Arthritis of the knee cap, also called patellofemoral arthritis, is a common cause of pain at the front of the knee. The cartilage behind the knee cap (patella) begins to wear out. When the cartilage is worn out, the bone rubs against the lower leg (femur), causing pain.
What is the patellofemoral joint?
The patellofemoral joint is part of the knee joint. It lies between the kneecap and the femur. When the knee bends, the knee cap glides on the femur, allowing smooth movement.
How do we diagnose arthritis in knee cap?
Generally, arthritis in knee cap causes the following symptoms:
- Pain under the knee cap, usually worse after sport or prolonged sitting
- Grinding or clicking with the movement of the knee
- Swelling of the knee joint
Importantly, your doctor must exclude other causes of pain in the front of the knee. Examples include patellar tendonitis, fat pad impingement, pes anserine bursitis, and meniscal tears.
Often, imaging is helpful to confirm the diagnosis. For example, an X-ray, ultrasound, or MRI can examine the health of the patellofemoral joint and diagnose patellofemoral arthritis. These investigations can also exclude other causes of pain in the front of the knee.
What are the treatment options for patellofemoral arthritis?
Generally, we manage most knee cap arthritis pain with simple conservative measures. Firstly, exercise therapy should be the basis of treatment. Examples of exercise treatments that are effective include:
- Strengthening of the hip and knee
- Stretching of the muscles around the hip and leg
- Taping or bracing of the kneecap
- Using proper shoes and orthotics
- Medications such as ibuprofen
Sometimes, we use injections to help with knee cap arthritis pain in complex cases. Generally, injection options include cortisone, hyaluronic acid, platelet-rich plasma, and Arthrosamid.
Finally, surgery should only be considered when all other treatments have failed. Joint replacement is the only effective surgical treatment for knee cap arthritis. However, the success of patellofemoral joint replacement is only 65%, which is considerably less than a traditional total knee replacement. You should avoid keyhole surgery for arthritis behind the kneecap, as evidence suggests it does not work.
More on injections for patellofemoral arthritis
Injections for knee cap arthritis can help in complex cases.
Cortisone injection for patellofemoral arthritis
Traditionally, we have used cortisone injections for arthritis pain and swelling. However, we know that cortisone injections are only a short-term fix. Generally, these positive analgesic effects only last for three months. A recent study found that cortisone injections were similar to placebo injections for knee arthritis at six months. Also, there are a few concerning trends with repeat cortisone injections, such as the potential to accelerate arthritis.
Overall, we should avoid cortisone injections in most arthritis cases. Cortisone injections for patellofemoral arthritis should be reserved for acute knee pain and swelling, which fail to settle with non-injection treatments.
Hyaluronic acid injection for patellofemoral arthritis
Next, we use hyaluronic acid injections.
Hyaluronic acid is a natural substance found in bones, tendons, and joints. Injecting hyaluronic acid into joints reduces inflammation and pain associated with patellofemoral arthritis. In addition, unlike cortisone, the effect can last 6-12 months. Also, hyaluronic acid does not have the adverse effects on cartilage that cortisone has.
Generally, we suggest using a high-molecular-weight hyaluronic acid due to its increased potency and more significant duration of effect. Durolane is an example of such a hyaluronic acid.
PRP injection for patellofemoral arthritis
Some doctors use platelet-rich plasma or PRP injections.
We get PRP from whole blood. We spin the blood in a centrifuge and separate the red and white cells. Then, the plasma is injected into the knee joint. We think PRP reduces inflammatory cells, improving pain and function.
Overall, recent evidence suggests that PRP may be a bit better than hyaluronic acid. However, you often need more than one injection. Studies suggest two injections separated by 1-2 weeks are best for knee arthritis, although patellofemoral arthritis responds less well to PRP.
Arthrosamid for patellofemoral arthritis
Arthrosamid is a non-degradable implant we inject into the knee joint to reduce pain and swelling from arthritis. The knee joint lining absorbs the implant, causing reduced joint swelling.
It is a more expensive but potentially longer-lasting injection. However, we are still awaiting longer-term data showing Arthrosamid works better and longer than hyaluronic acid or PRP.
Other frequently asked questions about patellofemoral arthritis:
Is chondromalacia arthritis?
Yes. Chondromalacia is a term for the softening of the back of the patella cartilage. It is a mild form of degenerative change in the patellofemoral joint, similar to early patellofemoral arthritis.
Patellofemoral joint injection: Which is best?
For acute pain, we suggest a cortisone injection. However, a high molecular weight hyaluronic acid such as Durolane is better for longer-term pain relief.
Final word from Sportdoctorlondon about arthritis in the knee cap
Knee cap arthritis is a common cause of pain in the front of the knee. Overall, most people improve with physiotherapy. Sometimes, we use injections to help. Generally, we recommend you start with a high-molecular-weight hyaluronic acid injection such as Durolane. Finally, you should avoid surgery unless you are thinking about joint replacement. Keyhole (arthroscopy) surgery does not work.
Very helpful info thanks so much