Knee Cap Problems

Diagram of a normal patella

What Is The Knee Cap?

The patella or knee cap forms part of the knee joint. It sits at the front of the knee. As the knee bends and straightens the patella glides within a groove or notch on the femur called the trochlea. This articulation is called the patella-femoral joint. Both surfaces of the joint – the groove and the knee cap – are covered with smooth articular cartilage which enables your knee to bend in a low-friction way.

The patella is embedded between two tendons: the quadriceps tendon above and the patella tendon, which extends from the lowest point of the patella to the tibia (shin bone).

Most people who have problems around the knee cap experience pain or a feeling of instability.

Pain At The Front Of The Knee

Pain at the front of the knee (anterior knee pain) is common and can be caused by a variety of conditions including injury to the joint, arthritis, maltracking of the patella (i.e. where the knee cap does not remain in its groove) or softening of the articular cartilage. Of these, instability or maltracking are the most common.

What Causes Pain Around The Knee Cap?

Anterior or patello-femoral pain is a poorly understood but very common clinical complaint. It can be caused by a variety of conditions including damage to the cartilage of the joint and problems relating to the soft tissue around it.

Pain at the front of the knee is often made worse by activities which involve flexing the knee. In daily activities you might find your symptoms become worse when descending stairs or hills, although this is not exclusive to patello–femoral disorders.

Patello femoral pain - patella knee condition
Healthy knees following successful knee surgery

How Do You Diagnose Anterior Knee Pain?

Many patients with pain at the front of the knee can find the condition is significantly improved with non-surgical treatment.

After taking a full history of the problem, your knee surgeon will examine the knee to look at the tracking of the patella, the strength of the muscles above the knee, the tightness of the tissues around the patella and areas of tenderness. We may also use specific tests to assess the patello-femoral joint.

Often we will need to take x-rays of the knee, sometimes using multiple views. We may also require MRI or CT scans.

After examination, one potential outcome is a diagnosis of anterior knee pain syndrome (AKPS). This means there is no identifiable cause of the pain. The important thing is that AKPS should only be diagnosed when all other possibilities have been excluded.

How Do You Treat Knee Cap Pain?

The majority of pain at the front of the knee can be resolved without surgery. This treatment is directed at improving the balance of the patella at the front of the knee and normally involves physiotherapy and a home exercise programme.

Occasionally you may require surgery. The size and the extent of surgery will vary according to the underlying problem. We may perform this arthroscopically (that is, via keyhole surgery) or, in some cases, via a larger open operation.


Knee injury physio treatment
Patella Osteoarthritis
Patella Osteoarthritis x-rays

What Is Patella Osteoarthritis?

Wear and tear (osteoarthritis) can affect the patello-femoral joint in isolation or more commonly be a part of a generalised process that affects the whole of the knee joint.

Less than 5% of people with osteoarthritis of the knee joint have it affecting solely the patello-femoral joint.

The treatment principles are the same as for other knee arthritis and sometimes joint replacement is required.

If the arthritic changes are confined to the patello-femoral joint, your knee may be suitable for a partial rather than full knee replacement.

What Is Patella Instability?

Patients with patella instability report a number of common symptoms. They often complain of lacking confidence in their knee and/or experience the sensation of the patella sliding out of the joint.

There are several types of abnormalities that may give rise to this problem. The patella may develop a tracking or centring problem within the joint, it may partially slip out of the trochlear groove or it may completely dislocate from it.

Talk to us about treatment for your knee problem
Patella Tracking - patella instability problems

Patella Tracking

A tracking problem occurs when the patella no longer remains centred in the trochlear groove.

There are three main factors responsible for keeping the patella in its groove. Absence or loss of any of them can increase the risk of instability:

1. Bones: the shape and size of the groove and the patella can cause tracking problems. The groove may be shallow or absent. In addition, some people have a “high” patella and this may make it more unstable.
2. Ligaments:  the medial patello-femoral ligament is attached to the inner side of the patella. It acts like a check rein, stopping the patella moving outwards too far, but damage to the ligament can cause problems.
3. Muscles:  several muscles act across the knee, including the VMO muscle of the quadriceps and the hamstring. These need to remain balanced to keep the patella centred.

Problems with any one of the above three factors might cause the patella to track towards the outside of the trochlear groove.

Patella Dislocation

Partial dislocation:

Partial dislocation is known as subluxation. Here the patella slips to a point where you may feel that the joint is unstable, but restricting movement of the joint may prevent further displacement. You may, however, experience further episodes of patella subluxation and this can often affect confidence in the knee joint.

Many patients feel forced to avoid certain activities as a consequence, which makes treatment the preferred option.

Patella Dislocation & Subluxation patella problems


Full dislocation tend to occur in two groups of patient:

Post-traumatic instability: these are patients who had a normal knee until an injury. For instance, some injuries sustained in contact sports may force the patella to dislocate outwards. The bones are normal, but an important stabilising ligament is torn and the muscles may be weak. Recurrent episodes of dislocation may occur in the future following the initial injury.

Developmental instability: Unfortunately, some patients, particularly adolescent girls, are prone to patella instability. The most common cause is an absent, or even domed, trochlea groove combined with a high patella. This means that there is an inborn high risk for the patella to be unstable. Poor muscles and a weak or stretched MPFL may be the last straw.

Anatomy of the Knee - joints
Physiotherapy can be beneficial before & after treatment

How Do You Treat A Dislocated Knee Cap?

The first step is an accurate diagnosis and an assessment of any associated secondary injuries to cartilage or bone.

Following diagnosis, a supervised course of physiotherapy normally returns most individuals to pre-injury levels of activity. The muscles can be toned and balanced to improve tracking and stability.

Recurrent episodes of dislocation of the patella need specialist assessment to establish the underlying cause. An abnormality of the bones and soft tissues of the hip, knee, foot and ankle can all contribute to persistent problems. Therefore, it is essential that you have a full assessment.

Initial treatment is non-operative and addresses muscle imbalances. You may need surgery to address ongoing problems including soft tissues or bone abnormalities. This will require a detailed discussion with your knee surgeon.

The various surgical treatments may include one or more of:


Repair of muscle inner aspect (VMO tightening)


MPFL reconstruction


Tibial tuberosity transfer- moving it inwards to improve tracking


Trochleoplasty – deepening of the trochlear groove

Orthopedic Surgeons Performing Knee Surgery

Pain At The Front Of The Knee?

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