Patients with acute ACL injuries (history 1-21 days, mean 11 days) were classified according to intra- and extra-articular injuries, and their arthroscopic presentation and management were summarized. Fifty-three cases were followed up for 8-46 months, all 14.5 months (48 cases with second arthroscopic surgery and 35 cases with K-T2000 examination). Intra-synovial rupture: 2.2% of all cases (4/179). There were 2 cases each of partial and complete rupture. Microscopic features: 1. synovial membrane; 2. microscopic ADT Diagnostic method: probing hook exploration, which can hook out the broken end. Intercondylar spine avulsion fracture: there were 11 cases, accounting for 6.1%. 5 cases were avulsed together with the anterior horn of the lateral meniscus; 3 cases were combined with tibial plateau fracture . Surgical management: arthroscopic tibial tract (steel wire, polyester braided wire) repositioning and internal fixation of the medial joint capsule injury: tear: 26 cases (over the meniscus: 23 cases; MCL fracture: 24 cases); contusion: 7 cases (congestion, bruising and swelling of the joint capsule wall; indirect evidence of MCL injury: 5 cases Discussion: combined injury of ACL is considered to be the most typical mechanism causing acute ACL fracture and medial knee The most typical mechanism of combined structural injury is manifested clinically as a typical triad: that is, a triad of ACL, MCL, and medial meniscus injuries. The incidence of combined lateral meniscus injury is much higher than that of medial meniscus in this group of cases. During external rotation of the knee joint, a subluxation occurs between the femur and tibia, and the lateral femoral condyle impacts with the posterior part of the lateral tibial plateau. The impact force from this instability is first applied to the lateral meniscus, which is partially cushioned by the meniscus before it is transmitted to the corresponding part of the subchondral bone. The clinical epidemiology of our clinic shows that combined injuries of ACL, MCL and lateral meniscus are common.ACL fracture site: the results observed in our group: complete fracture of the parenchyma: 160 cases in total, accounting for 88.3%. The upper part of the parenchyma of the ACL is the site where the ligament is easily damaged – this is related to the fact that the ligament tissue at the upper stop of the parenchyma of the ACL is the thinnest anatomically. Intra-synovial rupture is a rare pathological type of acute ACL injury. Four cases were found in this group accounting for 2.23% of the total. Microscopic manifestations: synovial bruising or microscopic fissures; probing hooks may reveal reduced ligament tension; significant depression at the site of injury; intraoperative drawer test ligament loss of tension; probing hooks hook out the fibers of the severed end of the ligament. A specific type of tibial intercondylar spine avulsion fracture ACL injury. The incidence of this group of patients was 6.1%. In 45.5% (5/11), there was a combined avulsion of the anterior horn of the lateral meniscus. In this group, arthroscopic suture or wire fixation was used. In all cases, good repositioning and fixation was obtained through arthroscopic surgery, and the anterior horn of the lateral meniscus, which is attached to the fracture mass, was also well repositioned. The type of injury to the medial meniscus was dominated by longitudinal fracture and edge separation, accounting for 64.1% of the cases, and the percentage of sutures reached 53.8%. Many of the medial meniscus injuries were due to tears of the medial capsule, and the medial meniscus could be well fixed by suturing the capsule in such cases. There are different opinions on the management of combined ACL and MCL injuries in clinical practice. In our institute, we have found that many Grade III MCL injuries treated conservatively in the acute phase develop chronic medial instability. If surgical exploration is performed, the superficial ligamentous tissue of the MCL will show significant thinning and scarring throughout, with poor tone. complete rupture of the superficial inferior stop of the MCL almost always shows rupture or avulsion at the stop. The distal end often detaches completely from under the goose palm, separating far from its broken inferior stop, and it is difficult for the severed end to heal on its own at the original stop, so stop reconstruction is required. Our institute experience: combined injuries of ACL and MCL require early surgical management and active and effective postoperative rehabilitation exercises to prevent joint adhesions.