Given the increase in the geriatric population, the prevalence of femoral neck fractures is steadily increasing. With developments in surgical techniques and implant technology, the healing rate of femoral neck fractures has considerably improved. However, incidental femoral head necrosis has not declined accordingly.2,8,9 Therefore, neck fractures of the femur are described as unsolved fractures10 and have presented challenges to orthopedic surgeons. A widely varying rate of femoral head necrosis after reduction and internal fixation has been reported (Table 4).1,2 In the current study, the incidence of femoral head necrosis was 14.4% (21 of 146), which was similar to previously reported rates.1
Possible Causes of Femoral Head Necrosis
After femoral neck fractures, the main cause of femoral head necrosis is the impairment of blood flow to the femoral head.11,12 The retinacular arteries from the medial femoral circumflex artery are considered the most important blood vessel to the femoral head. These arteries are always impaired at the time of femoral neck fracture, thus interrupting the arterial flow to the femoral head. The trauma at the moment of fracture can cause major damage to vessels and impair the blood circulation in the femoral head. Consequently, the blood supply to the femoral head is decreased and femoral head necrosis occurrence is increased.
The tamponade effect may be another cause of femoral head necrosis.13,14 The increased joint fluid caused by hemarthrosis after the intracapsular fracture of the femoral neck causes increasing intraarticular pressures that lead to the occlusion of the vascular supply to the femoral head.13 The extension and internal rotation of the hip joint and the traction position produce higher intracapsular pressure, thus increasing the intracapsular pressure by greater than 80 mm Hg. This is greater than the diastolic blood pressure, significantly diminishes the femoral head perfusion, and poses a high risk of femoral head necrosis.
Some scholars considered decreasing the intramedullary oxygen tension in the femoral head and neck, thus playing a central role in the development of posttraumatic femoral head necrosis.15,16 For femoral neck fractures, vessel lesions and increased outflow resistance may decrease the blood flow perfusion of the femoral head and intraosseous oxygenation. The tamponade effect decreases the subchondral perfusion and oxygen pressure. Finally, this condition might result in bone cells with hypoxic ischemic; death will occur if osteocyte hypoxic ischemic lasts for 2 to 3 hours.
Scholars have begun to emphasize the biomechanical factors in the development of femoral head necrosis. Femoral neck fractures change the anteversion and destroy Wolff’s law, which indicates the balance between bone structure and function.17 Abundant hip muscle contraction makes the fracture extremity produce considerable shear force and increases the instability of the extremity. Malreduction makes the anteversion shift and transforms the relationship between the femoral head and acetabulum, thus concentrating the stress on the surface of the femoral head and rearranging the internal ultrastructure of the trabecular bone. If the rearranged trabecular bone cannot accommodate the stress of the acetabulum demand, the trabecular bone degenerates, absorbs, collapses, and causes femoral head necrosis.18
Relationship Between Risk Factors and Femoral Head Necrosis
Garden Classification and Reduction Quality. Garden classification is considered an important factor in the development of femoral head necrosis after femoral neck fracture.19,20 Clinical results have demonstrated that the rate of femoral head necrosis for displaced fractures (20% to 40%) was higher than that for nondis-placed fractures (5% to 20%).21,22 Lu-Yao et al23 demonstrated a strong correlation between femoral head necrosis development and fragment displacement. The current study showed a femoral head necrosis rate of 20% for displaced fractures and 5.35% for nondisplaced fractures. Thus, fracture displacement is considered an important factor in femoral head necrosis.
The accurate apposition of the fragment is conducive to union and determines the fate of the femoral head. Beris et al19 reported that reduction quality was an important factor that affected the treatment of femoral neck fractures. Accurate reduction can restore stability and create beneficial conditions for the healing of femoral neck fractures. The mechanical stability of the fracture after reduction and fixation prevents early displacement. Min and Kim24 reported that the incidence of femoral head necrosis was 20% (26 of 130 hips) in patients with satisfactory reduction and 68.8% (11 of 16 hips) in patients with unsatisfactory reduction. Garden4 believed that malreduction would increase the rate of femoral head necrosis after femoral neck fractures. In the current study, the incidence of femoral head necrosis was 7.9%, 7.3%, and 37.5% in groups A, B, and C, respectively, which is statistically significant (P=.008). The results showed that Garden classification and reduction quality had a significant effect on femoral head necrosis development after femoral neck fracture fixation.
Preoperative Traction and Implant Removal. Previous research showed that preoperative traction provided effective stabilization and protection from potential displacement.1 This approach can restore the blood supply to the femoral head and neck segment and avoid the femoral head necrosis caused by a displaced fragment. However, some authors believe traction could increase the occurrence of femoral head necrosis.20,25 In the current study, logistic regression analysis showed that preoperative traction was significantly associated with femoral head necrosis (P=.000). The authors assumed that pre-operative traction could not effectively prevent the rotation of the injured limb. With the extension and internal rotation of the injured limb, the capsule became tense and the intraarticular volume decreased, thus leading to high intracapsular pressure or the so-called tamponade effect. Traction also impairs blood perfusion to the femoral head, blood flow in the retinacular arteries decreases, and the venous drainage becomes impeded.25 Thus, traction may be a major cause of femoral head necrosis after a femoral neck fracture.
Sun et al26 suggested that screw removal might be a primary inducing factor in the development of femoral head necrosis. They reported that all compressive, tensile, and shear stresses were concentrated on the fracture site after screw removal, thus changing the biological stress. This condition could lead to the adjustment of the trabecular bone and might increase the femoral head and neck ischemia, which ultimately lead to femoral head necrosis. In the current study, univariate analysis showed that the existence of the screw had a significant effect on the development of femoral head necrosis (P=.020). The intraosseous pressure of the femoral head might increase because of the presence of the screw and then increase the femoral head ischemia.27 On the contrary, in multivariate logistic regression analysis, screw removal had an insignificant effect on femoral head necrosis (P=.498). However, few studies have focused on the correlation between the removal or the presence of screws and femoral head necrosis in both domestic and foreign cases. Further research on this topic is needed in the future.
Time to Surgery. The time from injury to surgery is a controversial topic, and data are inconclusive. Some studies have suggested that early surgery could decrease the risk of femoral head necrosis.28,29 Szita et al28 reported that the rate of avascular necrosis was significantly lower (10.5%) in patients who underwent surgery within 6 hours of injury than in patients treated 6 hours after trauma (20%). They believed that the aim of surgical treatment was to protect arteries by early reduction, thus relieving the blood vessel compression to the femoral head and restoring the blood supply. On the contrary, Holmberg et al30 reported 2418 cases of femoral neck fracture and reported that no evidence suggested that a surgery delay of up to 7 days adversely affected the fate of the femoral head. In the current study, the authors considered 72 hours as the cutoff point in 2 groups: within 72 hours and after 72 hours. The rates of femoral head necrosis in these 2 groups were 11.3% and 16.7%, respectively (P=.360), thus showing that the injury-to-surgery interval did not significantly affect the development of femoral head necrosis. This observation was also in agreement with a previous meta-analysis.31
Other Risk Factors
Gender. The results of the current study show that sex does not have a significant effect on the development of femoral head necrosis. Bachiller et al32 reported that the femoral head necrosis rate after femoral neck fractures in males with good bone quality was higher than that in osteoporotic females. Nevertheless, the relationship between bone quality and femoral head necrosis is still unclear and demands further research.
Age. The traditional view of a higher incidence of femoral head necrosis among young adults than the elderly is related to good bone stock, high-energy trauma, displacement fracture, and severe blood vessel damage. By contrast, poor bone quality, low-energy trauma, and mild disruption of the blood supply in osteoporotic elderly patients contribute to lower rates of femoral head necrosis. The authors’ literature review found no correlation between femoral head necrosis and age.
Surgical Method. This study found no difference between the incidence of femoral head necrosis in patients who underwent ORIF compared with patients treated with CRIF. This observation was consistent with the research outcome of Upadhyay et al.33
First, this study is a retrospective study with inherent and well-known limitations and biases. Second, the study is a single-center study, and the number of patients was limited the authors’ ability to obtain definitive conclusions. Third, the authors did not consider the number and location of cannulated screws, which might influence the development of femoral head necrosis. Fourth, patients were treated by multiple surgeons. Surgeon level of experience and type of implant used might have some influence on healing complications.