The impact of nonstandard hip rotation on densitometric results of hip regions and potential misclassification of diagnosis

The present study is intended to investigate the degree to which insufficient internal rotation could impact the densitometric results and change the diagnosis. A significant difference was found between the results in nonstandard compared with standard rotation and an increase in the BMD and T- and Z-scores from nonstandard to standard rotation. Likewise, a change in diagnosis was observed in a significant proportion of patients.

To investigate the impact of nonstandard rotation of hip on the densitometric results of femoral neck and total femur region as well as the amount of change in diagnosis (i.e., misclassification of diagnosis) based on hip region.

Ninety-seven patients (88 females and 9 males) were included in the study. After receiving informed consent, each subject underwent a densitometric scanning in two modes, one with standard rotation of the leg and the other with nonstandard rotation (i.e., the leg in relaxed position without applying the positioner to strap the foot to) of the same leg. All data were analyzed using the auto-analysis option of the HOLOGIC® software. Bone densitometric results, T- and Z-scores, rate of change in diagnosis, and also the agreement between the diagnoses in the two modes are calculated and compared by using a paired-sample t test and cross-tabulation.

The mean age of 97 patients was 56.91 ± 11.70 years. A significant difference was found in the BMDs, T-scores, and Z-scores of the neck and total femur regions of interest in standard and nonstandard rotations. We found an increase in the BMD of the femoral neck and total femur of 0.020 and 0.010 g/cm², respectively, from standard to nonstandard leg rotation and that this, in turn, led to a 0.4 and a 0.13 increases in T-scores of the neck and total femur, respectively, from standard to nonstandard rotation. In the diagnosis based on femoral neck only, the diagnosis changed in 17 (17.5%) patients, i.e., 12 (12.4%) from osteopenia to normal, 3 (3.1%) from osteoporosis to osteopenia, and 2 (2.0%) from below the expected range for age to within the expected range for age. There was only a change of one level in diagnosis.

According to the results, the changes in the BMD and T- and Z-scores can be interpreted as underdiagnosis or, in simple terms, not finding the disease or underestimating the level of disease. Therefore, proper rotation of the leg is an important factor during densitometry. Any deviation from standard rotation changes the BMD of those regions, and thereby the T- and Z-scores accordingly, and thus the diagnosis.