1, the anatomy and tear site of the medial collateral ligament of the knee joint The medial collateral ligament is a flat and wide triangle, a thickened part of the fibrous layer of the joint capsule, the superficial layer of the medial collateral ligament is long, starting from the node of the medial adductor muscle at the top of the medial femoral epicondyle, ending at the medial surface of the tibial crest, 2-4cm from the tibial articular surface, to the distal 7cm, about 11cm long and 1.5cm wide, the anterior part is the anterior longitudinal part, the posterior part is the posterior superior oblique part, ending at the tibial The posterior border of the medial condyle, attached to the posterior border of the medial meniscus, and the posterior inferior oblique portion slopes upward posteriorly, crosses the semimembranous tendon, and ends at the posterior border of the medial tibial condyle, attached to the posterior border of the medial meniscus. A thickening of the joint capsule anterior to the superficial layer of the medial collateral ligament forms the deep layer of the medial collateral ligament. The tissue at the junction of the superficial and deep layers forms the posterior medial ligamentous structure of the knee (posteromedial capsule (PMC). mtiller found the posterior oblique ligament within the PMC and considered this ligament to be an important stabilizing structure of the medial knee. The tibial stops are widely distributed and the stresses are dispersed, while the stresses at the upper stops are concentrated and fixed, so the tear site is mostly on the femoral side, and the injury mechanism is a knee flexion valgus stress injury, and the extension valgus stress is mostly a superficial tibial side tear of the medial collateral ligament. 2, the medial collateral ligament of the knee injury grading and imaging tear range judgment The medial collateral ligament of the knee injury is divided into 3 degrees according to the degree. degree I injury: a small number of ligament tears, accompanied by local pressure pain but no joint instability; degree II injury: there are more ligament fiber tears, and accompanied by more important functional loss and joint reaction. Grade III injury: complete rupture of the ligaments, which can produce significant joint instability. The width of the medial joint surface gap is classified according to stress test radiographs: mild instability (5 mm), moderate instability (5-10 mm) and severe instability (>l0 mm). The medial collateral ligament (MCL) injury can be divided into three levels on MRI. level I injury: MRI shows low signal in T1WI and high signal in T2WI and STIR in the injury area, and T1WI can show high signal in the subacute phase of bleeding; while the morphology of MCL does not change and has obvious demarcation with the surrounding soft tissues, the coronal plane shows a band-like low signal shadow parallel to the bone cortex. Grade II injury with ligament tear shows high signal in the ligament and fluid in the bursa of the collateral ligament on T2WI (or STIR). The ligament may be displaced and no longer parallel to the cortical margin, and the surface of the ligament is edematous and bleeding, so that the ligament is not clearly demarcated from the surrounding adjacent fat. In Grade III injury, the ligament is completely torn, the continuity is interrupted, the ligament is thickened and swollen, and the whole ligament structure is mixed with muscle signal, and the boundary structure of the ligament cannot be distinguished. There is diffuse high signal on T2WI (or STIR), and the ligament is irregular at its severed end. For medial collateral ligament tears combined with meniscal tears, fork ligament ruptures, or complete tears of the medial structures including the joint capsule in knee dislocations, it is important to have pre-judgment so that treatment can be fully considered. 3. Indications, treatment methods and effects of surgery for medial collateral ligament injury of the knee Currently, scholars mostly advocate conservative treatment for degrees I and II, and surgical treatment for degrees III. However, different treatment methods will have different treatment effects. According to the Institute of Sports Medicine of the Third People’s Hospital of Peking University, a Z-shaped tear in the middle of the medial collateral ligament can be treated by direct suturing of the severed end. The body and joint capsule transverse tears should be reinforced with other tendons. Injuries to the inferior stop should be treated with a stop reconstruction, such as a drilled silk suture or portal nail fixation. The timing of surgical treatment should be no later than 2 weeks after the injury. After surgery, the knee should be flexed in a 30 degree position, and the anterior and posterior plaster braces should be fixed in an inversion and internal rotation position including the ankle joint, and the anterior plaster brace should be removed after 3 weeks, and the posterior plaster brace should be truncated to the ankle after 4 weeks to start functional exercises of the joint. This procedure is complex, with long postoperative rehabilitation and follow-up time, and prone to problems. In patients with severe injury, obsolescence, and tissue weakness, the medial collateral ligament is repaired by graft reconstruction using soft tissues near the knee such as semitendinosus tendon, thin femoral tendon, or broad fascia. The purpose of stabilizing the medial structure of the knee joint is achieved. Kenta Saiga has shown that the combined use of bFGF and GDF-5 in rabbits can improve the healing rate of medial collateral ligament injuries. Some scholars have also confirmed that hyperbaric oxygen therapy can shorten the healing time of the medial collateral ligament through animal experiments. However, all of the above traditional methods will have poor effect due to late exercise, prone to knee dysfunction, and difficult to restore early movement. Our department applies Fastin anchor nail to fix the medial collateral ligament with obvious advantages, which is titanium alloy composition material, vertical cross eye design, no pre-drilling, double suture, and self-tapping thread design. It is suitable for stop point reconstruction of ligament and bone surface tears and provides stronger fixation. Anchor staples are drilled perpendicular to the bone surface at the stop position of the medial collateral ligament. The medial collateral ligament is then closed with a braided double polyester suture at the end of the nail. This anchor nail fixation procedure is simple, minimally invasive, and provides firm fixation and anatomic repositioning, thus restoring the continuity of the medial collateral ligament. The deep threads of the anchor nail have a strong holding force. The braided suture at the end of the nail is a high-strength polyester thread that is braided within the medial collateral ligament, replacing and increasing the strength of the ligament early on and providing ample time for early ligament recovery. Early rehabilitation is possible, reducing knee dysfunction. Therefore, the application of anchor nail fixation for the treatment of medial collateral ligament tears of the knee has unique advantages in clinical practice. 4. Conclusion: Anchor nail fixation for medial collateral ligament injury of the knee can immediately stabilize the knee joint, reduce further damage to the knee joint, and reduce the occurrence of osteoarthritis, which is an effective method for early treatment of medial collateral ligament injury of the knee joint. It is worthy of clinical use and promotion.