Patellofemoral Syndrome (Runner’s Knee)

Anatomy

The patellofemoral joint is one of the knee joints. The main knee joint is formed between the thigh bone (femur) and the shin bone (tibia). The patella (kneecap) and the femur form another joint called the patellofemoral joint.
The patella (kneecap) itself is embedded in the quadriceps tendon (insertion point of the quads muscle) The quadriceps tendon is attached to the thigh muscle (quadriceps) at it’s upper end and to the tibia (shin bone) at it’s lower end.

As the quadriceps muscle contracts (shortens) it pulls the patella (kneecap) which in turn pulls on the shin bone which causes the knee to straighten. There are grooves located on the front of the thigh bone (femur) in which the patella sits. As the knee moves, the patella is designed to glide up and down within these grooves.

How injury occurs

Patellofemoral syndrome (runner’s knee) results from physical and biomechanical changes in the patellofemoral joint. These changes result in abnormal movement of the patella (kneecap) when the knee is being bent. This abnormal movement is commonly referred to as a tracking problem.

The abnormal movement or tracking problem basically means the kneecap isn’t gliding in the grooves of the thigh bone (femur) as it’s meant to when the knee bends. It’s gliding off centre. Pain arises due to increased pressure or friction on the underside of the kneecap as it glides incorrectly.

This abnormal movement is usually due to an imbalance developing between the muscles and ligaments on the outside of the knee and the muscles and ligaments on the inside of the knee.

If the lateral structures (those on the outside of the knee) namely the vastus lateralis, lateral ligaments and the iliotibial band, become tight and the medial structures (those on the inside of the knee), namely vastus medialis, becomes weak, the kneecap is pulled laterally as the knee bends causing pain.

Overloading

When participating in weight bearing exercise such as running (or sports that involve running), any increase in the amount of knee flexion (knee bending) will increase the load around the patellofemoral joint.

Increases in knee flexion can be caused by:

• Adding more hills/stairs while running
• Increasing the speed of running
• Increasing the frequency of training or running sessions per week.
• Introducing new exercises to training sessions such as jumping or bounding.

All things being equal, the patellofemoral joint should be able to cope with this increase in load. However, in most situations there are underlying factors present which contribute to patellofemoral pain arising when the joint is overloaded.

These underlying factors can be present for some time, but it is not until the patellofemoral joint is overloaded that they contribute to the development of pain.

Underlying Factors:

1.’Squinting Patellae’

This is when both kneecaps face inward (medially) due to inward rotation of the femur (thigh bone).

This inward rotation is exaggerated when running thereby altering the position of the kneecap and causing it to ‘track’ insufficiently.

The most common cause of increased rotation is lack of strength around the hip – in particular the hip external rotators and hip abductors.

2. Pronated Feet

Pronated or ‘flat feet’.

Pronation causes prolonged inward rotation of the lower leg and may force the patella out of it’s femoral groove. This in turn causes increased stress to the patellofemoral joint causing pain.

3. Increased Q angle

The ‘Q Angle’ (Quadriceps Angle) refers to the angle formed by two intersecting lines:

1. Line from the middle of the patella to the ASIS (a point on the pelvis where the upper quadricps attach) This line represents the line of pull of the quads muscle.

2. Line from the tibial tubercle (a point on the shin bone just below the kneecap) to the middle of the kneecap. This line represents the pull of the patellar tendon (often called the quadriceps tendon). This tendon is a band of tissue which connects the shin bone to the kneecap.

The normal measurement:
> 15 degrees for men
> 20 degrees for women

A larger than normal Q-angle can contribute to patella tracking problems. When the quads contract they pull the kneecap sideways which can cause increased pronation at the foot and inward rotation of the leg ultimately altering the biomechanics around the knee.

An increased Q-angle can be caused by many things including a tight hip joint and a weakness in the hip external rotator and abductor muscles and weakness of the quadriceps and or hamstring muscles.

4. lack of Flexibility

Tight muscles can limit joint motion and cause abnormal movement patterns.

Typically patellofemoral joint syndrome is associated with:

• Tight hamstrings: Limits knee flexion (bending) and can lead to increased load on the patellofemoral joint but also increase load on gluteal muscles
• Increased load on the gluteals puts them under increased tension with subsequent increased tension on the iliotibial band
• Tight rectus femoris will affect the movement of the kneecap during knee flexion (bending)
• Tight hamstrings can lead to increased dorsiflexion with running, increasing the amount of pronation at the foot in order to absorb shock, resulting in external rotation of the tibia, increased patellofemoral stress and increased Q-angle
• Tight iliotibial band will pull the patella laterally during knee flexion
• Tight calf muscles (gastrocnemius) restricts the range of motion at the ankle joint resulting in compensatory pronation at the foot.

5. VMO (vastus lateralis obliquus) Insufficiency

The quadriceps muscles are comprised of four muscles. If the VMO (inner part of the quads) is weak or the timing of the contraction of VMO is delayed, it can’t counteract the pull of the Vastus Lateralis (outer part of the quads) and therefore the kneecap is pulled laterally.

Correct muscle function requires both strength and co-ordination. Qalking and running requires a series of finely co-ordinated muscle contractions. If muscles aren’t co-ordinated efficiently, a muscle imbalance occurs.

Symptoms

Patellofemoral syndrome classically has a gradual onset. The isn’t one single episode or event that marks the beginning of the condition.

Pain is generally felt in and around the kneecap and is poorly localised. In some cases pain can be felt at the back of the knee.

There can be a feeling of the knee giving way and in some cases a locking sensation.

Pain is usually made worse by:

• Stairs and hills. Walking down is often more painful than walking up
• Prolonged sitting with knees bent (‘movie goer’s knee)
• Sporting activities
• Both knees can be affected
• Onset of pain after activity can be delayed – as late as the next day.

Rehabilitate

In order to fully recover from patellofemoral syndrome, the contributing factors need to be identified and properly addressed.

A skilled physiotherapist can properly diagnose the problem and identify the contributing factors. Treatment will then focus on addressing the problems found on examination.

Techniques a physiotherapist may use include:

• Stretching
• Massage
• Taping of the kneecap
• Mobilisations of the kneecap
• Discussing appropriate footwear
• Avoiding aggravating activities
• Planning an alternate training programme to do while recovering which may include swimming
• Strength programme addressing the key muscle weaknesses

The Home Program

“Rehabilitation of patellofemoral syndrome is aimed at restoring the normal mechanics around the kneecap” A home exercise programme is an essential part in ensuring full recovery is achieved.

Prevention

Once the pain of patellofemoral syndrome has subsided, the challenge is to remain pain free. By addressing all likely weaknesses and areas of inflexibility, the chances of the problem occurring again are reduced.

Strengthening core muscles results in more efficient movement for the lower limb, aiding recovery and decreasing further injury.

Perform

We all like to perform at our best. In order to make the return to sport following injury a success agility retraining is required. This ensures the athlete is gradually reintroduced to the demands of sport and any sign of symptoms returning can be addressed. Agility drills help to prepare the athlete for return to their sport, prevents serious injury and increases performance ensuring the athlete can continue to perform at their best.

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"Rehabilitation for Patellofemoral Syndrome"