Patients with IF often have multiple chronic diseases, such as osteoporosis, diabetes, chronic gastritis, chronic nephritis, organ transplantation, or rheumatoid arthritis needing immunosuppressive treatment, or tumor requiring radiation and chemotherapy. IF is more common in the elderly, and less common in men than women. Recently, Bakker et al  published a study about the diagnose of Sacral IF for 130 patients, who aged between 46 and 98 years (mean, 79.8 years), with 117 females and 13 males. Melton et al  analyzed the contribution of gender on the incidence of pelvic insufficiency fractures in a retrospective review of a Mayo Medical database, of which total of 198 patients with 204 fractures, showed the incidence of pelvic insufficiency fractures was nearly twice as common in women (47.5/100000) as it is in men (24.4/100000).
IF was produced by normal or physiological stress applied to bone with decreased bone mineral content and deficient elastic resistance, resulting in a weakened zone of the bone. As such, this kind of fracture are often caused by daily activities or even light exercise, and usually are not associated with trauma . Osteoporosis is the most common predisposing factor for IF . Bisphosphonates are considered the first-line therapy of postmenopausal osteoporosis, as they could improve bone density and inhibit bone resorption. However, several reports have suggested an association between the use of bisphosphonates and subtrochanteric IF in recent years, and recommended that care should be taken when using bisphosphonates for more than 5 years [10,11,12].
Due to the special characteristics and atypical basic clinical manifestations of IF, it is difficult to be diagnosed by conventional imaging examination. Therefore, IF is often misdiagnosed, resulting in delay of treatment. The findings from conventional radiographs often appear to be normal early in the course of IF. However, CT could depict subtle fracture lines allowing direct visualization of cortical and trabecular bone. MRI is a very sensitive tool to visualize bone marrow abnormalities associated with insufficiency fractures, and could help distinguish between benign and malignant fractures .
IF often occur in the sacrum and ilium. Therefore, IF at femoral neck are unusual, accounting for about 5% of all stress fractures. Bilateral femoral neck fractures are even more rare [2,3,4]. We find several cases about bilateral femoral neck fractures. Kalaci et al  described a case of a 18-year-old girl with bilateral femoral neck IF. The girl was treated surgically with in-situ internal fixation using cannulated screws. Baki ME et al  reported a 22-year-old female case with bilateral femoral neck fractures, of whom the diagnosis was delayed because the patient was pregnant and could not receive imaging examination. Finally, the female patient was treated surgically with internal fixation using cannulated screws and received medical treatment for vitamin D deficiency. Ahn DK et al  reported a bilateral femoral neck IF case of a 78-year-old woman who had a long history of using anti-resorptive drug, and bilateral internal fixations using cannulated screws were performed for the patient. Vaishya R et al  reported a 50-year old male patient who simultaneously suffered from chronic kidney disease and bilateral femoral neck IF with minor trochanter IF. Finally, the patient was managed with cannulated screws at unusual sites.
In our case, the patient had a 7-year history of drinking, about 60 g per day, and had a poor appetite with few breakfasts in daily life. These bad life styles possibly caused malnutrition and finally contributed to the development of bilateral femoral neck IF . Although no examinations related to nutrition evaluations were carried out, such as Vitamin D, the reduced BMD of his lumbar spine reflected a poor nutrition condition of the patient, which was a potential risk for the occurrence of femoral neck IF. However, the poor nutrition condition cannot fully explain the occurrence of bilateral femoral fracture. We suspected that the patient had fallen or done physically demanding work, while the patient denied this which he may forget.
In conclusion, from our experience with the patient with bilateral femoral neck IF, he complained of pain in left hip when walking, which led to suspicion of a femoral neck fracture. Although radiological examination was performed and indicated old fracture of the left femoral neck. The immediate CT and MRI examination was not followed for further examination, which is considered great value to evaluate fracture healing. Because of the pain on the left side, the upper body weight overload on the right side may have caused the subsequent IF on the right side. Due to the increase of the average age of the population, as the incidence of IF is increasing, it is of great importance to perform CT and MRI scan additionally.