Because not enough volunteers were recruited.

This study aims to research on the relationship between constitutional varus knee and patellofemoral pain. The standardized standing whole-lower-extremity radiographs, the knee lateral view and skyline view of the participants will be taken. The hip-knee-ankle angle will be obtained from the radiographs. According to the hip-knee-ankle angle, the knees will be labelled knee varus or knee nonvarus. The knee varus incidences of the two groups will be determined and compared.

The patellofemoral joint will be assessed in the skyline view and lateral view. The hip-knee-ankle angle will be obtained from the standing whole-lower-extremity radiographs. According to the hip-knee-ankle angle, the knees will be labelled knee varus or knee nonvarus. The knee varus incidences of the two groups will be determined and compared. It is hypothesized that constitutional varus knee is a risk factor for patellofemoral pain.

Inclusion Criteria:

• Patellofemoral pain during physical activities such as running, jumping, squatting, and going up or down stairs for at least 4 weeks.
• The onset of pain is required to be atraumatic in nature.
• Exhibit two of the following clinical criteria on assessment: pain on direct compression of the patella against the femoral condyles with the knee in full extension, tenderness of the posterior surface of the patell on palpation, pain on resisted knee extension, and pain with isometric quadriceps muscle contraction against suprapatellar resistance with the knee in 15° of flexion.
• Negative findings in the examination of knee ligaments, menisci, bursae, synovial plicae, Hoffa's fat pad, iliotibial band, and the hamstring, quadriceps, and patellar tendons and their insertions.

Exclusion Criteria:

• With patellofemoral instability, or With other knee diagnoses.
• Any previous surgery or severe trauma in the affected limb.
• Inflammatory joint disease or tumors in the affected limb.

Military personnel. Running at least 10 km per week for at least 3 months.