Insert Nails When Flexing the Knee in the Femoral Fracture External Fixation: A Technical Report

Background: The application of external femoral xation techniques often causes complications of knee exion dysfunction. We report on technical modications in the complications of external femoral xation leading to knee exion disorders. Methods: We exed the knee joint 90 degrees during the operation, and then placed the external xation nail. A retrospective review was performed for all patients undergoing repair by this technique. Results: A total of 52 children with femoral shaft fractures were included, the exion of the knee joint measured at the time of discharge was 80 degrees (70-90 degrees) on average; when the external xation is removed, the knee exion can reach an average of 95 degrees (90-115 degrees), no children have stiff knees. Conclusion: This technique is simple and easy to implement, and it is worthy of popularization and application in clinical practice. up the range of motion of the knee joint, nail tract infection, and recurrence of fracture; X-ray observation of fracture healing, delayed healing, and non-union.


Background
External xators are widely used in orthopedic trauma and orthopedics and have become a signi cant method for treating fractures, severe limb injuries, osteomyelitis, bone defects, and functional reconstruction [1][2][3]. Femoral external xators are commonly used for femoral lengthening, open femoral fractures, femoral bone defects, and bone reconstruction after resection of femoral tumors [4]. Compared with internal xation, external xation is more prone to complications such as needle tract infection, rebone fracture, delayed healing, or joint stiffness. However, the femoral external xator is still irreplaceable in open fractures, long oblique fractures, and multiple femoral fractures. Many complications can occur with external xators, such as pin site infections and even bone infections [5], osteoporosis leads to loosening or prolapse of the xed needle, and the osteotomy is healed ahead of time [6,7]. Besides, knee stiffness is also an essential complication of external femoral xation.
Stiffness of the knee extension can occur during the use of the femoral ring external xator or a unilateral external xator. Especially femoral prolongation requires long-term use of external femoral xation, and it is more likely to cause knee stiffness. Guidera [8] et al. reported that a decreased range of motion of the knee joint occurred when the external xator was used to extend the femur. Among them, 2 cases had a decreased knee joint motion of greater than 30° (loss ≥ 30°). Herzenberg [9] et al. reported that the knee joint mobility decreased during the femoral extension using the ring-shaped external xator. Finally, after the external xator was removed, the average value of the patient's activity also decreased. In 2 patients, knee mobility was lost by more than 15%. Knee stiffness is also often occur after femoral fractures with external xation. Dabezies et al. reported 9 cases(45%) of decreased range of motion of knee after external xation of femoral fractures, an average loss of exion of 50 degrees [10]. Murphy et al. reported that 44% of patients have a decreased range of motion of the knee joint, which exes less than 90° [11].
We consider that the stiffness of the knee joint is related to the xation of the iliac tibia bundle by the nail.
This study explores how to reduce the occurrence of knee stiffness complications and discusses the mechanism by improving the femoral external xation method.

Methods
Between January 2011 and June 2014, we collected all children who were operatively treated with external xation for a femoral diaphyseal fracture at our Department of Children's Hospital of Chongqing Medical University. Inclusion criteria: 1) younger than 18 years old, 2) unilateral or double Lateral femoral shaft fracture, 3) Treatment with external xation; exclusion criteria: 1) abnormal knee exion and extension before surgery, 2) fracture involving the knee, 3) combined use of internal xation and external xation; The X-ray of the patient admitted to the hospital showed a fracture of the femoral shaft. It was not suitable for open reduction and internal xation, so external xation treatment was performed. The range of motion of knee exion and extension before surgery was normal. Closed fractures under anesthesia are reduced by lower limb traction and manual reduction, then C-arm X-ray uoroscopy was used to con rm that the fracture alignment was proper. Open fractures were directly reduced after debridement.
Then cut approximately 1cm of skin at the proximal end of the fracture, the distal end, and the bone fragment; bluntly separate the subcutaneous tissue to the bone surface. Flex the knee of the affected limb 90 degrees, then insert the external xation nail with a diameter of 5 mm to the vertical bone surface( Figure 1). Correct the displacement of the fracture under X-ray uoroscopy again. After con rming that the external xing nail position is proper, install the external xator and tighten the xing bolt. The knee joint can be frequently exed and extended after the external xator is installed.
Three days after the operation, active and passive functional exercises of the affected limbs were performed, and measuring the knee exion and extension range of motion. The patient was discharged about 1-2 weeks after the operation. The range of motion of knee exion and extension was measuredoutpatient follow-up at 1, 3, and 6 weeks after discharge, and then monthly follow-up. Follow up the range of motion of the knee joint, nail tract infection, and recurrence of fracture; X-ray observation of fracture healing, delayed healing, and non-union.

Result
A total of 52 children with femoral shaft fractures were included, including 38 males and 14 females, with an average age of 7.5 years (3.5 years to 14.6 months). There were 28 cases of open fractures, 15 cases of long oblique fractures, 7 cases of severely comminuted fractures, and 2 cases of failure of femoral traction. The average hospitalization period was 10 (range 7-14) days. The average follow-up period was 12 (range 10-24)months. Under anesthesia, unilateral external xation was used to x fractures. After anesthesia, the child's knee exion can reach an average of 100 degrees (80 degrees to 125 degrees), and there is no restriction on the extension. During surgery, the knee joint can reach an average of 90 degrees (80 to 100 degrees) after external xation. The knee joint was actively and passively moved three days after surgery, and the exion of the knee joint measured at the time of discharge was 80 degrees (70-90 degrees) on average; the extension was not limited (Figure 2). An X-ray con rmed that the fracture was healed entirely and removed the external xator, external xators were removed on an average of 16 (range 12-20) weeks. When the external xation is removed, the knee exion can reach an average of 95 degrees (90-115 degrees). The usual range of motion can be restored entirely within two weeks after the external xation is removed. The remaining complications included seven patients with nail tract infections, controlled after dressing change, and antibiotic treatment; no deep infections occurred; no further fractures occurred, and no delayed or non-union fractures occurred.

Discussion
External xators are widely used in various elds of orthopedics. Femoral external xators are often used to correct shortened femoral deformities, femoral fractures, and reconstruction of femoral tumors. The use of femoral external xators has a high probability of reduced knee joint mobility and knee joint stiffness, especially the use of ring-shaped external xators. The external xator will x the thigh muscles and aponeurosis, so that the movement of the thigh muscles of the knee joint is restricted, thereby limiting the exion and extension of the knee joint. Reduced knee mobility can be signi cantly improved after removing the external xator. However, for patients who need to use an external xator for a long time, such as femoral prolongation, the patient's knee exion is limited during xation. The knee function cannot be quickly restored after the external xator is removed [13]. Although most patients' knee mobility can be signi cantly improved through functional exercise or secondary surgery, it may also lead to rebone fractures. Therefore, the complication of femoral external xation used to reduce knee mobility is still a relatively important issue. We found in the operation that by exing the knee joint to 90 degrees before placing the external xator nail, the patient can ex the knee joint by an average of 80 degrees 2-3 days after surgery. Moreover, the patient's knee exion is not limited during the post-surgery period, and it will not cause inconvenience to life. After removing the external xator, the patient's knee function quickly returned to normal, and no knee stiffness or mobility decreased signi cantly.
The exion disorder of the knee joint after the placement of the external femoral xator is related to the lateral femoral muscles' xation, 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, bula head, and knee joint capsule [14]. The iliac tibial bundle is an important organization for maintaining knee stability and knee motion and is involved in knee exion and extension essential [15]. The iliac tibial bundle is tougher and less elastic, it cannot be moved normally and cannot be stretched elastically after being xed by an external xator nail. After the iliac tibial bundle xed by an external xator nail, due to the poor elasticity of the lower part of the iliac tibial bundle, and the distance OG' required for knee exion is longer than OG( gure 3), it is di cult to ex the knee joint. And the iliac tibia bundle slides up and down along the lateral femoral muscle when extending and exing 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 xation nail xes the iliac tibial bundle, the upward and backward movement of the iliac tibial bundle is restricted, so that the knee exion function is limited.
Moreover, the child was unwilling to exercise because of pain when pulling the nailed iliac tibial bundle when exing the knee joint. Besides, the adhesion between the xed iliac tibial bundle and the muscle or aponeurosis aggravated the knee joint's exion activity after surgery, so that after removing the external xator, there was still a limited knee exion 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 x the external xation nail when exing the knee joint during surgery. The lower iliac tibial bundle OG segment xed when exing the knee joint is longer. The longer movable segment is reserved so that the iliac tibial bundle will not restrict the exion of the knee joint. Moreover, more space is reserved for the iliac tibial bundle to move backward and downward when exing the knee, to avoid the limitation of the exion activity of the knee joint after the operation.

Conclusion
In the external xation of the femur, the external xation nail placed in the knee exion position can effectively improve the knee joint's exion dysfunction, and the knee stiffness is avoided. This method is simple and easy to implement, and it is worthy of popularization and application in clinical practice.

Declarations
Ethics approval and consent to participate The study was approved by the Medical Ethics Committee for Clinical Ethical Review, Children's Hospital of Chongqing Medical University. Written informed consent was obtained for the study from the parents of the patients.

Consent for publication
Not applicable.

Availability of data and materials
All data generated or analyzed during this study have been included in the published article.

Competing interests
The authors declare that they have no competing interests. Figure 1 A eight-year-old girl, during surgery, exes the knee of the affected limb 90 degrees and then inserts the external xation nail(a). The knee joint can be normal exion and extension after external xation(b,c).

Figure 2
An eight-year-old girl whose range of motion of the child's knee joint was normal two weeks after surgery(a,b).