Pain in or around the knee that may indicate a condition affecting the knee joint itself or the soft tissue around the knee. Common causes of this symptom 1)Chondromalacia Patella:  This is a pathologic condition in which there is degeneration and softening of the cartilage on the underside of the kneecap.  Frequent bending motion of the knee causes the back portion of the kneecap to slide over the bones of the knee. The thigh and the shin bone are connected to the kneecap with tendons and ligaments. With repeated motion and flexion of the knee, any of these components of the kneecap may start to malfunction resulting in pain and discomfort and cause Anterior Knee Pain with Flexion. 2)Runner’s Knee:  As the name suggests, this condition is mostly found in runners or sprinters. It can be caused due to overuse of the knees which can irritate the patellofemoral joint, over-stretching of the tendons may also be a reason for Runner’s Knee because of which a person experiences Anterior Knee Pain with Flexion. 3)Lateral Patellar Compression Syndrome: Lateral Patellar Compression Syndrome is a pathologic condition in which the patella or the kneecap moves out of its groove in the knee joint.2 This results in pain in the anterior part of the knee which is often exacerbated with activities like standing, walking on inclines, or running. The patella may also move out of its groove if a person is in a sitting position for prolonged periods of time. Muscle imbalance or inflexibility of the muscles can also be a cause of lateral patellar compression syndrome. 4)Quadriceps Tendinitis:  The quadriceps muscle is connected directly to the knee joint by tendons and ligaments. Due to overuse and stressing of the quadriceps muscle may result in an inflammation of the tendons and ligaments connecting the quadriceps muscle to the knee joint causing anterior knee pain with flexion. 5)Maltracking Patella:  This is a condition in which the patella is unstable and frequently moves out of its groove causing anterior knee pain with flexion. This pain may get real bad with physical activities like walking on inclines, running or standing for long periods of time. 6)Biceps Tendinopathy:  This is a condition which is mainly caused by overuse such as running or playing sports like football where the posterior part of the knee is involved which results in inflammation of the Biceps Femoris Muscle which is an important muscle of the hamstring muscle group. This results in the patient experiencing posterior knee pain with flexion which may interfere with regular activities like walking and jogging. Again, this depends on the degree and extent of damage to the biceps femoris muscle. If the patient experiences a localized discomfort to the posterior part of knee which does not impede function in any way then it may be a referred pain from the lumbar spine and the spine needs to be investigated in that case. 7)Popliteus Tendinopathy:  This is quite an uncommon cause of posterior knee pain with flexion. In this condition, there is an inflammation of the muscle present behind the knee called as the popliteus muscle. This can also be caused due to extra stress being put on the knee with activities like standing, walking on inclines and running. Along with pain in the posterior knee the patient will also have an area of tenderness proximally to the knee to palpation and will have pain with range of motion of the knee. 8)Gastrocnemius Tendinopathy:  As the name suggests, this is a condition in which there is an inflammation of the gastrocnemius muscle. This condition is commonly found in marathon or cross country runners. Along with Posterior Knee Pain with Flexion the patient may also experience pain with calf raises and will not be able to jump or hop without discomfort. 9)Baker’s Cyst:  This is also one of the causes of posterior knee pain with flexion. It is the name given to localized swelling behind the knee. The main cause of a Baker’s Cyst is chronic degeneration or a meniscal problem and the amount of swelling may be variable. In some cases, the cyst may rupture leading to a condition called as venous thrombosis. 10)Arthritis:  This is a degenerative condition of the joint and occurs with advancing age and how much the knee has been overused.3 The most common type of arthritis which causes knee pain with flexion is osteoarthritis of the knee, although rheumatoid arthritis and septic arthritis can also cause knee pain with flexion. Arthritis as it is well known affects the working of the knee joint impacting the quality of life of the affected individual. The patient may have reduced range of motion, increased pain with activity, and decreased flexibility of the joint affecting the quality of life. 11)Patellofemoral Pain Syndrome:  This is a pathological condition of the knee in which the patient has pain beneath the kneecap or around it which gets worse with flexion or after sitting for long periods of time. 12)Bursitis:  In this the patient has inflammation of the bursal sac which provides a cushion to the knee joint.4 This condition may cause excruciating pain with flexion of the knee and the patient will have difficulty going up and down stairs or standing for long periods of time. 13)Osgood-Schlatter Disease:  This is a pathological condition in which there is inflammation of the bone, cartilage, and tendon of the shinbone. This is found mostly in adolescents who play and run around quite often. This condition hits a person when he or she is going through a growth spurt. The pain experienced with this condition is variable and gets worse with flexion and exercises