Pain located underneath the kneecap, medically known as the patella, is a very common complaint that often signals an issue within the patellofemoral joint. This joint is formed by the patella gliding in a groove at the end of the thigh bone, or femur. When this complex joint begins to hurt, it is usually a sign that mechanical forces are not being distributed evenly across the joint surfaces. Understanding why this pain occurs is the first step toward finding relief and preventing its recurrence.
Understanding Patellofemoral Pain Syndrome
The most frequent reason for pain under the kneecap is Patellofemoral Pain Syndrome (PFPS), often called “Runner’s Knee.” PFPS describes pain around or behind the patella that intensifies when the knee is bent under load. The pain is typically a generalized, dull ache at the front of the knee that comes on gradually over time.
The pain worsens during activities that place pressure on the flexed knee, such as walking up or down stairs, squatting, or running. Another common symptom is pain after prolonged periods of sitting with the knees bent, sometimes called “theater sign.” Some people also report a grinding, popping, or crackling sensation, known as crepitus, when they move their knee. PFPS is diagnosed after ruling out other causes of anterior knee pain, such as ligament tears or fractures.
Cartilage Changes and Misalignment
Pain in the patellofemoral joint often results from mechanical friction caused by the kneecap not tracking correctly within the femoral groove. This misalignment creates increased and uneven pressure on the joint surfaces, leading to irritation and inflammation. Repetitive stress can eventually cause changes in the articular cartilage, the smooth tissue on the underside of the patella. This softening and roughening of the cartilage is known as Chondromalacia Patellae.
Although cartilage does not contain nerve endings, its breakdown irritates the underlying bone and surrounding soft tissues, which are rich in nerve fibers. Patellar tracking issues push the kneecap out of its centered position, often toward the outside of the leg. This causes the kneecap to rub against the side of the groove instead of gliding smoothly, driving the pain and subsequent tissue changes.
Identifying Contributing Biomechanical Issues
The root cause of patellar misalignment often lies in imbalances and weaknesses outside the knee joint, particularly in the hip and foot. Weakness in the hip muscles, especially the abductors and gluteal muscles, commonly affects knee alignment. When these stabilizing muscles are weak, the thigh bone tends to rotate inward during activities like walking or running. This inward rotation creates a functional misalignment that places excessive stress on the patellofemoral joint.
The flexibility and strength of surrounding muscles also play a role. Tightness in the hamstrings or calf muscles can alter the biomechanics of the entire leg. For example, tight hamstrings increase the reaction force on the patellofemoral joint during knee extension, leading to greater pressure and pain. Issues with foot mechanics, such as excessive foot pronation (flat feet), can also cause the lower leg to rotate inward, contributing to misalignment and increased kneecap pressure.
Immediate Care and Seeking Professional Help
Initial management of pain under the kneecap focuses on reducing inflammation and avoiding aggravating activities. This involves modifying activities to avoid deep knee bending, squatting, or prolonged sitting with the knees flexed. Applying ice to the painful area for 15 to 20 minutes after activity minimizes swelling and discomfort. Gentle, frequent movement of the knee, such as flexing the joint while sitting, helps lubricate the joint and prevent stiffness.
Seek professional medical consultation if the pain persists for more than a few days despite home care, or if you experience “red flag” symptoms. Immediate medical attention is necessary if the knee becomes severely swollen, appears deformed, is warm to the touch, or if you are suddenly unable to bear weight or walk normally. A physical therapist can provide an assessment to identify underlying muscle imbalances and tracking issues, offering targeted strength and flexibility exercises for a long-term solution.