External fixators are widely used in various fields of orthopedics. Femoral external fixators are often used to correct shortened femoral deformities, femoral fractures, and reconstruction of femoral tumors. The use of femoral external fixators has a high probability of reduced knee joint mobility and knee joint stiffness, especially the use of ring-shaped external fixators. The external fixator will fix the thigh muscles and aponeurosis, so that the movement of the thigh muscles of the knee joint is restricted, thereby limiting the flexion and extension of the knee joint. Reduced knee mobility can be significantly improved after removing the external fixator. However, for patients who need to use an external fixator for a long time, such as femoral prolongation, the patient's knee flexion is limited during fixation. The knee function cannot be quickly restored after the external fixator is removed . Although most patients' knee mobility can be significantly improved through functional exercise or secondary surgery, it may also lead to re-bone fractures. Therefore, the complication of femoral external fixation used to reduce knee mobility is still a relatively important issue. We found in the operation that by flexing the knee joint to 90 degrees before placing the external fixator nail, the patient can flex the knee joint by an average of 80 degrees 2-3 days after surgery. Moreover, the patient's knee flexion is not limited during the post-surgery period, and it will not cause inconvenience to life. After removing the external fixator, the patient's knee function quickly returned to normal, and no knee stiffness or mobility decreased significantly.
The flexion disorder of the knee joint after the placement of the external femoral fixator is related to the lateral femoral muscles' fixation, aponeurosis, and iliac tibial bundle with nails, the main structure is the iliac tibial bundle. The iliac tibial bundle is a thickened part of the lateral fascia of the thigh. The upper end is connected to the lateral edge of the front end of the iliac bone. The lower end is connected to the lateral tibial condyle, fibula head, and knee joint capsule. The iliac tibial bundle is an important organization for maintaining knee stability and knee motion and is involved in knee flexion and extension essential . The iliac tibial bundle is tougher and less elastic, it cannot be moved normally and cannot be stretched elastically after being fixed by an external fixator nail. After the iliac tibial bundle fixed by an external fixator nail, due to the poor elasticity of the lower part of the iliac tibial bundle, and the distance OG’ required for knee flexion is longer than OG(figure 3), it is difficult to flex the knee joint. And the iliac tibia bundle slides up and down along the lateral femoral muscle when extending and flexing the knee, sliding up when extending the knee and sliding down when bending the knee. In addition to sliding up and down, there is also forward and backward movement: forward when the knee is extended, and backward when the knee is bent. After the external fixation nail fixes the iliac tibial bundle, the upward and backward movement of the iliac tibial bundle is restricted, so that the knee flexion function is limited. Moreover, the child was unwilling to exercise because of pain when pulling the nailed iliac tibial bundle when flexing the knee joint. Besides, the adhesion between the fixed iliac tibial bundle and the muscle or aponeurosis aggravated the knee joint's flexion activity after surgery, so that after removing the external fixator, there was still a limited knee flexion activity. Although the method of cutting the iliac tibial bundle at the nail tract used to improve the postoperative knee joint movement, this method is very invasive, and local adhesion formation will still affect the knee joint movement. Now we fix the external fixation nail when flexing the knee joint during surgery. The lower iliac tibial bundle OG segment fixed when flexing the knee joint is longer. The longer movable segment is reserved so that the iliac tibial bundle will not restrict the flexion of the knee joint. Moreover, more space is reserved for the iliac tibial bundle to move backward and downward when flexing the knee, to avoid the limitation of the flexion activity of the knee joint after the operation.