Patellofemoral arthritis (PFA) is a type of arthritis affecting the knee joint, specifically the connection between the kneecap and the thigh bone. This condition is a common source of anterior (front) knee pain, frequently impacting physically active individuals and older adults. PFA is a degenerative condition involving the breakdown of the joint’s protective surfaces, leading to discomfort and limited mobility.
Understanding the Patellofemoral Joint and Pathology
The patellofemoral joint is the articulation where the patella (kneecap) meets the femur (thigh bone). The patella rests in a shallow, channel-like groove on the femur called the trochlear groove. As the knee bends and straightens, the patella glides within this groove.
A smooth, slippery material called articular cartilage covers the surfaces of the patella and the trochlear groove. This cartilage acts like a cushion, allowing the bones to move against each other without friction. Patellofemoral arthritis occurs when this articular cartilage begins to wear down, becoming frayed and thinning.
The pathology of PFA involves the progressive loss of this cartilage, eventually exposing the underlying bone. When the bones move along this rough, unprotected surface, it creates friction, inflammation, and pain. This degenerative process is located in the patellofemoral compartment, though it may occur alongside arthritis in other parts of the knee.
Recognizing the Pain and Symptoms
The main characteristic of patellofemoral arthritis is pain felt primarily in the front of the knee, often described as being behind or around the kneecap. This pain is aggravated by activities that increase the load or pressure on the joint.
Increased pain when climbing or descending stairs is a frequent complaint, as these motions require significant movement of the patellofemoral joint. Deep knee bending activities like squatting or kneeling also exacerbate the discomfort.
Many individuals with PFA report the “theater sign,” which is pain that develops after sitting for a prolonged period with the knees bent. This pain is relieved once the person stands up and straightens the knee. Another common symptom is crepitus, a crackling, grinding, or clicking sensation within the joint during movement.
Causes and Risk Factors for Development
The development of patellofemoral arthritis is often multifactorial, resulting from a combination of underlying issues and external stresses. One significant factor is biomechanical misalignment, where the patella does not track correctly within the trochlear groove. This maltracking causes uneven wear, often overloading the lateral (outer) aspect of the joint surface.
Prior trauma is another contributor; a history of fracture, dislocation, or subluxation (partial dislocation) of the kneecap increases the risk. These injuries can directly damage the articular cartilage or cause chronic instability that leads to premature wear.
Repetitive stress from high-impact activities, such as running, jumping, or weight training, also contributes to the condition. These activities place substantial force on the patellofemoral joint, sometimes reaching up to seven times a person’s body weight during a deep squat. Age and obesity are non-mechanical risk factors, as increased body weight raises the load on the joint, accelerating degeneration.
Diagnosis and Management Strategies
Diagnosing patellofemoral arthritis begins with a thorough physical examination. A doctor assesses the knee’s alignment, range of motion, and checks for tenderness around the kneecap. The physician also looks for signs of crepitus during movement and muscle atrophy (loss), especially in the quadriceps.
Imaging tests, particularly X-rays, confirm the diagnosis and assess the severity of cartilage loss. These images show joint space narrowing between the patella and the femur, and help rule out other causes of anterior knee pain. Advanced imaging like a CT scan or MRI may be used to evaluate soft tissues and patella alignment more precisely.
Management of PFA starts with non-surgical strategies aimed at reducing pain and improving function. Physical therapy is a primary component, focusing on strengthening the muscles that support the knee, especially the vastus medialis obliquus (VMO) of the quadriceps, which stabilizes the kneecap. Activity modification is also recommended, involving limiting activities that provoke pain, such as deep squatting or excessive stair use.
Medications like nonsteroidal anti-inflammatory drugs (NSAIDs) help manage pain and reduce inflammation in the short term. Intra-articular injections may be used, including corticosteroids for acute flare-ups or viscosupplementation (injecting a hyaluronic acid substance to lubricate the joint). Surgical intervention, such as arthroscopy or a procedure to realign the patella, is reserved for severe cases where conservative treatments have failed.