Why Does My Knee Hurt? Understanding Common Causes and When to Seek Help

Knee pain is a very common problem, affecting people of all ages and activity levels. It can arise suddenly after an injury, or develop gradually over time. Understanding why your knee hurts is the first step towards finding relief and getting back to your daily activities. Knee pain can stem from a variety of issues, ranging from simple sprains to complex medical conditions like arthritis. This article will explore the common reasons for knee pain, the symptoms to watch out for, and when it’s important to seek medical attention.

Common Causes of Knee Pain

The knee joint is a complex structure made up of bones, ligaments, tendons, and cartilage, all working together to provide movement and stability. Pain in the knee can originate from any of these components, and the causes are broadly categorized into injuries, mechanical problems, types of arthritis, and other conditions.

Injuries

Knee injuries are a frequent cause of sudden knee pain, especially in active individuals and athletes. These injuries can affect any of the soft tissues or bones in the knee.

ACL Injury

An anterior cruciate ligament (ACL) injury is a tear in one of the major ligaments in your knee, the ACL. This ligament is crucial for stabilizing the knee joint, connecting your thigh bone (femur) to your shin bone (tibia). ACL tears often happen during sports that involve sudden changes in direction or stops, such as basketball, soccer, and skiing. Symptoms of an ACL injury can include a popping sound at the time of injury, severe pain, rapid swelling, and instability of the knee, making it difficult to bear weight. Treatment can range from conservative measures like bracing and physical therapy to surgical reconstruction, depending on the severity of the tear and the individual’s activity level.

Torn Meniscus

A torn meniscus refers to a tear in the meniscus, which is a C-shaped piece of cartilage acting as a cushion and shock absorber between your thighbone and shinbone. Meniscus tears can occur with sudden twisting motions of the knee, particularly when weight-bearing. Symptoms of a torn meniscus can include pain, stiffness, swelling, catching or locking sensations in the knee, and difficulty straightening the knee fully. Treatment for a torn meniscus varies depending on the tear’s size, type, and location, and can include physical therapy, pain management, or surgical repair.

Other common knee injuries include:

Fractures: The bones around the knee, including the kneecap (patella), and the ends of the femur and tibia, can be fractured due to high-impact trauma like falls or car accidents. In individuals with osteoporosis, even a minor misstep can lead to a knee fracture. Symptoms include severe pain, swelling, bruising, and inability to move the knee. Fractures usually require immobilization and may need surgery to ensure proper healing.
Knee Bursitis: Bursae are small, fluid-filled sacs that cushion the bones, tendons, and muscles around your joints. Knee bursitis, or inflammation of these sacs around the knee, can be caused by overuse, direct trauma, or prolonged kneeling. Symptoms include warmth, tenderness, swelling, and pain that may worsen with movement. Treatment typically involves rest, ice, compression, and elevation (RICE), along with pain medication and sometimes aspiration or corticosteroid injections.
Patellar Tendinitis: Also known as “jumper’s knee,” patellar tendinitis is an inflammation of the patellar tendon, which connects the kneecap to the shinbone. It’s often caused by repetitive stress from jumping, running, or kicking activities. Athletes in sports like basketball and volleyball are particularly susceptible. Symptoms include pain just below the kneecap that worsens with activity. Treatment includes rest, physical therapy to strengthen and stretch the tendon, and pain relief measures.

Mechanical Problems

Sometimes, knee pain arises from mechanical issues that affect how the knee joint moves.

Loose Body: Pieces of cartilage or bone can break off within the knee joint due to injury or degeneration. These “loose bodies” can float around in the joint space and may not cause problems unless they get caught between the bones of the joint, blocking movement and causing pain, locking, or clicking sensations. Depending on the symptoms, loose bodies may need to be surgically removed.
Iliotibial (IT) Band Syndrome: The iliotibial band is a thick band of tissue that runs from your hip down the outer thigh to your knee. When this band becomes too tight, it can rub against the outer part of the femur, causing pain on the outside of the knee. IT band syndrome is common in runners and cyclists, especially after increasing training intensity or mileage. Treatment focuses on stretching and strengthening exercises, particularly targeting the hip and thigh muscles, as well as activity modification.
Dislocated Kneecap: A dislocated kneecap (patellar dislocation) occurs when the kneecap slips out of its normal groove at the front of the femur. This is often caused by a sudden change in direction or a direct blow to the knee. Symptoms include visible displacement of the kneecap, pain, swelling, and inability to straighten the knee. While sometimes the kneecap may spontaneously relocate, medical evaluation and treatment are important to address any associated injuries and prevent recurrence.
Hip or Foot Pain: Pain in the hip or foot can indirectly cause knee pain. If you have pain in these areas, you might alter your walking pattern (gait) to compensate. This change in gait can place extra stress on the knee joint, leading to pain. Addressing the underlying hip or foot problem is crucial to resolve the secondary knee pain.

Types of Arthritis

Arthritis is a common cause of chronic knee pain. There are over 100 different types of arthritis, and several can affect the knee joint.

Osteoarthritis (OA): Osteoarthritis, often called “wear-and-tear” arthritis or degenerative joint disease, is the most common type of arthritis affecting the knee. It occurs when the cartilage in the knee joint, which cushions the bones, breaks down over time. This breakdown can be accelerated by age, overuse, and injury. Symptoms of knee OA develop gradually and include pain that worsens with activity and improves with rest, stiffness, swelling, and decreased range of motion.
Rheumatoid Arthritis (RA): Rheumatoid arthritis is an autoimmune disease where the body’s immune system mistakenly attacks the synovium, the lining of the membranes that surround the joints. This inflammation can damage cartilage and bone. RA is a systemic disease, meaning it can affect multiple joints throughout the body, including the knees. Symptoms include pain, swelling, stiffness (especially in the morning), warmth, and fatigue. RA is a chronic condition that requires ongoing medical management.
Gout: Gout is a type of inflammatory arthritis caused by the buildup of uric acid crystals in the joints. While gout often affects the big toe, it can also affect the knee. Gout attacks are characterized by sudden, severe pain, redness, warmth, and swelling in the affected joint. Managing gout involves medications to lower uric acid levels and lifestyle changes.
Pseudogout: Pseudogout, also known as calcium pyrophosphate deposition disease (CPPD), is similar to gout but is caused by calcium pyrophosphate crystals instead of uric acid. These crystals deposit in the joint fluid and cause sudden episodes of pain, swelling, warmth, and stiffness. The knee is a common joint affected by pseudogout.
Septic Arthritis: Septic arthritis is a serious infection of the joint space. Bacteria, viruses, or fungi can enter the joint, often through the bloodstream, and cause significant inflammation and damage. Septic arthritis in the knee is characterized by severe pain, swelling, redness, warmth, and often fever. It’s a medical emergency requiring prompt antibiotic treatment to prevent joint destruction.

Symptoms Accompanying Knee Pain

The specific symptoms you experience along with knee pain can provide clues about the underlying cause. Common accompanying symptoms include:

Swelling and Stiffness: Swelling is a common sign of inflammation in the knee joint, often due to injury or arthritis. Stiffness can also occur, particularly in the morning or after periods of inactivity.
Redness and Warmth to the Touch: These signs indicate inflammation and could suggest infection (septic arthritis) or inflammatory arthritis like gout or rheumatoid arthritis.
Weakness or Instability: A feeling of the knee giving way or being unstable can be due to ligament injuries (like ACL tear) or muscle weakness around the knee.
Popping or Crunching Noises: These sounds (crepitus) can occur with knee movement and may be associated with cartilage damage or osteoarthritis. While occasional popping is not always concerning, persistent or painful popping should be evaluated.
Inability to Fully Straighten or Flex the Knee: Limited range of motion can result from swelling, pain, injury, or mechanical blockage within the joint.

When to See a Doctor for Knee Pain

While minor knee pain may resolve with home care, it’s important to know when to seek medical advice. Consult a doctor if you experience any of the following:

Inability to bear weight on your knee: If you cannot stand or walk comfortably on the affected knee.
Feeling of knee instability or giving way: If your knee feels like it might buckle or collapse.
Marked knee swelling: Significant swelling that doesn’t improve with rest and ice.
Inability to fully extend or flex your knee: If you have a restricted range of motion in your knee.
Obvious deformity in your leg or knee: Visible misalignment or abnormal appearance of the knee.
Fever, in addition to redness, pain, and swelling in your knee: These could be signs of infection (septic arthritis), which requires urgent medical attention.
Severe knee pain associated with an injury: Especially if accompanied by any of the above symptoms.
Knee pain that persists or doesn’t improve with self-care measures: If your pain continues despite rest, ice, and over-the-counter pain relievers.

Risk Factors for Knee Pain

Several factors can increase your likelihood of developing knee problems:

Excess Weight: Being overweight or obese puts extra stress on your knee joints, increasing the risk of osteoarthritis and injuries.
Lack of Muscle Flexibility or Strength: Weak muscles around the knee provide less support, increasing the risk of injury. Tight muscles can also contribute to strain and pain.
Certain Sports or Occupations: Sports with high impact, pivoting, or repetitive stress on the knees (like running, basketball, skiing, construction work) increase the risk of knee problems.
Previous Knee Injury: Having a prior knee injury makes you more susceptible to future knee problems.

Prevention of Knee Pain

While not all knee pain is preventable, you can take steps to reduce your risk of injuries and joint deterioration:

Maintain a Healthy Weight: Losing excess weight reduces stress on your knees.
Warm Up and Cool Down: Properly prepare your muscles for activity and allow them to recover.
Strengthen Muscles Around the Knee: Focus on strengthening your quadriceps, hamstrings, and calf muscles to support and stabilize your knees.
Improve Flexibility: Regularly stretch your leg muscles to maintain flexibility and range of motion.
Use Proper Technique in Sports and Activities: Learn and practice correct form to minimize stress on your knees.
Choose Appropriate Footwear: Wear supportive shoes suitable for your activities.
Listen to Your Body: Avoid pushing through pain, and rest when needed.
Consider Low-Impact Exercise: If you have knee pain or arthritis, choose activities like swimming, cycling, or walking, which are gentler on the knees.

Understanding why your knee hurts is essential for effective management. While this article provides general information, it’s not a substitute for professional medical advice. If you are experiencing persistent or concerning knee pain, consult with a healthcare provider for proper diagnosis and personalized treatment.