Runner’s Knee Causes and Diagnosis

The primary cause of runner’s knee (patellofemoral pain syndrome) is overuse of the knee joint.¹Bump JM, Lewis L. Patellofemoral Syndrome. [Updated 2023 Feb 13]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK557657/ Weakness in the muscles and tendons around the knee and trauma to the knee joint contribute to patellofemoral pain syndrome.

The diagnostic process for runner’s knee involves a detailed review of the medical history and conducting a set of diagnostic tests.

Causes of Patellofemoral Pain Syndrome

Runner’s knee develops when there is increased stress in the patellofemoral joint – the joint between the patella (kneecap) and the femur (thighbone). This increase in stress occurs due to:

• Overuse and overtraining of the knee, which includes repetitive stress or excessive training from activities like running, jumping, cycling, or going up and down stairs
• Weak or tight muscles and tendons, such as tight quadriceps and hamstrings in the front and back of the thigh, or a tight iliotibial band (IT band syndrome) on the outer side of the thigh and knee²O’Connor FG, Wilder RP, Nirschl R, eds. Running Medicine. Second edition. Healthy Learning; 2014.
• Injury to the ankle, hip, or kneecap – altering the knee’s biomechanics and eventually leading to chronic stress in the patellofemoral joint

In most cases, a combination of the above causes results in runner’s knee. For example, weak hip muscles exert more stress on the kneecap, and when the knee is subject to sudden stress or overuse, it amplifies pressure and inflammation inside the kneecap, resulting in patellofemoral pain.

Risk Factors for Patellofemoral Pain Syndrome

The presence of one or more of the following risk factors increases the likelihood of developing runner’s knee:

• Sports and physical activities. Repetitive knee movements increase the risk of knee overuse, such as daily running, soccer, tennis, and basketball.
• Obesity. Being overweight increases stress on the patellofemoral joint.³American Academy of Orthopeadic Surgeons. "Patellofemoral pain syndrome." OrthoInfo. https://orthoinfo.aaos.org/en/diseases--conditions/patellofemoral-pain-syndrome/ Accessed May 06, 2024.
• Low fitness level or low exercise tolerance. Individuals who are not used to physical exercise or sports develop runner’s knee pain if they engage in such activities without prior training.
• Developmental anomalies. Structural variations in the patella (kneecap), femur (thighbone), or trochlear groove (V-shaped groove that contacts the inner surface of the patella) can result in instability of the patellofemoral joint, increasing the risk of kneecap pain.²O’Connor FG, Wilder RP, Nirschl R, eds. Running Medicine. Second edition. Healthy Learning; 2014.
• Altered hip mechanics. Weakness in the hip joint and muscles causes the thighbone to rotate internally, altering the position of the kneecap on the thighbone.²
• Specializing in a single sport. Repeatedly training for a single type of sport is associated with a higher risk of overuse knee injury compared to cross-training and involvement in multiple sports.¹Bump JM, Lewis L. Patellofemoral Syndrome. [Updated 2023 Feb 13]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK557657/^,4Hall R, Barber Foss K, Hewett TE, Myer GD. Sport specialization's association with an increased risk of developing anterior knee pain in adolescent female athletes. J Sport Rehabil. 2015;24(1):31-35. doi:10.1123/jsr.2013-0101
• Excessive foot pronation. Those who tend to slightly rotate their foot and land on the inner side of their soles while walking or running have excessive pronation or overpronation. This type of foot movement alters the biomechanics of the ankle and knee.⁵Barton CJ, Levinger P, Webster KE, Menz HB. Kinematics associated with foot pronation in individuals with patellofemoral pain syndrome: a case-control study. J Foot Ankle Res. 2011;4(Suppl 1):O4. Published 2011 May 20. doi:10.1186/1757-1146-4-S1-O4
• Gender. Women are more likely to develop runner’s knee due to their wider hips and different knee alignment than men.

Preventing or reducing the risk of runner’s knee involves adequately warming up and cooling down before and after a workout or sport, increasing training intensity in small increments, and maintaining a healthy weight.

Diagnosing Runner’s Knee

A clinical diagnosis of the cause of knee pain involves evaluating the knee joint and identifying or ruling out other conditions, such as jumper’s knee (patellar tendinitis), meniscal tears, iliotibial (IT) band syndrome, and knee osteoarthritis.

Physical evaluation

The initial evaluation involves collecting the medical history and performing a physical examination.

• Patient history: Specific questions are asked about the nature of the symptoms, including when they started, what movements cause pain, where the pain is located, and information on any past injuries and surgeries.
• Physical examination: The doctor tests the stability, motion, and function of the knee and evaluates the joint for:
  • Redness, swelling, and stiffness
  • Movement of the patella when the knee bends and extends
  • Bony abnormalities or tenderness

Neuromuscular examination including strength, sensation, reflexes, flexibility, and movement patterns of the hip, foot, and ankle are also examined, as they affect the motion of the knee.

Next, a series of clinical tests are done to trigger the patient’s knee pain symptoms.

Patellar pain tests

The following tests are used to check if the knee pain is originating from the patellofemoral joint:

• Patellar provocation test: This test involves stressing the patellofemoral joint to trigger runner’s knee pain.
  • The patient is asked to step up and down a step stool or one step of a staircase. Alternatively, the patient may be asked to squat.
  • Pain in the front of the knee during these movements may indicate runner’s knee.
• Patellar grind test: This test is used to analyze the movement of the patella (kneecap) when the tendon above it is tightened.
  • The patient lies on his or her back or sits upright with both knees straightened out.
  • The examiner presses the quadricep tendon located just above the kneecap with the web space of his or her hand.
  • The patient is instructed to tighten the thigh muscle, which contacts the quadriceps muscle.
  • Pain behind or around the kneecap indicates runner’s knee or patellofemoral pain syndrome.

Imaging tests

If the physical examination provides inconclusive results, radiographic imaging tests may be ordered.

• X-rays are the initial imaging test to evaluate runner's knee. They are used to identify bony abnormalities, such as abnormal articulation between joint surfaces, bone spurs, fractures, dislocations, or signs of arthritis. X-rays do not provide detailed information about soft tissues, such as tendons or ligaments.
  Images are captured from various angles, including front, top, and different degrees of knee flexion (bent knee).
• Magnetic resonance imaging (MRI) provides detailed images of soft tissues, including muscles, tendons, ligaments, and cartilage, and is used to identify inflammation, tears, or damage to these structures around the knee joint.
• Computed tomography (CT) scans use x-rays to create detailed cross-sectional images of bones and joints of the knee, including any fractures or structural abnormalities. CT scans are not as effective at visualizing soft tissues, so they are used less commonly than MRI for diagnosing runner's knee. They are ordered in specific cases where a detailed assessment of bone or joint anatomy is required.

These imaging tests are also utilized to monitor the progress of treatment and to investigate potential causes of persistent symptoms.