Geometric structure of the femoral neck measured using dual-energy X-ray absorptiometry

Abstract

An algorithm was developed to estimate the strength of the femoral neck from data generated by the dual-energy x-ray absorptiometry (DXA). This algorithm considers shape of the proximal femur as well as cross-sectional moment of inertia (CSMI) in the estimate. Proximal femora (10) from cadavers of white adults and an aluminum step wedge were scanned with the Lunar DPX to validate the calculation of CSMI. After scanning, each femoral neck was sectioned at its narrowest portion for direct measurement of CSMI. Three healthy young women were scanned five times each to evaluate the reproducibility of geometric measurements using DXA. There was a strong linear association between the CSMI measured directly and using DXA in both cadaver bones (r2 = 0.96) and the aluminum step wedge (r2 = 0.99). The coefficient of variation for CSMI from repeated measurements using DXA was less than 3%. This indicates that it is possible to estimate reproducibly the bending rigidity of bone from DXA measurements. The data from 306 normal subjects were analyzed to investigate geometric changes in the femoral neck with age. Although there was no strong correlation between CSMI and age in normal subjects of either sex, safety factor (SF, an index of strength of the femoral neck during walking) and fall index (FI, an index of the strength of the femoral neck during a fall) decrease with age in both sexes. We observed an alteration of the geometric structure of the femoral neck with age that may increase the stress on the femoral neck and decrease SF and FI.

Bone Geometry According to Menstrual Function in Female Endurance Athletes

“…Femoral strength index is the ratio of estimated compressive yield strength of the femoral neck to the expected compressive stress of a fall on the greater trochanter adjusted for the patient's age, height and weight. This is estimated from Z but incorporates other variables also (17,18) …”

Bone cross-sectional geometry in male runners, gymnasts, swimmers and non-athletic controls: a hip-structural analysis study

“…FSI is an advanced feature which has been added to more recent versions of enCORE and can be used for investigative purposes to indicate the risk of fracture for forces generated during a fall on the greater trochanter. It combines BMD, femur geometry, age, height and body mass, and is calculated as strength/stress, where stress is moment * y /CSMI + force /CSA, and is based on work by Yoshikawa et al (1994).…”

“…The Advanced Hip Structural Analysis (AHA) programme was used to determine conventional areal bone mineral density (aBMD), hip axis length (HAL), crosssectional area (CSA), and cross -sectional moment of inertia (CSMI). Bone strength indices were derived using the femoral strength index (FSI) (Yoshikawa et al, 1994). Gymnasts and runners had significantly greater age, height and weight adjusted aBMD than swimmers and controls (p<0.05).…”

Variation in the PTH Gene, Hip Fracture, and Femoral Neck Geometry in Elderly Women

“…The CSMI estimated with DXA has been found to be highly correlated with the CSMI measured directly on cadaver specimens (r 2 =0.96) [26]. The automatic identification of the weakest cross-section of the femoral neck is the central part of the hip strength analysis software and this cross-section level is then used for the subsequent calculations of section modulus (SM, cm 3 ) and the femoral neck width (FN width, cm).…”

“…CSMI is an estimate of the ability of the femoral neck to withstand bending forces and was calculated using the mass distribution of the absorption curve [26]. The CSMI estimated with DXA has been found to be highly correlated with the CSMI measured directly on cadaver specimens (r 2 =0.96) [26].…”