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Reproduced with permission of the publisher from ref. 31.

Reproduced with permission of the publisher from ref. 31.

Fig. 2-25. Images of the proximal femur acquired during a DXA study. In (A) the lesser trochanter is clearly seen but is small and rounded, indicating proper internal rotation of the proximal femur during positioning. Compare this lesser trochanter to the lesser trochanter seen in (B). This is the same patient seen in (A) but here the proximal femur was not rotated internally sufficiently causing the lesser trochanter to appear large and pointed.

shortening of the length of the neck and an increase in the BMC in the path of the beam. The combination results in an apparent increase in BMD. The only visual clue to consistent rotation is the reproduction of the size and shape of the lesser trochanter. Because the trochanter is a posterior structure, leg positioning in which the femur has not been rotated sufficiently internally tends to produce a very large and pointed lesser trochanter. Excessive internal rotation of the proximal femur will result in a total disappearance of the lesser trochanter. The size of the lesser trochanter in the DXA proximal femur image in Fig. 2-25A indicates correct internal rotation. This can be compared to the size of the lesser trochanter seen in the DXA proximal femur study in Fig. 2-25B. The lesser trochanter is very large and pointed, indicating insufficient internal rotation. Although this would be undesirable in a baseline study of the proximal femur, follow-up studies using the proximal femur in this patient should be done with this same degree of rotation. Any change in rotation from the baseline study would be expected to affect the magnitude of change in the BMD, decreasing the precision of the study.

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