Patellofemoral pain syndrome is the term given to pain originating from the patellofemoral joint (i.e. the joint between the knee cap (patella) and thigh bone (femur). It has been given many names, including patellofemoral disorder, patellar malalignment, runner's knee, and chondromalacia. Patellofemoral pain syndrome is usually associated with inflammation or damage to structures of the patellofemoral joint.
The knee comprises of the union of 3 bones – the long bone of the thigh (femur), the shin bone (tibia) and the knee cap (patella). The patella (knee cap) is situated at the front of the knee and lies within the tendon of the quadriceps muscle (the muscle at the front of the thigh). The quadriceps tendon envelops the patella and attaches to the top end of the tibia. Due to this relationship, the knee cap sits in front of the femur forming a joint in which the bones are almost in contact with each other. The surface of each bone, however, is lined with cartilage to allow cushioning between the bones. This joint is called the patellofemoral joint.
Normally, the patella is aligned in the middle of the patellofemoral joint so that forces applied to the knee cap during activity are evenly distributed. In patients with patellofemoral pain syndrome the patella is usually misaligned relative to the femur, which therefore places more stress through the patellofemoral joint during activity. As a result this may cause pain and inflammation to the patellofemoral joint. The misalignment of the patella may occur for various reasons. One of the main causes is an imbalance in strength between two parts of the quadriceps muscle.
The quadriceps muscle comprises of 4 muscle bellies, 2 lie centrally (rectus femoris and vastus intermedius), one lies on the inner leg (vastus medialis) and one lies on the outer leg (vastus lateralis) (figure 2). In the majority of patellofemoral pain syndrome cases, the outer quadriceps (vastus lateralis) is stronger than the inner quadriceps (vastus medialis), resulting in the knee cap being pulled towards the outside of the leg. This may result in abnormal movement of the knee cap when bending and straightening the knee. There are many factors which can cause this strength imbalance of the quadriceps. These need to be identified and corrected by a physiotherapist.
Patellofemoral pain syndrome is a very common condition that is frequently seen in clinical practice, particularly in runners. It often affects adolescents at a time of increased growth and usually affects girls more than boys. In older patients, patellofemoral pain syndrome is often associated with degenerative joint changes. A history of knee injury may increase the likelihood of developing patellofemoral pain syndrome.
Signs and symptoms of patellofemoral pain syndrome.
Patients with patellofemoral pain syndrome usually experience pain at the front of the knee and around or under the knee cap. Pain can sometimes be felt at the back of the knee or on the inner or outer aspects. Patients usually experience an ache that may increase to a sharper pain with activity. Pain is typically experienced during activities that bend or straighten the knee particularly whilst weight bearing. Activities that frequently aggravate symptoms include going up and down stairs or hills, squatting, running or jumping. Occasionally pain may be felt whilst sitting with the knee bent for prolonged periods. There may also be an associated clicking or grinding sound when bending or straightening the knee. Patients may also experience episodes of the knee giving way or collapsing due to pain. In more severe or chronic cases there may be evidence of quadriceps muscle wasting.
There are several factors which can predispose patients to developing patellofemoral pain syndrome. These need to be assessed and corrected with direction from a physiotherapist. Some of these factors include:
- muscle strength imbalances
- muscle weakness (especially the VMO and gluteal muscles)
- tightness in specific joints (hip, knee or ankle)
- tightness in specific muscles (especially the ITB or quadriceps)
- poor lower limb biomechanics
- excessive or inappropriate training or activity
- inappropriate footwear or training surfaces
- poor foot posture
- poor training technique
Physiotherapy or Remedial massage treatment for patellofemoral pain syndrome is vital to hasten the healing process and ensure an optimal outcome. Treatment may comprise:
- soft tissue massage
- taping or bracing to correct patella position
- dry needling
- ice or heat treatment
- progressive exercises to improve flexibility, balance and strength (especially the VMO muscle)
- activity modification advice
- biomechanical correction
- anti-inflammatory advice
- weight loss advice where appropriate
- the use of Real-Time Ultrasound to assess and retrain the VMO muscle
- a graduated return to activity program