Patellofemoral Pain Causes and Prevention
Patellofemoral pain is common in people who do a lot of sport and in particular adolescent girls. It occurs when the patella or kneecap rubs against the bone underneath and can have a number of causes.
It is often thought that incorrect tracking of the patella over the femur bone results in damage or irritation of the articular cartilage underneath the patella. However, damage to the cartilage itself cannot directly cause pain because there are no blood vessels or nerves but it can lead onto other problems which in turn cause pain.
Causes of pain include synovitis (inflammation of the synovial membrane or joint lining in the knee), erosion of the cartilage and bone, soft tissues injury or irritation such as to the lateral retinaculum and the infra patella fat pad.
The initial trigger for patellofemoral pain syndrome is likely to be overuse, however there are a number of factors which can increase the risk of suffering patellofemoral pain which include:
Incorrect running shoes for your running style can contribute to poor foot biomechanics. Some shoes are designed to resist pronation inwards by having a firmer block on the inside of the mid-sole. Looking at the wear pattern on a shoe can give an indication as to whether they are appropriate. Also the age of a running shoe is important. Most runners will replace them after 500 miles or 6 months. Some will have two or three pairs on the go at once which can extend the life of the shoe.
Increased training loads can be from increased volume for example increasing the number of miles run or days trained. This increases the overall load from repetitive strain on the patellofemoral joint. Increasing intensity such as through bounding or jumping exercises can also increase the load on the joint.
Training surfaces can increase the load through the joint. Hard surfaces such as roads or concrete floors will increase the load on the joint compared to grass or artificial 3G type training areas.
Increased internal rotation of the femur or thigh bone may contribute to the development of patellofemoral pain. The therapist will assess the patient in a standing position and will observe the patella facing inwards towards each other. This may be more prominent during running or walking or performing a single leg squat and could be due to weak hip muscles, particularly the gluteus medius.
Increase knee valgus is also known as genu valgum or an increased Q angle. Simply put, the knee bends inwards increasing the angle between the quadriceps and the patella tendon. This can be seen with the patient in a standing position or during a single leg squat exercise. A Q-angle greater than 18 to 20 degrees could indicate patella tracking problems.
Increased tibia rotation is where the tibia or shin bone rotates inwards too much. This can cause the femur to rotate inwards and the patella to track incorrectly. Rotation of the tibia is often due to an over pronated foot.
Over pronation of the foot is where the foot rolls in too much and flattening. This has a knock on effect of causing the tibia to rotate.
Poor flexibility of any of the muscles surrounding the knee joint can be a contributing factor, in particular tight muscles on the outside of the knee and hip such as the tensor fascia lata and iliotibial band.
Position of the kneecap can assessed through both active movements which the patient initiates and passive movements which are facilitated by the therapist. The patella may be rotated, tilted forwards or backwards or displaced sideways, any of which can be a contributing factor. Taping the patella back into place may also be used to determine the cause of pain.
Soft tissue surrounding the patella such as the lateral retinaculum and iliotibial band could be too tight whilst the vastus medialis muscle on the inside of the knee could be too weak. This could be obvious from assessing the patella position or through feeling or palpating the tissues.
Neuromuscular control of the vastus medialis is assessed to identify if the muscles are contracting at the right time. Just because there is plenty of muscle bulk does not mean the muscles are working properly. If the vastus medialis on the inside of the knee contracts slightly later than the rest of the quadriceps muscles then this could be a contributing factor. The therapist should assess this in a number of positions, particularly those which closely relate to the patients normal sporting activities.