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Results of postoperative anti - rotation on the intracapsular femoral neck fracture fixed with cannulated screws

Background: To investigate effect of postoperative anti - rotation on the union of intracapsular displaced femoral neck fracture treated with three cannulated screws. Methods: A retrospective analysis was performed on all the intracapsular femoral neck fractures treated in the department of orthopedics of the second Hospital of Shanxi Medical University from July 2015 to December 2018. Fractures of femoral neck were reduced and fixed with three cannulated screws. The patients who wore anti - rotation shoes in the affected side were kept at bed rest for 10 - 12 weeks after surgery. The results were analyzed. Results: A total of 135 patients were included in the analysis. patients (4.4%) were not united. There were 12 cases of avascular necrosis (9.3%). No wound infections, screw breakages was found. Conclusion: Anti - rotation after surgery can significantly reduce the rate of femoral neck fracture nonunion, but not significantly improve the femoral head necrosis

Femoral neck fracture is a common hip fracture, it can occur at any age. For displaced femoral neck fractures in the elderly, arthroplasty is preferred 1  Union of femoral neck fractures should be achieved through primary bone healing, which requires the absolute stability at the fracture site 7,8 . However, a clinical study has shown there was considerable rotational instability in the femoral neck fracture post fixation at four months follow-up 9 . Poor rotational stability is linked to high complications of a hip fracture. So, we adjust the postoperative rehabilitation program, instead of encouraging patients to mobilize with no restriction on range of motion of the hip after surgery in most literature. In our study the fracture of femoral neck was reduced and fixed with three parallel cannulated screws. After surgery, patient is kept at bed rest for 10-12 weeks and wore anti-rotation shoes in the fractured side. We hypothesis that would promote fracture healing.

Methods
This study was approved by the ethics committee of the local hospital. From July 2015 to December 2018, the clinical and imaging data of patients with intracapsular displaced femoral neck fracture fixed with cannulated screws, in the department of orthopedics of the second hospital of Shanxi medical university, were retrospectively analyzed.
Patients with a pathologic fracture, an ipsilateral concomitant femoral, preexisting abnormalities of the femoral head or acetabular fracture were excluded. In addition, patients without complete clinical and radiographic data were excluded.
Preoperatively the affected limb was pulled. Warfarin sodium were subcutaneously injected until 12 hours before surgery. A closed reduction was attempted in every patient by The Whitman technique.
Reduction attempts should not be forceful and should not be repeated more than two or three times. Once closed reduction was not satisfactory open reduction was admitted through a modified Smith-Petersen approach. Three partially threaded screws (7.3 mm) was be used after satisfactory reduction has been obtained(Fig1,2).
Postoperatively, the patients wearing anti-rotational shoes in the affected side were kept at bed rest for 10-12 weeks(Fig3). Then partial weight bearing was recommended until fracture was united.
Follow-up clinical and radiologic analyses were performed at 6 weeks and 3, 6, 12 months after the operation. Non-union and avascular necrosis of femoral head were defined from x-ray or magnetic resonance imagine.

Statistical analysis
This was carried out using SPSS 18.0 software (SPSS Inc., Chicago, Illinois) using chi-squared testing. The level of significance was set as a p-value < 0.05. There was significant difference in the quality of fracture reduction between the two groups (p < 0.001)( Table 1)

Discussion
To reduce complications is a challenge to orthopedic surgeons. High rate of failure indicated that implant available for internal fixation of femoral neck fractures may not provide sufficient stability as we expected 10,11,12 . Some accessory methods should be used to supplement internal fixation. Postoperative anti-rotation was helpful to supplement internal fixation.
In our study the rate of nonunion was 4.4% and the figure compare favorably with other published results, with rates of nonunion of 11-40% 13,14,15,16 . The result for a femoral head necrosis was 8.9% in the present study. In a meta-analysis, the author found the incidence of avascular necrosis of femoral head for those who sustained a displaced fracture was 20.6% 17 . In another meta-analysis, the study demonstrated the total pooled incidence of avascular necrosis (AVN) was 14.3% 15 .
There are two aspects of postoperative anti-rotation that can explain the results. First, according to the Whitman reduction technique, it involves applying traction to the abducted, extended, externally rotated hip with subsequent internal rotation. While patients were placed in the supine position, the lower extremities were in external rotation. Rotational force at fracture site easily resulted in a biomechanically unstable pattern, susceptible to the development of nonunion, osteonecrosis and implant failure 18,19 . Second, all movements of a ball-and-socket joint are rotational 19 and the early movement of hip will result in rotational instability for the proximal fragment whether weight bearing or not 20,21 ,22 .So the postoperative anti-rotation eliminates these rotational stresses and provided absolutely stability for vascular regeneration, Other factors also affected the results in this study. The average interval between the occurrence of fracture to surgery was 5.4 days in this study. In theory, early reduction and fixation is beneficial for reducing the initial vascular insult and revascularization in the setting of interrupted blood supply 23,24,25 . However the result of early fixation is contradictory. The effect of timing of internal fixation of femoral neck fracture needs to be further studied.
In our study, all femoral neck fractures were fixed with three parallel cannulated screws. The application of cannulated screw fixation is simple and causes little damage to the soft tissue. There was no loss of reduction, implant cut-off, infection of surgical location in our study. In some case, fracture was united although the three screws were too close to each other, resulting in insufficient stability and inability to withstand rotational stresses.
Postoperative anti-rotation in bed can be frustrating. Compared with the disastrous complications, it is easy to be accepted for patients to be kept at bed rest for 10-12 weeks. The patients with internal fixation were physiologically young. No complications were found when patients were kept at bed rest.
Our work had certain limitations: the study was retrospective. There was not control group. The follow up time was short. the function was not studied.
In conclusion, our study indicate postoperative anti-rotation is a simple and effective method which could provide suitable mechanical environments that facilitate direct bone formation and shorter healing times.

Abbreviations
Not applicable