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, 10).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 the previous experience in the treatment of FNFs, type 31B1.1,31B1.2,31B2.1,31B2.2and31B3 of the new AO classification are stable fractures. These types usually have good results after IF. In 31B1.1, 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.In practice, type 31B1.1(valgus impacted) and 31B1.2 fractures are often grouped together as nondisplaced fractures and are treated primarily with IF(11).31B3 is basicervical FNF, which is closer to trochanteric region. It has good blood supply and a high probability of healing. Observational study of of Sundkvist et al.(8) found 40,049 FNFs were registered in the Swedish Fracture Register.11.6% was basi-cervical FNFs. The treatment of patients over 60 years old is almost equally divided into IF and arthroplasty.They are both valid procedures for the treatment of basi-cervical FNFs,There is no difference in terms of survivorship between IF and arthroplasty in the overall population.The incidence of postoperative complications in patients with arthroplasty was higher than that in patients with IF(12). In the study of patients with FNFs aged 50–60 years, Wang et al.(13)found that patients with Pauwels type II had optimal outcomes after successful IF.In a long-term follow-up study of FNFs treated with cannulated IF by Ju et al.(14) found that,Garden fracture type was not significantly associated with femoral head necrosis or Harris score .Elderly patients aged ≥ 60 years with Pauwels I and II fractures exhibited a significantly lower necrosis rate than those with Pauwels III fractures, which means 31B2.1 and 31B2.2 can also have good outcomes by IF in elderly patients.
Johnson et al.(15)reported that the use of total hip arthroplasty(THA) in treatment of FNFs in patients from the age of 45–64 increased 4.2-fold from 2002 to 2014. Among them, some patients may achieve satisfactory results as long as they are treated with IF.Their study demonstrates that patients undergoing THA had higher in hospital complication rates and longer length of stay than patients undergoing IF. The in-hospital mortality for patients undergoing a hip hemiarthroplasty(HA) was higher (1.2%) than either THA (0.2%) or IF (0.5%).Two studies of nondisplaced FNF patients over the age of 70 found that among patients receiving IF and the arthroplasty, patients treated with arthroplasty had higher 30-days mortality rate(11%)(16) and patients treated with internal fixation have a higher 2-year mortality rate(36%)(17).Several studies have shown that IF may be more cost-effective than hip arthroplasty because the total cost is less(15, 18, 19).Lagergrenet et al.(20)reported that HA with baseline results in patient reported outcome measure indicating poorer health and function, as well as higher mortality and lower response rates with patients aged 60–69.IF tend to fail in up to 1/3 of the cases but can offer the benefits of a biologically intact hip if successful.In young elderly people, it is still worth for doctors to choose IF to preserve the native hip joint among the appropriate fracture types.
As Table 2, the proportion of 31B1.1,31B2.1,31B2.2 and 31B2.3 has decreased with age.And B1.3 has gradually increased with age. This type of FNF has a higher risk of complications after IF(21). Therefore, in the elderly group, most patients chose THA or HA. However, in the middle-aged group and the young elderly group, these stable fractures of 31B1.1,31B1.2,31B2.1,31B2.2 and 31B3 occupy a certain proportion, about 1 / 3 of the whole group. Most of these types of fractures can get good treatment results when treated with IF.Doctors can give priority to preserving the original hip joint when treating elderly patients with these fracture types.Two studies have shown that patients with a posterior tilt of greater than 20° have a high rate of revision surgery when treated with IF and may benefit from primary arthroplasty(22, 23).In the IF treatment of middle-aged and young elderly group, we should pay more attention to the posterior tilt of the proximal femoral neck.
Table 2
Distribution of new AO classification in different age groups
| B1.1 | B1.2 | B1.3 | B2.1 | B2.2 | B2.3 | B3 | 总计 |
The young(≤44) | 35(18.9%) | 9(4.9%) | 41(22.2%) | 7(3.8%) | 60(32.4%) | 18(9.7%) | 15(8.1%) | 185(100.0%) |
The middle-aged (45–59) | 61(17.6%) | 15(4.3%) | 110(31.7%) | 15(4.3%) | 111(32.0%) | 16(4.6%) | 19(5.5%) | 347(100.0%) |
The young elderly(60–74) | 96(15.0%) | 20(3.1%) | 301(47.1%) | 34(5.3%) | 124(19.4%) | 18(2.8%) | 46(7.2%) | 639(100.0%) |
The elderly(≥75) | 105(11.7%) | 24(2.7%) | 571(63.4%) | 37(4.1%) | 83(9.2%) | 7(0.8%) | 73(8.1%) | 900(100.0%) |
Total | 297(14.3%) | 68(3.3%) | 1023(49.4%) | 93(4.5%) | 378(18.3%) | 59(2.8%) | 153(7.4%) | 2071(100.0%) |
In the new AO classification ,31B1, 31B2, 31B3 corresponds to subcapital ,transcervical and basicervical. B1.1 (valgus impacted), B1.2 (nondisplaced) and B1.3 (displaced). B2.1 (< 30°, Simple fracture), B2.2 (30–70°, multifragmentary fracture), B2.3 (> 70°, shear fracture),B3(basicervical fracture). |
The proportion of fracture types varied among age groups, 31B2.2 (60,32.4%) was predominant in the young group. The proportion of type 31B2.3 shear fractures was the largest in the young group, with 18 patients (9.7%). Young patients generally have better bone quality.High-energy injury can cause a FNF pattern that is vertically oriented with a shear component making it biomechanically more unstable. In the young patients with shear FNFs, reoperations for painful implants, osteonecrosis, and nonunion are common. But because of the active patients following high-speed trauma when a head-sparing technique is required, almost all young patients choose IF. A 90-day reoperation rate was 9.4%, rate of conversion to THA was 6% and a 10-year reoperation rate was 34% and rate of conversion to THA was 14%, indicating that there is a substantial opportunity to improve the treatment of femoral neck fractures in the non-geriatric population(24, 25). Strict and accurate classification of fractures before operation is of great significance to reduce the reoperation rate of non-geriatric population.
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 elderly 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(26). However, there are also articles that suggest that femoral neck bone mineral density, physical function were not associated with FNFs(27).
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(28, 29).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(29).
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(30, 31). 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 indicating that people's health awareness is gradually improving, and the age of patients with FNF may be getting younger.