Patellofemoral joint (knee cap) pain and arthritis

Patellofemoral joint arthritis

Patellofemoral joint (PFJ) pain and PFJ arthritis

The patellofemoral joint is the part of the knee joint just behind the knee cap. Arthritis (osteoarthritis) refers to the wear and tear changes that usually happen with time and result in thinning or loss of the articular cartilage. The cartilage is the protective tissue that covers the bones at the joints, responsible for smooth and frictionless movement. Patellofemoral joint problems usually result in pain felt at the front of the knee (just behind the knee cap). Sometimes, the pain can be hard to pinpoint and felt as deep pain within the knee. The pain can be worse after periods of inactivity and can be associated with clicking. Overall, Patellofemoral joint osteoarthritis accounts for approx. 8% of all cases of osteoarthritis.

What factors can predispose for PFJ arthritis?

The risk factors for developing patellofemoral arthritis include:

Femoral and patellar structure and position: The patellofemoral joint is formed by the articulation between the femur (the long leg bone) and the patella (the knee cap). Thus, altered anatomy to either of these can increase the stress upon the patellofemoral joint leading to osteoarthritis. Such conditions would include changes at the hip level, like change in the normal angle at the upper end of the femur bone (referred to as femoral anteversion), and change in the normal anatomy and alignment of the patella (referred to as patellofemoral dysplasia).
Certain activities like running and jumping can result in repetitive overloading of the patellofemoral joint and predispose it to arthritis.
Weight (High body mass index)
Age. As with other degenerative conditions, patellofemoral arthritis increases with age and is more common in people over 50. Studies also showed a slightly increased incidence in females.

What are the symptoms of patellofemoral joint osteoarthritis?

The usual symptoms of patellofemoral joint arthritis are:

Pain at the front of the knee, usually worsened by walking, squatting and stair climbing. The pain can be associated with swelling around the patella.
Pain and stiffness after inactivity. Typically, patellofemoral pain is worse first thing in the morning or after prolonged periods of inactivity.
A clicking sensation or audible click coming from the patella on bending the knee or performing the above-mentioned activities. This can be intermittent.

What other knee conditions can mimic patellofemoral joint osteoarthritis?

Other conditions that can cause pain at the front of the knee and can be mistaken for PFJ pain include:

Knee joint osteoarthritis

Fat pad inflammation

Patellar tendinosis (Jumper’s knee)

Iliotibial (IT) band friction syndrome (Runner’s knee)

Pes anserine bursitis

For see our article about pain at the front of the knee for more information.

Patellofemoral joint pain vs patellar tendinopathy

Patellofemoral joint pain is felt at the front of the knee (just behind the knee cap). Sometimes the pain can be deep in location and difficult to pinpoint. In comparison, patellar tendinopathy pain is very local and usually felt just below the knee cap (as this is where the tendon attaches to the patella and is most prone to inflammation here). Deep palpation (pressing) of the patellar tendon at the front of the knee just below the knee cap usually worsens the pain.

How is patellofemoral joint arthritis diagnosed?

Usually, the diagnosis is suspected clinically and confirmed by a knee X-ray. The X-ray is usually very useful in confirming the diagnosis and assessing the severity of the osteoarthritis. Diagnostic musculoskeletal ultrasound can also help assess for patellofemoral joint osteoarthritis. Furthermore, Ultrasound is an excellent tool to assess for the presence of fluid within the knee joint (referred to as effusion) or joint inflammation (referred to as synovitis).

Ultrasound can also assess the surrounding structures for any other problems, such as

Patellar tendinosis (Jumper’s knee)

Iliotibial (IT) band friction syndrome (Runner’s knee)

Pes anserine bursitis

What is the treatment for patellofemoral joint pain?

Most patellofemoral joint pain responds to physiotherapy. The physiotherapy course may involve strengthening exercises and a progressive loading programme aiming to increase strength and improve leg mechanics. The treatment also includes avoiding aggravating factors, taping techniques to reduce the pain, anti-inflammatory tablets and ice packs to help reduce joint inflammation.

Patellofemoral joint ultrasound guided injection

Can I have a knee injection for patellofemoral joint (PFJ) arthritis?

If there is inadequate response from conservative treatment, an ultrasound-guided injection might be helpful. Injection therapy can be very useful to settle down the inflammation (and subsequently the pain), allowing you to undertake a rehabilitation program. One injection option is ultrasound guided steroid injection. Corticosteroids are potent anti-inflammatory medicines and usually provide rapid pain relief. They are usually followed by physiotherapy treatment to utilise the pain relief window achieved by the injection. Hyaluronic acid injections are an alternative to corticosteroids, and they are based on a naturally occurring substance within our bodies and joint. Hyaluronic acid injections have been shown effective in managing knee arthritis. More recently, platelet-rich plasma (PRP) injections have been used for the treatment of PFJ osteoarthritis. The PRP is obtained by taking a blood sample from the patient. Then, this will be spun in a centrifuge to separate the different components, including the plasma which is rich with growth factors. After that, the plasma is injected into the knee joint. PRP injections work by reducing inflammatory cells, thereby improving pain and function. In ultrasound guided patellofemoral joint injections, the ultrasound is used to visualise the needle, guiding it accurately to the targeted area. There is plenty of evidence showing that doing these injections under ultrasound guidance is more accurate, less painful and produce better results compared to non-guided injections.