Posterior cruciate ligament injury

　　The cause of this disease is due to injuries caused by the posterior force of the proximal tibia in the flexed knee position and the overextension force of the knee.
　　1. Violent action on the proximal tibia in the flexed knee position:It causes the upper part of the lower leg to move forward abruptly, causing the PCL to break. 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 the fracture and dislocation and missed.
　　2. Overextension violence:The violent force forces the knee to be in an overextension position, first causing the PCL to break, if the violent force continues to overextend the knee, the ACL will also be damaged, the PCL breakage 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 proximal tibia is subjected to a violent force from the front and is simultaneously rotated, this injury mechanism often causes a compound injury, that is, an injury to the lateral structure, and the semilunar dislocation of the tibia posteriorly is more serious than simple PCL injury.

　　If the treatment of posterior cruciate ligament injury is not timely, it may lead to serious complications. Improper treatment may cause intra-articular fractures or avulsion fractures, and late complications may include degenerative osteoarthritis of the knee joint.

　　When the injured knee is damaged, it is often accompanied by a tearing sound or a sensation of falling to the ground, with severe knee pain and rapid swelling, initially limited to the joint, when the posterior joint capsule breaks, the swelling spreads to the popliteal fossa, and involves the posterior side of the lower leg. Subcutaneous ecchymosis gradually appears, indicating that bleeding from the joint cavity leaks into the posterior knee and the interval between the gastrocnemius and soleus muscles. If there is a concurrent injury to the knee MCL or LCL, abnormal movements of inversion and eversion, as well as instability of internal and external rotation, may occur, and local pain and swelling may occur in the ligament, and the Jerk test may be positive. A positive Jerk test indicates instability of the anterior lateral rotation of the knee, proving that there is a posterior cruciate ligament injury (including MCL and medial joint capsule ligament).

　　Exercise enthusiasts or athletes are prone to this disease. Proper landing technique is very important for preventing knee joint injuries. It is recommended that when landing, the front 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 joint. 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 done:
　　1. It is important to warm up before exercise to heat up the joints first;
　　2. Do not exercise when tired, as this can cause delayed reaction and make movements difficult to coordinate;
　　3. Strengthen the exercises of lower limb strength, 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 hot compress and massage at a fixed time every day.
　　6. Avoid overexerting the knee joint, try not to do knee squats.
　　7. Those who are overly 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 to the ground, with severe knee pain and 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. Subcutaneous ecchymosis gradually appears, indicating that joint bleeding has leaked into the posterior knee and the interval between the gastrocnemius and soleus muscles. If there is a combined injury of knee MCL or LCL, abnormal internal and external翻 movement and instability of internal and external rotation may occur, local pain and swelling of the ligament may occur, and the Jerk test is positive. A positive Jerk test indicates instability of the anterior lateral rotation of the knee, proving that there is a knee MCL injury (including MCL and medial joint capsule ligament). It often needs to be checked after the acute stage. The method is: ask the patient to lie on their back, flex the hip to 45°, flex the knee to 90°, simultaneously internally rotate the tibia, and apply an external force to the upper part of the lower leg. Then gradually extend the knee to 20°～30°, the lateral femoral and tibial joint surfaces may occur subluxation. If the knee is further extended, natural reduction occurs with a rebound feeling and sound, which is positive. Another method is: in the extended knee position, rotate the lower leg externally or neutrally, apply an external force to the knee joint, and gradually flex it to 20°～30°, with a popping sound and a sense of dislocation, which is positive. In addition to the above methods, other auxiliary examinations include:

　　1. X-ray examination
　　It shows that the knee joint space is widened, the tibial attachment point of the PCL is visible with avulsion fracture. For suspected cases, the author uses femoral and sciatic nerve block, bends the knee to 90° before and after drawer test, takes knee lateral X-ray film, measures it, draws a perpendicular line from the center of the femoral condyle to the tibial plateau horizontal line, divides the horizontal line into two segments, any segment longer than 5mm than the same segment on the healthy side is positive. The longer the anterior segment is, the more likely it is an ACL tear, and the longer the posterior segment is, 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, resolve stasis, and relieve pain can be selected, such as Panax notoginseng, scallion whites, tangerine peel, rose, crab, Brassica chinensis, lotus root, eggplant, hawthorn, etc. However, it is important to note that if there is still bleeding, it is not advisable to choose these 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 supplement 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:

      1. Non-surgical treatment
　　The common standard for non-surgical treatment is the 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 and lateral corner injury, emergency surgery should be performed, especially early repair of posterior and lateral corner injury.

　　(2) Key points of surgery: The incision for PCL repair depends on whether there is injury to other ligaments.
　　① For simple PCL injury, or PCL injury with knee MCL injury, a posterior and medial knee incision should be chosen, entering from behind the MCL bundle.
　　② For PCL injury with posterior and lateral structure injury, a posterior and lateral knee incision should be chosen, entering through the anterior edge 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 is pulled outward to protect the popliteal vessels and nerves, larger bone fragments are fixed with screws, and smaller ones are wrapped with钢丝, pulled from the bone hole to the anterior and medial side of the tibia and fixed (Figure 4). This type of injury advocates early repair.
　　④ For actual rupture of the ligament, autologous or allogeneic tendons are used for reconstruction. When there is knee MCL, LCL injury, LCL should be sutured first, and then the posterior cruciate ligament is tightened and fixed.

　　(3) Postoperative management: For simple PCL injury, fixation in extension for 6 weeks, if the posterior joint capsule is also injured, then fixation at 20° of flexion for 6 weeks, remove the cast, and exercise knee joint movement. The best treatment result is the repositioning and suture of the tibial avulsion fracture, all of which recover 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 (reduction >10mm), generally considered for surgical reconstruction. If there is also posterior and lateral or posterior and medial rotational instability at the same time, it is an absolute indication for surgery. For athletes, the indication for surgery can be slightly relaxed.