Statistical quantification of hip radiograph assessment using Shenton line femur neck length ratio

Identification of a poorly positioned hip radiograph often requires a subjective assessment by the radiographer, which, due to the observer dependency of this method, may have conflicting opinions between radiographers. A quantitative approach may be a better personnel independent approach for assessing an optimally positioned hip radiograph. A Shenton line length femur neck length ratio (SLFLR) could be used to achieve this, which is the aim of this study.

Seventy-three (48 digital and 25 analog) optimally positioned non-pathological hip radiographs of asymptomatic patients aged between 20 and 59 years and reported by the consultant radiologist as normal were conveniently selected. Three different radiographers, each blinded to the results of the other two, measured the Shenton line length and the femur neck length with the aid of flexible and straight meter rules for the analog images and inbuilt electronic calipers for the digital images. Bland-Altman method of agreement was used to assess for reproducibility and reliability of the measurements while the 5th, 25th, 75th, and 95th percentiles of the SLFLR were computed.

The mean ± SD SLFLR for both genders were 1.07 ± 0.08 cm (females: 1.06 ± 0.09 and males: 1.08 ± 1.07 cm). The measurements demonstrated high reproducibility and reliability between (interclass correlation coefficient: 0.993) and within (intraclass correlation coefficient: 0.998) radiographers. The 5th, 25th, 75th, and 95th percentile values of the SLFLR are 0.90, 1.03, 1.12, and 1.18.

For a hip radiograph to be reported as optimal for patients aged 20-59 years, the SLFLR should be between 0.90 and 1.18. This method is highly reproducible and repeatable and could be adopted for quantitative assessment of radiographs.

The SLFLR could be used as an additional tool by the radiographer to quantitatively assess for a well-positioned hip radiograph.