Pain underneath the knee cap or patellofemoral syndrome is a common injury in female soccer players after the age of 14 years. There are a number of factors that can combine together to place stress on the knee cap or patella. These factors include: stability of the soccer shoe, outdoor or indoor field surface, anatomy around the knee joint of female soccer player, intensity of training, and foot instability.
To make sense of this injury, you need a basic understanding of the anatomy in the front of the knee. The quadriceps muscle originates in the pelvis above the hip joint and continues toward the knee joint where it attaches to the patella. The patellar ligament continues from below the patella and attaches into the tibia below the knee joint. The quadriceps keeps your knee joint straight when you stand, but more importantly, the quadriceps keeps the knee stable as the knee bends. The quadriceps are a grouping of 4 muscles. The patella acts like a pulley as the knee bends causing the patella to be pressed in to a groove in the femur. If all of the 4 quadriceps muscles are balanced, the patella will move within the femoral groove without causing any pain.
Causes of patellofemoral syndrome
Weakness of one of the quadriceps muscles called the vastus medialis. If the muscle is weak it will cause the patella to displace out of the femoral groove.
The patella can be displaced from the femoral groove due to a large Q angle. Females have a wider pelvis resulting in a larger Q angle when compared to males. The Q angle is formed from the intersection of two lines through the patella. The first line is drawn from a point in the front of the hip bone called the iliac crest to the middle of the patella. The second line is from the middle of the patella to a bony tubercle on the tibia. Displacement of the patella results in less surface between the patella and the femur. This causes an increase in pressure underneath the knee cap resulting in pain.
The Q angle can increase if the foot is excessively pronated. The Q angle can be measured while lying down and standing. A custom foot orthotic is indicated if there is an increase in the Q angle from lying to standing.
Unfortunately, fitting an custom foot orthotic inside a soccer shoe can be difficult. I will discuss soccer shoes and orthotic fit in one of my upcoming blogs.
Chiropodists and podiatrists will evaluate if a pronated foot is having an impact on the Q angle, however, a referral to a physiotherapist, sports medicine physician or orthopedic surgeon maybe required if other causes of patellofemoral syndrome are identified. If your daughter is complaining of pain underneath the knee cap get it evaluated a soon as possible.