Developing and cross-validation of new equations to estimate fat mass in Italian population.

OBJECTIVE: Obesity is a global burden that involves more than 500 million people. The objective of this work is to develop and cross-validate the new sex-specific equations to estimate fat mass, based on anthropometric parameters and to compare with other equations. PATIENTS AND METHODS: We evaluated 38762 subjects by dual-energy X-ray absorptiometry (DXA) and enrolled 1434 women and 640 men, aged between 18 and 65 years. Then, we randomized 480 men and 1080 women in developing set and 160 men and 354 women in the cross-validation set. Statistical analysis as multiple regression and Bland-Altman methods were performed. RESULTS: Sex-specific equations were created based on developing set. Then, based on the cross-validating set, these equations were validated and were observed to agree with fat mass by DXA, better than other equations, such as BAI and RFM. CONCLUSIONS: These new sex-specific equations represent an easy tool, since they require only two circumferences, to be used in clinical practice. In the next future, these equations could be validated and refine on specific Italian sub-populations, divided by gender and age, such as the military.

Femoral imaging artifacts associated with dorsal recumbency craniocaudal radiographic positioning. Description of a modified bisecting angle technique.

OBJECTIVES: To describe the radiographic length distortion associated with femoral tilt during cranio-caudal positioning. To describe a modified bisecting angle technique to alleviate image foreshortening. METHODS: Five pairs of femurs were imaged. The femurs were tilted from 0 to 50 degrees and the X-ray anode was tilted from 0 to 40 degrees. Femoral length was measured on the resulting images. A geometric model depicting sagittal femoral positioning was described with two trigonometric formulas. Trigonometric formula 1 (TF¹) was designed to predict apparent femoral length. Data generated by TF¹ were compared to the cadaveric study results. Trigonometric formula 2 (TF²), based on the same model, was used to predict the ideal anode angle (iAA) to alleviate foreshortening. Unrelated to the model, a simplified linear formula (SF) was created to approximate the TF². Data generated with the SF and the TF² were compared. RESULTS: When the femoral specimens were tilted to 20 degrees or greater, significant foreshortening was appreciated (p <0.001). Increasing the anode angle increased apparent length, eliminating foreshortening. Data generated by the TF¹ agreed closely with the results of the cadaveric study (R² = 0.999). The SF and the TF² demonstrated close agreement and were able to predict an iAA consistent with the results of the cadaveric study. CLINICAL SIGNIFICANCE: A femoral tilt of 20 degrees or greater results in significant image foreshortening and may warrant alternate radiographic techniques. If the femur is tilted, adjusting the anode angle can alleviate femoral foreshortening.