The accuracy of measurements of femoral neck fractures

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Abstract
Postoperative displacement of the femoral head center was measured in 60 intracapsular hip fractures at repeated conventional radiographic (CR) and roentgen stereophotogrammetric (RSA) examinations. The measurements of the conventional radiographs (405 pairs) were done on a digitizing table. Totally, 105 pairs of these radiographs (AP and lateral, CR) were measured by 2 observers. Manual measurements were also made on 176 pairs of the conventional radiographs. Conventional radiographs tended to overestimate or underestimate the average displacements up to about 2 mm. Two standard deviations of the differences (RSA-CR) varied from 5.8 to 9.6 mm depending on the direction of the movements. The accuracy of the measurements on conventional radiographs did not differ between the 2 examiners. The digitizing table was found to be more accurate than the manual measurements. The accuracy of conventional radiography can most likely be improved by using a strictly standardized examination technique.