Knee pain when bending and straightening the leg is a common complaint. Understanding its causes is important for effective relief and prevention.
The Knee’s Mechanics
The knee is a complex hinge joint, connecting the thigh bone (femur) to the shin bone (tibia). A smaller bone, the kneecap (patella), sits at the front of the joint. These bones are covered with articular cartilage, a smooth, slippery tissue that allows them to glide effortlessly against each other during movement.
Two C-shaped pieces of cartilage, known as menisci, act as shock absorbers between the femur and tibia, distributing weight and providing stability. Strong, fibrous bands called ligaments connect the bones, holding them together and stabilizing the joint. These include the anterior cruciate ligament (ACL), posterior cruciate ligament (PCL), medial collateral ligament (MCL), and lateral collateral ligament (LCL). Tendons, which connect muscles to bones, also play a role, with the quadriceps tendon above the patella and the patellar tendon below it working to straighten the knee.
Common Reasons for Pain
Patellofemoral Pain Syndrome (Runner’s Knee)
Patellofemoral pain syndrome (PFPS), also known as runner’s knee, causes pain around or behind the kneecap. It often results from overuse or improper kneecap alignment. Repetitive knee bending activities like squatting, climbing stairs, or prolonged sitting with bent knees commonly worsen the pain. Discomfort is often a dull ache, but can be sharp during movements like running or jumping.
Meniscus Injuries
The menisci cushion the knee joint. An injury, often a tear, can occur from forceful twisting or rotating the knee, especially while bearing weight. Symptoms include pain, swelling, stiffness, and difficulty bending, straightening, or moving the knee. A torn meniscus might also cause a popping, clicking, or locking sensation, or make the knee feel unstable.
Osteoarthritis
Osteoarthritis is a condition where the protective cartilage in the knee joint gradually wears down over time. This breakdown leads to increased friction between the bones, causing pain and stiffness during movement. Pain is often worse after periods of inactivity, such as in the morning, and can increase with activities like walking or stair climbing. The knee may also experience a grinding or creaking sound with movement, and difficulty fully bending or straightening the leg.
Tendinitis
Tendinitis involves inflammation of a tendon, commonly affecting the patellar tendon (just below the kneecap) or the quadriceps tendon (above the kneecap). This inflammation results in pain during activities that strain the affected tendon, such as bending or straightening the knee against resistance, jumping, or running. Pain from patellar tendinitis is often felt at the base of the kneecap, while quadriceps tendinitis causes pain above or in front of the knee. The pain can be sharp, particularly with movements like squatting or going down stairs.
Bursitis
Bursitis occurs when bursae, small fluid-filled sacs cushioning bones, tendons, and muscles around joints, become inflamed. In the knee, this causes localized pain that worsens with movement or direct pressure, such as kneeling. The affected area might feel warm, tender, and appear swollen or red. Bursitis can lead to stiffness and difficulty bending or straightening the knee.
When to Seek Professional Help
Seek medical attention for knee pain if you experience severe pain, sudden swelling, or cannot bear weight. Immediate evaluation is needed for a popping sound at the time of injury, instability, or visible deformity. Professional assessment is advisable if pain worsens, does not improve with self-care, or significantly interferes with daily activities or sleep.
Initial Self-Care Approaches
For initial knee pain management, the R.I.C.E. method is recommended: Rest, Ice, Compression, and Elevation. Rest involves avoiding activities that worsen pain. Apply ice packs for 15-20 minutes every few hours, avoiding direct skin contact, to reduce swelling and pain.
Compress with an elastic bandage to limit swelling, ensuring it’s snug but not too tight. Elevate the knee above heart level to promote fluid drainage. Over-the-counter pain relievers like NSAIDs (ibuprofen, naproxen) or acetaminophen can manage pain and inflammation. Gentle movement and stretching, such as lying knee bends or straight leg raises, can help maintain flexibility and strength. These measures are temporary and not a substitute for professional diagnosis if symptoms persist or worsen.