In the past application of the classification of FNF, the position of fracture line is not distinguished, and the classification of FNF is often confused.
Studies on the classification consistency of FNFs in recent years indicate that the previous AO classification, Pauwels classification and Garden classification have interobserver variation, and the AO classification is the most obvious(2, 3, 6).This is mainly because the original AO classification was based on X-ray images and was self-concluded based on patient imaging data.The rules for fracture typing are not used frequently and are not well understood by clinicians.However, the new AO classification cleverly combines the three types of FNF classification commonly used by clinicians, so that the widely used classification has been standardized and improved, which will bring great help to the clinical classification of FNF.
In this classfication, 31B1, 31B2, 31B3 corresponds to subcapital ,transcervical and basicervical. 31B1 is divided into three subgroups, B1.1 (valgus impacted), B1.2 (nondisplaced) and B1.3 (displaced). 31B2 is also divided into three subgroups according to Pauwels Angle and bone block type, B2.1 (< 30°, Simple fracture), B2.2 (30-70°, multifragmentary fracture), B2.3 (> 70°, shear fracture). In 31B2,we mainly use the Pauwels Angle to judge the classification. However, in this classification, the Angle in the original Pauwels classfication is not used, maybe a larger shear angle helps to distinguish between the stability of the fracture(7).
In the previous experience in the treatment of FNFs, B1.1, B1.2, B2.1 and B3 of the new AO classification are stable fractures. In B1.1, the cortex of the femoral neck is inserted into the cancellous bone, and the fracture ends overlap. It is a stable fracture, with high probability of healing. It is generally difficult to release the insertion state with closed reduction. If it can not be reset accurately, it should be fixed in situ(8).31B3 is basal FNF, which is closer to trochanteric region. It has good blood supply and a high probability of healing.In the clinical treatment in China, these two types of FNF have good curative effects in closed or open reduction and internal fixation. After comprehensive consideration of the patient's will, age, bone condition and complications, most of them choose to perform closed or open reduction and internal fixation to delay the time of arthroplasty.
The proportion of fracture types varied among age groups, B2.2 (60,32.4%) was predominant in the young group, B2.3 fractures with high shear angle had the largest proportion in the young group, 18 (9.7%). Young patients generally have better bone quality.High-energy mechanism can cause a FNF pattern that is vertically oriented with a shear component making it biomechanically more unstable. Most cause transcervical fractures. Young patients are the same with elderly people,big shear angle of the fracture non-union, implant failure,osteonecrosis rate is higher than other type in B2. But because of the active patients following high-speed trauma when a head-sparing technique is required, almost all young patients choose ORIF(9–11).
As Table 2, the proportion of B1.1,B2.1,B2.2 and B2.3 has decreased with age.And B1.3 has gradually increased with age. The risk of complications is high after internal fixation treatment. Therefore, in the elderly, most patients chose THA or HA.However, in the middle-aged group and the young old group, these stable fractures of B1.1,B1.2,B2.1 and B3 occupy a certain proportion, about 1 / 3 of the whole group. If the posterior tilt angle <20°in B1.1 and B1.2, we can choose internal fixation treatment(12, 13).After multiple considerations,we can devise a more rational protocol for these patients.
In previous studies on Garden classification of femoral neck fracture, the existence of Garden TYPE I has been controversial(14, 15).In this study, a total of 6 incomplete fractures based on radiographic evaluation. By observing its CT scan, only 1 patient looks like incomplete fracture and the patient was only 22 years old, similar to greendstick fracture.
Femoral neck fractures are affected by a variety of factors and are generally considered to be closely associated with Femoral neck bone mineral density and osteoporosis. In our study, FNFs were more common in women, with an overall male to female ratio of 1:1.79. In the young group, The male/female ratio was 2.19:1. In the middle-aged group, the ratio of male to female was 1:1.18, the male/female ratio was almost equal. In the young old group and the elderly group, the ratio of male to female was seriously unbalanced, which was 1:2.46 and 1:2.24.
Women in both age groups are in postmenopause.The loss of estrogen in the body leads to osteoporosis which leads to more serious bone loss than that of men. Elderly women are more likely to have such fractures(16). However, there are also articles that suggest that femoral neck bone mineral density, physical function were not associated with FNFs(17).
In the study of FNF, the main injury mechanism of the elderly is fall with low energy. And high energy injury is the main cause of femoral neck fracture in young people(18, 19).In our study, the main injury mechanism of all age groups is low energy injury dominated by fall, and high energy injury accounts for 42.7% of the young group and only 2.4% of the elderly group.A large sample survey of hip fracture in Japan found that fall was the injury mechanism of 80% of hip fracture patients.The number of patients is the highest in January of every year(19).In Catalonia, Spain and Czech Prague, the incidence rate of femoral neck fracture is related to seasonal changes, and more in winter(20, 21).
In recent years, international studies on the incidence trend of femoral neck fracture show that the incidence of the elderly population has a decreasing trend year by year, which may be related to the safety awareness of the elderly and the formation of prevention of osteoporosis(20, 22). In this study, there was no obvious trend in the proportion of the elderly over 60 years old, but the proportion of patients in the young group increased, which may mean the improvement of people's health awareness, indicating that the age of patients with femoral neck fracture is getting younger. In some European countries, the COVID-19 has great influence on the incidence of FNF, compared to the past few years have a certain percentage of the drop.This is related to the decrease in people going out during the pandemic.In the UK, the number of femoral neck fractures decreased from 410 to 327 during the 12-week coronavirus lockdown period, a decrease of 20.2% compared to the same period in the previous year(23).In Italy(ASST Sette Laghi, Varese, Lombardy, Italy), the number of femur neck fractures fell from 54 last year to 46 in the two months of the pandemic emergency, a decrease of 14.8%(24).The Clinical Center of Nis (Nis, Serbia) decreased from 28 to 17, with a decrease rate of 39.3%(25).Xi 'an city of Shaanxi Province is a medium-low risk area. From January 23, 2020 when Wuhan was closed to April 8, 2020 when Wuhan was lifted, a total of 199 patients with femoral neck fracture were admitted to our hospital during the three months from January to April, 190 in the same period in 19 and 192 in the same period in 18. The number of patients with femoral neck fracture was not affected.