How is the knee structured?
The knee joint is formed primarily between the femur and the tibia. The kneecap slides in a groove on the femur and enhances the power of the thigh muscle. The joint surfaces are covered by cartilage that reduces friction.
Two menisci lie between the femur and tibia and distribute load. Anterior and posterior cruciate ligaments control movement and rotation, while lateral ligaments prevent the knee from bending to the sides.
Tendons, muscles, joint capsules and bursae contribute to movement and stability. Problems can occur in one or more of these structures.
What function does the knee have?
Knees bend and extend but also allow for a small amount of rotation. They must be stable when the body is loaded and at the same time be able to adapt to uneven surfaces, stairs, running and jumping.
Thigh muscles, hamstrings, calves and hip muscles affect knee control. Decreased strength or sudden increased training load can contribute to pain without major structural damage.
Menisci and cartilage distribute pressure. Ligaments control movement and help the nervous system perceive the position of the joint.
The load on the knee is affected by the hip, foot, body weight, training dose and surface. A temporary increase in activity can cause pain without the joint being seriously damaged. Gradual adaptation and strength are key to being able to withstand the load.
Common knee problems
Knee pain can be caused by overload, meniscus damage, cruciate ligament damage, cartilage changes, osteoarthritis, irritation around the kneecap or inflammation. Read more about knee pain, meniscus injury and osteoarthritis in the knee.
Acute injuries often occur after a twist, fall, or direct blow. A rapidly swollen knee may indicate bleeding into the joint or a larger injury. Gradual pain is more often linked to strain or osteoarthritis.
Clicking sounds are common and not always a sign of injury. Locking, instability, and inability to bear weight are more important symptoms to describe.
Pain in the front of the knee can occur when the load around the kneecap becomes greater than the tissues are used to. This does not necessarily mean that the cartilage is damaged. Training dose, strength and recovery need to be assessed together.
When should you seek care for your knee?
Contact your healthcare provider if the pain does not improve, if your knee repeatedly swells, bends or locks, or if you have difficulty putting weight on your leg. Assessment is also important after a clear sprain.
Seek immediate medical attention if your knee is misaligned, locked in one position, very painful, or swells significantly within a few hours. A red, warm, and swollen knee along with a fever may be due to infection and should be evaluated quickly.
After trauma with numbness, cold feet or impaired circulation, emergency care is required.
How is the knee examined?
The examination includes gait, swelling, mobility, stability, tenderness, and specific tests for menisci and ligaments. Often, clinical findings can delineate which structure is affected.
X-rays are used for fractures and osteoarthritis. Ultrasound can show fluid, tendons, and some superficial structures. MRI provides detailed images of menisci, cruciate ligaments, collateral ligaments, cartilage, bone marrow, and soft tissues.
MRI is not needed for all knee problems. In cases of clear osteoarthritis, X-rays and clinical assessment may be sufficient. Physiotherapy assessment is often important regardless of imaging.
In acute injuries, the mechanism of injury is important: a twist, a snap, immediate swelling and instability raise suspicions other than gradual strain pain. Clinical tests may need to be repeated when the initial swelling and pain have subsided.
When can MRI of the knee be relevant?
MRI knee may be relevant in cases of suspected meniscus or cruciate ligament injury, locking, instability, cartilage damage, unexplained long-term pain or when the result may affect treatment.
MRI can show changes that do not cause symptoms, especially degenerative meniscal changes. Therefore, the answer should be linked to age, mechanism of injury, clinical tests and functional problems.
In the case of a suspected fracture, an X-ray or CT scan is usually the first step. MRI can later show hidden fractures or bone marrow involvement.
Limitations and next steps
Many knee problems improve with appropriate loading and physiotherapy. An MRI finding does not automatically lead to surgery. Degenerative meniscus injuries are often treated without surgery, especially when osteoarthritis is also present.
The next step may be exercise, pain relief, activity modification, injection treatment or orthopedic assessment. In the event of new locking, pronounced instability or deterioration, the knee should be reassessed.
Rehabilitation is often gradual and measured in terms of function: swelling, range of motion, strength, balance, and ability to walk, run, or change direction. Return to sports should be based on testing and not just how many weeks have passed.