Eliminating projection error of measuring Pauwels’ angle in the femur neck fractures by CT plane manipulation - 28/11/19

Doi : 10.1016/j.otsr.2019.09.029

Gyu Min Kong ^a, Jae-Man Kwak ^b, Gu-Hee Jung ^c,^d,⁎
^a Department of Orthopaedic surgery, Inje university, Busan Paik hospital, 75, Bokji-ro, Busanjin-Gu, Busan, Republic of Korea
^b Department of Orthopedics, Biomechanics Laboratory, Mayo Clinic, Rochester, MN, USA
^c Department of Orthopaedic surgery, Gyeongsang national university, college of medicine, Gyeongsang national university changwon hospital, 11, Samjeongja-ro, Seongsan-gu, Changwon-si 51472, Republic of Korea
^d Medical ICT Convergence research center, institute of Health Sciences, college of Medicine, Gyeongsang National University, 816 Beongil 15, Jinju-si 52727, Republic of Korea

^⁎Corresponding author at: Department of Orthopaedic surgery, Gyeongsang national university, college of medicine, Gyeongsang national university changwon hospital, 11, Samjeongja-ro, Seongsan-gu, Changwon-si 51472, Republic of Korea.Department of Orthopaedic surgery, Gyeongsang national university, college of medicine, Gyeongsang national university changwon hospital11, Samjeongja-ro, Seongsan-guChangwon-si 51472Republic of Korea

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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 64years old (13 females and 17 males) were retrospectively analyzed. Their average age was 47.9years (range: 22–64years; 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® 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°; II, 30–50°; and III>50°) and differences were analyzed.

Results

Average Pauwels’ angle was 52.9° (range: 28.6–68.3°; SD: 9.9; type II, 17 cases; type III, 13 cases) for conventional CT images and 68.7° (range: 29.8–91.2°; 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° (range: 1.2–34.9°; 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.