Patellofemoral arthritis (PFOA) is a form of degenerative joint disease affecting a specific compartment of the knee. Arthritis involves the breakdown of smooth cartilage in a joint, which leads to pain and restricted movement. PFOA specifically targets the area where the kneecap interacts with the thigh bone, making it a distinct entity from other types of knee arthritis. It is a common cause of pain at the front of the knee and can occur in isolation or alongside arthritis in other parts of the joint.
Where Patellofemoral Arthritis Occurs
The knee is a complex joint with three main sections, and PFOA is centered in the compartment at the front. This joint is formed by the patella (kneecap) and the trochlear groove, a channel located on the end of the femur (thigh bone).
Both the back surface of the kneecap and the trochlear groove are covered with a layer of smooth, resilient articular cartilage. This cartilage functions as a shock absorber, allowing the kneecap to glide frictionlessly as the knee bends and straightens. PFOA develops when this specialized cartilage wears down, frays, and thins. When the cartilage is severely eroded, the underlying bone becomes exposed, leading to painful friction between the patella and the femur.
Identifying the Symptoms
The primary indicator of patellofemoral arthritis is pain located directly behind or around the kneecap, often referred to as anterior knee pain. This discomfort is typically aggravated by activities that increase the load on the joint, especially when the knee is bent. Common actions that provoke this pain include climbing or descending stairs, squatting, or kneeling.
Patients frequently report pain when rising from a low chair or after prolonged periods of sitting with the knees bent, known as the “theater sign.” Stiffness and swelling may also be present, particularly after periods of rest or inactivity. Another noticeable symptom is crepitus, a grinding, popping, or clicking sensation that occurs when the knee moves. When associated with PFOA, crepitus often indicates the rough surfaces of the damaged joint rubbing together.
What Causes Patellofemoral Arthritis
The erosion of cartilage that defines PFOA results from a combination of factors, including age-related wear and mechanical issues. In some cases, the arthritis develops simply from chronic degeneration, often seen in older individuals. PFOA can also be a secondary condition resulting from previous injury or underlying alignment problems.
A history of traumatic events, such as a kneecap fracture or repeated patellar dislocations, significantly increases the risk of developing the condition. Biomechanical abnormalities, such as patellar maltracking (where the kneecap does not glide correctly), cause uneven and excessive wear. Furthermore, factors like being overweight or having a genetic predisposition to cartilage breakdown can accelerate the degenerative process.
Treatment and Management
The initial approach to managing PFOA focuses on non-operative methods to reduce pain and improve joint function. Activity modification is a foundational step, involving avoiding movements that severely load the joint, such as deep squats or high-impact sports. Weight loss is also recommended for individuals who are overweight to reduce pressure on the joint surfaces.
Conservative Management
Physical therapy is a cornerstone of conservative management, aiming to strengthen the muscles surrounding the knee and hip. Strengthening the quadriceps, specifically, helps improve the kneecap’s tracking within the groove, which can alleviate painful friction. Anti-inflammatory medications (NSAIDs) are often used to control pain and reduce inflammation in the joint.
Intermediate Treatments
Intermediate treatment options include injections into the knee joint for temporary relief. Corticosteroid injections offer short-term reduction of inflammation and pain. Viscoelastic supplementation involves injecting hyaluronic acid to restore some of the joint fluid’s lubricating and shock-absorbing properties.
Surgical Intervention
When conservative measures fail to provide adequate relief, surgical intervention may be considered. For severe, isolated PFOA that involves bone-on-bone contact, joint replacement surgery offers a definitive solution. Surgical options include:
- Minimally invasive arthroscopic procedures, such as debridement, to smooth frayed cartilage surfaces.
- Procedures to correct patellar malalignment, such as a tibial tubercle osteotomy, to change the kneecap’s position and tracking.
- Patellofemoral arthroplasty, which replaces only the damaged patellofemoral compartment.
- Total knee replacement, which addresses all three compartments of the knee.