Posterior cruciate ligament injury

　　The cause of this disease is due to the injury caused by the backward violent force on the upper end of the tibia in a flexed knee position and the hyperextension of the knee.
　　1. Violent action on the upper end of the tibia in a flexed knee position:It causes the upper part of the lower leg to move backward suddenly, leading to PCL rupture. If the upper part of the tibia continues to move backward, the posterior joint capsule of the knee is also torn. This injury can also be accompanied by fractures and dislocations of the femur, tibia, and patella. At this time, the PCL injury is easily concealed by fractures and dislocations and missed.
　　2. Hyperextension violence:The violent force forces the knee into hyperextension, first causing PCL rupture, if the violent force continues to hyperextend the knee, the ACL will also be injured, the PCL rupture site is mostly at the attachment of the femoral condyle, and the incidence of injury at other sites is relatively low.
　　3. Posterior rotational violence:When the foot is fixed, the upper end of the tibia is subjected to a violent force from the front and at the same time rotated, this injury mechanism often causes complex injuries, that is, combined with injuries to the lateral structure, the posterior half-dislocation of the tibia is more serious than simple PCL injury.

　　If the treatment of posterior cruciate ligament injury is not timely, it can produce relatively serious complications. Improper treatment can cause intra-articular fracture or avulsion fracture, and late complications may include degenerative knee osteoarthritis.

　　When the injured knee is damaged, it is often accompanied by a tearing sound or a sense of tearing, followed by severe pain in the knee, rapid swelling, initially limited to the joint, when the posterior joint capsule ruptures, the swelling spreads to the popliteal fossa, and involves the posterior side of the lower leg, gradually appearing subcutaneous ecchymosis, indicating that the joint bleeding leaks into the posterior knee and the gap between the gastrocnemius and soleus muscles. If combined with knee MCL or LCL injury, abnormal movements of internal and external valgus and internal and external rotation instability may occur, and local pain and swelling may occur in the ligament, and the Jerk test is positive. A positive Jerk test indicates instability of the anterior lateral rotation of the knee, proving that the knee MCL (including MCL and medial joint capsule ligament) is injured.

　　Athletes or sports enthusiasts are prone to this disease. Proper landing techniques are very important for preventing knee injuries. It is recommended that when landing, the front part of the foot should land first, the knee should be bent, and the trunk should be slightly forward. Try to avoid lateral or forward and backward movements of the knee. Remember that the knee should not be twisted inward when landing, and the impact force should be reduced as much as possible. In daily life, the following points should be followed:
　　1. Before exercising, it is important to do warm-up activities to heat up the joints first;
　　2. Do not exercise when tired, as this may cause delayed reaction and difficult coordination of movements;
　　3. Strengthen the exercises of lower limb strength to ensure the stability and flexibility of the knee joint;
　　4. In sports, prevent rough actions from causing accidental injuries.
　　5. Pay attention to the warmth of the knee joint, and perform knee heat compress and massage regularly every day.
　　6. Avoid overexerting the knee joint, try not to do knee bending exercises.
　　7. People who are too overweight should lose weight.
　　8. Avoid overloading during physical exercise.

　　When the injured knee is damaged, it is often possible to hear a tearing sound or have a sensation of falling due to tearing, with severe pain in the knee, rapid swelling, initially limited to the joint, when the posterior joint capsule ruptures, the swelling spreads to the popliteal fossa, and affects the posterior side of the lower leg, gradually appearing subcutaneous ecchymosis, indicating that bleeding within the joint has leaked to the back of the knee and the gap between the gastrocnemius and soleus muscles. If there is a concomitant knee MCL or LCL injury, abnormal internal and external inversion and rotation instability may occur, and the local ligament may appear pain and swelling. A positive Jerk test indicates anterolateral rotation instability of the knee, proving that there is a knee MCL injury (including MCL and medial joint capsule ligament). It often requires examination after the acute phase. The method is: ask the patient to lie on their back, flex the hip to 45°, and flex the knee to 90°, while internally rotating the tibia, and applying an external valgus stress to the upper part of the lower leg. Then gradually extend the knee to 20° to 30°, and the lateral femoral condyle and tibial articular surface may occur subluxation. If the knee is further extended, a natural reduction with a snap and sound occurs, which is positive. Another method is: in the extended knee position, rotate the lower leg externally or neutrally, and apply an external valgus stress to the knee joint. Gradually flex the knee to 20° to 30°, and a popping sound and a sense of dislocation indicate positivity. In addition to the above methods, other auxiliary examinations include:

　　1. X-ray examination
　 　It shows that the gap between the knee joint is widened, the tibial attachment point of the PCL is visible with avulsion fracture. For suspected cases, the author uses the femoral nerve and sciatic nerve block, bends the knee to 90° before and after the drawer test, takes knee lateral X-ray films, and measures from the center of the femoral condyle to the horizontal line of the tibial plateau to draw a perpendicular line dividing the horizontal line into two sections. If any section is more than 5mm longer than the same section on the healthy side, it is considered positive. The longer the anterior section, the more likely it is an ACL tear, and the longer the posterior section, the more likely it is a PCL injury.

　　2. MRI diagnosis
　　Acute PCL injury has a 100% diagnosis rate, but for old injuries, there may be false negatives.

　　General soft tissue injuries often have symptoms of Qi stagnation and blood stasis. Foods that can promote Qi, activate blood circulation, remove blood stasis, and relieve pain can be selected, such as Sanqi, scallion whites, tangerine peel, rose, crab, rapeseed, lotus root, eggplant, hawthorn, etc. However, it must be noted that if there is still bleeding, it is not suitable to choose such foods.
　　The ligaments are mainly composed of collagen, so in terms of diet, one can consume foods rich in collagen, such as chicken feet, pork feet, fish gelatin, etc., which contain a large amount of collagen. It is also appropriate to pay attention to the supplementation of calcium, choosing small fish and shrimp, seaweed, and so on.

　　According to the degree of ligament injury, surgical treatment and non-surgical treatment can be chosen: Western medicine treatment for posterior cruciate ligament injury

      1. Non-surgical treatment
　 　The common criteria for non-surgical treatment are: tibial rotation neutral position posterior drawer sign
　　2. Early surgical repair of ligaments
　　(1) Indications:
　　① For patients with tibial avulsion fracture with displacement;
　　② For patients with meniscus injury and joint locking that cannot be relieved, early surgical repair should be performed;
　　③ For severe knee dislocation, anterior and posterior cruciate ligament rupture, and posterior lateral corner injury, emergency surgery should be performed, especially early repair of the posterior lateral corner injury.

　　(2) Key points of surgery: The incision for PCL repair depends on whether there is concomitant injury to other ligaments.
　　① For simple PCL injury, or PCL injury with knee MCL injury, a posterior medial knee incision should be chosen, entering from behind the MCL posterior bundle.
　　② For PCL injury with posterior lateral structure injury, a posterior lateral knee incision should be chosen, entering through the anterior margin of the biceps femoris, exploring and repairing the lateral ligament and popliteal tendon.
　　③ For PCL injury with tibial avulsion fracture, a posterior S-shaped incision can be chosen, the medial head of the gastrocnemius muscle can be pulled outward to protect the popliteal vessels and nerves, larger bone fragments can be fixed with screws, and smaller ones can be wrapped with钢丝, pulled through the bone hole to the anterior medial side of the tibia and fixed (Figure 4). This type of injury advocates early repair.
　　④ For ligamentous实质断裂，采用自体或异体肌腱重建，合并膝MCL，LCL损伤时，应先缝合LCL，最后拉紧后十字韧带固定。

　　(3) Postoperative management: For simple PCL injury, the knee is fixed in extension for 6 weeks. If the posterior joint capsule is also injured, the knee should be fixed in 20° flexion for 6 weeks, remove the cast, and exercise knee movement. The best treatment outcome is the reduction and suture of the tibial avulsion fracture, with all patients recovering well.

　　3. Late PCL injury
　　Indications for surgery: patients are young, generally under 45 years old, with recurrent knee pain, swelling, and instability, posterior drawer sign grade III (posterior laxity >10mm), generally considered for surgical reconstruction. If there is also posterior lateral or posterior medial rotational instability, it is an absolute indication for surgery. The indication for surgery for athletes can be slightly relaxed.