The knee joint is the most complex joint in the human body, and there are many causes of knee pain, including a high incidence of patellofemoral joint disease, which afflicts many people. Patients often complain of “pain when going up and down stairs,” “inability to squat or kneel,” “frictional sounds and pain when I flex my knee,” and ” Two years ago, I hit my knee on the dashboard, and since then, my knee hurts after every skiing and climbing”. These are common complaints of patients with patellofemoral syndrome. Patellofemoral syndrome represents symptoms caused by the patellofemoral joint, including chondromalacia patellae, patellar subluxation, high patellae, and patellofemoral arthritis. While some cases are due to direct trauma (knee dashboard injury), the majority of cases are due to repetitive irritation of the abnormal patellofemoral trajectory. Arthroscopy may show defects in the articular cartilage of the inferior surface of the patella. After several decades, the articular cartilage will show extensive irregular changes. Painful retropatellar twisting pronation can be detected by passive movement of the patella on examination. Patellar popping can be palpated by placing the palm of the hand on the patella during passive extension and flexion of the knee joint. Knee effusion is uncommon, and more effusion indicates progression of the disease. Three x-rays are recommended, orthogonal, lateral and axial patellar views of the knee in the standing position. Typical changes include lateral subluxation, narrowing of the lateral patellofemoral space, and sclerosis of the lateral aspect of the patella. In severe cases, manifestations such as osteophytes and subchondral cysts are seen. Treatment: The goal of treatment is to improve patellofemoral trajectory and force lines, reduce pain and swelling, and slow the progression of patellofemoral arthritis. Treatment options when limiting repetitive joint flexion and quadriceps isometric contraction exercises. 1. First step (initial patient): (1) Apply ice and elevate the knee joint, especially if there is knee effusion. (2) Absolutely avoid knee squatting and kneeling. (3) Limit repetitive knee flexion according to the condition (only 30° internal flexion for severe patients and 60° internal flexion for moderate patients). (4) Recommend exercises such as swimming, skiing exercises on an exercise machine, and fast walking instead of jogging, cycling, and variable speed running that cause too much joint flexion, extension, and impact. (5) Perform straight leg raise isometric contraction exercises in external rotation of the leg and strengthen medial femoral tone exercises in full extension of the lower extremity, thereby improving patellofemoral trajectory. 2. Step 2 (for cases lasting 4-8 weeks): Enhancement of functional exercises and joint movement restriction. (1) Use non-steroidal anti-inflammatory drugs at full dose for 3 weeks, followed by gradual dose reduction over 4 weeks. (2) Recommend patellar splint ring or adhesive patellar brake to resist the harmful effects of patellofemoral joint movement, especially in patients with a lot of movement. 3. Step 3 (for cases lasting 3-4 months) Local corticosteroid injections or sodium glacial injections are administered to patients with symptoms lasting >6-8 weeks or with knee oozing. If symptoms do not improve by 50%, repeat injections at 4-6 weeks. 4. Step 4 (4-6 months for chronic cases) Re-emphasize continuous straight leg raising exercises 3 times a day or 1 week. (1) Long-term restriction of knee squatting, kneeling and flexion activities is recommended for patients with chronic symptoms. (2) Patients with persistent joint pain, functional abnormalities, high patella or Q-angle greater than 20° may require surgical treatment. Straight leg raising exercises: Perform straight leg raising exercises in the supine and prone positions for 20 exercises per set daily. Begin exercises without weight and as symptoms improve, add 2-5 kg of weight to the ankle joint. Note: Active activity exercises, especially on apparatus, must be performed with caution. Cycling exercises, rowing equipment exercises and functional exercises requiring full knee flexion and extension should be avoided initially. Brisk walking, swimming, and skiing exercises on exercise machines are more appropriate because they are less impacting on the joint and require less joint flexion. Prognosis: Patellofemoral syndrome is common in adolescent, middle-aged and elderly patients and generally has a good prognosis.