BMD predicts osteoporotic hip fractures relatively well, except for fractures caused by high energy trauma . However, it does not explain the differences that exist between these fractures occurring in the vicinity of the proximal femur region. Fractures occur when the external force exceeds the bone's ability to absorb energy through the combined effects of elastic and plastic deformation . Decreases in bone density due to aging and osteoporosis are accompanied by geometrical changes, which alter the bone's ability to absorb energy that resists fractures. These changes cannot be explained simply by BMD, however, they can be analyzed through HSA .
Bending and axial compression forces are applied to the proximal femoral area when an elderly person falls . In a previous comparative study of HSA between hip fracture patients and non-fracture patients, the hip fracture patients were characterized by lower bending (section modulus) and axial strength (coronal sectional area), thinner cortex, and wider diameter . This study also reported that the HSA parameters were more consistent with the identification of intertrochanteric fractures than femoral neck fractures. We hypothesized that there would be differences in HSA parameters between these fractures occurring at close anatomical locations and the main finding in this study was that the CSMI was significantly lower in basicervical fractures. The CSMI is used to measure the distribution of material around the neck axis necessary to calculate the resistance to bending. The mechanical stress within a cross-section subjected to bending is inversely related to the CSMI and varies with the distance from the neutral axis [20, 21]. In other words, basicervical fractures have a lower bending strength compared to femoral neck fractures, which occurs near the intertrochanteric line.
Lower CSMIs in basicervical fractures can have clinical significance from two perspectives. The first is the importance in terms of diagnostic prediction. Several HSA studies on the prediction of various hip fracture incidences reported that various HSA parameters were important, including bone cross-sectional area, outer diameter, selection modulus, buckling ratio, the HAL and the strength index [22, 23]. Among them, the section modulus is a strength parameter derived from the CSMI and is equal to the CSMI divided by the centroidal distance, the distance from the centroidal axis to the edge of the section . Also, in a study by Kaptoge et al., BMD, CSA, the CSMI, section modulus, and the cortices in the hip fracture group were lower than those in the fracture-free group . Resistance to bending strength is important for the prediction of hip fracture occurrence. Moreover, the CSMI, an indicator of bending strength, can be used as an index to predict the location of hip fractures. Second in importance is the therapeutic aspects of the fractures. Various studies have reported a high rate of treatment failure for basicervical fractures [4, 7, 9, 10]. These studies noted the morphological characteristics that tended to collapse into the intertrochanteric area due to their anatomical location and identified them as the major causes of treatment failure. Although the use of extramedullary or intramedullary devices in implants is controversial, clinically, the current study found that the use of a fixed angle device for the internal fixation of basicervical fractures is a reasonable treatment option to reinforce the weakness of this bending strength.
Leslie et al. hypothesized that different types of bone geometry can predict fractures. In the Fracture Risk Prediction Model using DXA-based finite element analysis, a study reported that the HAL and strength index were significantly associated with the incidence of hip fracture. In a study by Faulkner et al., the HAL of the hip fracture group was also significantly shorter than that of the control group,  indicating a reduced capacity to withstand a fall and identifying the HAL as an independent predictor of hip fractures. They reported that an increase in HAL equivalents to 1 SD was associated with a 1.8-fold increase in the risk of hip fractures in women. The results of this study showed that the average HAL of the basicervical fracture patient was shorter than that of the femoral neck fracture patients and the diagnostic significance of basicervical fractures was found in the ROC analysis. Thus, HAL is not only a predictor of fracture risk but also a significant predictor of fracture type.
The European Working Group on Sarcopenia in Older People developed a clinical definition of sarcopenia based on low muscle mass and reduced muscle function . Grip strength is recommended as a good simple measure of muscle strength. In older people, falls are associated with lower physical activity, which is one of the signs of reduced physical function [26, 27]. Sarcopenia is also closely related to osteoporosis and osteoporotic hip fractures. A study by Travison et al. on the correlation between body mass index and proximal femur strength reported a fracture prevention effect in people with high BMI, not because of fat, but because of muscle mass. Our study confirmed that the handgrip strength was decreased statistically in the basicervical fracture group and proven statistically as a predictive factor for basicervical fracture diagnosis. We do not know the exact mechanism to explain this result, but it is thought that it affects the loading occurring during falls or the absorption of impact force. Therefore, further studies are needed.
There were several limitations to this study. First, the study sample size was small. However, we used propensity score matching to address this problem. Second, the study design was retrospective and we cannot exclude the possibility of selection bias. Third, we did not consider comorbidity and the use of anti-osteoporotic medications by the patients. However, we tried to complement this by analyzing factors, such as skeletal muscle index, grip strength, and vitamin D levels.
In conclusion, proximal femoral geometric analysis using HSA is a useful method for predicting the type of hip fracture. Additionally, lower CSMI, shorter HAL, and lower grip strength are major predictors of basicervical fractures.