linked to kneecap alignment<ref name="KneeLinTomo"/> and knee pain<ref name="KneeVMOAtrophy"/>.** '''[[VMO]] Delay.''' There is some evidence that people suffering from knee pain (PFPS) have a delay in the activation of the [[VMO]] compared with the main quad muscles<ref name="KneeVMODelay"/><ref name="KneeVMODelayMeta"/>, which reduced the lateral force by 25%<ref name="KneeVMODelayPower"/>. Detecting this timing difference is normally requires sophisticated clinical equipment, but there is some suggestion that the delay can be felt directly by placing fingers on the belly of the [[VMO]] and the VL<ref name="PFClinical"/>. ** '''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|right|thumb|200px|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. * '''Baker's cyst'''. A baker's cyst causes pain behind the knee joint rather than under the knee cap. * '''ITBS'''. Another common source of knee pain is [[Iliotibial band syndrome]] which generally causes pain to the outside of the knee.* '''Fracture'''. A fracture of the kneecap will obviously cause knee pain, but is normally the result of trauma. If you suspect you have a fractured kneecap, seek medical help. * '''NSAIDs'''. Cartilage destruction is a major cause of concern with NSAIDs<ref name="KneeNSAID"/>, but I found no long term studies that link NSAID use with knee problems, so it's not clear if this is a widespread cause of knee pain.* '''Chondromalacia'''. The term Chondromalacia means soft cartilage and was once thought to be a common cause of knee pain. However, studies have shown that people with advanced Chondromalacia can be pain free<ref name="PPConcepts"/>.* '''Leg length discrepancy'''. A difference in leg length can be a factor in knee pain<ref name="PFClinical"/>.

<br style="clear: both" />

==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" />

==Weak Quads==

It is common for people with knee pain to have weak quads<ref name="PFClinical"/>. However, I have found no research to suggest that weak quads are a cause of knee pain, a rather than a result of knee pain. I believe that it is more reasonable to conclude that knee pain results in less exercise as the patient avoids activities that cause pain, and thus the quads become weaker through inactivity.

==Maltracking/malalignment==

[[File:Kneecap.png|right|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 (femur), 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. While this belief is not well supported by the evidence<ref name="patellaralignment"/>, the following underlying problems may still cause knee pain through other mechanisms.

* '''Weak [[VMO]].''' 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. The quads consist of four muscles, and a relative weakness in a subdivision of one muscle, the Vastus Medialis Obliquus or [[VMO]], has been linked to kneecap alignment<ref name="KneeLinTomo"/> and knee pain<ref name="KneeVMOAtrophy"/>.

* '''[[VMO]] Delay.''' There is some evidence that people suffering from knee pain (PFPS) have a delay in the activation of the [[VMO]] compared with the main quad muscles<ref name="KneeVMODelay"/><ref name="KneeVMODelayMeta"/>, which reduced the lateral force by 25%<ref name="KneeVMODelayPower"/>. Detecting this timing difference is normally requires sophisticated clinical equipment, but there is some suggestion that the delay can be felt directly by placing fingers on the belly of the [[VMO]] and the VL<ref name="PFClinical"/>.

* '''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.

* '''[[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"/>.

* '''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.

==Baker's cyst==

A baker's cyst causes pain behind the knee joint rather than under the knee cap.

==ITBS==

Another common source of knee pain is [[Iliotibial band syndrome]] which generally causes pain to the outside of the knee.

==Fracture==

A fracture of the kneecap will obviously cause knee pain, but is normally the result of trauma. If you suspect you have a fractured kneecap, seek medical help.

==NSAIDs==

Cartilage destruction is a major cause of concern with NSAIDs<ref name="KneeNSAID"/>, but I found no long term studies that link NSAID use with knee problems, so it's not clear if this is a widespread cause of knee pain.

==Chondromalacia==

The term Chondromalacia means soft cartilage and was once thought to be a common cause of knee pain. However, studies have shown that people with advanced Chondromalacia can be pain free<ref name="PPConcepts"/>.

==Leg length discrepancy==

A difference in leg length can be a factor in knee pain<ref name="PFClinical"/>.

=Treatments=

This list is roughly in order of the viability and priority of the treatments.

* '''Reduce Knee Stress'''. Stress on the knee should be reduced to prevent further damage<ref name="PFClinical"/>. Personally, I do not believe in complete rest, but prefer reduced exercise, trying to avoid or minimize pain as I believe the exercise promotes healing.

* '''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.

* '''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.

* '''Check for ITBS'''. ITBS produces pain to the outside of the knee, rather than under the kneecap. It's possible to have both kneecap pain and ITBS, so read [[Iliotibial band syndrome]].

* '''Taping'''. The use of tape has been shown to be effective at reducing knee pain<ref name="KneeLongTerm"/><ref name="KneeTapeBrock"/><ref name="KneeTapeMcConnel"/>, by over 90% in one study<ref name="KneeTapeEMG"/>. One study used tape to pull the knee cap towards the midline of the body<ref name="KneeTapeMedial"/>, others relied on evaluation to define the correct direction<ref name="KneeTapeBrock"/>. The most common method mentioned is 'McConnell taping'<ref name="KneeTapeMcConnel"/><ref name="KneeTapeBrock"/>, and instructions can be found by Googling 'McConnell taping'.

* '''[[VMO]] Re-timing.''' If the firing of your [[VMO]] is delayed, it may be possible to correct this. Ideally, the correction uses a combination of training and down in EMG biofeedback device. These devices can be quite expensive, but it may be possible to detect the difference in timing between the [[VMO]] and the VL using your fingertips<ref name="PFClinical"/>. The goal should be retraining control rather than strengthening, with 200 repetitions per day (20x 10 reps) being required<ref name="PFClinical"/>. (I did find instructions for a [http://www.instructables.com/id/EMG-Biofeedback/ DIY EMG].)In addition, it may be possible to mitigate the [[VMO]] timing problem with taping<ref name="KneeLongTerm"/><ref name="KneeTapeMcConnel"/> (see below).

* Knee brace? * '''[[Joint Supplements]]'''. The joint supplements glucosamine and chondroitin provide marginal benefit, but are considered safe, so they may be worth considering if you can justify the expense. Other supplements such as Omega 3 oils and Vitamin C/E may be worth considering. For more details, see [[Joint Supplements? ]].* '''TapingKnee brace/sleeve/strap'''. A knee sleeve is a simple elastic wrap that goes around the knee, sometimes with a hole to avoid pressure on the kneecap. A knee brace usually provides hard plastic support in addition to the sleeve. The use of tape has been shown to be effective at reducing evidence supporting knee painbraces is limited<ref name="KneeLongTermKneeBracingBrouwer2005"/><ref name="KneeTapeBrockKneeBracing"/>, with many of the studies having poor quality<ref name="KneeTapeMcConnelKneeBracing"/>. One reasonable study showed improvement with a brace<ref name="KneeBracingPowers2004"/>, by over 90% in one studybut better quality studies showed no benefit<ref name="KneeTapeEMGKneeBracingMiller1997"/>. One study used tape to pull the knee cap towards the midline of the body<ref name="KneeTapeMedialKneeBracingLun2005"/>, others relied on evaluation to define the correct direction<ref name="KneeTapeBrockKneeBracingHunder2011"/>. The most common method mentioned is 'McConnell taping'There are even fewer studies for knee sleeves<ref name="KneeTapeMcConnelKneeSleeveBea09"/>. The only study on knee straps showed no benefit<ref name="KneeTapeBrockKneeBracingMiller1997"/>. I found no indications of the long term effects or safety of knee braces, sleeves or straps. Based on the available evidence, the use of these approaches does not seem justified. I found no studies that looked at [[A review of graduated compression wear|Compression Tights]] but they may act in a similar way to a knee sleeve and instructions can be found by Googling 'McConnell taping'they have [[Why compression clothes|other benefits]].  

=Anti-treatments=

The following 'treatments' are not recommended.

* '''Quad strengtheningresistance training'''. A common recommendation is to strengthen the quad muscles to improve the tracking of the kneecap, especially the [[VMO]]. However, resistance training of the quads puts extra strain on the kneecap and can cause a worsening of the symptoms<ref name="PPConcepts"/>.

* '''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=

<references>

<ref name="KneeSleeveBea09">Clinical practice guidelines for rest ortho... [Joint Bone Spine. 2009] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/19467901 </ref>

<ref name="KneeBracingBrouwer2005">Braces and orthoses for treating ... [Cochrane Database Syst Rev. 2005] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/15674927 </ref>

<ref name="KneeBracingHunder2011">A randomized trial of patellofemora... [Osteoarthritis Cartilage. 2011] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/21232620 </ref>

<ref name="KneeBracingLun2005">Effectiveness of patellar bracing for treat... [Clin J Sport Med. 2005] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/16003037 </ref>

<ref name="KneeBracingMiller1997">The efficacy of orthotics for anterior knee p... [Am J Knee Surg. 1997] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/9051172 </ref>

<ref name="KneeBracingPowers2004">The effect of bracing on patella alignm... [Med Sci Sports Exerc. 2004] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/15235330 </ref>

<ref name="RunningInjuries">A retrospective case-control analysis of 2002 running injuries -- Taunton et al. 36 (2): 95 -- British Journal of Sports Medicine http://bjsm.bmj.com/content/36/2/95 </ref>

<ref name="Glutes">Gluteal muscle activation durin... [Clin Biomech (Bristol, Avon). 2011] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/21388728 </ref>

<ref name="KneeTapeBrock">Effects of patella taping on patella po... [Med Sci Sports Exerc. 1993] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/8231783 </ref>

<ref name="KneeTapeMcConnel">The effect of patellar taping on the onset of vast... [Phys Ther. 1998] - PubMed - NCBI http://www.ncbi.nlm.nih.gov/pubmed/9442193 </ref>

<ref name="KneeBracing">Patellar taping and bracing for the treatment of chronic knee pain: A systematic review and meta-analysis - Warden - 2007 - Arthritis Care & Research - Wiley Online Library http://onlinelibrary.wiley.com/doi/10.1002/art.23242/full </ref>

<ref name="KneeRunnersKnee">Runner's Knee (Patellofemoral Pain) - OrthoInfo - AAOS http://orthoinfo.aaos.org/topic.cfm?topic=a00382 </ref>

</references>

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