Posterolateral corner (PLC) injury is a serious injury to the knee joint and is often associated with other ligament injuries such as the posterior cruciate ligament (PCL).The function of the PLC in preventing knee inversion, tibial external rotation, and posterior drop is the basis for the successful repair of other ligamentous structures, and therefore the repair and reconstruction of PLC injuries is crucial for the recovery of the knee joint function. In the past, there was a lack of clear diagnosis and treatment for PLC injuries due to the lack of understanding of the anatomy and function of the PLC. In addition, due to the complex structure of PLC, it is difficult to recognize the tissue structure after injury, which also affects the correct and active treatment. If its injury treatment is neglected or delayed, it will lead to knee instability and even failure of surgical reconstruction of other ligaments [1]. To summarize, 32 cases of knee cruciate ligament combined with posterior lateral corner multiligament injury were admitted to our hospital from 2004, 05 to 2009, 02. All of them were reconstructed with minimally invasive surgery assisted by autologous semitendinosus tendon arthroscopy to reconstruct the cruciate ligament and posterior posterolateral corner ligament. Clinical efficacy is satisfactory, reported as follows: I. Data and Methods 1.1 General Data From May 2004 to February 2009, 32 cases were admitted, 22 male, 10 female, age,27-63 years old, average 38±2,15 years old. The time between injury and surgery ranged from 3 to 18 weeks, with an average of 4,2 weeks. Preoperative stability examination was performed, and the posterior-lateral instability of the knee was typed according to Fanellli [2]: type A, 1 case; type B, 14 cases; type C, 17 cases. All cases were combined with cruciate ligament structural injuries. 28 cases were combined with meniscus injuries. 1 case was combined with pelvic fracture, abdominal organ injury and hemorrhagic shock, and was transferred from another department more than three months after the injury, at which time ossified myositis had appeared in the posterior lateral knee. 1,2 Methods After the injury, the lower limb should be immobilized with cast or brace in knee extension position for 2-3 weeks, and then remove the external fixation and perform knee flexion and extension functional exercises. After the flexion and extension activities are basically normal, the stability of the knee joint is evaluated again, and the reconstruction of the posterior lateral structures and the reconstruction of the cruciate ligament are carried out if the posterior lateral structures are unstable. 1,2,1 Anesthesia is usually lumbar or epidural. The knee is re-examined under anesthesia. To further clarify the diagnosis. The patient is in supine position, and a tourniquet is tied after routine disinfection and laying of towels. 1,2,2 First, an open or closed tendon extractor was applied to take autologous bilateral semitendinosus tendons and thin femoral tendons, and the tendons were taken as long as possible when extracting tendons in order to have enough length to reconstruct the posterior lateral angle. 1,2,3 Arthroscopic examination of intra-articular structures was performed first, focusing on damage to the cruciate ligaments, damage to the menisci, and the integrity of the posterior-lateral joint capsule and N tendon. Intra-articular lesions, such as treatment of meniscal tears and reconstruction of the cruciate ligament, are treated first. 1,2,4 Reconstruction of the posterior lateral corner A longitudinal incision of approximately 2 cm in length is made in the lateral epicondyle of the femur (located in the middle of the attachment point of the lateral collateral ligament and the N tendon to the lateral epicondyle of the femur) From this point, a kernickele pin is made from the lateral to the medial side and passed through in order to facilitate the drawing of the ligament. According to the thickness of the removed semitendinosus muscle after folding the 3 strands, the lateral femur is reamed with the Kirschner’s needle as the center, and the depth is about 2 to 2.5 cm. A longitudinal incision is made proximally at the posterior edge of the fibular head, about 4 cm long in the skin, the superficial and deep fascial layers, and from the biceps femoris tendon, iliotibial fascia, the lateral condyle of the femur and the posterior edge of the fibular head within the triangle, the medial side of the separation is done until the posterior lateral angle of the tibial plateau can be palpated across the joint capsule. The posterior medial aspect of the fibular head is also probed to clarify that there is no tissue mechanism tightly attached to its posterior medial aspect. From the anterior side of the fibular head to the posterior medial side, a 6-mm-diameter drill was made from the anterior side of the posterior lateral corner of the anterior Gerdy’s bone under the plateau surface, and the tendon was threaded through the fibular tunnel, and the tendon was divided into the anterior and posterior ends according to the position relative to the fibula, and the anterior end was pulled through the iliotibial fascia deeper and submerged to the femoral tunnel to be used for reconstruction of the collateral ligaments; the posterior segment was folded back, and the folded portion was pulled through the iliotibial fascia deeper and submerged to the femoral tunnel. The folded end was pulled into the posterior lateral bone cavity of the tibial plateau for reconstruction of the N peroneal and N musculocutaneous tendons. After the ligaments were placed, they were pulled tight and the femoral and tibial ends were secured separately. Each incision was sutured, and cotton pads were used for compression bandaging. 1, 2, 5, Postoperative management and follow-up After surgery, the knee was immobilized with a brace in the fully extended position for 2 weeks, and muscle isometric contraction training and patellar pushover training were performed. The knee mobility training and proprioceptive function training were gradually started from the 3rd week after surgery. The degree of knee instability in full knee extension and 30° knee flexion, external rotation of the lower leg at 30° knee flexion, and reverse axial shift test were examined during the postoperative period. The follow-up period ranged from 12 to 48 months. 1,3 Results All patients had grade A healing of the incision without complications such as vascular and nerve injuries. At the 1-year postoperative follow-up, there was no inversion instability in the fully extended knee position, one case of 30° inversion instability with hard termination point in the flexed knee, and no inversion instability in the rest. In bilateral comparison, there was an increase in calf external rotation on the affected side at 30° knee flexion in 2 cases, both less than 10°. All patients had a negative reverse-phase axial shift test. At final follow-up, all patients had no sensation of knee instability in the hyperextended position associated with posterior lateral knee instability during uprighting, walking, or descending stairs; no inward knee throws during walking were noted. Joint mobility, flexion 110-130°, mean 118°; extension 0-5°. According to IKDC (internationalkneedocumentortioncommittee) knee scoring standard[3], subjective evaluation: normal 10 cases (31%), approximately normal 16 cases (50%), abnormal 6 cases (19%), no serious abnormality; objective evaluation: 48-95 points, an average of 83±1.8 points. Discussion 1, PLC injury diagnosis of the posterior lateral stabilizing structure of the knee joint, including a group of static stabilizing structure and a group of dynamic stabilizing structure. Among them, the static structures include lateral collateral ligament, N fibular ligament, arcuate ligament complex, bean fibular ligament and posterior lateral joint capsule; the dynamic stabilizing structures include biceps femoris tendon, iliotibial bundle, and N muscle musculotendinous complex. Among these complex anatomical structures, the strongest and most important for the stability of the posterolateral corner of the knee are the lateral collateral ligament, the N fibular ligament, and the N musculotendinous complex. Functionally, the lateral collateral ligament mainly prevents internal rotation of the knee and also assists in preventing external rotation and posterior fall of the tibia; the N fibular ligament and N tendon mainly prevent external rotation of the tibia and also assist in preventing posterior fall of the tibia and internal rotation of the knee. The diagnosis of lateral collateral ligament injury is mainly determined by 30° knee flexion, because at this time the N tendon and N peroneal ligament are in a state of laxity, and have no role in preventing knee inversion. The degree of ligament injury can be determined according to the degree of knee inversion and the presence or absence of the hard termination point.The diagnosis of N tendon and N peroneal ligament injuries is mainly based on the flexion of the knee at 30° of external rotation of the lower leg, and an increase of more than 10° in external rotation compared with that of the healthy side implies that the two groups of structures are injured[4] 2. The significance of posterior lateral corner reconstruction Because most of the injuries to the posterior lateral corner of the knee are caused by high-energy injuries, and therefore often combined with other structures, such as the cruciate ligament, and other structures. Because most injuries to the posterolateral corner of the knee are high-energy injuries, they are often combined with injuries to other structures such as the cruciate ligaments, resulting in severe instability of the knee joint. If the posterolateral corner is not well recognized in the early stage, the judgment of the injury is often neglected. Sekiya et al.[5] found that if the PCL is reconstructed while the posterolateral corner is neglected, the PCL will be subjected to more stress because of the abnormal posterior tibial drop and external rotation, which will cause the PCL to become lax and the reconstruction will fail. Fanelli[6] concluded that all knee ligament injuries should be handled carefully, the degree of injury should be correctly evaluated, and necessary repair or reconstruction should be performed on each injured structure to ensure the stability of the knee joint. Therefore, for cruciate ligament injuries combined with posterolateral corner instability, it is necessary to test the stability of the posterolateral structures before reconstructing the cruciate ligament and give the necessary repair and reconstruction. In all of our cases, we used a three-week, one-stage reconstruction of the cruciate ligament and posterior posterolateral corner. The reason for choosing subacute reconstruction is that injuries to the posterior posterolateral corner are often combined with injuries to the cruciate ligament and injuries to the joint capsule, and arthroscopic reconstruction of the cruciate ligament within three weeks is likely to result in saline exposure, and after three weeks, the edema of the tissues is significantly reduced, which is conducive to the reconstruction of the ligaments. Knee braking within three weeks after injury is beneficial to the repair of mild injury of some posterior lateral corner ligaments, thus reducing unnecessary reconstruction. The reconstruction method used in this group of cases was non-anatomical reconstruction. The anatomical structure of the posterior lateral horn is complex, and it is difficult to recognize the anatomical structure after the injury, so true anatomical reconstruction or repair is difficult to do. And the injury of the posterior lateral horn is mostly an injury of multiple ligaments of the knee joint, often multiple ligaments need to be reconstructed, and there are difficulties in establishing multiple tunnels in the femoral condyle sometimes. Zhao Jinzhong [7] and others found that strengthening the PLC was able to satisfactorily restore the stability of the posterior lateral knee despite non-anatomic reconstruction. Our clinical practice also verifies the opinion of [7].