Anterior knee pain (AKP) describes discomfort localized to the front of the knee, around or underneath the kneecap (patella). This is a common musculoskeletal complaint, particularly among physically active individuals. AKP is a broad symptom arising from several distinct conditions affecting the patellofemoral joint. Understanding the specific cause is the starting point for addressing this pain.
Patellofemoral Pain Syndrome and Maltracking
Patellofemoral Pain Syndrome (PFP) is the most frequently diagnosed cause of AKP, often involving a problem with how the kneecap moves. The patella is designed to glide smoothly within the trochlear groove of the thigh bone (femur) as the knee bends and straightens. When the patella is misaligned or tracks poorly, maltracking occurs, which is the primary mechanical issue in PFP.
This abnormal movement causes friction and increased compressive forces between the undersurface of the patella and the femur’s groove. The repeated friction irritates the joint surfaces, leading to a dull ache felt deep behind or around the kneecap.
PFP symptoms are aggravated by activities that increase pressure on the joint, such as walking up or down stairs. Prolonged sitting with the knee bent, sometimes called the “movie-goer’s sign,” can trigger pain due to sustained compression. Individuals may also experience crepitus, a grinding or crunching sensation when the knee is moved.
PFP is frequently linked to overuse, such as a sudden increase in physical activity or training volume. Identifying the specific pattern of maltracking helps determine the appropriate interventions to restore the kneecap’s correct path.
Inflammatory Conditions of the Tendons
Anterior knee pain can originate from the inflammation of the large tendons that form the knee extensor mechanism. Patellar Tendinitis and Quadriceps Tendinitis are common tendinopathies resulting from excessive loading of the soft tissues, involving micro-tears and irritation within the tendon structure.
Patellar Tendinitis, often called Jumper’s Knee, involves the tendon below the kneecap, connecting the patella to the shinbone (tibia). This tendon is subjected to high tensile forces during explosive movements like jumping and landing. The repeated strain causes pain and tenderness at the lower pole of the patella or along the tendon itself.
Quadriceps Tendinitis affects the tendon immediately above the kneecap, connecting the quadriceps muscles to the top of the patella. This condition results from chronic overuse, such as repetitive running or deep squatting movements. The pain is localized directly above the patella, originating specifically from the inflamed tendon structures, distinguishing it from the joint surface irritation seen in PFP.
Structural Changes and Growth Plate Issues
Pain in the anterior knee can result from physical breakdown within the joint or irritation at a growth center. Chondromalacia Patellae is characterized by the softening and deterioration of the articular cartilage on the underside of the kneecap.
Although articular cartilage lacks nerve endings, its damage can lead to inflammation of the surrounding synovial lining and pain originating from the sensitive subchondral bone. This condition represents physical deterioration of the joint surface, distinct from simple maltracking.
Osgood-Schlatter Disease is primarily seen in active adolescents. This condition involves the area where the patellar tendon attaches to the growth plate (tibial tuberosity) at the top of the shinbone.
During periods of rapid growth, the repetitive pulling of the quadriceps muscle creates stress on this soft growth center. This chronic pulling causes inflammation and microtrauma, leading to pain and often a noticeable bony bump below the knee. Osgood-Schlatter disease is temporary and linked to skeletal immaturity.
Contributing Biomechanical Factors
Anterior knee pain frequently arises due to underlying biomechanical imbalances that disrupt the knee’s natural alignment and load distribution. Weakness in the hip and pelvis muscles is a significant contributing factor, particularly the gluteal muscles responsible for hip abduction and external rotation.
When these muscles are insufficient, the thigh bone tends to rotate inward during activities like running or squatting. This rotation causes the kneecap to track improperly in its groove.
Tightness in muscles surrounding the knee, such as the hamstrings or calf muscles, can also alter the forces transmitted through the joint. For instance, Achilles tendon tightness affects foot mechanics and subsequently the knee’s alignment.
Improper foot mechanics, such as excessive pronation where the arch flattens and the foot rolls inward, transmits rotational stress up the kinetic chain to the knee. This poor foundation places undue strain on the patellofemoral joint and surrounding tendons.
These biomechanical issues are root causes that predispose an individual to joint irritation or tendon inflammation. Training errors, such as increasing activity level too quickly, compound these vulnerabilities by overloading the system. Addressing these strength and flexibility deficits is paramount to restoring proper knee function.