Glenoid version by CT scan: an analysis of clinical measurement error and introduction of a protocol to reduce variability.

ABSTRACT

OBJECTIVE: Recent studies have challenged the accuracy of conventional measurements of glenoid version. Variability in the orientation of the scapula from individual anatomical differences and patient positioning, combined with differences in observer measurement practices, have been identified as sources of variability. The purpose of this study was to explore the utility and reliability of clinically available software that allows manipulation of three-dimensional images in order to bridge the variance between clinical and anatomic version in a clinical setting. MATERIALS AND METHODS: Twenty CT scans of normal glenoids of patients who had proximal humerus fractures were measured for version. Four reviewers first measured version in a conventional manner (clinical version), measurements were made again (anatomic version) after employing a protocol for reformatting the CT data to align the coronal and sagittal planes with the superior-inferior axis of the glenoid, and the scapular body, respectively. RESULTS: The average value of clinical retroversion for all reviewers and all subjects was -1.4° (range, -16° to 21°), as compared to -3.2° (range, -21° to 6°) when measured from reformatted images. The mean difference between anatomical and clinical version was 1.9° ± 5.6° but ranged on individual measurements from -13° to 26°. In no instance did all four observers choose the same image slice from the sequence of images. CONCLUSIONS: This study confirmed the variation in glenoid version dependent on scapular orientation previously identified in other studies using scapular models, and presents a clinically accessible protocol to correct for scapular orientation from the patient's CT data.