Glenoid Version Assessment When the CT Field of View Does Not Permit the Friedman Method: The Robertson Method

Douglas D Robertson; Gulshan B Sharma; Patrick J McMahon; Spero G Karas

doi:10.1177/23259671221083589

Glenoid Version Assessment When the CT Field of View Does Not Permit the Friedman Method: The Robertson Method

Orthop J Sports Med. 2022 May 10;10(5):23259671221083589. doi: 10.1177/23259671221083589. eCollection 2022 May.

Authors

Douglas D Robertson^{1

2

3}, Gulshan B Sharma⁴, Patrick J McMahon^{5

6}, Spero G Karas^{1

3}

Affiliations

¹ Emory Orthopaedics and Spine Center, Atlanta, Georgia, USA.
² Author deceased.
³ Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, Georgia, USA.
⁴ Department of Psychiatry, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada.
⁵ VA Pittsburgh Healthcare System, Pittsburgh, Pennsylvania, USA.
⁶ Department of Orthopedic Surgery and Department of Bioengineering, University of Pittsburgh, Pittsburgh, Pennsylvania, USA.

Abstract

Background: To improve spatial resolution, current clinical shoulder cross-sectional imaging studies reduce the field of view of the shoulder, excluding the medial scapula border and preventing glenoid version measurement according to the Friedman method.

Purpose: To evaluate a method to accurately and reliably measure glenoid version on cross-sectional shoulder images when the medial scapula border is not included in the field of view, and to establish measurements equivalent to the Friedman method.

Study design: Controlled laboratory study.

Methods: Sixty-five scapulae underwent computed tomography (CT) scanning with an optimal shoulder CT-positioning protocol. Glenoid version was measured on CT images of the full scapula using the Friedman method. We developed a measurement method (named the Robertson method) based on the glenoid vault version from partial scapula images, with a correction angle subtracted from the articular-surface-glenoid vault measurement. Comparison with the Friedman method defined the accuracy of the Robertson method. Three observers tested inter- and intraobserver reliability of the Robertson method. Accuracy was statistically evaluated with t tests and reliability with the intraclass correlation coefficient (ICC).

Results: The statistical distribution of glenoid version was similar to published data,-0.5° ± 3° [mean ± SD]. The initial measurement using the Robertson method resulted in a more retroverted angle compared with the Friedman method, and a correction angle of 7° was then applied. After this adjustment, the difference between the 2 methods was nonsignificant (0.1° ± 4°; P > .65). Reliability of the Robertson method was excellent, as the interrater ICC was 0.77, the standard error of measurement (SEM) was 1.1° with P < .001. The intrarater ICC ranged between 0.84 and 0.92, the SEM ranged between 0.9° and 1.2° with P < .01.

Conclusion: A validated glenoid version measurement method is now available for current clinical shoulder CT protocols that reliably create Friedman-equivalent values.

Clinical relevance: Friedman-equivalent values may be made from common clinical CTs of the shoulder and compared with prior and future Friedman measurements of the scapula.

Keywords: CT; cross-sectioning imaging; glenoid version; shoulder; shoulder replacement; total shoulder arthroplasty.