What causes knee pain?

author : AMSSM
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Triathletes often encounter knee pain. Here's why and how to prevent problems.

Anterior knee pain or pain in the front of the knee is one of the most common running injuries. It is also a common complaint among cyclists, triathletes, and other athletes. There are several specific conditions that comprise anterior knee pain including: most commonly patellafemoral pain- pain surrounding the knee cap or underneath the kneecap; patella tendonitis - irritation or injury to the tendon that connects the knee cap to the lower leg; chondromalacia - a condition where the cartilage on the underside of the knee cap becomes inflamed and softens; plica syndrome- irritation of the lining of the knee joint; Osgood - Schlatter disease - irritation of the growth plate in growing patients. There are other less common causes that can result in pain in the front of the knee thus if you have had pain in this area, it is important to be evaluated by a physician to ensure you don’t have a more serious condition such as arthritis, injury to the internal knee structures, or osteochondritis dissecans especially if you have had any swelling or feelings of instability in the knee area. This article will focus on patellafemoral pain as it is the most common cause of anterior knee pain.

Anatomy: The knee joint includes the lower part of the thigh bone called the femur, the upper part of the shin bone called the tibia, and the patella or knee cap. The knee cap tracks along a groove in the femur when the knee flexes and extends. In addition to bones, the knee joint includes tendons, ligaments, muscles, and connective tissue which also help control how the knee caps move.

Symptoms: Patellafemoral pain is typically worse with activities such as running, jumping, kneeling, or walking up and down steps. The pain is in the front of the knee and sometimes felt underneath the knee cap. The pain is often mild at first occurring only with activity but as it progresses, patellafemoral pain may cause pain even at rest. The pain can also occur with prolonged sitting with a flexed knee. The pain is commonly relieved by rest. Occasionally people may notice some popping in the front of the knee with motion or feelings that the knee gives out and these symptoms are important to be discussed with a physician to ensure that they aren’t caused by other conditions. Joint swelling is uncommon with patellafemoral syndrome.

Causes: While common, the source of the pain is not fully understood. Likely the pain is generated from nerves in the connective tissue surrounding the patella. There are many things that predispose someone to getting patellafemoral pain with the basic idea that there is imbalance in the forces that control the patella tracking resulting in overload to the joint. Things that can predispose one to this overload include:

  1. Overuse/ Training Error: Too much physical activity without enough rest or increasing activity too quickly without an appropriate period of acclimation. Training error also includes errors in appropriate technique, poor running form, too much of a particular exercise such as squatting, lunges, hill work, using too much resistance on the bike.

  2. Inappropriate equipment can also cause this pain including inappropriate footwear or poor bike fit.

  3. Trauma to the knee cap area

  4. Lack of flexibility in quadriceps or hamstrings muscle groups

  5. Lack of core, hip, or quadricep strength

  6. Anatomical issues: Includes alignment of the knee cap, shallow or deep groove of the femur, loose knee ligaments, and tight ligaments that hold the patella in a suboptimal position. Also feet anatomy, leg alignment and anatomy also contribute to alteration in forces through the knee which can result in overload and pain. The pain is also more common in woman which is probably multifactorial and caused by differences in ligament flexibility as well as anatomy as women have wider hips. Most of these issues are not modifiable except by surgical intervention which is uncommon but can be helpful in refractory cases.

  7. Previous injury, trauma, surgery to the lower extremity or knee

As you can see there are many potential contributors to this type of pain and identifying the cause can be complicated. Your physician will identify which ones they think contributed to you getting this pain. Addressing your individual causes can result in a tailored treatment method and will help treat the pain as well as prevent the pain from recurring when you go back to your activities.

. Diagnosis: First the physician will obtain a history and then do a thorough exam of the knee and surrounding joints. Common PE findings is tenderness underneath and around the knee cap, weak quadriceps and hip stabilizing muscles, and tight hamstrings or quadricep muscles. The knee cap maybe very mobile and able to be moved back and forth from side to side too easily or it may be very immobile. The knee cap may also be visualized to be track abnormally. Commonly there will be deficits in terms of strength and flexibility. X-rays may be done but are not necessary in all cases. Rarely an MRI, ultrasound, or other imaging modality if the diagnosis is not clear or if the pain does not respond as expected.

Treatment: There are several common things that your physician will likely suggest you do to treat the pain, however your individual treatment should be tailored to what your physician views as the cause of your pain and the severity of your symptoms. It is important to note that you should not expect overnight improvement. If your pain has been occurring for weeks to years it will not go away overnight. Treatment will often take weeks to notice an improvement. The most important part of recovery and treatment includes addressing the causes that set you up with the pain to begin with.

  1. Rest: If your pain is happening even at rest and is severe, your physician may have you rest from all activities that are likely to result in pain including running, jumping, squats, lunges, cycling, or breast stroke for a time. If you can do some activities pain-free, however you are likely going to still be able to do some activities such as low resistance cycling or other swimming strokes. If your pain is less severe you may just be asked to cut back on the activities that typically cause your pain. If you typically have pain after running 6 miles but no issues with 5 then likely you can still run 5 miles until your pain improves with treatment. Decreasing mileage or intensity to a pain free level can be helpful for the less severe cases whereas in the severe cases total avoidance of painful activities may be necessary in the early stages of treatment.

  2. NSAIDs or anti-inflammatories may be recommended. These should always be taken with food and water. They should not be taken if you have GI ulcers or kidney disease and should not be taken for more than two weeks unless instructed by a physician.

  3. Ice: ice therapy especially after exercise is thought to be helpful. Ice should be applied for 15-20 minutes at a time. A cloth should always be placed between the ice and the skin.

  4. Physical Therapy: Physical therapy has been shown in multiple research studies to be effective in treating patellafemoral pain. It is important to realize that for physical therapy to work, you must often do the exercises at home as well as in the office and up to 5-6 days a week. Additionally many times people do not give physical therapy enough time to work before quitting, make sure to that you do at least a month of physical therapy before judging whether it is working. Where you go to physical therapy is also important as some PT offices do not specialize in sports rehab, thus I recommend asking a physician knowledgable in sports rehab to recommend a therapist or therapy group.

    A common biomechanical factor that causes anterior knee pain is weak hip and core muscles. Weak hip stabilizing muscles alters the mechanics of the body as the foot impacts the ground. When the hip muscles are weak the pelvis tilts to the side of the leg that is not supported by the standing leg and can put more stress on the knee. Thus hip and core stabilizers are important exercises to work on for anterior knee pain and include: double and single leg bridges, hip abductor exercises, planks, side planks, clam shells, and more. Also strengthening the quadriceps and hamstrings are helpful. Squats and lunges are often a mainstay of lower extremity strengthening but can actually make anterior knee pain worse especially if done with poor mechanics or too much weight. If these exercises cause pain, altering them to be less deep or doing different exercises may be needed.

    Lack of flexibility especially in the hamstring but less commonly in the quadriceps can also cause anterior knee pain. In this case stretching the hamstrings and quadriceps are critical.

    As unmodifiable biomechanical factors can also influence your likelihood of getting anterior knee pain. People with loose ligaments or those who may be called double jointed are more likely to have knee pain. Because the ligaments and stabilizers are so loose, these people rely more on the muscles to stabilize the knee cap. Also if your ligaments in the knee that hold together the knee cap to the adjacent structure are too tight or hold the knee cap too low or too far to the side one may be more likely to have this pain. Even with these factors, physical therapy is still typically recommended to address other factors first. Most of the time though athletes can reduce their pain without surgical intervention.

    Additionally therapists may look at your running gait through a gait analysis. Your heal strike, stride length, stride frequency, and position of your core, as well as other factors can impact your knee pain. Through a gait analysis, any issues in your gait can be identified and corrected over additional visits.

    If the pain is worse when on the bike, the pain pay be caused by incorrect bike fit or bike technique. A common cause of anterior knee pain can be a seat that is too low, however anterior knee pain can be caused by other errors in bike fit thus getting a professional bike fit or looking up how to appropriately fit a bike yourself may be helpful. Additionally using high resistance and lower cadence is a common cause of anterior knee pain thus trying to spin more at lower resistance on your rides may also be helpful.

  5. Knee braces/ knee taping.: Knee braces with a hole in the center to control the tracking of the patella have not been shown to be effective in large studies but some individuals do feel that they result in less pain. They may be worth trying but should not be a substitute for methods that have been shown to be effective such as rest or physical therapy.

  6. Orthotics: Occasionally people may benefit from a change in shoe type or even orthotics.

Preventing recurrence: If the problem appears to be training error or increasing mileage or intensity too quickly, once you are pain free you should increase your mileage and intensity at a slower rate than before. A good rule of thumb is no more than 10% increase a week. Also take into consideration your other activities including cycling, lifting, etc. If you begin to have pain again back off and increase again when pain free again. It is also often necessary to stay on a maintenance program of your recommended physical therapy exercises so the pain doesn’t recur.

Good luck with your knee pain and hope that you will be returning to triathlons and running soon.

Caitlyn Mooney, MD


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date: May 31, 2017


The American Medical Society for Sports Medicine (AMSSM) was formed in 1991 to fill a void that has existed in sports medicine from its earliest beginnings. The founders most recognized and expert sports medicine specialists realized that while there are several physician organizations which support sports medicine, there has not been a forum specific for primary care non-surgical sports medicine physicians.



The American Medical Society for Sports Medicine (AMSSM) was formed in 1991 to fill a void that has existed in sports medicine from its earliest beginnings. The founders most recognized and expert sports medicine specialists realized that while there are several physician organizations which support sports medicine, there has not been a forum specific for primary care non-surgical sports medicine physicians.


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