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Knee Bone or Joint Injury

Patellofemoral Pain Syndrome (Runners Knee)

Minute Read


Posted 1 year ago


Last updated: 29/11/2022


by James McCormack

What is Patellofemoral Pain Syndrome?

Also known as ‘Runners Knee’ or PFPS, patellofemoral pain syndrome is a painful condition that affects the front of the knee. It is generally felt behind the knee cap and is linked with activities such as walking, running and going up and down stairs. It is common among runners hence the name but can be caused by any activity which repeatedly moves the knee through flexion and extension under weight, such as squatting or cycling, or maintaining the knee at a specific angle of knee bend such as sitting with restricted leg room or driving.

Who Gets Patellofemoral Pain Syndrome?

The populations with the highest incidence are amateur runners and new military recruits. This is suggested to be due to the change and increase in the use of the knee, possibly with poor strength and conditioning (Smith et al, 2018). There is a higher risk for women compared to men, and slightly more likely in adolescents than adults. We will discuss the causes of patellofemoral pain syndrome in more detail later.

Anatomy of the Patellofemoral Joint

The knee joint is made up of two weight-bearing bones, the tibia and the femur, and a third bone the patella which is the knee cap. The patella is a sesamoid bone which means it sits within the tendon of a muscle, in this case, the quadriceps muscle. The patella is in contact with the femur bone and this contact changes as the knee is bent or straightened.

Diagram of patellofemoral joint anatomy

The patella acts like a pulley over the knee and improves the function of the quadriceps muscle. It also acts to protect the tendon of the quadriceps which would have high compression and friction with each knee bend if the patella wasn’t there. The back of the patella is covered with 4-5mm thick cartilage to cope with and dissipate the contact, compression and friction of the femur during movement. The back of the patella has two main facets with a ridge running vertically down the middle. The ridge corresponds to the groove on the femur and helps it to stay in the correct position through movement.

Mechanics of the Patellofemoral Joint

As the knee bends the contact area of the patella on the femur changes. The further the knee bends the contact is closer to the top of the patella and with less it bends, the closer the contact is to the bottom. Between the angle of 60-90º knee bend, the patella has the greatest contact with the femur and sits firmly in the intercondylar groove. The forces across the patellofemoral joint, therefore, are affected by the angle and impact of the activity.

Force across the patellofemoral joint as a percentage of body weight:

  • Walking and cycling 50%
  • Jogging 700%
  • Ascending stairs 330%
  • Descending stairs 500%
  • Deep squatting 2000%

(Servi et al, 2021).

Runner’s Knee Symptoms

Runner’s knee is commonly described as a feeling of pain underneath or behind the knee cap, and can be in one or both knees. Pain is typically felt with activities such as walking, running, walking down stairs or walking downhill. But can also be felt with sitting or driving, when the knee is fixed in a bent position. Pain can last for several hours or days after the aggravating activity. The duration of will vary depending on several factors: pain severity, duration of aggravation and condition of the patellofemoral joint.

As well as pain, a common complaint is stiffness or clicking of the joint. Clicking, popping or crackling sounds of the joint may be heard or felt, and this can be described as crepitus. In more severe cases, the knee might feel like it gets stuck or locks up in particular positions. And many people say they need to move the knee through that position to click the knee and it will feel like it has been released. Some people may feel they can’t walk due to the pain, and pain at night might keep them awake.

Diagram of Patellofemoral Pain Syndrome

What Causes Runner’s Knee?

Runner’s knee is caused by an irritation to the patellofemoral joint. This can be caused by repeated low-level irritation over a longer period of time or by a sudden overload to the joint such as from the trauma of a fall onto the knee. Some sports and activities put high levels of stress and load through the patellofemoral joint, such as those sports that include running, jumping and squatting (see above in the anatomy of the patellofemoral joint section). Participating in these sports will put you at greater risk but this depends on the biomechanics of the individual.


Specific biomechanical movement patterns have a greater risk of developing this condition of overload of the patellofemoral joint.

Risk factors include:

(Waryasz and McDermott, 2008)

  • Lower limb weakness especially in the quadriceps, glutes and hamstrings
  • Tightness in the calf, hamstring and quadriceps muscles
  • Tightness in the iliotibial band
  • Ligament laxity
  • Large Q angle (an inward angle of the thigh and knee)
  • Abnormal timing of individual parts of the quadriceps muscles
  • Patella malalignment 

Diagnosis of Runner’s Knee

Discussing the history of recent changes of activity, and the mechanism of injury can reveal overload to the joint which can indicate that patellofemoral syndrome is a likely diagnosis. Then a thorough physical examination to look at movement patterns and symptoms patterns with movement will clarify suspicions.

The American Physical Therapy Association have a diagnostic criteria which involves excluding other potential causes of anterior knee pain, the location of pain being retro patella (behind the patella) or around it, and reproduction of this pain with deep squatting or other movements that load the patellofemoral joint. In addition, a runners knee test cluster of comprising the patella against the femur, palpation of the retro-patella surface, and active inner range knee extension, can be performed.

If there is uncertainty about the diagnosis or if symptoms are not improving as expected with treatment and management strategies, then addition information from imaging may be necessary. Such as using x-ray to rule out boney injury, or MRI to show inflammation or damage to the back of the patella. 

How Long Does Runners Knee Last?

If caught early and managed effectively runners knee symptoms can subside in 4-6 weeks. However, if the pain has persisted for a significant period of time and the aggravating activities have been continued, this can dramatically lengthen the duration of recovery and return to activity without pain.

Physiotherapy with James McCormack

This is not medical advice. We recommend a consultation with a medical professional such as James McCormack. He offers Online Physiotherapy Appointments for £45.

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