Pain in the front, or anterior, part of the knee is often due to an abnormality of the patellofemoral joint and called “runner’s knee.” The patellofemoral joint is where the patella (kneecap) slides along the femur during knee movement. It is the most common running-related injury1 as well as a common problem for many other types of athletes. The medical term for this condition is patellofemoral pain syndrome.
While runner’s knee has many underlying causes, the hallmark symptom is pain at front of the knee, around or behind the kneecap, particularly during movement such as running or squatting, or with prolonged sitting. It is most common in individuals who repetitively stress the patellofemoral joint through sports that involve running.
The Anatomy of Runner's Knee
The patella lays over the front of the knee joint, and helps the quadriceps (large thigh muscles) straighten the knee by providing a mechanical advantage, similar to the action of a pulley system. With knee flexion and extension, the patella glides along a groove at the end of the femur, called the trochlear groove. In patellofemoral pain syndrome, pain results from increased stress between the patella and the femur.
Many factors can influence how the patella and femur move in relation to each other.
Causes and Risk Factors for Runner’s Knee
Runner’s knee can be caused by several factors, including one or a combination of the following:
- Training errors. A sudden increase in the volume or intensity of training may place excessive stress on the patellofemoral joint. Likewise, inadequate recovery time or excessive hill work may do the same.
- Overuse and overtraining of the knee. Prolonged periods of heavy use and training can cause runner’s knee in even the most conditioned athletes, if adequate time for recovery is not provided. For example, a distance runner completing a particularly rigorous week of training may develop runner’s knee pain.
- Injury. An injury to the ankle, hip, or knee can change the knee’s biomechanics, eventually leading to runner’s knee symptoms.
- Focal weakness. Weak or underdeveloped thigh or hip muscles can cause the patellofemoral joint to bear a larger stress burden with activity. Over time this can lead to the development of runner’s knee.
- Excessive body weight. Being overweight can cause unwanted stress on the knees. When walking across level ground, each step places 1.5 times an individual’s body weight worth of pressure on their knees.2
- Flexibility. Particularly tight quadriceps (top of thigh), gastrocnemius (calf), iliotibial band (outside of thigh), or hamstrings may predispose someone to runner’s knee.
- Gender. Women have an increased risk of runner’s knee, as women have wider hips and different knee alignment than men.
Certain lifestyle factors can also increase the chances of an individual developing runner’s knee. For example, someone whose profession required frequent squatting, such as a carpet layer, would be more likely to develop runner’s knee.