1. What are the clinical manifestations of patellofemoral joint malalignment? Most patients with patellofemoral malalignment have a history of patellar instability and pain. History of patellar dislocation. The main symptoms include: sudden knee weakness, weakness, kneeling, and a sense of instability. Knee pain, aggravated by activity, especially when squatting up and down stairs and relieved after rest; joint swelling, effusion and pseudocollapse may occur in the combined presence of severe degeneration of patellar cartilage. Physical examination can be seen as follows: outward patellar displacement or deformity of the knee; increased Q angle; excessive patellar mobility, if pushing outward more than 1/2 of the patella, it indicates a weak medial patellar structure; pressure pain at the posterior edge of the patella or patellofemoral joint space, pain when sliding inside and outside, positive patellar percussion pain; patellofemoral joint friction sound, positive floating patella sign; patellar activity test, fear test, quadriceps impedance test, squat test can be positive. 2.How to detect patellofemoral joint misalignment? X-ray radiographs: ordinary anterior-posterior radiographs of the knee joint are of little diagnostic value. Lateral radiographs can measure the ratio of the patellar ligament to the length of the patella and determine whether there is a high patella or a low patella. A tangential radiograph of the patellofemoral joint (or patellofemoral axial radiograph, mostly taken with Mechant’s knee flexed at 45 degrees) is the most effective way to observe the presence of patellofemoral malalignment. The type of patellofemoral malalignment can be determined by measuring indicators such as the slot angle (SA), the overlap angle (CA), the lateral patellofemoral angle (LPA), the lateral patellar tilt angle, and the patellofemoral displacement distance (LPD). CT scan: A cross-section of the patella at 15-30° of knee flexion can reveal patellofemoral misalignment that is not easily diagnosed by X-ray radiography. Magnetic resonance imaging (MRI): Highly accurate for the diagnosis of articular cartilage lesions. Bone scan: It can determine whether there is intrapatellar hypertension, which is valuable for choosing the surgical procedure. 3.What are the clinical types of patellofemoral malalignment? The clinical staging of patellofemoral malalignment should be combined with the degree of cartilage lesion, and is generally divided into patellar tilt type, patellar subluxation type and patellar tilt combined with subluxation type, according to the clinical type to guide the choice of treatment.