knee/ Patellofemoral pain syndrome

What is patellofemoral pain syndrome?

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) usually as a result of inflammation or tissue 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) (figure 1). 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 (figure 1). 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.

Figure 1 - Relevant Anatomy for Patellofemoral Pain Syndrome

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 tissue damage and inflammation to structures of the patellofemoral joint (such as cartilage or connective tissue), with subsequent patellofemoral pain. When this occurs, the conditions is known as patellofemoral pain syndrome.

In patients with patellofemoral pain syndrome, 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 numerous factors which can cause this strength imbalance of the quadriceps (such as abnormal lower limb biomechanics, pain inhibition etc.). These need to be identified and corrected by a physiotherapist. 

Figure 2 - Quadriceps Muscle (N.B. vastus intermedius lies deep to rectus femoris and is therefore not shown)

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.

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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. In less severe cases, patients may only experience an ache or stiffness in the knee that increases with rest (typically at night or first thing in the morning) following activities that place stress on the patellofemoral joint. These activities typically include excessive walking (especially up and down stairs or hills or on uneven surfaces), heavy lifting (particularly with knees bent), deep squatting, lunging, kneeling, running, hopping, jumping, or other activities that bend and straighten the knee during weight bearing. The pain associated with this condition may also warm up with activity in the initial stages of injury. As the condition progresses, patients may experience symptoms that increase during sport or activity, affecting performance. Symptoms typically increase on firmly touching the margins of the patellofemoral joint.

Occasionally, patients with this condition may experience pain 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. In more severe cases, patients may walk with a limp and sometimes may experience episodes of the knee giving way or collapsing due to pain. In chronic cases there may be evidence of quadriceps muscle wasting (particularly of the vastus medialis).

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Diagnosis of patellofemoral pain syndrome

A thorough subjective and objective examination from a physiotherapist is usually sufficient to diagnose patellofemoral pain syndrome. Investigations such as an X-ray or MRI may be used to assist with diagnosis.

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Prognosis of patellofemoral pain syndrome

Most patients with this condition heal well with appropriate physiotherapy and return to normal function in a number of weeks. Occasionally, rehabilitation can take significantly longer and may take many months in those who have had their condition for a long period of time. Early physiotherapy treatment is vital to hasten recovery in all patients with this condition.

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Contributing factors to the development of patellofemoral pain syndrome

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) 
• excessive or inappropriate training or activity 
• inadequate recovery periods from training or activity
• inappropriate footwear or training surfaces 
• poor training technique
• a shallow femoral groove (i.e. the groove that the knee cap sits within) 
• genu valgum ('knock knees') 
• femoral anteversion (where the thigh bones turn inward) 
• patella alta (abnormally high patella in relation to the thigh bone) 
• poor lower limb or foot biomechanics (e.g. flat feet, high arches or increased Q angle) 
• poor balance 
• poor pelvic or core stability 
• poor landing strategies 
• poor coordination 
• gender (i.e. greater likelihood in females) 
• a current or past lower limb injury (particularly the knee) that has been poorly rehabilitated

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Physiotherapy for patellofemoral pain syndrome

Physiotherapy treatment for patellofemoral pain syndrome is vital to hasten the healing process and ensure an optimal outcome. Treatment may comprise: 

• soft tissue massage 
• electrotherapy 
• the use of crutches 
• patella taping or bracing to correct patella position 
• foot taping to improve foot posture and biomechanics
• joint mobilization 
• dry needling 
• ice or heat treatment 
• progressive exercises to improve flexibility, balance and strength (especially the VMO muscle) 
• activity modification advice 
• biomechanical correction (e.g. the prescription of orthotics)
• 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

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Other intervention for patellofemoral pain syndrome

Despite appropriate physiotherapy management, some patients with patellofemoral pain syndrome do not improve. When this occurs the treating physiotherapist or doctor can advise on the best course of management. This may include pharmaceutical intervention, corticosteroid injection, further investigation such as an X-ray, MRI or CT Scan or a referral to a sports doctor or orthopaedic specialist who will advise on any procedures that may be appropriate to improve the condition. A review with a podiatrist may also be indicated for the prescription of orthotics to correct any foot posture abnormalities.

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Exercises for patellofemoral pain syndrome

The following exercises are commonly prescribed to patients with this condition. You should discuss the suitability of these exercises with your physiotherapist prior to beginning them. Generally, they should be performed 2 - 3 times daily and only provided they do not cause or increase symptoms.

Your physiotherapist can advise when it is appropriate to begin the initial exercises and eventually progress to the intermediate, advanced and other exercises. As a general rule, addition of exercises or progression to more advanced exercises should take place provided there is no increase in symptoms.

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Initial Exercises

Static Quadriceps Contraction

Tighten the muscle at the front of your thigh (quadriceps) by pushing your knee down into a towel (figure 3). Put your fingers on your inner quadriceps (vastus medialis – figure 2) to feel the muscle tighten during contraction. Hold for 5 seconds and repeat 10 times as hard as possible without increasing your symptoms.

Figure 3 – Static Quadriceps Contraction (left leg)

Adductor Squeeze (Supine)

Begin this exercise lying on your back in the position demonstrated with a Pilates ball or rolled towel between your knees (figure 4). Tighten your thigh muscles (quadriceps) by straightening your knees and then slowly squeeze the ball between your knees tightening your inner thigh muscles (adductors). Hold for 5 seconds and repeat 10 times as hard as possible and comfortable provided the exercise is pain free.

Figure 4 – Adductor Squeeze (Supine)

Knee Bend to Straighten

Bend and straighten your knee as far as you can go without pain and provided you feel no more than a mild to moderate stretch (figure 5). Gradually increase movement as tolerated provided the exercise is pain free. Repeat 10 - 20 times provided there is no increase in symptoms.

Figure 5 – Knee Bend to Straighten (left leg)

Hip Extension in Standing

Begin this exercise standing at a table or bench for balance. Keeping your back and knee straight, slowly take your leg backwards, tightening your bottom muscles (gluteals) (figure 6). Hold for 2 seconds then slowly return to the starting position. Repeat 10 times provided the exercise is pain free.

Figure 6 – Hip Extension in Standing (right le