Recurrent patellar dislocation: If the patella is dislocated more than twice, affecting normal life and sports, surgery is recommended. Surgery can not only stabilize the patella and reduce the recurrence of patellar dislocation, but also reduce the damage to the patellar cartilage caused by the dislocation and prevent the occurrence of osteoarthrosis of the patellofemoral joint. However, if the patellar dislocation recurrence interval is long, even once or twice a few years, and daily life is not affected, conservative treatment can also be considered, strengthening quadriceps strength exercises, using patellar braces, avoiding movements that can easily cause patellar dislocation (such as flexion and valgus of the affected knee or turning the body to the side of the healthy knee), especially squatting with both knees separated to both sides as much as possible. Patients with patellar dislocation often have anatomical abnormalities of the knee joint, including patellar hypoplasia, talus hypoplasia, patellar valgus, high patella, large tibial tuberosity talus groove distance (TT-TG value) and joint laxity, etc. The appropriate surgical procedure should be selected according to the patient’s age, mobility and imaging assessment. Reconstruction, medial support band tightening, tibial tuberosity displacement, lateral support band release, and pulleyplasty are the most common surgical approaches. In patients with unclosed epiphyses, I generally use the greater retractor tendon to reconstruct the MPFL. In patients with closed epiphyses, I generally use the thin femoral tendon to reconstruct the MPFL. a single bone tract is used on the patellar side and a single resorbable extrusion screw is used to fix the graft on the femoral side (see figure below). Accurate tract placement and proper graft tension are key to MPFL reconstruction surgery. Post-operative rehabilitation plan for MPFL reconstruction: 1. 4 weeks of straight splint fixation, full weight-bearing walking with splint, moderate activity, and gradual early release from the crutches; 2. Quadriceps contraction, ankle pump and straight leg raising exercises were started on the first day after surgery, with straight leg raising as the main focus; 3. Knee flexion exercises were started on the 4th day after surgery, reaching 90 degrees at 4 weeks, 120 degrees at 6 weeks, and normal knee flexion at 2-3 months. After each knee flexion exercise, the knee must be iced with an ice water mixture for 20 minutes. Swelling and heat in the joint after the knee flexion exercise is normal and can be relieved by ice, and if the swelling is obvious, the number of ice packs can be increased. If the external deviation of the tibial tuberosity is large (TT-TG value is large), MPFL reconstruction and internal displacement of the tibial tuberosity can be performed at the same time. I usually use internal rotation displacement of the tibial tuberosity, and compared to MPFL reconstruction surgery alone, a 1-2 cm extension of the surgical incision for medial tibial tuberosity tendon retrieval is sufficient (see the figure below, MPFL reconstruction with medial knee incision above, tendon retrieval and tibial tuberosity displacement with medial tibial tuberosity incision below (internal displacement). The tibial tuberosity internal rotation shift will have less impact on patellofemoral joint pressure and the risk of increased postoperative patellofemoral cartilage damage will be lower. Habitual patellar dislocation: In some patients, the patella is dislocated laterally whenever the knee is flexed to a certain degree, called habitual dislocation. In severe cases, the patella is dislocated regardless of knee extension or flexion, which is called persistent dislocation. The patient has obvious atrophy of the quadriceps muscle, weakness of the lower limbs, weakness of the legs, difficulty in squatting and walking up and down stairs, and even difficulty in walking. The main pathogenesis of habitual patellar dislocation is external rotation of the quadriceps muscle, as well as contracture of the lateral head of the quadriceps muscle and the lateral support band, and contracture of the patellar tendon leading to shortening of the knee extension device. Since it is difficult to surgically correct the external rotation of the quadriceps muscle and the shortening of the patellar tendon, the treatment of habitual patellar dislocation is difficult, and even in severe cases, inoperable. Habitual patellar dislocation is usually seen in children and should be operated on as soon as it is detected, as only early surgery can restore the patella to its normal position. Extensive and complete release of the lateral knee is performed, along with tight sutures and MPFL reconstruction of the medial knee, and in severe cases, a combined internal superior tibial tuberosity displacement is required. After surgery for habitual patellar dislocation, rehabilitation is generally difficult, and it usually takes more than 3 months of practice to normalize the angle of knee flexion. Some patients may still experience mild external deviation of the patella when the knee is flexed at a large angle, but it usually does not affect normal life and sports. Below is a film of an 11-year-old girl who underwent surgery for habitual patellar dislocation in her right knee about 10 months after the surgery, and basically resumed normal life and sports 7 months after the surgery. 30-, 60- and 90-degree axial X-rays of the flexed knee showed good patellar position (above). Due to habitual patellar dislocation resulting in patellar tendon shortening, the right knee remained low on the patella although postoperatively the flexion was normalized through rehabilitation exercises to elongate the quadriceps muscle (thus flexion exercises are generally more difficult and prolonged) (lower image). Below is a film of a 22-year-old female patient with 10 years of habitual patellar subluxation of the left knee. 7 months after surgery, the knee extension and flexion angles are normal and she can walk normally, and axial radiographs of 30, 60 and 90 degrees of knee flexion show a well positioned patella (upper image), and the three surgical wounds are shown in the lower image.