1.What is the patella? The patella, the kneecap, is located in front of the knee joint and is the largest seed bone in the body, embedded in the quadriceps tendon, and is a triangular flat bone. The patella is the largest seed bone in the body and is buried in the quadriceps tendon. It is a triangular-shaped flat bone with the bottom facing up and the tip down, with a rough front and a smooth articular surface behind, opposite to the patellar surface of the femur. 2.What is external patellar dislocation? External patellar dislocation is a disease in which the patella is dislodged from the femoral trochlea during activity or trauma, resulting in knee pain and impaired movement, often occurring in adolescents, and most patellar dislocations can be reset immediately or partially. 3.How does patellar dislocation occur? Patellar dislocation often occurs in direct trauma such as running (especially when bending and turning), lateral shift in a half squat (playing basketball with a defensive shift) or lateral knee impact. It is clinically proven that most patients with patellar dislocation are accompanied by anatomical abnormalities, which may explain why some people dislocate their knee with just a slight touch. The stability of the patellofemoral structure is the result of a combination of dynamic and static supporting structures. Static stabilizing structures include the articular connection between the femoral talar recess and patellar cartilage, as well as ligamentous connections such as the medial patellofemoral ligament and patellar meniscal ligament; dynamic structures mainly include the quadriceps and N cord tendons along with the gastrocnemius muscle. Usually the anatomical structures are abnormal because the outward pulling muscles or ligaments are too strong or the inward supporting structures are too weak, and a minor trauma leads to an outward dislocation of the patella. Dislocation can lead to rupture of certain ligamentous structures within the patella, which, if not repaired, may make it more susceptible to dislocation than before. 4. What are the common anatomical abnormalities? The main ones are high patella, femoral talus hypoplasia, increased Q angle (angle between quadriceps axis and patellar ligament axis), knee valgus, medial femoral muscle atrophy or lateral femoral muscle hypertrophy, generalized joint laxity, etc. 5.What are the symptoms of discomfort in the knee joint after patellar dislocation? Patients feel sudden and severe pain in the knee joint, and may have a feeling of patella dislocation to the outside or weakness. The patella often resets itself after the knee joint is straightened, and a “clicking” sound can often be heard during the resetting. This is followed by swelling and pain in the knee joint. These symptoms can be confused with meniscal tears, but unlike meniscal tears, in patients with patellar dislocation, swelling and pain can be evident at the medial border of the patellofemoral joint, rather than the medial knee space. A positive pushing patellar flexion fear test can be found on examination. 6.If the diagnosis of patellar dislocation is uncertain, what tests are useful for diagnosis? Routine frontal and lateral X-rays of the knee joint are necessary. 30 degree lateral films of the knee in flexion can be taken to observe the presence of a high patella; 30 degree or 45 degree axial films of the patella in flexion or CT films can reveal a lateral subluxation of the patella, and sometimes small torn bone fragments can be found in the lower part of the patella. The most ideal examination method is MRI, which can clearly show patellofemoral subluxation, knee joint effusion and patellofemoral ligament tear, and also determine whether there is accompanying femoral condyle cartilage injury or other intra-articular structure injury. 7.What types of external patellar dislocation are there? External patellar dislocation is mainly divided into two types: traumatic dislocation and habitual dislocation. Traumatic dislocation is an external force acting on the knee, causing the patellar ligament and knee capsule to rupture or tear off, resulting in patellar displacement and dislocation, and the damage to the ligamentous tissue around the patella caused at the moment of dislocation often cannot be repaired by itself, which becomes the pathological basis for habitual patellar dislocation. Habitual patellar dislocation refers to the patella being dislocated and reset several times during the activity process. 8.Why should patellar dislocation be treated promptly? What kind of damage will be caused to the joint if left untreated? After patellar dislocation, the medial stabilizing structures of the patellofemoral joint, including the medial patellofemoral support band, medial femoral muscle and medial patellofemoral ligament, are torn, resulting in hematoma and synovitis in the knee cavity, which can cause long-term symptoms such as knee pain, instability, locking, dislocation and swelling, and seriously affect daily activities, so treatment is definitely needed. Conservative treatment is often ineffective, and patellar dislocation can recur repeatedly, leading to the development of habitual patellar dislocation. Repeated patellar dislocations can cause cartilage damage or bone contusions, leading to traumatic patellofemoral arthritis, joint degeneration, and late formation of osteoarthritis, which means long bone spurs, because the medial side of the patella impacts with the lateral side of the femoral condyle during the dislocation self-repositioning process. Therefore, whether it is habitual or first occurrence, it should be treated with surgery as early as possible. 9.What are the surgical methods for treating external patellar dislocation? There are many surgical procedures for the treatment of external patellar dislocation, generally divided into: ① proximal patellar rearrangement; ② distal patellar rearrangement; ③ distal and proximal patellar rearrangement at the same time. Specifically, proximal patellar rearrangement mainly includes lateral support band release, medial support band tightening, and medial patellofemoral ligament repair or reconstruction; while distal patellar rearrangement mainly includes lateral semi-internal patellar ligament migration and internal tibial tuberosity elevation. As habitual patellar dislocation has different local structural developmental deformities, it cannot be solved by one type of surgery and should be treated with comprehensive surgery according to the different deformities. Regardless of the surgical approach, the aim and core of treatment is to correct the patellar alignment abnormality and reconstruct the knee extension device. At present, orthopedic surgeons at home and abroad tend to carry out medial patellofemoral ligament repair or reconstruction surgery, which has its unique advantages compared with other surgical procedures. It not only has a small impact on the knee extension device and is suitable for many types of patellar dislocation, but also can be combined with other surgical procedures to treat severe patellar dislocation, and has a low recurrence rate after surgery, making it one of the most commonly used procedures for treating patellar dislocation. 10.How to recover after patellar dislocation surgery? How long does it take? The knee is protected by a brace in the straight position for 6 weeks. The knee flexion exercises can be started on the 2nd to 3rd postoperative day, using CPM or with the assistance of a rehabilitation therapist, and generally the knee can be flexed to 90o within 3 to 4 weeks postoperatively; if the patient is still unable to flex the knee to 90o 4 to 6 weeks postoperatively, physical therapy must be intensified; isometric contraction of the quadriceps, straight leg raising (4 weeks postoperatively if there is tibial tuberosity displacement), mild pushing of the patella, and mild active knee flexion exercises can be started on the 2nd postoperative day. and mild active knee flexion exercises. On the second to third postoperative day, the patient may perform partial weight-bearing with the aid of crutches as long as the patient can tolerate, but not more than 50% of the patient’s body weight. Patients must wear a brace when performing weight bearing or walking exercises. Full weight-bearing is usually performed 4 weeks after surgery. At 2 weeks postoperatively (after stitch removal), patients are allowed to remove the brace while bathing, however, for 6 weeks postoperatively, patients are required to wear the brace while walking and sleeping. After 3 months postoperatively, patients were allowed to start jogging and light physical activity. When resuming physical activity, patients can wear a simple knee brace and patella stabilization brace for protection. If the patient’s knee flexion and extension range of motion and quadriceps muscle strength return to normal, full physical activity can begin, which generally takes 6 months.