What is Patellofemoral Arthritis?
Patellofemoral arthritis is a common reason for pain at the front of the knee. The patellofemoral joint is made up of the patella (kneecap) and the femur (thigh bone). The patella, a round, flat bone, is inside the quadriceps and patella tendons. A layer of fluid-filled sac called a prepatellar bursa separates the patella from the skin. The patella sits in a groove in the femur, and one side is slightly thicker than the other. This joint has four facets, or surfaces, namely the inferior (lower), superior (upper), middle, and medial (inner) vertical.
The kneecap is mainly held in place on the inside by the medial patellofemoral ligament (MPFL). This ligament connects the inner thigh muscle to the kneecap, and it prevents the kneecap from being pulled to the outside. Similarly, the lateral patellofemoral ligament (LPFL) connects the outer thigh bone to the kneecap and prevents the kneecap from being pulled inside. Other ligaments give the joint a steady hold. The large thigh muscles provide additional dynamic stability, helping keep the kneecap from moving side-to-side. Also, the quadriceps tendon near the top of the kneecap creates an angle that adds pressure on the joint. The blood supply to the kneecap comes from six arteries.
The nerve supply to the front of the knee comes from the lateral and anterior cutaneous branches of the femoral nerve as well as an offshoot of the saphenous nerve.
In healthy knees, the cartilage of the patellofemoral joint is thick, up to 7 to 8 mm. This makes it an excellent cushion. A complex network of sugar-proteins reduces the friction and creates a neat surface for bending and extending the knee. The chondrocytes, cells which build and maintain cartilage, regulate the production and breakdown of these proteins based on the needs of the joint.
The function and stability of the kneecap are maintained by both the static and dynamic structures around it. During bending, the kneecap glides within the femur groove acting like a lever to lengthen the function of the femur. Along with this up-and-down movement, the kneecap also has a side-to-side motion moving in a “J” pattern during the extension. The straightness or bow-leggedness of the knee and any twist in the thigh bone or shin bone also influence how the kneecap functions.
What Causes Patellofemoral Arthritis?
Patellofemoral arthritis is a condition where the knee joint degenerates or breaks down over time. This is often caused by the wearing down of the cartilage (cushioning tissue that surrounds the knee cap), a condition known as chondromalacia. The wear and tear of the cartilage can lead to osteoarthritis, a common form of arthritis where the joint cartilage wears away.
Patellofemoral arthritis is counted as a different disease from arthritis affecting other parts of the knee (the inner and outer parts, medically referred to as medial and lateral compartment femorotibial arthritis). It can affect only the knee joint (also known as unicompartmental), or coincide with arthritis in either the inner, outer parts of the knee or both.
People with patellofemoral arthritis often have a history of unstable knees, including knee dislocation or partial dislocation, loose knee, knee cap not aligned properly (often moving towards the outer part of the knee), muscle imbalance, or what’s known as “patella alta” (a condition where the knee cap sits higher than normal). Another cause linked to patellofemoral arthritis is having a surgery called the anterior cruciate ligament (ACL) reconstruction, a surgery done to repair a major knee ligament (ACL) using either a hamstring or patella tendon graft.
Common risk factors for patellofemoral arthritis include age, obesity, a past injury or fracture in the knee, previous knee dislocation or partial dislocation, excessive use due to high-intensity activities such as running or weight training, and having arthritis in other parts of the body. Additionally, people who have systemic inflammatory disorders (conditions causing inflammation throughout the body), such as rheumatoid arthritis, psoriatic arthritis, ankylosing spondylitis, juvenile idiopathic arthritis, and systemic lupus erythematosus, also have a higher risk of developing patellofemoral arthritis.
Risk Factors and Frequency for Patellofemoral Arthritis
Osteoarthritis in the knee is a widespread issue estimated to affect 14 million people in the United States alone. Notably, half of these individuals are under the age of 65. As per a systematic review, half of the individuals suffering knee pain have an associated condition known as patellofemoral involvement, making it a common issue. Studies on post-mortem bodies aged over 65 found presence of patellofemoral osteoarthritis in an overwhelming 79% of cases. Furthermore, over 50% patients that underwent a surgical procedure known as meniscectomy displayed evidence of chondromalacia, a condition related to osteoarthritis.
Signs and Symptoms of Patellofemoral Arthritis
Patellofemoral arthritis commonly leads to knee pain at the front, usually increased by standing, sitting, walking on inclines or stairs, and kneeling. Exercises such as lunges and squats can also exacerbate the pain as these activities put more stress on the joint between the kneecap (patella) and thighbone (femur). Patients might describe popping, cracking, or grinding sensations, as well as stiffening, and a feeling of instability as if the knee could “give way”. They might also refer to previous incidents where the kneecap had slid out of place (subluxation) or dislocated.
During examination, the doctor or healthcare provider might take note of walking patterns to assess the alignment of the foot, knee, lower leg (tibia), or thighbone. In cases of patellofemoral arthritis, common findings may include a forward tilt of the pelvis when walking, increased lateral pelvic tilt on the side opposite to the affected knee, and less hip extension when walking. Quadricep or hamstring muscle atrophy, increased fluid around the joint (effusion), and the inward or outward tilt of the kneecap may be observed. The practitioner usually checks how the kneecap moves during extension and flexion of the knee.
Examining the joint by feel during passive bending and straightening can identify a crackling sound or grating sensation (crepitus), which often suggests patellofemoral arthritis. Tenderness might be found around the medial or lateral parts of the kneecap or on the corresponding parts of the thighbone. The Clarke test, where the patient is asked to contract their quadricep muscle against resistance applied on the kneecap, helps in the diagnosis. Pain in the knee joint signifies a positive test. The provider may also move the kneecap while applying pressure from the back or perform the patellar apprehension test (a lateral force is applied to the patella with knee angulation) to check for knee pain reactions and knee cap laxity or mobility.
Testing for Patellofemoral Arthritis
Standard X-rays are usually enough to examine the patellofemoral joint, which is located at the front of the knee, where the thighbone (femur) and kneecap (patella) meet. From these images, doctors can assess different aspects like signs of arthritis such as joint space narrowing or bone spurs (osteophytes), changes in the kneecap, and health of the bone beneath the cartilage (subchondral sclerosis). They take front (AP), side (lateral), and top-down (axial) views for a complete evaluation.
The side view can help evaluate the position of the kneecap while axial view (also known as the “merchant” or “sunrise” view) can examine the kneecap alignment, the depth of the groove the kneecap moves in, and signs of arthritis. Both these views can also assess the patellofemoral joint space to look for arthritis. Another useful view, called the Rosenberg or AP view, is best used to examine the compartments of the knee. It is estimated that arthritis in the patellofemoral joint can be seen in as many as 34% of women and 19% of men aged 55 or older.
X-rays can be used to measure specific changes in the kneecap in cases of suspected patellofemoral arthritis. For instance, the sulcus angle, which should typically be about 138 degrees, or the congruence angle, often around negative 6 degrees, which can indicate lateral (sideways) movement of the kneecap.
Additionally, the Insall-Salvati ratio, which compares the length of the ligament in front of the kneecap to the length of the kneecap itself, can help assess for patella alta, a condition where the kneecap sits too high. The patellofemoral index ratio compares the distance between the spaces on the inside and outside of the kneecap.
If a diagnosis is unclear from X-rays, a CT scan can provide a more detailed view of the patellofemoral joint. However, this isn’t usually necessary for most patients who already have known or suspected arthritis. A CT scan might be used to identify issues like kneecap dislocation to the side or abnormal shapes of the thigh’s groove. If there’s been trauma or a suspected injury to the kneecap or its surrounding ligaments, doctors would likely choose MRI as the preferred imaging study.
Ultrasound might be used in situations where X-rays are not available, but its ability to diagnose patellofemoral arthritis is limited due to its inability to view the side of the kneecap that connects to the joint. In some cases, arthroscopy, a minimally invasive surgical procedure, can be used both for diagnosis and treatment.
In certain cases, if the patient’s symptoms suggest, doctors might consider inflammatory diseases as possible causes of patellofemoral arthritis. Specific blood tests for diseases like Lyme disease, rheumatoid arthritis, and gonococcal arthritis may be conducted when deemed appropriate.
Treatment Options for Patellofemoral Arthritis
Patellofemoral arthritis, a type of knee arthritis affecting the front of the knee, can be challenging to treat due to various causes and the complexities of cartilage regeneration. Most of the time, treatment doesn’t involve surgery, and patients are recommended to follow conservative treatment methods.
Physical therapy is a primary way to manage this condition. It can help reduce knee pain by strengthening specific muscles in the thigh (like the vastus medialis), and stretching the tissues around the kneecap. Improving these areas can enhance knee joint movement and alignment. Interestingly, many people with knee pain, including those with patellofemoral arthritis, report significant pain reduction or even complete relief after a few months of physical therapy. Apart from therapy, losing weight and modifying daily activities that cause stress to the front of the knee can help alleviate pain.
Over-the-counter pain relievers, like NSAIDs and acetaminophen, can help manage the pain. Supplements like glucosamine and chondroitin sulfate may also ease knee pain. In some cases, doctors might recommend injections into the knee joint to soothe the symptoms. An option could be corticosteroids, which have proven to be quite effective. Other types of injections are also available, but their effectiveness varies from person to person.
Applying a special type of tape (kinesio-tape) to the knee can provide relief by preventing the kneecap from moving towards the outside of the leg. This technique is often referred to as McConnell taping. Wearing simple knee sleeves or specialized braces can also help, but they might not work for everyone.
For some patients, surgical treatment can be a choice, especially if conservative treatments haven’t been effective. Surgical options could include a minor procedure to clear out damaged cartilage (arthroscopy), or procedures to adjust the alignment of the knee cap. Another surgical procedure, called tibial tubercle osteotomy, involves shifting a bony part of the shinbone to reduce pressure on the knee cap, which can ease pain.
There are also more complex surgical procedures aimed at regenerating or replacing the knee cartilage, but these are typically reserved for severe cases or those patients who have not benefited from other treatments. One such procedure, autologous chondrocyte implantation, involves transferring cartilage from one area of the knee to another. Placement of a prosthetic knee cap (patelloplasty) or total knee replacement might be suggested for certain patients with advanced arthritis. However, total knee replacement is usually kept for older patients with extensive knee arthritis.
What else can Patellofemoral Arthritis be?
When a doctor is trying to diagnose patellofemoral osteoarthritis, there are a number of other conditions that she or he needs to consider. These conditions can cause similar symptoms to patellofemoral osteoarthritis, so they need to be ruled out to make an accurate diagnosis. The conditions include:
- Primary or secondary osteoarthritis
- Iliotibial band syndrome
- L3-L4 radiculopathy (disc herniation)
- Tendonitis (quadriceps, patella)
- Neuroma
- Crystal arthropathy (gout, pseudogout)
- Infectious arthropathy (Lyme disease, septic, gonococcal)
- Inflammatory arthropathy (rheumatoid, psoriatic, seronegative)
Making the correct diagnosis is very important, so the doctor may perform a variety of tests to ensure that the diagnosis of patellofemoral osteoarthritis is accurate.
What to expect with Patellofemoral Arthritis
The outlook for patients with patellofemoral arthritis, a type of knee arthritis, can differ significantly. In general, it’s a condition that tends to worsen over time and may require increasingly aggressive treatment as the wear and tear on the knee joint continues to progress.
Younger patients or those who are otherwise healthy can often manage their symptoms successfully with conservative treatments. This means they can continue with their daily activities without significant disruption. However, for some patients, the condition may be more advanced.
Patients with more advanced disease, those who also have issues with the femorotibial joint (another part of the knee), those who are obese, or those dealing with other chronic health conditions may generally need more aggressive management strategies.
Possible Complications When Diagnosed with Patellofemoral Arthritis
For patients who have chosen not to undergo surgery, complications can include continued pain, joint instability, as well as a worsening of their condition over time. For those who have had surgical treatments, potential complications include infection, weak quadriceps muscles, loss of regular functionality, and continued pain even after the operation. There is also a possibility that patients may develop a type of arthritis called femorotibial osteoarthritis which could require a total knee replacement.
Potential Complications:
- Continued pain
- Joint instability
- Worsening of the condition over time
- Infection after surgery
- Weak quadriceps muscles
- Loss of regular functionality
- Persistent pain even after surgery
- Development of femorotibial osteoarthritis
- Potential need for a total knee replacement
Recovery from Patellofemoral Arthritis
The recovery process for patellofemoral arthritis, whether you had surgery or not, usually involves strengthening certain muscles in the thigh, hip, and core. Specifically, it targets the ‘vastus medialis oblique’ – a specific thigh muscle involved in leg movement. The aim of this is to reduce the ‘Q angle’ which is the angle between your thigh and lower leg, move the kneecap (patella) more towards the outside, and enhance the movement in the ‘trochlear groove’ – a natural depression in the thigh bone where the kneecap slides up and down. If you have had surgery, your surgeon will have special instructions tailored to the specific surgical procedure performed.
Preventing Patellofemoral Arthritis
The most effective way to deal with patellofemoral arthritis, a type of knee arthritis, is to prevent it from happening in the first place. This includes taking steps to keep key muscle groups – like the quadriceps (the large muscles in front of the thighs), hip, and core (muscles in your abdomen and back) – strong.
For those already experiencing knee pain due to this type of arthritis, altering their activities can help slow down the progress of the disease. This could mean performing lower impact exercises or avoiding certain activities that aggravate the knee pain.
Maintaining a healthy body weight is also important as it reduces the amount of stress and strain on the patellofemoral joint, which is where the kneecap (patella) and the thigh bone (femur) meet. The less pressure there is on this joint, the slower the disease might progress.