Over the 24-year observation period (1998–2021) covered in the present analysis, femoral fractures were numerically increasing, especially in men, and followed epidemiological patterns differing by fracture localization, sex, age groups, and age at admission for acute hospitalization. The incidence of typical osteoporotic femoral fractures, also referred to as hip fractures, was decreasing in both men and women living in Switzerland. However, the analysis by fracture localization unveiled that this decrease in hip fracture incidence, also referred to as a reversal of the secular trend, was mainly driven by a reduction in femoral neck fracture incidence while, in contrast, the incidence of pertrochanteric fractures remained either unchanged (in men) or decreased only slightly (in women). The incidence of subtrochanteric fractures decreased slightly in both sexes, but the incidence of femoral shaft fractures markedly increased, even more so in women than in men. Overall, median age at admission increased for all fractures but more so in men than women, consistent with the faster ageing of the male population aged 45 years or older.

Hip fractures, a typical and severe complication of underlying osteoporosis in both men and women, involve the proximal part of the femur and usually include fractures of the femoral neck and pertrochanteric fractures [11, 12], but may also include subtrochanteric fractures [9, 13, 21]. In a recent analysis covering years 1998 through 2018, the number of hip fractures (including subtrochanteric fractures) was shown to have increased by 42% and 11% in men and women aged 45 years or older, respectively, with decreasing age-standardized incidences in both (− 15% and − 22%, respectively) [13]. The latter has also been referred to as a reversal of a secular trend, first reported by Melton et al. in their seminal work in Rochester, Minnesota [10]. In Switzerland, such a reversal of the secular trend in hip fracture incidence was first shown in the female population of Geneva, but not in males, in a prospective study covering 10 years (1991 to 2000) with a sample size of approximately one-twentieth of the one used for the present analysis [11, 12]. While pooling fractures under the header of hip fractures does have its merits, including simplified analysis and reporting, it may dissimulate more discrete changes of clinical relevance occurring at the individual fracture localization level.

The statistically significant decreasing trend in hip fracture incidence observed in both sexes over the past 24 years covers in fact a marked decrease in femoral neck fractures, more so in women than in men, and much smaller (women) or even inexistent (men) decrease in pertrochanteric fractures. This suggests that the observed reversal of the secular trend may not occur with the same magnitude at all hip fracture sites and should ultimately, if continuing, lead to a shift from femoral neck fractures to pertrochanteric fractures becoming the predominant fracture localization. This is of concern as pertrochanteric fractures are usually considered as more severe than femoral neck fractures and typically associated with longer hospital stays, higher functional impairment, reduced likeliness of early recovery, and higher mortality [4, 22]. A recent study performed in the Kyoto Prefecture of Japan, which compared two recent 5-year time periods (2008–2012 and 2013–2017) reported that the number of femoral neck and pertrochanteric fractures had increased in all age groups beyond 65 years of age, except for pertrochanteric fractures in 75–84-year-old women. The estimated incidences showed an increase in femoral neck fractures in men aged 75 years or more and in women aged 85 years or more only [23]. The findings in Japan are discrepant with our findings according to which the incidence of femoral neck fractures decreased in all age groups between 1998 and 2021, more so in women than in men. The reasons for these differing observations may be multiple, including the duration of observation (24 vs. 10 years), the population base used for calculating the incidences (full country vs. regional/prefectural population), and Caucasian vs. Japanese hip fracture patients. However, also this study unveiled a difference in epidemiological “behavior” between femoral neck and pertrochanteric fractures deserving more research.

In the present analysis, median age at admission for a femoral fracture increased over time in both sexes, more so in men than in women, but was the same for femoral neck and pertrochanteric fractures in men (80 years in 2021) while women were generally older (83 years for femoral neck and 85 years for pertrochanteric fractures). This is consistent with the observed incidence trends and the faster ageing of the male population but is of further concern as increasing age is associated with more comorbidities and poorer outcomes [22]. On the other hand, osteoporosis treatment is far more frequent in women than in men [24], which would be consistent with the larger magnitude of decrease of the age-standardized hip fracture incidence observed in women. However, no association was found between the change in hip fracture incidence and the treatment rate with antiresorptives at the population level [9]. Furthermore, the proportion of patients at increased risk for fractures treated for osteoporosis remains low leading to a dilution of effect hampering signal detection at the population level [9]. Finally, antiresorptives increase bone mineral density more at the trochanter than at the femoral neck, possibly in relation with the larger amount of trabecular bone at the former, but may decrease the risk of both types of hip fractures by the same order of magnitude [25, 26] although some clinical endpoint trials showed a lower effect with regard to pertrochanteric fracture risk reduction [27, 28]. Thus, at the population level, an effect of treatment would expectedly be seen, if at all, rather in women than in men and with a similar effect size at both fracture localizations. The marked decrease seen in femoral neck fractures in both sexes and the discrepant changes seen with pertrochanteric fractures are not consistent, neither in quantity nor in quality, with a to-be-expected effect of osteoporosis drug therapy at the population level.

A task force of the American Society for Bone and Mineral Research proposed a case definition for atypical femoral fractures (AFF) which included the following major features: a localization in the subtrochanteric region or the femoral shaft, transverse or short oblique orientation, minimal or no associated trauma, a medial spike when the fracture is complete, and absence of comminution [5, 6]. In a population of female patients with osteoporosis included in three fracture endpoint trials, of which 50% were treated with placebo, the overall incidence of AFF was estimated at 23 per 100,000 patient-years (12 AFFs of 283 hip or femoral fractures during 51,287 patient-years) [25]. For the present work, neither radiological nor fall or trauma information was available. Thus, only fracture localization could be used as an indicator for suspicion of an AFF, and the terminology of non-typical femoral fracture was used to prevent any confusion. Subtrochanteric fractures exhibited a flat to slightly decreasing incidence trend. By contrast, femoral shaft fractures showed a marked increase in incidence in men and even more so in women. Considering the low incidence of AFF, the increase in shaft fractures observed in both sexes, although men are undertreated, and following the above argumentation regarding signal detection at the population level, it appears unlikely that the use of antiresorptives may explain an increase of this magnitude. Rather, this increase should be seen in the context of increased physical and injury-prone high-velocity activities at ever older ages. The latter include heavily advertised e-biking but also skiing and mountain-trekking for seniors. Men hospitalized for a femoral shaft fracture in 2021 were 7 years older than in 1998 and women 5 years older. Furthermore, the incidence increase was observed in the 10-year age groups beyond 65 with the largest increases observed in the oldest old. In January 2009, a new tariff-system based on diagnosis-related groups (DRG) was implemented in Switzerland. Briefly, acute hospitalizations became reimbursed by health insurances based on flat rates. Despite quality control measures aimed at preserving longitudinal data consistency, an effect of such an important change on the use of diagnostic codes cannot be excluded. However, femoral shaft fractures started increasing earlier (in 2005 in men and in 2008 in women), and the magnitude of increase renders an intended or unintended pure effect of changes in diagnostic coding highly unlikely.

The present study has strengths and limitations. Among the strengths, the 24 years of observation were derived from the same database, covering more than 95% of all Swiss hospitals since 2002 (100% since 2010), managed with consistent and sustained quality standards over time. Furthermore, only femoral fractures were considered which virtually all end up with an acute hospitalization such that the observed longitudinal trends should be considered reliable. Another key strength is the analysis by fracture localization which unveiled yet unknown and still unexplained epidemiological differences between fractures of the femoral neck and pertrochanteric fractures. A sensitivity analysis restricted to the subset of hospitals which had participated throughout the whole period of observation, i.e., from the beginning in 1998 onwards, could not be performed. For preserving comparability with previously published work, age-standardization was performed based on data pooled by 10-year age groups. Owing to the exponential increase of femoral fractures with increasing age, this comes at the expense of a loss in granularity. However, with femoral neck fractures taken as an example and using year 1998 as reference year, using 10-year age groups instead of 5-year age groups led to an overestimation of the age-standardized incidence of 1.5% in men and 1.6% in women in year 2021. This overestimation in the extremes is expected to be less in years closer to the reference year. Another limitation of the study pertains to the absence of easily accessible comorbidity and trauma indicators which precluded a more detailed analysis involving trauma velocity and health status at admission. More work is thus needed for better understanding these differences. Similarly, the marked increase in femoral shaft fractures observed in both sexes deserves more research.

In conclusion, femoral fractures are frequent and increasing in number more in men than in women, consistent with a more rapid ageing of the male population aged 45 years and older. While a reversal in the secular trend for hip fractures was confirmed in both sexes, it appeared to occur at the femoral neck fracture level mainly with little or no contribution from the clinically usually more severe pertrochanteric fractures. Fractures of the femoral shaft, albeit remaining at a low incidence, have almost doubled in number over the period of observation in both sexes. Overall, osteoporosis in men requires increased clinical attention.