Summary

Uncorrected 2D CT scans inaccurately estimate glenoid width and the degree of anterior glenodi bone loss, suggesting a role for the utilization of 3D reconstructions corrected to allow for measurements in the axis of the glenoid in order to accurately define the anatomy and quantity of anterior glenoid bone loss in patients with shoulder instability.

Abstract

Introduction

Computed tomography (CT) of the shoulder is the most commonly utilized imaging modality in the evaluation of patients with shoulder instability associated with glenoid bone loss (GBL).
As standard 2-dimensional (2D) CT scans of the shoulder are often aligned to the body as opposed to the plane of the scapula/glenoid, the 3-dimensional (3D) anatomy of the glenoid may be distorted, which may impede the ability to accurately measure glenoid width, version, and degree of GBL. The ability to correctly align the axial CT scan to the axis of the glenoid may allow for more accurate GBL measurements, which will ultimately impact surgical decision-making. The purpose of this study was to determine the effect of sagittal rotation of the glenoid on axial anterior-posterior (AP) glenoid width measurements in the setting of clinically significant anterior GBL.

Methods

A total of 44 CT scans from patients with a minimum of 10% anterior GBL were reformatted utilizing open-source DICOM software Osirix MD (version 2.5.1 65-bit) multi-planar reconstruction (MPR). Patients were grouped according to degree of anterior GBL measured via the surface method on 3D CT reconstructions as follows: I) 10-14.9% (N=8), II) 15-19.9% (N=18), and III) >20% (N=18). The uncorrected (UCORR) and corrected (CORR) images were assessed in the axial plane at 5 standardized cuts and measured for AP glenoid width by two independent observers (Figure 1). When the measured AP width of the UCORR scan was less than that measured on the CORR scan, the AP width of the glenoid was considered underestimated, and the degree of GBL was considered overestimated.

Results

For Groups I and III, the UCORR scans underestimated the axial AP width (and thus overestimated anterior GBL) in cuts 1 and 2, while in cuts 3-5, the axial AP width was overestimated (GBL underestimated). In Group II, the axial AP width was underestimated (GBL overestimated), while in cuts 2-5, the axial AP width was overestimated (GBL underestimated). Overall, AP glenoid width was consistently underestimated in Cut I, the most caudal cut, while AP glenoid width was consistently overestimated in cuts 3-5, the more cephalad cuts.

Discussion And Conclusion

Uncorrected 2D CT scans inaccurately estimate glenoid width and the degree of anterior GBL. The clinical implications of these findings are profound, and suggest a role for the utilization of 3D reconstructions corrected to allow for measurements in the axis of the glenoid in order to accurately define the anatomy and quantity of anterior GBL in patients with shoulder instability.