Eliminating projection error of measuring Pauwels' angle in the femur neck fractures by CT plane manipulation

Abstract

Objectives: The aim for the present study was to determine whether projection error of measuring Pauwels' angle in young femur neck fracture could be eliminated by CT plane manipulation. Methods: Clinical data of displaced femur neck fractures in young adults aged 20 to 64 years old (13 females and 17 males) were retrospectively analyzed. Their average age was 47.9 years (range: 22-64 years; SD: 11.3). Using modified measurement method for Pauwels' angle using central line of the shaft as a guideline, the angle of a conventional coronal CT image was measured. CT images were imported into Mimics (R) software. The scanning plane was then reformatted parallel to the neck axis to eliminate projection error of injured limb. Measured angles were classified into three types (I< 30 degrees ; II, 30-50 degrees; and III>50 degrees) and differences were analyzed. Results: Average Pauwels' angle was 52.9 degrees (range: 28.6-68.3 degrees; SD: 9.9; type II, 17 cases; type III, 13 cases) for conventional CT images and 68.7 degrees (range: 29.8-91.2 degrees; SD: 13.4; type II, 1 cases; type III, 29 cases) for reformatted CT images. Difference between these two measurements on average was 15.7 degrees (range: 1.2-34.9 degrees; SD: 7.3). Conclusions: Reformatting CT scanning plane by manipulating the proximal fragment to be parallel with the neck axis of the distal neck-shaft fragment is a convenient and reliable technique for eliminating the projection error of measuring Pauwels' angle in the femur neck fractures. (C) 2019 Elsevier Masson SAS. All rights reserved.