To pass or not to pass? Determining the acceptability of anteroposterior and lateral knee radiographs

Abstract

Introduction

The criteria for determining the acceptability of total knee replacement (TKR) radiographs are not established in current clinical practice. In TKR patients, the implant components replaced the anatomical landmarks, making it more difficult for radiographers to determine the degree of rotation. This study aims to establish an acceptable range of knee rotation for TKR radiographs.

Methods

Rejected TKR radiographs (199 AP and 186 lateral) were analysed retrospectively. Radiographers objectively measured rotation on the radiographs. A subset of 46 AP and 46 lateral radiographs were rated by orthopaedic surgeons for rotation and diagnostic value. Inter-rater reliability (IRR) of radiographic measurements and surgeons' ratings were analysed using Bland–Altman and Cohen's kappa, respectively. Spearman's rank-order correlation and Receiver Operator Characteristic analyses were used to determine the correlation and diagnostic performance of the radiographic measurements against the surgeon's ratings.

Results

Strong IRR was observed for the radiographic measurements. Only slight to fair agreement was observed for the surgeons' rotation and diagnostic value ratings of the radiographs. Moderate to strong correlation was observed between the radiographic measurements and the surgeons’ ratings. The radiographic measurements provided acceptable to excellent discrimination of acceptable and unacceptable radiographs. The acceptable range of measured rotation for usability was AP: 0–5.29 mm and lateral: 0–6.01 mm.

Conclusion

The proposed measurement methods and the established rotation range could potentially be used by radiographers in clinical practice to determine the acceptability of TKR radiographs. Follow-up studies could investigate uncommon knee implants and seek consensus across different institutions on the acceptable degree of rotation.

Implications for practice

The proposed method suggests that accepting radiographs within the threshold (AP: 5.29 mm, lateral: 6.01 mm) reduces repeated examination and radiation exposure and improves imaging efficiency.