Complications after knee ligament reconstruction or other arthroscopic-assisted procedures include, in addition to joint infection, swelling, and limitation of motion commonly seen after knee surgery, complications arising from periarticular tissue damage due to the patient’s initial trauma and complications resulting from inappropriate treatment modalities. Neurovascular injury I. N artery injury: Clinical manifestations: ischemia below the lower leg and diminished (or absent) pulsation of the dorsalis pedis artery are predominant. In case of severe blood supply deficiency in the lower leg, ischemic peripheral neuritis with pain, allergy and numbness may occur. Physical examination: Check the skin temperature, distal arterial pulsation and peripheral nerve sensation of the affected limb. Laboratory tests: Currently, there are no definitive laboratory tests to confirm the diagnosis of N artery injury. Arteriography can be performed to assist in the diagnosis. Currently, CT arteriography can clearly show the blood flow in the arterial travel area. This test is noninvasive and can quickly and effectively determine the extent of vascular injury in the lower extremity. Diagnosis is based on a history of knee fracture and dislocation or corresponding violent trauma, clinical manifestations of inadequate blood supply to the N artery as described above, and arteriography showing no visualization of the N artery supply area. Treatment options: As far as peri-knee surgery is concerned, reconstruction or repair surgery for ligament injury caused by knee dislocation should be performed with priority treatment of N artery exploration and repair for suspected arterial injury. Clinical manifestations of lower extremity deep vein thrombosis: The main clinical manifestation is the sudden swelling of the affected limb, which needs to be compared with the healthy lower limb. Calf DVT can be manifested as mild edema in the affected calf and ankle often. Physical examination: Physical examination has the following features: ① swelling of the affected limb. ②Pressure pain. ③Homans sign. When the foot is sharply bent to the dorsal side, it can cause pain in the deep calf muscle. Homans’ sign is often positive in the case of deep calf vein thrombosis. This is caused by the passive extension of gastrocnemius and hallux valgus muscles when they stimulate the blood all over the calf veins; ④ superficial varicose veins. Laboratory tests: including radioactive fibrinogen test, ultrasonography, electrical impedance volumetric tracing, etc. D-dimer test also helps in diagnosis, and D-dimer results are significantly higher in patients with traumatic lower limb deep vein thrombosis than in normal population. Diagnosis is based on: In patients with high-energy violent trauma to the knee joint, the affected limb is swollen and stiff, painful, and worsens after activity, accompanied by fever and rapid pulse. There is pressure pain at the thrombus site, swelling of the limb distal to the thrombus or the whole limb, cyanotic skin, decreased skin temperature, diminished or absent dorsal foot and posterior tibial artery pulsations, or venous gangrene. Superficial varicose veins, hyperpigmentation, ulceration, and swelling. Doppler ultrasound and venous flow mapping are useful for diagnosis. Venography can confirm the diagnosis. Treatment options: Non-surgical treatment as long as it includes bed rest and elevation of the affected limb, application of anticoagulant therapy and thrombolytic therapy if necessary. Surgical treatment mainly includes venous exploration and thrombectomy, etc. At present, the clinical prevention of pulmonary embolism mostly uses vena cava filter placement to intercept the larger thrombus in the blood flow to avoid entering the pulmonary artery with the blood flow and causing lethal pulmonary embolism. However, complications such as filter displacement, obstruction and bleeding can occur, and the cost is high, so the clinical indications should be strictly controlled. Second, common peroneal nerve injury Clinical manifestations: paralysis of the anterolateral extensor muscles of the lower leg, dorsiflexion and valgus dysfunction of the foot, inversion and ptosis deformity. Loss of bunion and toe extension function, flexion, and anterolateral calf and anterior and medial dorsal foot sensory disorders. Physical examination: mainly check the skin sensation of anterolateral calf and dorsal foot, and the function of anterolateral calf extensor muscle group. Laboratory tests: There is no clear laboratory test to detect nerve injury, electromyography can determine the injury and the degree of injury. Diagnosis: The diagnosis is mainly based on the history of trauma and clinical manifestations. Treatment options: The common peroneal nerve is located on the posterior lateral side of the knee joint, so internal knee valgus, internal rotation, and anterior tibial dislocation are far more effective in pulling on the nerve than external rotation, external rotation, and posterior tibial dislocation. In patients with posterior cruciate ligament, lateral collateral ligament, and posterior lateral complex injuries of the knee, it is critical to examine and determine the presence of common peroneal nerve injury. In particular, when exposing the lateral structures of the knee joint during surgery, care should be taken to select a reasonable interfascial compartment incision to adequately protect the common peroneal nerve. In addition to the initial trauma to the common peroneal nerve, surgery-related factors may also cause common peroneal nerve palsy. Intraoperative tourniquet application is a factor that should not be overlooked. With the increasing understanding of the diagnosis and treatment of knee dislocation and multiple ligament injuries, more and more surgical approaches are being used in the clinical setting, and the duration of surgery has increased accordingly. Both the traditional incisional approach and the arthroscopic knee ligament reconstruction can take too long to perform and may result in lower extremity nerve palsy due to tourniquet compression. Newer tourniquet straps are wider, reducing the pressure per unit area, but despite this, a procedure lasting longer than 120 minutes may result in significant postoperative lower extremity nerve palsy. Most patients heal spontaneously, but adequate attention should be paid to the problems associated with this procedure. (a) Plaster braking: The use of plaster braking in the flexed knee position after knee ligament repair or reconstruction may result in limited knee extension, and long-term residual knee extension restriction may lead to symptoms such as claudication. For some patients with multiple ligament injuries, the braking treatment based only on “soft tissue injury” may also lead to severe limitation of joint movement due to insufficient understanding of the treatment and rehabilitation of ligament injuries at the time of initial injury. (b) Inappropriate surgical options: In some patients with ligament injuries, inadequate knowledge of the natural course of the ligament injury may lead to inappropriate treatment options, which may result in postoperative knee motion restriction. For example, in patients with medial collateral ligament injuries, the blind use of traditional incision repair surgery can easily lead to postoperative functional limitations in flexion and extension of the knee Inflammatory reactions caused by internal fixation materials The bone tunnel fixation material used during ACL reconstruction may react inflammatoryly with the surrounding soft tissues, leading to local symptoms. In addition, absorbable fixation screws for ligament reconstruction are currently widely used. The advantage of this method is that the internal fixation is an absorbable material, which can eliminate the need for the patient to have a second surgery to remove the internal fixation. However, due to the reaction between the absorbable material and the surrounding tissues of the body, it may cause a sterile inflammatory reaction in the local soft tissues, and in severe cases, local tissue redness, swelling, pain and even sinus tract formation may occur.