Femoral Neck Shaft Angle and Management of Proximal Femur Fractures: Is the Contralateral Femur a Reliable Template?

Abstract

To (1) assess interrater reliability of a novel technique for measurement of neck shaft angle (NSA); (2) use pelvic anteroposterior (AP) radiographs of unaffected hips to assess variability of NSA; and (3) evaluate the side-to-side variability of NSA to determine reliability of using the contralateral hip as a template. Retrospective cohort study. Academic Level 1 regional trauma center. Four hundred six femora (203 patients) with standing AP pelvis radiographs were selected. Exclusions included lack of acceptable imaging, congenital abnormalities, or prior hip surgery. An AP pelvis radiograph in the standing position. Bilateral NSA measurements obtained in a blinded fashion between 2 reviewers. Pearson coefficients and coefficient of determination assessed correlations and variability between left and right NSA. Concordance correlation coefficients assessed the interrater reliability between measurements performed by the 2 reviewers. Two hundred three patients (406 femora) were assessed. Male patients had a lower overall NSA mean of 131.56 degrees ± 4.74 than females with 133.61 degrees ± 5.17. There was no significant difference in NSA side-to-side in females (P = 0.18), 0.3 degrees [95% confidence interval (-0.15 to 0.75)], or males (P = 0.68), 0.19 degrees [95% confidence interval (-0.74 to 1.12)]. There was a strong linear relationship between left and right femora (r2 = 0.70). Forty-one percent of patients fell within the 131-135 degrees range bilaterally. Eighty-eight percent of patients had <5 degrees difference in NSA bilaterally and 0% had >10 degrees difference. There is no significant variability between bilateral femora in males and females. Use of this measurement method and contralateral NSA for proximal femur fracture planning is supported.